U.S. patent application number 10/363717 was filed with the patent office on 2005-11-24 for refining agent and refining method.
This patent application is currently assigned to NKK CORPORATION. Invention is credited to Isawa, Tomoo, Kawashima, Takeshi, Kikuchi, Yoshiteru, Matsuno, Hidetoshi, Murai, Takeshi, Nakai, Yoshie, Nimura, Yoichi, Okamura, Tatsuya, Shimizu, Hiroshi, Takahashi, Kenji.
Application Number | 20050257644 10/363717 |
Document ID | / |
Family ID | 26600019 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050257644 |
Kind Code |
A1 |
Nakai, Yoshie ; et
al. |
November 24, 2005 |
Refining agent and refining method
Abstract
A refining agent contains Al, MgO, and CaO as main components,
and uses dolomite as a MgO source and CaO source. When the refining
agent is supplied into molten iron, it produces Mg vapor due to a
reaction in the molten iron, and causes a refining reaction by the
Mg vapor.
Inventors: |
Nakai, Yoshie; (Tokyo,
JP) ; Murai, Takeshi; (Tokyo, JP) ; Matsuno,
Hidetoshi; (Tokyo, JP) ; Kikuchi, Yoshiteru;
(Tokyo, JP) ; Takahashi, Kenji; (Tokyo, JP)
; Nimura, Yoichi; (Tokyo, JP) ; Shimizu,
Hiroshi; (Tokyo, JP) ; Isawa, Tomoo; (Tokyo,
JP) ; Kawashima, Takeshi; (Tokyo, JP) ;
Okamura, Tatsuya; (Tokyo, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 5TH AVE FL 16
NEW YORK
NY
10001-7708
US
|
Assignee: |
NKK CORPORATION
1-2, Marunouchi 1-chome, Chiyoda-ku
Tokyo
JP
100-0005
|
Family ID: |
26600019 |
Appl. No.: |
10/363717 |
Filed: |
March 7, 2003 |
PCT Filed: |
September 14, 2001 |
PCT NO: |
PCT/JP01/08011 |
Current U.S.
Class: |
75/315 |
Current CPC
Class: |
C21C 7/072 20130101;
C21C 1/025 20130101; C21B 3/04 20130101; C21C 7/04 20130101; C21C
7/076 20130101; C21C 7/06 20130101; Y02W 30/50 20150501; C21C
7/0645 20130101; Y02P 10/20 20151101 |
Class at
Publication: |
075/315 |
International
Class: |
C21C 007/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2000 |
JP |
2000-280315 |
Sep 7, 2001 |
JP |
2001-271824 |
Claims
1. A refining agent containing Al, MgO, and CaO as main components,
and including a material as a MgO source and CaO source, in which
MgO and CaO are close to or in contact with each other in a minute
state, the refining agent being arranged to produce Mg vapor due to
a reaction in molten iron, when the refining agent is supplied into
the molten iron.
2. A refining agent according to claim 1, which performs
desulfurization and/or deoxidation of the molten iron.
3. A refining agent according to claim 1, which contains MgO, CaO,
and Al summing to 75 mass % or more.
4. A refining agent containing Al, MgO, and CaO as main components,
and including dolomite as a MgO source and CaO source, the refining
agent being arranged to produce Mg vapor due to a reaction in
molten iron, when the refining agent is supplied into the molten
iron.
5. A refining agent according to claim 4, which performs
desulfurization and/or deoxidation of the molten iron.
6. A refining agent according to claim 4, which is in a state
prepared by mixing or crushing and mixing a raw material including
dolomite and an Al source containing 25 mass % or more metal Al, or
a raw material including at least one of another MgO source and
another CaO source in addition to them, to obtain mixture powder
with an average particle size of 1 mm or less, or in a state
prepared by changing the mixture powder into a pelletized or lumped
form with a size of 3 mm to 40 mm.
7. A refining agent according to claim 6, wherein the raw material
in a pelletized or lumped form includes a forming binder mixed
therein.
8. A refining agent according to claim 7, wherein the binder has a
viscosity of 2 to 10 poise at 60.degree. C.
9. A refining agent according to claim 4, wherein Al/MgO is 0.05 or
more in mass ratio, and CaO/MgO is in a range of 0.5 to 10.0 in
mass ratio.
10. A refining agent according to claim 9, wherein Al/MgO is 0.2 or
more in mass ratio.
11. A refining agent according to claim 9, wherein CaO/MgO is more
than 1.5 and up to 10.0 in mass ratio.
12. A refining agent according to claim 9, wherein CaO/MgO falls in
a dolomite composition range.
13. A refining agent according to claim 9, wherein the MgO source
and CaO source are formed of dolomite and another MgO source or CaO
source for compensating for part of CaO and MgO, which exceeds
dolomite composition, so as to obtain a predetermined CaO/MgO.
14. A refining agent according to claim 4, which contains MgO, CaO,
and Al summing to 75 mass % or more.
15. A refining agent containing Al, MgO, and CaO as main
components, and including dolomite as a MgO source and CaO source,
wherein Al/MgO is 0.05 or more in mass ratio, and CaO/MgO is in a
range of 0.5 to 10.0 in mass ratio.
16. A refining agent according to claim 15, wherein Al/MgO is 0.2
or more in mass ratio.
17. A refining agent according to claim 15, wherein CaO/MgO is more
than 1.5 and up to 10.0 in mass ratio.
18. A refining agent according to claim 15, wherein CaO/MgO falls
in a dolomite composition range.
19. A refining agent according to claim 15, wherein the MgO source
and CaO source are formed of dolomite and another MgO source or CaO
source for compensating for part of CaO and MgO, which exceeds
dolomite composition, so as to obtain a predetermined CaO/MgO.
20. A refining agent according to claim 15, which contains MgO,
CaO, and Al summing to 75 mass % or more.
21. A refining agent containing Al, C, MgO, and CaO as main
components, and arranged to produce Mg vapor due to a reaction in
molten iron, when the refining agent is supplied into the molten
iron.
22. A refining agent according to claim 21, which includes a
material as a MgO source and CaO source, in which MgO and CaO are
close to or in contact with each other in a minute state.
23. A refining agent according to claim 22, which includes dolomite
as the MgO source and CaO source.
24. A refining agent according to claim 21, which performs
desulfurization and/or deoxidation of the molten iron.
25. A refining agent according to claim 21, which is in a state
prepared by mixing or crushing and mixing a raw material including
dolomite, an Al source containing 25 mass % or more metal Al, and
carbon powder, or a raw material including at least one of another
MgO source and another CaO source in addition to them, to obtain
mixture powder with an average particle size of 1 mm or less, or in
a state prepared by changing the mixture powder into a pelletized
or lumped form with a size of 3 mm to 40 mm.
26. A refining agent according to claim 25, wherein the raw
material in a pelletized or lumped form includes a forming binder
mixed therein.
27. A refining agent according to claim 26, wherein the binder has
a viscosity of 2 to 10 poise at 60.degree. C.
28. A refining agent according to claim 21, wherein Al/MgO is 0.05
or more in mass ratio, C/MgO is 0.1 or more in mass ratio, and
CaO/MgO is in a range of 0.5 to 10.0 in mass ratio.
29. A refining agent according to claim 28, wherein Al/MgO is 0.2
or more in mass ratio.
30. A refining agent according to claim 28, wherein CaO/MgO is more
than 1.5 and up to 10.0 in mass ratio.
31. A refining agent according to claim 21, which contains MgO,
CaO, Al, and C summing to 75 mass % or more.
32. A refining agent containing Al, C, MgO, and CaO as main
components, wherein Al/MgO is 0.05 or more in mass ratio, C/MgO is
0.1 or more in mass ratio, and CaO/MgO is in a range of 0.5 to 10.0
in mass ratio.
33. A refining agent according to claim 32, wherein Al/MgO is 0.2
or more in mass ratio.
34. A refining agent according to claim 32, wherein CaO/MgO is more
than 1.5 and up to 10.0 in mass ratio.
35. A refining agent according to claim 32, which contains MgO,
CaO, Al, and C summing to 75 mass % or more.
36. A refining method of performing desulfurization treatment of
molten pig iron by adding a refining agent to the molten pig iron
held in a container, the refining agent containing Al, MgO, and CaO
as main components, and including a material as a MgO source and
CaO source, in which MgO and CaO are close to or in contact with
each other in a minute state.
37. A refining method of performing desulfurization treatment of
molten pig iron by adding a refining agent to the molten pig iron
held in a container, the refining agent containing Al, MgO, and CaO
as main components, and including dolomite as a MgO source and CaO
source.
38. A refining method according to claim 37, which performs the
desulfurization treatment while stirring the molten pig iron in the
container by a mechanically stirring method.
39. A refining method according to claim 38, which performs a
treatment of creating a new surface on desulfurization slag
obtained by performing the desulfurization treatment with stirring
by the mechanically stirring method, and uses the desulfurization
slag thus treated to perform desulfurization treatment of molten
pig iron.
40. A refining method according to claim 37, which adds the
refining agent to the molten pig iron in the container by
injection.
41. A refining method according to claim 37, which adds the
refining agent to the molten pig iron in the container by a
putting-in or putting-on method.
42. A refining method according to claim 37, which adds the
refining agent to the molten pig iron in the container, in a form
prepared by mixing raw materials of the refining agent in
advance.
43. A refining method according to claim 42, which adds the
refining agent to the molten pig iron in the container at one time
or dividedly at several times.
44. A refining method according to claim 37, which adds the
refining agent to the molten pig iron in the container, in a form
prepared by not mixing raw materials of the refining agent in
advance.
45. A refining method according to claim 44, which adds the raw
materials to the molten pig iron in the container at the same
position or at different positions.
46. A refining method according to claim 44, which adds the raw
materials to the molten pig iron in the container at the same time
or at different times.
47. A refining method according to claim 44, which adds the raw
materials to the molten pig iron in the container at one time or
dividedly at several times.
48. A refining method according to claim 37, wherein the molten pig
iron in the container is set to have a temperature of 1,200.degree.
C. or more.
49. A refining method according to claim 48, wherein the molten pig
iron in the container is set to have a temperature of 1,300.degree.
C. or more.
50. A refining method of refining molten pig iron by performing a
series of treatment, which is formed of desulfurization treatment
and at least one of desiliconization treatment and
dephosphorization treatment, on molten pig iron after tapping from
blast furnace and before decarburization in converter, wherein the
desulfurization treatment is performed by adding a refining agent
to the molten pig iron held in a container, the refining agent
containing Al, MgO, and CaO as main components, and including
dolomite as a MgO source and CaO source.
51. A refining method according to claim 50, wherein silicon
concentration in molten pig iron is 0.2 mass % or less before the
dephosphorization treatment, phosphorus concentration in molten pig
iron is 0.03 mass % or less after the dephosphorization treatment,
and sulfur concentration is 0.005 mass % or less after the
desulfurization treatment.
52. A refining method according to claim 50, which performs at
least one of the desiliconization treatment and dephosphorization
treatment before the desulfurization treatment.
53. A refining method according to claim 52, which performs a
treatment immediately before the desulfurization treatment, such
that molten pig iron temperature becomes 1,300.degree. C. or more
before the desulfurization treatment.
54. A refining method according to claim 53, which performs a
treatment immediately before the desulfurization treatment, such
that molten pig iron temperature becomes 1,350% or more before the
desulfurization treatment.
55. A refining method of refining molten pig iron by performing a
series of treatment, which is formed of desulfurization treatment
and at least one of desiliconization treatment and
dephosphorization treatment, on molten pig iron after tapping from
blast furnace and before decarburization in converter, wherein the
desulfurization treatment is performed by adding a refining agent
to the molten pig iron held in a container, the refining agent
containing Al, MgO, and CaO as main components, and including
dolomite as a MgO source and CaO source, and wherein a total
consumption of fluorite in the series of treatment is set to be 0.1
kg or less per ton of molten pig iron.
56. A refining method according to claim 55, wherein the refining
agent contains substantially no fluorine.
57. A refining method according to claim 55, wherein fluorine
concentration is 0.2 mass % or less in slag generated in each
treatment of the series of treatment.
58. A refining method according to claim 55, wherein fluorine
concentration is 0.2 mass % or less in slag in tapping from blast
furnace.
59. A refining method of performing at least one of desulfurization
treatment, deoxidation treatment, and inclusion control of molten
steel by adding a refining agent to the molten steel, the refining
agent containing Al, MgO, and CaO as main components, and including
dolomite as a MgO source and CaO source.
60. A refining method according to claim 59, which adds the
refining agent to one of molten steel in a melting furnace, molten
steel pouring flow from a melting furnace, molten steel in a ladle,
molten steel in a vessel incidental to a ladle, and molten steel in
a tundish for continuous casting.
61. A refining method according to claim 60, wherein the melting
furnace is a converter for treating molten pig iron, or an electric
furnace for melting a cold iron source.
62. A refining method according to claim 60, wherein the vessel
incidental to a ladle is a vacuum vessel of an RH vacuum degassing
apparatus.
63. A refining method according to claim 59, which uses the
refining agent to perform a treatment of causing inclusions in the
molten steel to contain MgO.
64. A refining method according to claim 63, wherein the treatment
is performed to control alumina inclusions to a spinel composition
in all or in part in the molten steel, which contains 0.01 mass %
or more solute Al and 30 ppm or less solute oxygen after
deoxidation.
65. A refining method according to claim 63, wherein the treatment
is performed to increase MgO concentration in inclusions, formed
mainly of silicate, in all or in part in the molten steel, which
contains less than 0.01 mass % solute Al and 30 ppm or less solute
oxygen after deoxidation.
66. A refining method of performing making high clean molten steel
by adding a refining agent to molten steel deoxidated by a
predetermined element, the refining agent containing Al, MgO, and
CaO as main components, and including dolomite as a MgO source and
CaO source.
67. A refining method of performing desulfurization treatment of
molten pig iron by adding a refining agent to the molten pig iron
held in a container, the refining agent containing Al, C, MgO, and
CaO as main components.
68. A refining method of refining molten pig iron by performing a
series of treatment, which is formed of desulfurization treatment
and at least one of desiliconization treatment and
dephosphorization treatment, on molten pig iron after tapping blast
furnace and before decarburization in converter, wherein the
desulfurization treatment is performed by adding a refining agent
to the molten pig iron held in a container, the refining agent
containing Al, C, MgO, and CaO as main components.
69. A refining method of refining molten pig iron by performing a
series of treatment, which is formed of desulfurization treatment
and at least one of desiliconization treatment and
dephosphorization treatment, on molten pig iron after tapping from
blast furnace and before decarburization in converter, wherein the
desulfurization treatment is performed by adding a refining agent
to the molten pig iron held in a container, the refining agent
containing Al, C, MgO, and CaO as main components, and wherein a
total consumption of fluorite in the series of treatment is set to
be 0.1 kg or less per ton of molten pig iron.
70. A refining method of performing at least one of desulfurization
treatment, deoxidation treatment, and inclusion control of molten
steel by adding a refining agent to the molten steel, the refining
agent containing Al, C, MgO, and CaO as main components.
71. A refining method of performing making high clean molten steel
by adding a refining agent to molten steel deoxidated by a
predetermined element, the refining agent containing Al, C, MgO,
and CaO as main components.
72. A desulfurization slag recycling method of performing
desulfurization treatment of molten pig iron by adding a refining
agent to the molten pig iron, and then recycling desulfurization
slag thus generated as a raw material to be sintered for a blast
furnace, the refining agent containing Al, MgO, and CaO as main
components, and including dolomite as a MgO source and CaO source.
Description
TECHNICAL FIELD
[0001] The present invention relates to a molten iron refining
agent and refining method.
BACKGROUND ART
[0002] Refining agents for molten iron or molten steel are required
to be inexpensive, as well as causing an effective refining
reaction. For example, desulfurization flux widely used in
desulfurization of molten pig iron, such as 95 mass % CaO and 5
mass % CaF.sub.2, contains CaO, which is inexpensive, as the main
component. Metal Mg is also known as desulfurization flux for
molten pig iron. Metal Mg readily reacts with S contained in molten
pig iron and produces MgS. Since Mg has a low boiling point of
1,107.degree. C., it is vaporized in molten pig iron at a
temperature of 1,250 to 1,500.degree. C., and generates Mg vapor. A
desulfurization reaction by Mg and a desulfurization reaction by
CaO are expressed by the following formulas (1) and (2).
Mg+S.fwdarw.(MgS) (1)
(CaO)+S.fwdarw.(CaS)+O (2)
[0003] Specifically, Mg vapor dissolves in molten pig iron, reacts
with sulfur S contained in the molten pig iron to produce MgS, and
rises to the surface of the molten pig iron bath. CaO reacts with S
contained in molten pig iron to generate CaS, and rises to the
surface of the molten pig iron bath.
[0004] Mg desulfurization set out in the formula (1) has a
desulfurization rate higher than CaO desulfurization set out in the
formula (2). Accordingly, where Mg desulfurization is used, a
predetermined target level [S] can be attained with a smaller
desulfurization agent unit requirement and in a shorter time.
[0005] However, although Mg desulfurization has such an advantage,
it is out of the mainstream. This is so, because the raw material,
i.e., metal Mg, is expensive, and there has been found no merit,
which can surpass inexpensive CaO, where being used as the main
component in desulfurization flux.
[0006] On the other hand, Jpn. Pat. Appln. KOKAI Publication No.
10-17913 discloses a method of desulfurizing molten pig iron by
adding a desulfurization agent containing MgO and Al to the molten
pig iron; causing Al and MgO to react with each other in the molten
pig iron thereby producing Mg vapor and MgO.Al.sub.2O.sub.3; and
causing the Mg vapor thus produced to react with S dissolved in the
molten pig iron, thereby producing and precipitating MgS. In this
technique, the Mg vapor is effectively generated in the molten pig
iron, using a reaction expressed by the following formula (3).
4MgO+2Al.fwdarw.3Mg(g)+MgO.Al.sub.2O.sub.3 (3)
[0007] According to this method, since the main raw materials are
MgO and Al, which are less expensive than metal Mg, the economical
disadvantage of Mg desulfurization can be reduced.
[0008] However, the technique of Jpn. Pat. Appln. KOKAI Publication
No. 10-17913 cannot allow all the Mg of MgO to change into metal
Mg, but causes the Mg of MgO to be partly left as magnesia spinel
MgO.Al.sub.2O.sub.3, as shown in the formula (3). Accordingly,
since the refining efficiency of this technique is not necessarily
sufficient, it is less than enough to exert the economical effect
described above. In addition, although MgO and Al are less
expensive than Mg, they are not so inexpensive; which creates
demands for flux still less expensive.
DISCLOSURE OF INVENTION
[0009] An object of the present invention is to provide a refining
agent, which uses a Mg source and allows molten iron refining to be
performed efficiently and inexpensively, and a refining method
using the agent.
[0010] According to a first aspect of the present invention, there
is provided a refining agent containing Al, MgO, and CaO as main
components, and including a material as a MgO source and CaO
source, in which MgO and CaO are close to or in contact with each
other in a minute state, the refining agent being arranged to
produce Mg vapor due to a reaction in molten iron, when the
refining agent is supplied into the molten iron.
[0011] According to a second aspect of the present invention, there
is provided a refining agent containing Al, MgO, and CaO as main
components, and including dolomite as a MgO source and CaO source,
the refining agent being arranged to produce Mg vapor due to a
reaction in molten iron, when the refining agent is supplied into
the molten iron.
[0012] According to a third aspect of the present invention, there
is provided a refining agent containing Al, MgO, and CaO as main
components, and including dolomite as a MgO source and CaO source,
wherein Al/MgO is 0.05 or more in mass ratio, and CaO/MgO is in a
range of 0.5 to 10.0 in mass ratio.
[0013] According to a fourth aspect of the present invention, there
is provided a refining agent containing Al, C, MgO, and CaO as main
components, and arranged to produce Mg vapor due to a reaction in
molten iron, when the refining agent is supplied into the molten
iron.
[0014] According to a fifth aspect of the present invention, there
is provided a refining agent containing Al, C, MgO, and CaO as main
components, wherein Al/MgO is 0.05 or more in mass ratio, C/MgO is
0.1 or more in mass ratio, and CaO/MgO is in a range of 0.5 to 10.0
in mass ratio.
[0015] According to a sixth aspect of the present invention, there
is provided a refining method of performing desulfurization
treatment of molten pig iron by adding a refining agent to the
molten pig iron held in a container, the refining agent containing
Al, MgO, and CaO as main components, and including a material as a
MgO source and CaO source, in which MgO and CaO are close to or in
contact with each other in a minute state.
[0016] According to a seventh aspect of the present invention,
there is provided a refining method of performing desulfurization
treatment of molten pig iron by adding a refining agent to the
molten pig iron held in a container, the refining agent containing
Al, MgO, and CaO as main components, and including dolomite as a
MgO source and CaO source.
[0017] According to an eighth aspect of the present invention,
there is provided a refining method of refining molten pig iron by
performing a series of treatment, which is formed of
desulfurization treatment and at least one of desiliconization
treatment and dephosphorization treatment, on molten pig iron after
tapping from blast furnace and before decarburization in converter,
wherein the desulfurization treatment is performed by adding a
refining agent to the molten pig iron held in a container, the
refining agent containing Al, MgO, and CaO as main components, and
including dolomite as a MgO source and CaO source.
[0018] According to a ninth aspect of the present invention, there
is provided a refining method of refining molten pig iron by
performing a series of treatment, which is formed of
desulfurization treatment and at least one of desiliconization
treatment and dephosphorization treatment, on molten pig iron after
tapping from blast furnace and before decarburization in converter,
wherein the desulfurization treatment is performed by adding a
refining agent to the molten pig iron held in a container, the
refining agent containing Al, MgO, and CaO as main components, and
including dolomite as a MgO source and CaO source, and wherein a
total consumption of fluorite in the series of treatment is set to
be 0.1 kg or less per ton of molten pig iron.
[0019] According to a tenth aspect of the present invention, there
is provided a refining method of performing at least one of
desulfurization treatment, deoxidation treatment, and inclusion
control of molten steel by adding a refining agent to the molten
steel, the refining agent containing Al, MgO, and CaO as main
components, and including dolomite as a MgO source and CaO
source.
[0020] According to an eleventh aspect of the present invention,
there is provided a refining method of performing making high clean
molten steel by adding a refining agent to molten steel deoxidated
by a predetermined element, the refining agent containing Al, MgO,
and CaO as main components, and including dolomite as a MgO source
and CaO source.
[0021] According to a twelfth aspect of the present invention,
there is provided a refining method of performing desulfurization
treatment of molten pig iron by adding a refining agent to the
molten pig iron held in a container, the refining agent containing
Al, C, MgO, and CaO as main components.
[0022] According to a thirteenth aspect of the present invention,
there is provided a refining method of refining molten pig iron by
performing a series of treatment, which is formed of
desulfurization treatment and at least one of desiliconization
treatment and dephosphorization treatment, on molten pig iron after
tapping from blast furnace and before decarburization in converter,
wherein the desulfurization treatment is performed by adding a
refining agent to the molten pig iron held in a container, the
refining agent containing Al, C, MgO, and CaO as main
components.
[0023] According to a fourteenth aspect of the present invention,
there is provided a refining method of refining molten pig iron by
performing a series of treatment, which is formed of
desulfurization treatment and at least one of desiliconization
treatment and dephosphorization treatment, on molten pig iron after
tapping from blast furnace and before decarburization in converter,
wherein the desulfurization treatment is performed by adding a
refining agent to the molten pig iron held in a container, the
refining agent containing Al, C, MgO, and CaO as main components,
and wherein a total consumption of fluorite in the series of
treatment is set to be 0.1 kg or less per ton of molten pig
iron.
[0024] According to a fifteenth aspect of the present invention,
there is provided a refining method of performing at least one of
desulfurization treatment, deoxidation treatment, and inclusion
control of molten steel by adding a refining agent to the molten
steel, the refining agent containing Al, C, MgO, and CaO as main
components.
[0025] According to a sixteenth aspect of the present invention,
there is provided a refining method of performing making high clean
molten steel by adding a refining agent to molten steel deoxidated
by a predetermined element, the refining agent containing Al, C,
MgO, and CaO as main components.
[0026] According to a seventeenth aspect of the present invention,
there is provided a desulfurization slag recycling method of
performing desulfurization treatment of molten pig iron by adding a
refining agent to the molten pig iron, and then recycling
desulfurization slag thus generated as a raw material to be
sintered for a blast furnace, the refining agent containing Al,
MgO, and CaO as main components, and including dolomite as a MgO
source and CaO source.
[0027] According to the present invention, since Al, MgO, and CaO
are used as main components, the rate of MgO changing into Mg vapor
is increased. Since a material, in which MgO and CaO are close to
or in contact with each other in a minute state, is used as a MgO
source and CaO source, the reactivity is increased. Accordingly,
refining of molten iron, using a Mg source, can be performed with
an extremely high efficiency. Where dolomite, which is inexpensive,
is used as a MgO source and CaO source having a material, in which
MgO and CaO are close to or in contact with each other in a minute
state, refining of molten iron, using a Mg source, can be performed
with an extremely high efficiency and inexpensively.
[0028] Where Al, MgO, and CaO are used as main components, while
the Al used as a reducing agent is partly replaced with C, which is
inexpensive, refining of molten iron can be also performed
inexpensively. In this case, where a material having a material, in
which MgO and CaO are close to or in contact with each other in a
minute state, is used as a MgO source and CaO source, refining of
molten iron, using a Mg source, can be performed with an extremely
high efficiency. Where dolomite, which is inexpensive, is used as
such a MgO source and CaO source, refining of molten iron, using a
Mg source, can be performed with an extremely high efficiency and
inexpensively.
[0029] A refining agent according to the present invention exerts
an excellent refining effect, where it is applied to
desulfurization of molten pig iron, or desulfurization or
deoxidation of molten steel, and it allows inclusion control after
deoxidation of molten steel to reduce the number of product
defects.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a view showing existence images of CaO and MgO in
dolomite and in a mixture of lime and brucite, to perform a
comparison between them;
[0031] FIG. 2 is a view showing the relationship between the Al/MgO
value of a refining agent and the Mg reduction rate;
[0032] FIG. 3 is a view showing the relationship between the Al/MgO
value of a refining agent and the desulfurization rate;
[0033] FIG. 4 is a view showing the relationship between the
CaO/MgO value of a refining agent and the Mg reduction rate;
[0034] FIG. 5 is a view showing the relationship between the Al/MgO
value of a refining agent and the Mg reduction rate, in the case of
containing no C, and in the case of adding C(C/MgO=0.3 and
1.0);
[0035] FIG. 6 is a schematic view showing a state of desulfurizing
molten pig iron by a mechanically stirring type desulfurization
apparatus, using a refining agent according to the present
invention;
[0036] FIG. 7 is a schematic view showing a state of desulfurizing
molten pig iron by an injection method, using a refining agent
according to the present invention;
[0037] FIG. 8 is a view showing a state of refining molten steel by
an RH vacuum degassing setup, using a refining agent according to
the present invention;
[0038] FIG. 9 is a view showing a state of molten pig iron
desulfurization slag by a mechanically stirring type and a state of
creating a new surface, to perform a comparison with molten pig
iron desulfurization slag by an injection method;
[0039] FIG. 10 is a view showing a treatment pattern for recycling
desulfurization slag by a practical machine;
[0040] FIG. 11 is a graph showing the relationship between the
CaO/MgO ratio and the desulfurization rate in a example 1;
[0041] FIG. 12 is a graph showing the relationship between the
Al/MgO ratio and the desulfurization rate in the example 1;
[0042] FIG. 13 is a graph showing the relationship between the
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.alpha..sub.siO2+.alpha..sub.Al2O3)
value and the desulfurization rate, in the case of setting
Al/MgO=0.45 to be constant, and setting the CaO/MgO value of flux
at 0, 0.88, 2, 4.5, and .infin., in a example 5; and
[0043] FIG. 14 is a graph showing the relationship between the
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value and the desulfurization
rate, in the case of setting Al/MgO=0.45 to be constant, and
setting the CaO/MgO value of flux at 0, 0.88, 2 (dolomite), 4.5,
and .infin., in the example 5.
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] Embodiments of the present invention will now be described
in detail, while dividing them into items.
[0045] I. Refining Agent
(1) First Embodiment
[0046] A refining agent according to the first embodiment of the
present invention contains Al, MgO, and CaO as main components, and
includes a material, in which MgO and CaO are close to or in
contact with each other in a minute state, as a MgO source and CaO
source. Typically, it includes dolomite as a MgO source and CaO
source. When the refining agent is supplied into molten iron, it
produces Mg vapor due to a reaction in the molten iron, and causes
a refining reaction by the Mg vapor.
[0047] In the present invention, since CaO is added, Mg vapor is
produced in accordance with the following formulas (4) to (7), in
place of the formula (3).
6MgO+4Al+CaO.fwdarw.6Mg(g)+CaO.2Al.sub.2O.sub.3 (4)
3MgO+2Al+CaO.fwdarw.3Mg(g)+CaO.Al.sub.2O.sub.3 (5)
21MgO+14Al+12CaO.fwdarw.21Mg(g)+12CaO.7Al.sub.2O.sub.3 (6)
3MgO+2Al+3CaO.fwdarw.3Mg(g)+3CaO.Al.sub.2O.sub.3 (7)
[0048] In the formula (3), MgO in the starting substance is partly
consumed in producing MgO.Al.sub.2O.sub.3, and thus the ratio of
MgO changing into Mg vapor is suppressed to 75% at most. On the
other hand, in the formulas (4) to (7), in place of MgO, CaO
produces a complex oxide in cooperation with Al.sub.2O.sub.3, and
thus the efficiency of MgO changing into Mg vapor is high.
Theoretically, all the MgO can change into Mg vapor, thereby
further improving the cost efficiency
[0049] In order to allow the reaction set out in the formulas (4)
to (7) to effectively proceed, it is important MgO and CaO are
close to or in contact with each other in the minute state.
Accordingly, a material in which MgO and CaO are close to or in
contact with each other in a minute state is used as a CaO source
and MgO source. Dolomite is preferably used as such a CaO source
and MgO source. FIG. 1 is a view showing existence images of CaO
and MgO in the case of using dolomite (see the left side) and in
the case of mixing lime used as a CaO source and brucite used as a
MgO source (see the right side), to perform a comparison between
them. Since dolomite is a solid solution of CaO and MgO, MgO and
CaO always coexist in any fine powder state, thereby providing a
mixed state remarkably minute, as compared to the right side case
where MgO particles and CaO particles are mechanically mixed.
Accordingly, dolomite is very effective to provide a form in which
MgO and CaO are close to or in contact with each other in a minute
state.
[0050] In addition, where dolomite is used as a CaO source and MgO
source, CaO in the dolomite also sufficiently contributes to a
refining reaction, especially to a desulfurization reaction, so
that the refining can be performed with a very high efficiency.
Dolomite is less expensive than conventional MgO sources, and thus
the raw material itself becomes inexpensive. As a result, molten
iron refining, using a Mg source, can be performed with a high
efficiency and inexpensively.
[0051] Dolomite used as a CaO source and MgO source in the present
invention is defined by a concept including any of raw dolomite
(dolomite as a mineral), burnt dolomite obtained by burning raw
dolomite, and a mixture of them. Particularly, light-burnt dolomite
(obtained by heating and burning raw dolomite at a temperature of
1,000 to 1,300.degree. C.), which is very reactive, is preferably
used as the dolomite. Specifically, light-burnt dolomite has a
large specific surface area and large porosity, and is active. In
addition, it contains CaO and MgO uniformly mixed in a
micro-structure. Accordingly, light-burnt dolomite remarkably
increases the rate of the reaction set out in the formulas (4) to
(7), thereby greatly improving the desulfurization rate, as
compared to a case where CaO particles and MgO particles are
mechanically mixed.
[0052] Mineral dolomite has a theoretical composition of
CaMg(CO.sub.3).sub.2, but greatly varies in CaO and MgO contents
depending on the producing district, with a CaO/MgO mass ratio
falling in a range of about 1 to 2. Dolomite decomposes and emits
CO.sub.2 in air or CO.sub.2 by the following two steps, and, when
being heated more, it becomes a solid solution of CaO and MgO.
CaMg(CO.sub.3).sub.2.fwdarw.CaCO.sub.3+MgO+CO.sub.2 (730 to
810.degree. C.)
CaCO.sub.3.fwdarw.CaO+CO.sub.2 (890 to 930.degree. C.)
[0053] For example, dolomite produced from Tochigi Prefecture,
Japan, approximately contains 63 to 66 mass % CaO and 30 to 35 mass
% MgO, after being burnt.
[0054] A material containing 25 mass % or more metal Al is used as
an Al source functioning as a reducing agent. The Al purity is
preferably higher, because the quantity of effective components
becomes larger in flux. An Al purity of 25 mass % suffices refining
functions, such as desulfurization, without a hindrance. Aluminum
dross is preferably used as such an Al source, because it is
inexpensively available. As a matter of course, another Al source,
such as atomized powder obtained by atomizing molten aluminum
liquid with gas, or powder from cutting, which is generated by
grinding and cutting an aluminum alloy, may be used.
[0055] The MgO source and CaO source may include a MgO source and
CaO source other than dolomite. Where MgO and CaO are to be
contained at the same ratio as in dolomite, a raw material other
than dolomite and an Al source does not have to exist. In order to
further increase the MgO ratio, another MgO source is combined to
adjust the composition. As another MgO source, brucite or magnesite
is preferably used in light of the price, but seawater MgO can be
used. In order to further increase the CaO ratio from the dolomite
composition, another CaO source is combined to adjust the
composition. As another CaO source, lime, calcium carbonate or
calcium hydroxide may be used.
[0056] The particle size of these raw materials is an important
factor, which dominates the reactivity. In order to produce Mg
vapor at a high reaction rate, it is preferable that the primary
particles of 1 mm or less of each raw material form a powdered
refining agent. Furthermore, in order to efficiently perform a
refining operation in molten iron, such powdered body having
primary particles of 1 mm or less may be formed into a pelletized
or lumped form sized to be 3 to 40 mm. In this case, dry forming is
preferably used. It is necessary, however, for the pelletized and
lumped forms to readily break down in molten iron so that the area
of a reaction surface is ensured.
[0057] In a refining agent according to this embodiment, it is
preferable that Al/MgO is 0.05 or more in mass ratio, and CaO/MgO
is in a range of 0.5 to 10.0 in mass ratio.
[0058] The reasons for this will be explained with reference to
FIGS. 2 to 4. FIG. 2 is a view showing the relationship between the
Al/MgO value, which is on the horizontal axis, of a refining agent,
and the Mg reduction rate, which is on the vertical axis. FIG. 3 is
a view showing the relationship between the Al/MgO value, which is
on the horizontal axis, of a refining agent, and the
desulfurization rate, which is on the vertical axis, obtained by
actually performing desulfurization treatment. FIG. 4 is a view
showing the relationship between the CaO/MgO value, which is on the
horizontal axis, of a refining agent, and the Mg reduction rate,
which is on the vertical axis. These results were obtained by using
a temperature range of 1,300 to 1,400.degree. C. The Mg reduction
rate was defined as follows:
Mg reduction rate=(MgO quantity reduced to Mg)/(the whole MgO
quantity in a refining agent)
[0059] As shown in FIG. 2, where the Al/MgO mass ratio is 0.05, the
Mg reduction rate is about 20%. As shown in FIG. 3, even in such a
case, the desulfurization rate obtained is more than 80%.
Accordingly, the Al/MgO mass ratio is preferably 0.05 or more.
Where the Al/MgO is 0.2 or more, the Mg reduction rate is 40% or
more, and the desulfurization rate is more that 90%, which is a
high level, and thus this is more preferable. The upper limit of
the Al/MgO does not specifically exist. In this respect, the Al
source is most expensive in the raw materials, and the effect is
saturated where the Al/MgO is more than 0.6. Accordingly, in light
of the cost efficiency, the Al/MgO is preferably set at 0.6 or
less.
[0060] As clearly shown in FIG. 4, where the CaO/MgO is 0.5 or
more, the Mg reduction rate abruptly increases. On the other hand,
where the CaO/MgO is 1.1 or more, the Mg reduction rate does not
increase any more. However, since CaO itself has a desulfurization
function, a desulfurization reaction is effectively caused until
the CaO/MgO is 10.0. Accordingly, the CaO/MgO is preferably in a
range of 0.5 to 10. Where the CaO/MgO is 0.75 or more, about 90% or
more of Mg changes into Mg vapor without producing
MgO.Al.sub.2O.sub.3, and thus it is preferable.
[0061] Where the CaO/MgO is more than 1.5 and up to 10, dolomite
can be used as a Mg source at a high rate, and thus the amount of
the other MgO sources to be used can be reduced, thereby being
economical. Particularly, where the CaO/MgO is in the dolomite
composition range, essentially only dolomite is used as a CaO
source and MgO source. In this case, the Mg gas generation
efficiency can be increased to the maximum and is remarkably
economical. Where the CaO/MgO is larger than the dolomite
composition range, lime or the like is added as a CaO source. In
this case, since the price of lime or the like used as a CaO source
is not more than that of dolomite, and thus it is economical.
However, where the CaO/MgO is more than 10, the CaO ratio is too
high and the effect of dolomite is reduced.
[0062] In this embodiment, it is preferable that the sum of MgO,
CaO, and Al is set at 75 mass % or more in a refining agent. Where
it is less than 75 mass %, components effective in the refining
function are reduced, and thus it is uneconomical and brings about
a low reaction rate.
[0063] In order to change raw materials into a pelletized form or
lumped form, a binder is preferably used. Where a binder is used, a
non-water-based binder is used, because a MgO source, such as
light-burnt dolomite or brucite, is active to water, and does not
allow a water-based binder to be used. A binder used preferably has
a fixed carbon content of 30 to 40 mass %, and has a viscosity of 2
to 10 poise at 60%. Where such a binder is combined at 1 to 4 mass
% of the whole raw material powder, a formed body having a
sufficient strength can be obtained. Where the viscosity of a
binder exceeds 10 poise, it is difficult to obtain a uniformly
kneaded state of the binder and raw material powder. Where the
viscosity of a binder is less than 2 poise, the formation strength
decreases, and the formed body tends to easily change into powder
upon handling in transfer after forming.
(2) Second Embodiment
[0064] A refining agent according to the second embodiment of the
present invention contains Al, C, MgO, and CaO as main components.
When the refining agent is supplied into molten iron, it produces
Mg vapor and a complex oxide of CaO and Al.sub.2O.sub.3 due to a
reaction in the molten iron, and causes a refining reaction by the
Mg vapor.
[0065] In the embodiment described above, although Al is used as a
reducing agent, Al is relatively expensive. Accordingly, in this
embodiment, Al and C are used together as a reducing agent, so that
the Al quality is reduced to make flux inexpensive.
[0066] FIG. 5 is a view showing the relationship between the Al/MgO
value, which is on the horizontal axis, of a refining agent, and
the Mg reduction rate, which is on the vertical axis, in the case
of containing no C, and in the case of adding C(C/MgO=0.3 and 1.0).
This result was obtained by adding a refining agent to molten iron
at a temperature of 1,300 or more, with CaO/MgO=2.0.
[0067] As is understood from FIG. 5, the Mg reduction rate slightly
increases, as C is added and C increases. It is thus drawn that C
is effective as a reducing agent.
[0068] In this embodiment, the MgO source and CaO source are not
limited to a specific one. However, as in the first embodiment, it
is preferable to use a material as a MgO source and CaO source, in
which MgO and CaO are close to or in contact with each other in a
minute state. Dolomite is preferably used such a CaO source and MgO
source.
[0069] Also in this embodiment, a material containing 25 mass % or
more metal Al, such as aluminum dross powder, is used as an Al
source functioning as a reducing agent. Graphite powder, coke
powder, fine powder coal, or the like may be used as a C
source.
[0070] Also in this embodiment, in order to increase the Mg
reduction rate, and improve the reaction efficiency of a refining
reaction, primary particles of each raw material preferably form a
powdered refining agent of 1 mm or less. Furthermore, in order to
efficiently perform a refining operation in molten iron, such
powdered body having primary particles of 1 mm or less may be
formed into a pelletized or lumped form sized to be 3 to 40 mm. It
is necessary, however, for the pelletized or lumped forms to
readily break down in molten iron so that the area of a reaction
surface is ensured.
[0071] In refining flux according to this embodiment, it is
preferable that Al/MgO is 0.05 or more in mass ratio, C/MgO is in a
range of 0.1 or more in mass ratio, and CaO/MgO is in a range of
0.5 to 10.0 in mass ratio. Where the Al/MgO is 0.05 or more, Mg
vapor is generated to some extent by the reduction action of Al,
thereby allowing the refining reaction to effectively proceed, as
described above. Where the C/MgO mass ratio is less than 0.1, the
effect of C is not effectively exerted. As in the embodiment
described above, where the CaO/MgO is 0.05 or more, the Mg
reduction rate abruptly increases. Since CaO itself has a
desulfurization function, a desulfurization reaction is effectively
caused until the CaO/MgO is 10.0.
[0072] Also as in the embodiment described above, where the CaO/MgO
is 0.75 or more, about 90% or more of Mg changes into Mg vapor
without producing MgO.Al.sub.2O.sub.3, and thus it is preferable.
Also as in the embodiment described above, where the CaO/MgO is
more than 1.5 and up to 10, dolomite can be used as a Mg source at
a high rate, and thus the amount of the other MgO sources to be
used can be reduced, thereby being economical.
[0073] Particularly, where the CaO/MgO is in the dolomite
composition range, essentially only dolomite is used as a CaO
source and MgO source. In this case, the Mg gas generation
efficiency can be increased to the maximum and is remarkably
economical. Where the CaO/MgO is larger than the dolomite
composition range, lime or the like is added as a CaO source. In
this case, since the price of lime or the like used as a CaO source
is not more than that of dolomite, and thus it is economical.
[0074] In this embodiment, it is preferable that the sum of MgO,
CaO, Al, and C is set at 75 mass % or more in a refining agent.
Where it is less than 75 mass %, components effective in the
refining function are reduced, and thus it is uneconomical and
brings about a low reaction rate.
[0075] A refining agent according to the present invention can be
applied to any molten iron, such as molten pig iron, molten steel,
or cast pig iron, and can be applied to deoxidation as well as
desulfurization. Specifically, although a refining agent according
to the present invention is effective as a desulfurization agent
especially for molten pig iron, it also exerts a desulfurization
effect for molten steel or molten pig iron for castings, and
further exerts an effect as a deoxidation agent for molten steel.
In addition, desulfurization and deoxidation can be performed at
the same time.
[0076] A refining agent according to any one of the embodiments
described above of the present invention allows desulfurization of
molten pig iron to be performed without using a F-containing
substance, such as fluorite. Conventionally, such a substance is
essentially used as slag formation flux, when a refining agent is
used as a desulfurization agent. Accordingly, where selected
dolomite, an Al source, another CaO source, and another MgO source,
which are raw materials, essentially contain no F, it is possible
to provide a refining agent containing substantially no F in
itself. As a result, the F content of slag becomes very low after
desulfurization treatment, thereby preventing ill effects on the
environment. Some of Al sources inevitably contain F. Even where
such an Al source is used, its quantity can be regulated, so that
the F content of slag is 0.1 mass % or less after desulfurization
treatment, thereby preventing ill effects on the environment.
Although it depends on conditions, such as the Al source addition
quantity, desulfurization agent charge quantity, and other slag
mixed therein, the F content in an Al source is preferably set at
0.15 mass % or less, to allow the F content of slag to be 0.1 mass
% or less after desulfurization treatment.
[0077] II. Refining Method
[0078] Next, an explanation will be given of a refining method,
using a refining agent according to the present invention.
[0079] (1) Desulfurization of Molten Pig Iron
[0080] Where a refining agent according to the present invention is
applied to desulfurization treatment of molten pig iron, the
refining agent is added to molten pig iron held in a container,
such as a ladle, a torpedo car, or a runner in a cast house, so
that desulfurization treatment for the molten pig iron is
performed. In the desulfurization of molten pig iron, using the
refining agent, the components or the like of the molten pig iron
are not limited to specific ones. It may be applied to any molten
pig iron, e.g., to low Si pig iron with no problem. A method of
adding the refining agent to cause the desulfurization reaction is
also not limited to a specific one. It is possible to adopt one of
various types of methods, such as a method of charging a refining
agent from directly above molten pig iron, and mechanically
stirring it by, e.g., an impeller; a method of injecting a refining
agent into molten pig iron; a method of placing a refining agent on
molten pig iron; a putting-in method of putting a refining agent in
a container in advance, and then introducing molten pig iron into
the container; and a method of adding a refining agent to molten
pig iron in a runner in a cast house. Among these methods, the
mechanically stirring method or the injection method is preferably
used.
[0081] In relation to the grain size of the refining agent, any of
lumped, pelletized, and powdered forms, and any of grain sizes can
be used, but an optimum shape and grain size may be selected,
depending on the container, process, or desulfurization method to
be used. For example, where a large amount of refining agent is
added from directly above molten pig iron in the mechanically
stirring method or the like, it is preferable to use the refining
agent with a size almost not smaller than the grain size that is
optimum in operation or economy, so that yield loss due to
scattering or the like is reduced. On the other hand, where the
refining agent is used in the injection method, it should be
powdered at a level to prevent nozzle clogging. In any case, the
particle size of the refining agent is an important factor, which
dominates the reactivity. As described above, it is preferable that
the primary particles of each raw material form a powdered refining
agent of 1 mm or less. Furthermore, in order to efficiently perform
a refining operation in molten iron, such powdered body having
primary particles may be formed into a pelletized or lumped form
sized to have a diameter of about 3 to 40 mm, depending on the
container, process, or desulfurization method to be used. It is
necessary, however, for the pelletized or lumped forms to readily
break down in molten iron so that the area of a reaction surface is
ensured.
[0082] Where a refining agent according to the present invention is
added to molten pig iron, dolomite and an Al source, and another
CaO source and/or another MgO source, which are added as the need
arises, may be added as a mixture formed by mixing them all
together in advance, or may be added without mixing them in
advance. This is so in any of the preferable methods described
above, i.e., the mechanically stirring method and injection method,
and in any of other methods, e.g., the putting-on method and
putting-in method.
[0083] Where the raw materials are not mixed in advance, the
addition position and addition timing of each raw material can be
variously adjusted. Specifically, the raw materials may be added at
the same position or at different positions. The raw materials may
be added at the same time or at different times. In any case, the
raw materials are added together or separately at several times.
The same or different addition positions and addition timing of the
raw materials can be combined in a large number of addition
patterns.
[0084] Such a large number of addition patterns can be realized by,
e.g., (i) an addition setup including a plurality of raw material
hoppers for independently storing respective raw materials, and a
mechanism for independently performing taking-out or injection of
the respective raw materials from the raw material hoppers into
molten pig iron in a container; (ii) an addition setup including a
plurality of raw material hoppers for independently storing
respective raw materials, an intermediate hopper for temporarily
storing the raw materials supplied from the plurality of raw
material hoppers at arbitrary quantities, and a mechanism for
performing taking-out or injection of the raw materials from the
intermediate hopper into molten pig iron in a container; or (iii)
an addition setup including a plurality of hoppers for
independently storing respective raw materials, an intermediate
hopper for temporarily storing the raw materials supplied from the
hoppers at arbitrary quantities, a mixing apparatus for mixing the
raw materials stored in the intermediate hopper, and a mechanism
for performing taking-out or injection of the raw materials from
the intermediate hopper into molten pig iron in a container.
[0085] In the case of using the addition setup (i), the addition
times of the raw materials may be set the same in part or in all,
or may be set different from each other, while the addition
positions of the raw materials are set different from each other.
In this case, the addition positions of the raw materials may be
set the same by adjusting the orientations of the raw material
addition ports. In the case of using the addition setup (ii), the
addition times of the raw materials may be set the same in part or
in all, or may be set different from each other, while the addition
positions of the raw materials are set the same. In the case of
using the addition setup (iii), the addition times of the raw
materials can be set the same, while the addition positions of the
raw materials are set the same.
[0086] As described above, a concrete example of adding a refining
agent in a non-mixed state according to the present invention to
molten pig iron may be made such that an Al source in part or in
all is added to molten steel separately from the other raw
materials, using the addition setup (i) or (ii). In this case, the
Al source may be added to molten pig iron before or after, or both
of before and after dolomite or the like is added. Furthermore, the
Al source may be added while dolomite or the like is added. For
example, a recipe may be made such that a part of the Al source is
first added to the molten pig iron, and then the rest of the Al
source is added at a time or over several times while or after
dolomite or the like is added.
[0087] Where raw materials are mixed in advance, a method may be
adopted such that the mixed raw materials are stored in one hopper,
and then added to molten pig iron in a container at a time or over
several times. This method has a merit in that the number of
hoppers can be small. Pre-mixing of raw materials and non-mixing of
raw materials may be used together. In this case, an addition setup
having a hopper, which stores the raw materials mixed in advance,
and the addition setup (i), (ii), or (iii) may be used
together.
[0088] A refining agent according to the present invention can be
added by various kinds of addition setups, from which an
appropriate setup is selected in accordance with the addition
pattern.
[0089] In desulfurization treatment using a refining agent
according to the present invention, since the molten pig iron
temperature greatly influences Mg gas generation from MgO, the
molten pig iron temperature, before the treatment, is important. In
order to effectively generate Mg gas by the reaction set out in the
formula (6), the temperature is preferably 1,300.degree. C. or more
in view of thermodynamics. However, where the temperature is
1,300.degree. C. or less, the reaction set out in the formula (6)
actually proceeds. In practice, even where the temperature is
1,200.degree. C. or more, the reaction can proceed. Accordingly,
before the desulfurization treatment, the molten pig iron
temperature is set at 1,200.degree. C. or more, and preferably at
1,300.degree. C. or more.
[0090] When the necessary charge quantity of a used refining agent
according to the present invention is determined in desulfurization
treatment, the following matters should be considered. As a matter
of course, if the addition quantity is short, the necessary
desulfurization quantity cannot be obtained. If the charge is
excessive, ill effects are brought about such that the treatment
time is prolonged, the molten pig iron temperature is lowered, and
the generated slag quantity increases. It is necessary, therefore,
to add a refining agent at an optimum quantity relative to a
required desulfurization quantity.
[0091] In a refining agent according to the present invention, a
material, typically dolomite, having a material in which MgO and
CaO are close to or in contact with each other in a minute state,
is used as a MgO source and CaO source. Furthermore, another MgO
source and CaO source are used, as the need arises. These materials
contribute to desulfurization conceivably in terms of the following
three items. It should be noted as an important point, that MgO in
dolomite and MgO in a further added MgO source differ from each
other in both of the Mg gas generation quantity and desulfurization
efficiency, and thus they need to be separately considered.
[0092] (i) Desulfurization by Mg gas and Mg generated from MgO in
dolomite.
[0093] (ii) Desulfurization by Mg gas and Mg generated from MgO in
a further added MgO source.
[0094] (iii) Desulfurization by CaO.
[0095] Influential factors of each of them will be discussed.
[0096] In the following formula (8) to (11), symbols stand for the
following matters: W1.sub.MgO for MgO unit requirement (kg/t) in
dolomite; W2.sub.MgO for MgO unit requirement (kg/t) in other MgO
source than dolomite; W.sub.CaO for CaO unit requirement (kg/t)
W.sub.Al for added Al unit requirement (kg/t); T for molten pig
iron temperature (.degree. C.) before treatment; [S]i for S
concentration (%) before treatment; .omega. for stirring power
(W/t); c for Al contribution rate to MgO reduction;
.alpha..sub.1.multidot..alpha..sub.2 for desulfurization efficiency
(reaction efficiency with S in molten pig iron) of Mg gas and Mg
dissolved in molten pig iron, generated from MgO;
.beta..sub.1.multidot..beta..sub.2 for generation rate of Mg gas
and dissolved Mg, from MgO; .gamma. for desulfurization efficiency
(reaction efficiency with S in molten pig iron) of CaO; and
.DELTA.S for required desulfurization quantity (kg/t).
[0097] Re (i):
[0098] The generation rate .beta. of generating Mg gas and
dissolved Mg from MgO will be considered. This is greatly
influenced by the molten pig iron temperature and Al addition
quantity. The Al contribution rate c to MgO reduction also needs to
be considered. The contribution rate c depends on a method of
crushing a refining agent. For example, where a mixing and crushing
manner of crushing aluminum dross and dolomite while mixing them is
adopted, the contact probability is higher, thereby increasing the
contribution rate. On the other hand, where aluminum dross and
dolomite are separately charged, the contact probability is lower,
thereby reducing the contribution rate c. The contribution rate c
is also influenced by the oxygen concentration in molten pig iron
before the treatment. Where the oxygen concentration is high, the
Al quantity contributing to deoxidation increases, thereby
relatively reducing the contribution rate c to MgO reduction.
Furthermore, the efficiency a at which generated Mg gas and Mg
react with S in molten pig iron will be considered. It is thought
that the .alpha. depends on the S concentration in molten pig iron
and stirring power. The degree of dependence on the stirring power
varies depending on the treatment method or the form of a setup,
and thus it is a coefficient empirically obtained in practical use.
For example, as the S concentration before the treatment or
stirring power increases, the .alpha. increases. In consideration
of all these factors, desulfurization quantity .DELTA.S.sub.1
(kg/t) by Mg gas and dissolved Mg generated from MgO in dolomite is
expressed by the following formula (8).
.DELTA.S.sub.1.dbd.{W2.sub.MgO.times..alpha..sub.1.times..beta..sub.1.time-
s.32/40 } (8)
[0099] where .alpha..sub.1=f([S]i, .omega.), .beta..sub.1=f(T, c,
W.sub.Al)
[0100] Re (ii):
[0101] As in (i) described above, the same influential factors need
to be considered. In this case, since MgO in dolomite and MgO in
other MgO source than dolomite differ from each other in both of
the Mg gas generation quantity and desulfurization efficiency even
under the same conditions, the .alpha. and .beta. need to be
separately set. Where the Mg gas generation rate and
desulfurization efficiency in other MgO source than dolomite are
.beta..sub.2 and .alpha..sub.2, respectively, desulfurization
quantity .DELTA.S.sub.2 by Mg gas and dissolved Mg generated from
MgO in other MgO source than dolomite is expressed by the following
formula (9). If only dolomite is used, this term is negligible.
.DELTA.S.sub.2={W2.sub.MgO.times..alpha..sub.2.times..beta..sub.2.times.32-
/40} (9)
[0102] Re (iii):
[0103] The reaction efficiency .gamma. of CaO with S in molten pig
iron will be considered. Ii is thought that this efficiency depends
on the S concentration in molten pig iron, molten pig iron
temperature, and stirring power. As in the .alpha., the degree of
dependence on the stirring power varies depending on the treatment
method or the form of a setup, and thus it is a coefficient
empirically obtained from actual results in, e.g., the case of
using a lime-based desulfurization agent. As the S concentration
before the treatment, molten pig iron temperature before the
treatment, or stirring power increases, the .gamma. increases. In
consideration of these factors, desulfurization quantity
.DELTA.S.sub.3 by CaO is expressed by the following formula
(10).
.DELTA.S.sub.3={W.sub.CaO+.gamma..times.32/56} (10)
[0104] where .gamma.=f(T, [S]i, .omega.)
[0105] In consideration of (i) to (iii) described above, the
relationship between the charge unit requirement of a refining
agent and the desulfurization quantity .DELTA.S can be
obtained.
[0106] Accordingly, where a refining agent according to the present
invention is used to perform desulfurization, the refining agent
according to the present invention is added at a value not less
than the quantity obtained by the following formula (11) in
accordance with the desulfurization quantity .DELTA.S (kg/t). As a
result, the refining agent is added at an optimum quantity relative
to the desulfurization quantity to perform the desulfurization
treatment.
.DELTA.S={W1.sub.MgO.times..alpha..sub.1.times..beta..sub.1.times.32/40}+{-
W2.sub.MgO.times..alpha..sub.2.times..beta..sub.2.times.32/40}+{W.sub.CaO+-
.gamma..times.32/56} (11)
[0107] Where the mechanically stirring method is used, the
desulfurization efficiencies .alpha..sub.1, .alpha..sub.2, and
.gamma. can be increased in the formula (11), and thus the
desulfurization agent can exert the effects most effectively.
[0108] As the molten pig iron temperature before the treatment,
1,200.degree. C. or more is enough, as described above, but it is
preferably 1,300.degree. C. or more in view of thermodynamics. As
the temperature is higher, the generation rates .beta..sub.1 and
.beta..sub.2 of Mg gas and dissolved Mg from MgO are increased.
With a change in the molten pig iron temperature, the
desulfurization efficiency of a refining agent according to the
present invention changes, but the necessary refining agent
quantity can be appropriately obtained from the formula (11).
[0109] Furthermore, in relation to a method of adding the refining
agent, there is a case where it is effective that aluminum dross or
metal Al and lime used as an Al source is added separately from the
refining agent, depending on the oxygen concentration in molten pig
iron or the presence and absence of slag on molten pig iron before
the treatment. However, in consideration of the formula (11), it is
preferable to use a method of mixing an Al source with a MgO source
and CaO source including dolomite while crushing them (mixing and
crushing), and then adding them, in order to increase the contact
efficiency of the Al source with dolomite, and to increase the Al
contribution rate c to MgO reduction.
[0110] Desulfurization treatment using the formula (11) is not
limited to a specific operation method, but may be applied to any
of desulfurization operation methods, such as the mechanically
stirring method, the injection method, the putting-on method, and
the putting-in method.
[0111] In general, desulfurization treatment is usually performed
after desiliconization treatment or dephosphorization treatment,
and thus there is a case where, due to SiO.sub.2 and
Al.sub.2O.sub.3 in slag carried from the process before the
desulfurization treatment, the desulfurization function of the slag
is lowered. Consequently, depending on the slag composition, the
reaction set out in the formulas (4) to (7) does not efficiently
proceed, thereby hardly attaining a predetermined desulfurization
efficiency. It is important, therefore, to appropriately control
the composition of desulfurization slag, and to ensure the
desulfurization function of the slag. For this reason, it is
effective to grasp the composition of a refining agent to be
charged, and the composition of slag carried from a process before
the desulfurization treatment, and to control the slag quantity
before the desulfurization treatment and the refining agent charge
quantity, so that the desulfurization slag has an appropriate
composition range. Specifically, where the slag quantity is W
(kg/t) before the treatment, the charged refining agent quantity is
Q (kg/t), and the composition ratio of a substance i is .alpha.i,
it is effective for the slag quantity before the desulfurization
treatment, and the refining agent charge quantity to satisfy the
following formula (12).
Q(.alpha..sub.CaO+.alpha..sub.Mgo)/W(.alpha..sub.SiO2+.alpha..sub.Al2O3).g-
toreq.4 (12)
[0112] Furthermore, it is preferable to satisfy the following
formula (13), for the composition of desulfurization slag in
desulfurization treatment, formed by charging a refining agent
according to the present invention.
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3).gtoreq.3 (13)
[0113] As a consequence, the desulfurization slag comes to have a
appropriate composition range, so that the reaction set out in the
formulas (4) to (7) is effectively caused, thereby obtaining a high
desulfurization efficiency.
[0114] Next, a concrete explanation will be given about an
preferable example of a method of desulfurizing molten pig iron,
using a refining agent according to the present invention, as
described above.
[0115] Molten pig iron desulfurization will be first explained in a
case where a refining agent according to the present invention is
used in a mechanically stirring type desulfurization setup. FIG. 6
is a schematic view showing a state of desulfurizing molten pig
iron by such a mechanically stirring type desulfurization
apparatus.
[0116] Molten pig iron 13 is stored in a molten pig iron ladle 12
supported on a cart 11. The molten pig iron ladle 12 is placed such
that a set of blades (impeller) 16 made of a refractory and mounted
in an impeller stirring type desulfurization apparatus 14 is
positioned at a predetermined position. The impeller stirring type
desulfurization apparatus 14 includes, in addition to the impeller
16, a hydraulic motor 15 for rotating the impeller, a weighing
hopper 17, a rotary feeder 19 for taking out a refining agent 18
stored in the hopper 17. A dust-collecting hood 21 is equipped to
perform dust-collecting, and is moved down and used when the
treatment is performed. Weighing hoppers and charge ports for
miscellaneous materials, other than those for the refining agent,
are also disposed, although they are not shown.
[0117] In the impeller stirring type desulfurization apparatus, the
impeller 16 is moved down and immersed into the molten pig iron.
Upon the immersion, the hydraulic motor 15 is driven to rotate the
impeller 16, and to gradually increase the number of revolutions.
At the same time, an exhaust device is operated to suck generated
dust. When the number of revolutions of the impeller 16 rises to a
predetermined steady number of revolutions, the rotary feeder is
driven to supply a predetermined amount of desulfurization agent to
the molten pig iron.
[0118] At this time, the shape of the refining agent may be any one
of lumped, pelletized, and powdered forms, with any grain size.
Where the refining agent used is powdered, it should not be too
fine so as to prevent scattering loss during addition. On the other
hand, the refining agent is lumped or pelletized, it preferably has
strength such that it does not break down during transportation or
charge, but breaks down in the molten pig iron. Where it does not
break down in the molten pig iron, the reaction surface is reduced
and brings about an undesirable low reactivity. Furthermore, as the
case may be, it is effective to further add aluminum dross and
metal Al from miscellaneous materials charge ports before the
refining agent is added, depending on the presence and absence of
slag or quantity of slag on the molten pig iron in the molten pig
iron ladle before the desulfurization treatment, or the oxygen
concentration in the molten pig iron.
[0119] After supply of the refining agent is finished and stirring
for a predetermined time is finished, the impeller 16 is moved up
while the number of revolutions of the impeller 16 is reduced. When
slag rises up to cover the surface of the molten pig iron, and
becomes stationary, the desulfurization treatment of the molten pig
iron is completed.
[0120] Next, molten pig iron desulfurization will be explained in
the case of using a refining agent according to the present
invention in the injection method. FIG. 7 is a schematic view
showing a state of desulfurizing molten pig iron by the injection
method, using a refining agent according to the present
invention.
[0121] Molten pig iron 32 is stored in a container 31, and a lance
34 for injection is vertically inserted in the molten pig iron 32.
A refining agent 33 according to the present invention is injected
along with an inert gas, such as argon gas or nitrogen gas, into a
deep portion of the molten pig iron 32, through the lance 34, using
a dispenser, which is not shown. With this operation, a
desulfurization reaction is caused while the refining agent 33 goes
up to the molten metal surface and is present on the molten metal
surface, so that the desulfurization reaction of the molten pig
iron 32 proceeds. As the container 31, a ladle or torpedo car may
be used.
[0122] Where injection is adopted, the refining agent preferably
has pelletized or powdered body, and needs to be powdered with a
grain size to prevent nozzle clogging. Furthermore, as the case may
be, it is effective to further add aluminum dross and metal Al to
the molten pig iron 32 in the container 31 in advance, depending on
the presence and absence of slag or quantity of slag on the molten
pig iron in the ladle before the desulfurization treatment, or the
oxygen concentration in the molten pig iron. After an Al source is
added, bubbling may be performed by an inert gas, such as argon gas
or nitrogen gas, for a short time, so that the added Al source is
dissolved in the molten pig iron. The Al source may be put in the
container before the molten pig iron is introduced.
[0123] After injection of a predetermined amount of the refining
agent is finished, the refining agent stops being blown in, and the
lance is moved up. When slag rises up to cover the surface of the
molten pig iron, and becomes stationary, the desulfurization
treatment of the molten pig iron is completed.
[0124] Desulfurization treatment of molten pig iron, using a
refining agent according to the present invention has three steps
of (i) effectively generating Mg vapor from a refining agent, (ii)
causing the Mg vapor to react with sulfur in molten pig iron to fix
the sulfur content, and (iii) also fixing the sulfur content by a
CaO content added at the same time. In order to efficiently perform
these steps, it is necessary to control the shape, grain size,
adding method, and addition rate of the refining agent, as well as
the composition of the refining agent, depending on the container,
desulfurization method, or state of the molten pig iron, so as to
select optimum conditions to the case.
[0125] (2) Series of Molten Pig Iron Treatment Including
Desulfurization
[0126] Molten pig iron treatment is performed to increase the
purity of molten pig iron or molten steel obtained by decarburizing
molten pig iron, or to minimize the consumption of a refining agent
or energy for providing molten steel with a specific quality. For
this reason, in molten pig iron treatment in recent years, not only
molten pig iron desulfurization as described above is performed,
but also molten pig iron dephosphorization treatment is performed
at the same time, in general. Furthermore, in order to efficiently
perform dephosphorization treatment, it has been proposed and is
applied to a practical machine to perform desiliconization in
advance. In other words, desulfurization treatment as described
above is performed along with desiliconization treatment and/or
dephosphorization treatment as a part of molten pig iron treatment,
which is performed in a series, between tapping from a blast
furnace and decarburization.
[0127] However, desiliconization treatment or dephosphorization
treatment greatly differs from desulfurization treatment, in that
the former is "oxidation refining" entailing oxygen feed or
addition of a solid oxidation agent, while the latter is "reduction
refining" in which the efficiency can be increased with an increase
in the reduction ability.
[0128] Since molten pig iron desulfurization promotes a sulfide
production reaction involving reduction of a refining agent, such
as CaO, to efficiently remove sulfur in molten pig iron, it is
important to control the oxidation level of the molten pig iron,
which influences the reduction reaction. Where desulfurization
treatment is performed for molten pig iron with an increased
oxidation level after desiliconization treatment or
dephosphorization treatment, it is difficult to perform the
desulfurization with a high efficiency because the consumption of a
refining agent or reducing agent is increased, or the treatment
time is prolonged. In order to increase the desulfurization
efficiency under such a situation, it is important to use a
process, which is hardly affected by the desiliconization treatment
or dephosphorization treatment, or to control the oxidation level
after the treatment.
[0129] In general, desulfurization treatment can be performed
either before or after desiliconization treatment or
dephosphorization treatment, and can be appropriately placed,
depending on the temperature conditions suitable for each
treatment, steel type to be manufactured, setup positioning, or
distribution. In recent years, in view of the pursuit of efficiency
and environmental measures, it is required to reduce refining
agents and slag generation quantity. As a result, there is a case
where desiliconization or the like is performed immediately after
tapping from blast furnace, or desiliconization or
dephosphorization is further performed in a transportation
container. In other words, part of them is performed as a pre-step
of desulfurization in many cases. Desiliconization treatment or
dephosphorization treatment employs an oxidation agent, such as gas
oxygen or a solid oxidation source, and its reaction is hardly
performed together with a desulfurization reaction with a high
efficiency. Accordingly, in general, it is performed to (i)
exchange refining containers, (ii) temporarily exhaust slag before
the desulfurization treatment, i.e., slag after the
desiliconization or dephosphorization treatment, and (iii) reduce
the oxidation level of molten pig iron in a pre-process.
[0130] In relation to the object described above, where a refining
agent according to the present invention is used, molten pig iron
desulfurization can be more efficiently performed.
[0131] Specifically, a refining agent according to the present
invention contains Al, MgO, and CaO as main components, and
includes a state of a MgO source and CaO source, in which MgO and
CaO are close to or in contact with each other in a minute state.
Typically, dolomite is used for it. With this arrangement, it is
conceived to efficiently reduce MgO, and to efficiently fix sulfur
in molten pig iron as sulfide. Since Al is used as a refining
agent, the reduction reaction and the sulfide production reaction
described above are maximized, without being affected so much by
the oxidation level of molten pig iron. Accordingly, the order of
performing desulfurization step is not restricted in a series of
steps of molten pig iron treatment. Since such desulfurization
treatment is adopted, the series of treatment of molten pig iron
can be achieved inexpensively with a high efficiency, thereby
providing a very low concentration of phosphorus and sulfur, i.e.,
impurities.
[0132] Where a refining agent according to the present invention as
described above is used in desulfurization treatment of such a
series of treatment of molten pig iron, the desulfurization can be
performed with a low refining agent unit requirement and a high
efficiency. As a result, it is possible to reduce the total
refining agent unit requirement in the molten pig iron treatment
including the desulfurization treatment, and desiliconization
treatment and/or dephosphorization treatment, and to lower the slag
quantity exhausted from the series of treatment of molten pig
iron.
[0133] The series of treatment of molten pig iron is formed such
that at least one of desiliconization treatment and
dephosphorization treatment is performed in addition to
desulfurization treatment of molten pig iron, before
decarburization of the molten pig iron obtained by tapping from
blast furnace is finally performed. Removal of silicon may be
performed during dephosphorization treatment, thereby omitting
desiliconization treatment. In order to efficiently perform
dephosphorization, however, desiliconization treatment may be
separated from dephosphorization treatment, thereby performing both
of the desiliconization treatment and dephosphorization treatment
independently of each other. In such a series of treatment of
molten pig iron, the treatment order is basically not limited to a
specific one. For example, the treatment order is set to be (i)
desiliconization treatment--desulfurization
treatment--dephosphorizat- ion treatment in this order, (ii)
desiliconization treatment--dephosphoriz- ation
treatment--desulfurization treatment in this order, (iii)
desulfurization treatment--desiliconization
treatment--dephosphorization treatment in this order, (iv)
desulfurization treatment--dephosphorizatio- n treatment in this
order, or (v) desiliconization treatment--desulfurizat- ion
treatment in this order.
[0134] In desiliconization treatment of such a series of molten pig
iron treatment, it is preferable to reduce the silicon
concentration after the treatment to 0.2 mass % or less, in order
to improve the dephosphorization efficiency. Except for a case
where the silicon concentration in molten pig iron from a blast
furnace is low enough not to require specific desiliconization
treatment, desiliconization treatment is performed by a
desiliconization method in which a solid oxidation agent is added
by various methods in a blast furnace or in the course up to a
transportation container for molten pig iron; or a desiliconization
method in which gas oxygen or a solid oxidation agent, and a
refining agent are added by various methods, such as top blowing,
putting-on, and injection, while using a molten pig iron ladle,
transportation container, e.g., torpedo car, or special
furnace.
[0135] Dephosphorization treatment also uses transportation period
of molten pig iron after tapping, or a transportation container or
special furnace. In general, a flux, such as fluorite, is added
along with lime to perform the treatment, but lime alone may be
used to perform the treatment, in light of environmental measures.
In this case, a method of increasing the fusibility of lime, or
increasing the dephosphorization reaction rate is adopted. In order
to increase the fusibility of lime, it is possible to adopt various
methods, such as a method of using particulate or powdered lime,
and a refining method of adding a melting point lowering substance
having a fusing effect on lime, or increasing molten iron oxide.
Among them, where such a method is adopted that blows powdered lime
with oxygen by oxygen feeding means, such as bottom blowing or top
blowing, lime easily fuses and is supplied to positions where
oxygen acts on molten pig iron to produce iron oxide, thereby
allowing dephosphorization to efficiently proceed. A boron-based
compound or alumina is used as the melting point lowering
substance. On the other hand, in order to increase the
dephosphorization reaction rate, oxygen feed conditions or stirring
conditions are made proper to increase the mobility of phosphorus
in iron oxide or molten pig iron. In this case, it is possible to
select and use the number and form of lance nozzles or bottom
blowing tuyeres for oxygen feed. Furthermore, where a series of
molten pig iron treatment is performed, as described above,
phosphorus can be efficiently removed, so that, after molten pig
iron dephosphorization, the phosphorus concentration in the molten
pig iron is lowered to 0.03% or less, i.e., an ultra low phosphorus
concentration. In order to control the phosphorus concentration,
the silicon concentration is preferably 0.2% or less, before the
treatment. In this case, blast furnace molten pig iron with a
silicon concentration of 0.2% or less may be used, or molten pig
iron is used after it is subjected to desiliconization treatment to
have a low silicon concentration of 0.2% or less, without reference
to blast furnace molten pig iron with a silicon concentration of
0.2% or more or less.
[0136] Where a refining agent according to the present invention is
used, as described above, desulfurization treatment provides a
larger desulfurization effect by a smaller refining agent quantity,
as compared to conventional techniques. It can readily provide a
sulfur concentration of 0.005% or less in the molten pig iron
stage.
[0137] Conventionally, in a series of molten pig iron treatment
performed as described above, a large amount of a flux, such as
fluorite, which increases fluorine (F) in slag, is used. This is
so, because the molten pig iron treatment temperature is relatively
low, and a higher basicity of slag is preferable for refining
reactions in desiliconization, dephosphorization, and
desulfurization. Accordingly, it is necessary to increase slag
formability by adding fluorite or the like.
[0138] However, recently, environmental measures are required in
relation to the quantity and quality of steelmaking slag. It is
necessary to provide environmental measures in relation not only to
converter slag, but also to all the molten pig iron treatment
slag.
[0139] For this reason, recently, in dephosphorization treatment,
it has been proposed to lower the silicon concentration in molten
pig iron in advance so that a lime source is reduced, and lime
fusing is conducted by oxygen feed or iron oxide, which is a solid
oxygen source, without using fluorite. Also in desulfurization
treatment, it has been thought to charge soda ash, or to use
expensive metal magnesium as described above, so as to perform
refining without using fluorite. However, the former entails a
problem in that the alkaline content is increased, and thus is not
effective in slag environmental measures, while the latter has a
problem in the cost efficiency. Accordingly, conventional
techniques cannot help using fluorite.
[0140] Furthermore, in a series of molten pig iron treatment, in
order to prevent slag in each treatment from being carried over to
the next step, a large-scale setup is required, and a problem
arises in that the cost efficiency, such as yield, or productivity
is impeded. Under the circumstances, slag in a former step cannot
help being carried over to the next step. As a result, where the
former step performs refining using fluorite, the slag of the next
step comes to contain F therein. Accordingly, even if
dephosphorization treatment can be performed without using
fluorite, as described above, when desulfurization treatment
employs fluorite, the end slag finally contains F to a large
extent. It is necessary, therefore, to reduce F in slag generated
in each treatment.
[0141] In relation to such requirements, where a refining agent
according to the present invention is used in desulfurization
treatment in a series of treatment of molten pig iron, the
desulfurization treatment can be performed without using fluorite,
in contrast to that of conventional techniques in which fluorite is
inevitably used. Consequently, the consumption of fluorite is
remarkably reduced in a series of treatment of molten pig iron, as
compared to conventional techniques. In addition, where the
composition of a refining agent is further adjusted in
desiliconization treatment and/or dephosphorization treatment, the
total consumption of fluorite can be 0.1 kg or less per ton of
molten pig iron, which likely defines a permissible range in terms
of influence on the environment caused by F quantity in slag after
refining.
[0142] As described above, a series of treatment of molten pig iron
can be performed with a refining agent using a very little
fluorite. Where other materials containing substantially no F are
selected for the refining agent, the F content in slag can be very
low after molten pig iron treatment.
[0143] A refining agent according to the present invention includes
an Al source, and aluminum dross used as the Al source sometimes
contains F. Even in such a case, if the Al quantity is low, the F
quantity in the generated slag can be suppressed at a level to
prevent it from affecting the environment. It is preferable,
however, to use a raw material containing less F as the Al source,
and the most preferable to use a raw material containing
substantially no F as the Al source.
[0144] In such a series of treatment of molten pig iron, the F
concentration in slag generated in each treatment is preferably 0.2
mass % or less. Not only the F concentration in slag in the molten
pig iron treatment, but also the F concentration in slag at tapping
from blast furnace needs to be low. In this case, the F
concentration is also preferably 0.2 mass % or less.
[0145] As described above, in a series of treatment of molten pig
iron, a refining agent according to the present invention is used
to perform desulfurization treatment. Consequently, an
environmental measure is attained such that the F concentration in
slag generated in the series of treatment of molten pig iron is
lowered.
[0146] Next, an explanation will be given of preferable operation
conditions for performing desulfurization treatment in a series of
treatment of molten pig iron.
[0147] As described above, molten pig iron desulfurization is
"reduction refining", and thus mainly causes temperature-lowering
due to heat radiation or the like, thereby hardly allowing thermal
control, although there is heat transfer in a small part of
oxidation reduction reactions. On the other hand, desiliconization
treatment or dephosphorization treatment is "oxidation refining"
entailing oxygen feed or addition of solid oxidation agent.
Accordingly, molten pig iron desiliconization or molten pig iron
dephosphorization has a feature in that it allows temperature
control, depending on how to supply an oxygen source. For example,
where gas oxygen is used, the molten pig iron temperature can be
raised due to a large amount of heat generated by an oxidation
reaction. Where solid oxygen is mainly used, the molten pig iron
temperature can be lowered due to an endothermic reaction.
[0148] In other words, it is difficult to control the molten pig
iron temperature only by desulfurization treatment, while the
temperature can be raised by selecting the oxidation agent quantity
or the oxidation agent type in desiliconization or
dephosphorization treatment. Accordingly, where at least one of the
desiliconization treatment and dephosphorization treatment is
performed before the desulfurization treatment, the molten pig iron
temperature can be controlled to be a temperature suitable for the
desulfurization treatment, in which a higher temperature is
advantageous. In this case, in view of thermodynamics, before the
desulfurization treatment, the molten pig iron temperature is
raised to 1,300.degree. C. or more, at which the reaction set out
in the formula (6) can effectively proceed, and is raised
preferably to 1,350.degree. C. or more. In this case, it is
preferable to control the temperature to prevent damages of a
setup, such as wear of a lance or the refractory of impeller. For
this, it is preferable to control the molten pig iron temperature
at the end of a treatment immediately before the desulfurization
treatment, in light of lead time between treatments, and the
heat-retaining state of a molten pig iron container, so that the
molten pig iron temperature satisfies the temperature described
above before the desulfurization treatment.
[0149] In a series of treatment of molten pig iron as described
above, desulfurization treatment using a refining agent according
to the present invention can be performed by any one of the methods
described above. In order to obtain a higher desulfurization
efficiency, the mechanically stirring method is preferably used. In
this case, a stirring power not less than a predetermined power is
preferably applied to allow the desulfurization reaction to
effectively proceed. The silicon concentration and the phosphorus
concentration respectively in molten pig iron desiliconization and
molten pig iron dephosphorization, which are performed in advance,
should be as low as possible, thereby preventing a treatment from
overlapping after desulfurization, although it depends on the steps
after the desulfurization.
[0150] (3) Refining of Molten Steel (Desulfurization, Deoxidation,
and Inclusion Control)
[0151] According to the present invention, a refining agent as
described above is added to molten steel in various stages, so as
to perform refining of the molten steel, i.e., desulfurization
treatment, deoxidation treatment, and inclusion control. Where a
refining agent as described above is used to perform refining of
molten steel, the components of the molten steel are not limited to
specific ones. It may be applied to almost any molten steel. For
example, it may be applied to high carbon steel for bearing steel,
high silicon steel sheet for electromagnetic steel or the like,
ordinary medium carbon steel, ultra low carbon steel containing 20
ppm or less carbon, low carbon steel hardly containing silicon for
thin sheets, high tensile steel containing about 0.2 to 0.8%
silicon for thick plates, or the like.
[0152] In relation to the deoxidation level of molten steel, a
refining agent according to the present invention contains metal
Al. In consideration of the permissible level of the influence of
the metal Al on the molten steel, Al deoxidation steel is most
easily treated, as a matter of course. However, deoxidation steel
by Si, C, or the like, hardly containing Al, may be used, so long
as molten steel has an oxygen concentration at which produced Mg
vapor acts on molten steel or inclusions. For example, it is
possible to apply the treatment to steel containing high carbon and
silicon for tire cords, without any problem. Relative to steel of
the type that extremely disagrees with Al, a refining agent
according to the present invention may be added with a smaller Al
content. Relative to steel of the type that causes no problem by Al
to be contained, a refining agent according to the present
invention may be added with an excessive Al content corresponding
to the deoxidation part or contained part in molten metal.
[0153] A typical process of manufacturing molten steel is a process
of subjecting molten pig iron manufactured by a blast furnace or
the like to desulfurization, dephosphorization, and decarburization
in a converter or pretreatment; or a process of subjecting steel
scrap to melting or refining treatment in an electric arc furnace,
although any other process, such as an induction furnace or burner
furnace, can be used.
[0154] Where a refining agent according to the present invention is
used to perform refining (desulfurization, deoxidation, and
inclusion control) of molten steel, the refining agent is added to
molten steel finally manufactured in a melting furnace; a pouring
flow from a melting furnace into a ladle; molten steel in a ladle,
tapped from a melting furnace; molten steel in an incidental vessel
used for treating molten steel in a ladle while moving it to the
vessel by vacuum refining or the like; or molten steel in a tundish
directly connected to a continuous casting machine.
[0155] A refining agent can be added by, e.g., the putting-on
method of adding a refining agent from directly above molten steel
in a melting furnace, ladle, or tundish; a method (powder blasting)
of disposing a lance above a bath, and blowing a refining agent
along with gas from the lance; or an injection method of injecting
a refining agent from an injection lance immersed from the surface
of a bath, or a tuyere (nozzle) arranged in the bottom or side wall
under the surface of a bath. Where a ladle or tundish is provided
with an incidental treatment setup, such as a vacuum vessel, a
refining agent can be also added to molten steel in such an
incidental treatment setup, e.g., the vacuum vessel, by the same
method.
[0156] In order to promote the refining action of a refining agent
according to the present invention, stirring may be applied to
molten steel. For example, when a refining agent is added by the
putting-on in a converter, electric furnace, ladle, or incidental
setup as described above, gas stirring or electromagnetic stirring
is applied by a nozzle, top blowing lance, or the like. Falling
flow stirring may be utilized in the case of a pouring flow from a
melting furnace to a ladle. As a matter of course, since a vacuum
degassing apparatus having a ladle provided with a vacuum vessel
operates to form recirculation flow of molten steel in the ladle
and the vacuum vessel so as to stir it, this stirring can be
utilized. Furthermore, as a matter of course, a refining agent
according to the present invention may be added, while molten steel
is heated by a secondary refining apparatus provided with an arc
electrode for heating a ladle. Since such a secondary refining
apparatus originally has a stirring function, and the molten steel
is heated, the reaction of the refining agent is effectively
promoted.
[0157] Also where a refining agent according to the present
invention is used to perform refining of molten steel, the grain
size and shape may be selected to be optimum, depending on the
treatment purpose, process, setup, objective steel type, or the
like. Where the injection method is employed, a refining agent
should be powdered at a level to prevent nozzle clogging. As the
need arises, a refining agent may be pelletized. However, where a
large amount of refining agent is used in a melting furnace or the
like, and the refining agent is pelletized, it may cause a problem
in the cost efficiency. In general, where scattering loss is large
due to the influences of a dust-gathering setup or heat convection
when a refining agent is added, problems arise in the cost
efficiency or operability. Where a refining agent is added in a
process close to a casting step, such as a tundish, a slight amount
of a powdered refining agent caught in molten steel is not
sufficiently removed thereafter, and thus is carried over into
steel materials, as the case may be. Accordingly, in this case, the
refining agent is preferably pelletized to be pellets or briquettes
in advance, because using a large amount of fine powdered refining
agent causes a problem. Also where a refining agent according to
the present invention is used to perform desulfurization or
deoxidation of molten steel, it is preferable to form each raw
material into primary particles of 1 mm or less in order to
increase the reaction efficiency. In view of operability, such
primary particles may be shaped into pelletized or lumped form
sized to be 3 to 40 mm.
[0158] Inclusion control in refining of molten steel as described
above is performed by adding a refining agent according to the
present invention to molten steel deoxidated by a predetermined
element. As described above, a refining agent according to the
present invention produces Mg vapor by a reduction reaction due to
Al and causes a refining action. The Mg vapor acts on oxide-based
inclusions to prevent the oxide-based inclusions from being
large-sized due to agglomeration or the like. Alumina inclusions
are dominant in molten steel, which contains 0.01% or more
dissolved Al, and 30 ppm or less solute oxygen after deoxidation.
Where a refining agent according to the present invention is added
to this molten steel, the refining agent acts on the alumina
inclusions and performs composition control to change them into
spinel inclusions in part or in all, thereby restraining the
alumina inclusions from being large-sized. Inclusions mainly
containing silicate are dominant in molten steel, which contains
less than 0.01% solute Al, and 30 ppm or less solute oxygen after
deoxidation. Where a refining agent according to the present
invention is added to this molten steel, the refining agent acts on
the inclusions mainly containing silicate and performs composition
control to increase the MgO concentration therein in part or in
all, thereby restraining the inclusions mainly containing silicate
from being large-sized. As usual, high clean steel, in which
oxide-based inclusions are reduced as low as possible to obtain an
extremely small number of surface defects, is in demand.
Conventionally, there is a method of causing oxide-based inclusions
to be agglomerated and large-sized so as to separate them by
floating, or a method of causing metal Mg to act on inclusions to
change them into spinel. The former entails problems in that
large-sized inclusions do not necessarily rise up entirely between
refining and casting, but are left in part and form product
defects. The latter entails problems in that metal Mg for forming
spinel evaporates at a high temperature of molten steel, and thus
greatly disturbs the molten steel when it is added to the molten
steel, thereby lowering the yield. However, where a refining agent
according to the present invention is used in the latter case, high
clean steel can be stably manufactured without causing the
problems. Such inclusion control can be preferably performed by an
RH vacuum degassing apparatus described later, but the same effect
can be obtained by various ways, such as a ladle refining furnace,
and continuous casting tundish.
[0159] Next, a concrete explanation will be given of such refining
of molten steel.
[0160] An example will be first explained where a refining agent
according to the present invention is add to molten steel in an
electric furnace to perform desulfurization and deoxidation of the
molten steel. The electric furnace is formed of an arc type melting
furnace, which can melt a large amount of ordinary iron scrap.
Electric power is supplied from a direct current or alternating
current power supply to the molten steel by a graphite electrode
disposed to be movable up and down at an upper portion of the
furnace. In general, the electric furnace is provide with an upper
lid, which is rotatable and movable up and down, an exhaust duct at
a position connected to the upper lid, a gas combustion tower, a
dust-gathering apparatus, or the like, other than the furnace main
body. It is also provided with a nozzle at the bottom of the
furnace and a lance near the side wall of the furnace, from which
gas is blown in to perform gas stirring. The refining agent may be
added from a gate on the front of the furnace by a bucket, or added
from a hopper or shooter above the furnace. It may be added from a
nozzle or lance. Where the refining agent is added from the hopper,
it is possible to select whether it is added at a time or
continuously by controlling a taking-out apparatus. As described
above, a refining agent according to the present invention produces
Mg vapor to directly cause a desulfurization reaction or
deoxidation reaction by Mg, and, at the same time, increases the
efficiency of the desulfurization reaction or deoxidation reaction
by the CaO content added thereto. Accordingly, in order to complete
the treatment in a shorter time, an appropriate adding method are
selected, such that intensive stirring is applied, or the grain
size of the refining agent is made smaller, to swiftly reduce the
oxidation level of slag, or to promote the desulfurization
reaction, as well as depending on the reactions by Mg.
[0161] Where it is applied to molten steel in another melting
furnace such as a converter, ladle, or tundish, there is no large
difference in the function or treatment method itself. For example,
a converter is used mainly for decarburization of molten iron, and
is provided with a lance for blowing oxygen from above into the
molten iron therein, and an exhaust duct disposed at an upper
opening and connected to a gas combustion tower, dust-gathering
apparatus, or the like. It is also provided with a nozzle for
blowing gas at the bottom of the furnace, from which gas is blown
in to perform gas stirring. The refining agent may be added from a
hopper or shooter above the furnace. It may be added from a nozzle
or lance. Similarly to the method described above, in order to
complete the treatment in a shorter time, an option may be used
such that intensive stirring is applied, or the grain size of the
refining agent is made smaller, to swiftly reduce the oxidation
level of slag, or to promote the desulfurization reaction. A
tundish is disposed in continuous casting, between a ladle and a
mold of a continuous casting setup. Molten steel is poured into it
from the ladle at a rate of 2 to 10 tons per minute, while it is
exhausted into the mold at the same time. Where the cross-sectional
area of the horizontal section of the tundish is 0.5 m.sup.2, the
average velocity of flow is 0.5 m to 2.5 m per minute, which
provides a mild flow as a treatment condition. Also in the tundish,
a refining agent can be added by various adding method. However,
since the tundish is disposed near a casting machine, as described
above, a problem of contamination may arise, depending on the
adding method. It may be effective, therefore, to adopt a method of
using a coarse-grained material subjected to pelletizing as the
refining agent so as not to greatly disturb the molten steel, or
calmly adding the refining agent by the putting-on method.
[0162] An example will be then explained where a refining agent
according to the present invention is add to molten steel in an RH
vacuum degassing process to perform desulfurization, deoxidation,
and inclusion control of the molten steel. The RH vacuum degassing
process is the mainstream as a secondary refining setup used after
refining of molten steel is performed by a converter method or
electric furnace method. FIG. 8 is a sectional view showing such an
RH vacuum degassing setup.
[0163] The RH vacuum degassing setup includes a ladle 41 for
storing molten steel 42, and a degassing section 43 for degassing
molten steel 42. The degassing section 43 is formed of a vacuum
vessel 44, which is immersed in the molten steel from above the
ladle, and an exhaust setup 45 connected thereto. The vacuum vessel
44 is provided with two immersion pipes 46 and 47 on the bottom,
and an exhaust port 48 connected to the exhaust setup 45 in an
upper portion of the side surface. A charge port 49 is formed in an
upper portion of the vessel, for adding miscellaneous materials,
such as alloy, flux, or the like. A water-cooled lance 50 is
inserted into the vacuum vessel 44, for blowing a refining agent
according to the present invention therein. A pipe 51 is connected
to one 46 of the immersion pipes, for introducing therein an inert
gas, such as Ar gas. The two immersion pipes 46 and 47 are immersed
in the molten steel 42 in the ladle 41, while the vacuum vessel 44
is vacuum-exhausted by the exhaust setup 45, so that the molten
steel 42 is introduced into the vacuum vessel 44. At the same time,
an inert gas is supplied into the immersion pipe 46 through the
pipe 51, so that the molten steel 42 moves up in the immersion pipe
46 and moves down in the immersion pipe 47 to form recirculation
flow, as the inert gas moves up. As described above, in the RH
vacuum degassing setup, the molten steel 42 is subjected to the
vacuum degassing treatment while the molten steel forms
recirculation flow. The treatment is performed at a vacuum level of
133 Pa or less. For example, the RH vacuum degassing setup has a
300-ton scale, the inner diameter of the immersion pipes is about
0.6 m, and Ar gas used as a gas for circulation is blown in at a
rate of several m.sup.3 per minute, to circulate molten steel at a
rate of about 100 to 200 tons per minute. In this case, the average
velocity of flow of the molten steel in the immersion pipes 46 and
47 reaches 0.75 to 1.5 m per second, and the molten steel 42 is
intensively stirred. Accordingly, where a refining agent according
to the present invention is used to perform desulfurization and
deoxidation of molten steel in an RH vacuum degassing process, such
a intensively stirred state is utilized to remarkably promote a
reaction, so that the treatment can be performed with a smaller
refining agent quantity in a shorter time. In order to utilize such
a intensively stirred state of molten steel for the refining
reaction by a refining agent according to the present invention, it
is effective to add a powdered refining agent through the lance 50
as shown in FIG. 8. Other than this, it is effective to blow it
into the vacuum vessel 44 through a nozzle, or to blow it into the
molten steel in the ladle 41 through a lance or nozzle.
Furthermore, it is also effective to stir the molten steel in the
vacuum vessel 44 by a circulating gas while the refining agent is
present on the surface of the molten steel, or to disperse the
refining agent by forcibly involving it in a down flow from the
vacuum vessel 44 to the ladle 41.
[0164] As explained above with reference to examples applied to
concrete processes, where a refining agent according to the present
invention is used to efficiently perform refining of molten steel,
it is necessary to cause Mg to efficiently act on the flowing
molten steel, or to increase the reaction efficiency of the CaO
content added thereto at the same time. For this, it is important
to control the adding method or the current of the added refining
agent, as well as the composition of the refining agent, in
accordance with the current of the molten steel or the place for
addition, so as to optimize the Mg production rate or the like. For
example, in order to cause Mg to act on inclusions present in
molten steel by a vacuum degassing setup, so as to change the
composition or form of the inclusions, just causing a refining
agent to float on the bath surface in a vacuum vessel is not
enough. This is so, because produced Mg is scattered toward a
pressure-reduced gas phase side, thereby reducing the efficiency of
the produced Mg in acting on the molten steel. In this respect, as
described with reference to the RH vacuum degassing process, where
the refining agent is forcibly involved in the down flow, Mg can
easily act on inclusions in the molten steel to increase the
efficiency. As an example of controlling inclusions, since
cluster-like inclusions formed mainly of alumina form defects in Al
deoxidation steel, there is a case where inclusions are changed
into spinel by means of MgO to restrain them from forming clusters,
or where inclusions are controlled to silicate-based inclusions
containing moderate MgO, avoiding alumina, to make the inclusions
ductile. In accordance with the purpose of control, the production
rate or production quantity of Mg to be produced is made proper.
For example, in order to change 20 ppm alumina scattered in molten
steel into spinel (MgO.Al.sub.2O.sub.3), the necessary quantity of
Mg is 3.7 ppm in stoichiometry. In consideration of the efficiency,
however, addition conditions are selected such that Mg is properly
generated from a refining agent, on the basis of the contact
reaction time of the refining agent with circulating molten
steel.
[0165] III. Recycling of Molten Pig Iron Desulfurization Slag
[0166] (1) Recycling of Desulfurization Slag to Molten Pig Iron
Desulfurization, Using a Mechanically Stirring Type Desulfurization
Method
[0167] It has been found that, where a refining agent according to
the present invention is used to perform molten pig iron
desulfurization, using a mechanically stirring type desulfurization
method, the effective rate of use of the refining agent according
to the present invention is not always high, but a certain amount
of non-reacted part is left after the molten pig iron
desulfurization. Accordingly, if the non-reacted part can be
recycled to a desulfurization agent, the desulfurization agent cost
is lowered, and the slag quantity is reduced.
[0168] In consideration of this, after a refining agent according
to the present invention is used to perform mechanically stirring
type desulfurization treatment, desulfurization slag thus generated
is subjected to a treatment of creating a new surface, and then the
treated desulfurization slag is used for other molten pig iron
desulfurization treatment. With this operation, the desulfurization
slag generated by the mechanically stirring type desulfurization
treatment can be effectively recycled. The recycling is not limited
to any specific molten pig iron desulfurization treatment, but can
be applied to any molten pig iron desulfurization treatment
performed in general. The recycling can be applied to a process the
same as or different from the process of generating the
corresponding desulfurization slag. Since desulfurization slag can
be recycled even in the same process, this is effective in a setup
only for one molten pig iron desulfurization treatment process. The
recycling in molten pig iron desulfurization can be applied not
only to the mechanically stirring type desulfurization treatment,
but also to other treatment, such as the injection type. However,
the recycling is most effectively applied to the mechanically
stirring type desulfurization treatment, because the recycling
efficiency is high.
[0169] Desulfurization slag generated by the mechanically stirring
type desulfurization method is suited to recycling for the
following reason. Specifically, in the injection method, a fine
powder refining agent is added to a deep portion of a bath, and
causes a desulfurization reaction while it rises up in the bath.
Accordingly, the reaction can be expected to occur for a short
time, but a desulfurization-produced substance is formed in a
superficial layer of the fine powder. After it rises to the bath
surface, a desulfurization reaction can be hardly expected.
Agglomeration starts after it rises to the bath surface, and brings
about a form in which the desulfurization-produced substance is
present on the surface of each of fine powder pieces, which have
been agglomerated. On the other hand, in the mechanically stirring
type desulfurization method, since a refining agent is added to a
bath surface and stirred, the refining agent is involved from the
bath surface into the bath, and agglomeration of the refining agent
is caused near the bath surface from the beginning of addition.
Consequently, the refining agent is agglomerated, while scarcely
reacted components are wrapped therein. After the agglomeration
starts, a surface portion of the refining agent in contact with
metal reacts and produces a desulfurization-produced substance.
This reaction is caused over the treatment time, and thus the
reaction can be held for a long time. Under the reaction mechanism
described above, after the desulfurization, the surface of
agglomerated coarse grains is covered with the
desulfurization-produced substance with a certain thickness, while
a lot of non-reacted components are present inside it. As described
above, the mechanically stirring type desulfurization method
produces coarse grains in which a lot of non-reacted components are
left therein, and thus allows a treatment of creating a new surface
effective in a desulfurization reaction to be easily performed. The
treatment time can be short, thereby increasing the effect of
lowering generated slag quantity. On the other hand, in the
injection method, as described above, fine powder of a
desulfurization agent is covered with a desulfurization-produced
substance. Accordingly, it is necessary to perform a difficult
treatment of changing the fine powder into finer powder to create a
new surface effective in a desulfurization reaction. This is not
practical, because the steps and time are increased, and a loss due
to scattering is caused. FIG. 9 is a view schematically showing a
difference between molten pig iron desulfurization slag generated
by a mechanically stirring type desulfurization method, and molten
pig iron desulfurization slag generated by an injection method. In
FIG. 9, desulfurization slag particles generated by the injection
method is shown with a particle size almost the same as that of
desulfurization slag particles generated by the mechanically
stirring type desulfurization method, for the sake of convenience,
but the former particles are actually smaller.
[0170] Next, a concrete treatment of desulfurization slag generated
by a mechanically stirring type desulfurization method will be
explained.
[0171] FIG. 10 is a view showing a desulfurization slag treatment
pattern by a practical machine. In this treatment, desulfurization
slag generated in the desulfurization step of a mechanically
stirring type desulfurization method is removed from the bath, and
transported to a slag treatment place. Then, as the need arises,
the metal content having a large diameter is removed from the
desulfurization slag by magnetic selection or screening with a
sieve, and the desulfurization slag thus obtained is subjected to a
treatment of creating a new surface by an arbitrary method. Then,
as the need arises, the desulfurization slag is subjected to
treatments, such as screening, drying, and mechanical crushing, and
then it is transported to a desulfurization setup and recycled to a
desulfurization agent.
[0172] A concrete treatment will be explained. The treatment at
this time is exemplified by (i) crushing by watering treatment,
(ii) crushing by watering and stirring treatment, (iii) crushing by
allowing to cool, and (iv) screening of hot slag.
[0173] (i) Crushing by Watering Treatment
[0174] In this example, desulfurization slag generated in the
desulfurization step is cooled and crushed at the same time by
watering treatment, and then is subjected to drying treatment to
create a new surface, and is recycled to a desulfurization agent.
Specifically, a watering setup is used to excessively perform
watering, so that the hot slag from the desulfurization treatment
completely contains water. Then, the water-containing slag is
completely dried by a drying apparatus, so that a fine-grained
desulfurization agent with a maximum particle size of about 100 mm
or less is obtained. The maximum of the particle size at this time
is preferably 30 mm or less, and more preferably 5 mm or less. The
drying method at this time is not limited to a specific one, but
may be performed by a drying machine, or large-scaled setup, such
as a rotary kiln, which is suitably selected, depending on the
necessary treatment quantity or the like.
[0175] (ii) Crushing by Watering and Stirring Treatment
[0176] In this example, desulfurization slag generated in the
desulfurization step is cooled and crushed at the same time
appropriately by watering and stirring treatment to create a new
surface, and is recycled to a desulfurization agent. Specifically,
the watering is performed by a watering setup uniformly on the hot
slag from the desulfurization treatment to cool it, while the
stirring is performed by a heavy machine, such as a shovel. Then,
slag is cooled down to a normal temperature by leaving it, so that
a fine-grained desulfurization agent with a maximum particle size
of about 100 mm or less is obtained. The maximum of the particle
size at this time is also preferably 30 mm or less, and more
preferably 5 mm or less. A cooling target temperature by an
appropriate amount of watering can be suitably set, depending on
the necessary treatment or the like. However, where the watering is
performed down to 100.degree. C. or less, drying treatment is
required, and thus the watering is preferably stopped at
100.degree. C. or more. The stirring is performed to increase the
cooling rate, and make the watering uniform. The stirring may be
performed after the watering. The frequency of performing it can be
suitably set. Furthermore, the stirring can be omitted, as the case
may be.
[0177] (iii) Crushing by Allowing to Cool
[0178] In this example, desulfurization slag generated in the
desulfurization step is cooled and crushed at the same time by
allowing to cool to create a new surface, and is recycled to a
desulfurization agent. Specifically, the hot slag from the
desulfurization treatment is left in a state where the area of it
in contact with air is as large as possible, while stirring is
performed by a heavy machine, such as a shovel. For example, the
hot slag is expanded with a thickness of 0.5 m or less, and stirred
about 1 to 3 times per day, so that a reproduced desulfurization
agent, which is sufficiently fine-grained and has a temperature of
200.degree. C. or less, is obtained in three days. At this time,
the thickness of the hot slag can be suitably set, depending on the
requirement. The stirring is performed to increase the cooling
rate. The frequency of performing it can be suitably set.
Furthermore, the stirring can be omitted, where there is leeway in
treatment time and quantity. The maximum particle size of the
cooled and crushed desulfurization slag particles is 100 mm or
less, preferably 30 mm or less, and more preferably 5 mm or less.
As the need arises, mechanical crushing may be used together.
[0179] (iv) Screening of Hot Slag
[0180] In this example, desulfurization slag generated in the
desulfurization step is subjected to screening by a sieve with a
mesh size of about 30 mm.times.30 mm to 100 mm.times.100 mm, while
the slag is still heated at 900 to 1,200.degree. C., so that metal
having a large diameter and desulfurization slag having a small
diameter are separated from each other. The desulfurization slag
having a small diameter has a new surface created thereon after the
screening, and is recycled as it is to a desulfurization agent
after natural cooling. At this time, although a Fe content of about
20 to 30% is left after screening, it is retrieved to the molten
pig iron side when used in the next desulfurization, thereby
increasing the iron yield.
[0181] Where the treatment is performed as described above,
desulfurization slag, obtained by using a refining agent according
to the present invention in the mechanically stirring type molten
pig iron desulfurization method to perform molten pig iron
desulfurization, can be effectively recycled. As a result, the
molten pig iron desulfurization cost is lowered, and the slag
generation quantity is reduced, thereby solving environment
problems.
[0182] (2) Recycling of molten pig iron desulfurization slag to raw
material to be sintered for blast furnace.
[0183] Conventionally, slag generated by desulfurization treatment
is subjected to removal of the metal content, and is recycled to
blast furnace cement, concrete material, fertilizer, or roadbed
material for roads. However, since the desulfurization slag
contains CaO and MgO contents as the main components, it absorbs
moisture in the air and is powdered, with the laps of time. For
this reason, the slag can be hardly used other than a cement raw
material. Even where it is used for a cement raw material, a large
cost is required for pre-treatment in practice.
[0184] Where a refining agent according to the present invention is
used to perform desulfurization treatment, the amount of the MgO
content in desulfurization slag is larger, as compared to the
conventional techniques. Where the desulfurization slag is used for
a cement raw material, the MgO concentration therein is so large
that a sufficient strength cannot be obtained, as the case may be.
Accordingly, new recycling use needs to be considered, for
desulfurization slag generated when a refining agent according to
the present invention is used to perform desulfurization.
[0185] For this reason, after a refining agent according to the
present invention is used to perform desulfurization treatment of
molten pig iron, desulfurization slag generated thereby is
subjected to grain adjustment by crushing so as to use it as a raw
material to be sintered.
[0186] The present inventors pay attention to the composition
characteristics of desulfurization slag generated when a refining
agent according to the present invention is used. As described
above, the refining agent basically formed mainly of dolomite, in
which CaO/MgO ratio is preferably 0.5 to 10, and more preferably
more than 1.5 and up to 10.0. Desulfurization slag generated
therefrom is formed mainly of CaO and MgO, with a high CaO ratio.
At the end, S in molten pig iron is fixed as solid CaS, and
non-reacted part of dolomite is left. In addition, a large amount
of T.Fe content is present in the slag. Accordingly, it can be used
in place of lime stone, serpentine, brucite, or magnesite, which is
conventionally combined as a raw material to be sintered.
Furthermore, an iron source can be retrieved, thereby obtaining a
large cost merit. In view of the total desulfurization cost, the
cost of pre-treatment for the sell-off of the slag is reduced.
[0187] Where desulfurization slag is used for a raw material to be
sintered, following desulfurization treatment, desulfurization slag
is collected by a suitable method, and subjected to grain
adjustment by a crushing, and then it is combined as an ordinary
raw material to be sintered. In this case, the composition of the
desulfurization slag is grasped to combine it, thereby causing no
problem. Even where the S concentration in the slag is high, the S
can be lowered by a desulfurization setup, thereby causing no
problem. As component control of blast furnace slag,
(Al.sub.2O.sub.3) control is important, but, where the
desulfurization slag is combined by 10 mass % or less, the
(Al.sub.2O.sub.3) quantity increase is 0.5 mass % or less, thereby
causing substantially no problem.
[0188] Next, a concrete structure for performing recycling of such
desulfurization slag to raw material to be sintered for blast
furnace will be explained.
[0189] At first, desulfurization slag, generated by using a
refining agent according to the present invention to perform
desulfurization treatment, is separated and collected from molten
pig iron, and cooled by an arbitrary method. The method of this is
not limited to a specific one, but employs an ordinary method.
Then, the metal content having a large diameter is removed
therefrom by magnetic selection or screening with a sieve, and the
remaining desulfurization slag is collected for a raw material to
be sintered. The grain size or particle size of the desulfurization
slag is preferably suited to the raw material to be sintered, with
a grain-adjusted size of, e.g., about 1 to 5 mm. There is a case
where the desulfurization slag includes remaining metal having a
small diameter. This part can be reused as an iron source in the
next molten pig iron pretreatment step, thereby bringing about a
merit, which greatly contributes to improvement of iron yield.
[0190] The desulfurization slag thus obtained for a raw material to
be sintered is used by mixing it with iron ore, and other raw
materials to be sintered for a blast furnace, while the
representative components of the slag are grasped. The other
conditions can follow conventional conditions.
[0191] As described above, where the desulfurization slag is used
as a raw material to be sintered for a blast furnace, it is
possible to realize recycling of the desulfurization slag at a low
cost, without lowering the yield and productivity.
[0192] Desulfurization slag, generated by treating desulfurization
slag generated in the mechanically stirring type desulfurization
method described above, and applying it to molten pig iron
desulfurization, may be also used for such a raw material to be
sintered.
EXAMPLES
[0193] An explanation will be given of examples according to the
present invention.
Example 1
[0194] In this example, refining agents according to the present
invention and refining agents according to comparative examples
were used to desulfurize 200 tons of molten pig iron in a ladle, by
a mechanically stirring setup. The molten pig iron used in the
treatment was, in advance, subjected to desiliconization treatment
at two stages of a runner in a cast house of a blast furnace, and a
molten pig iron ladle used as a pig iron-receiving container,
following tapping from a blast furnace. With the
pre-desiliconization, the molten pig iron composition was set such
that [Si]=0.05 to 0.10 mass %, [C]=4.3 to 4.6 mass %, [Mn]=0.22 to
0.41 mass %, [P]=0.10 to 0.13 mass %, and [S] before the
treatment=0.040 to 0.042 mass %. The molten pig iron temperature
was 1,330 to 1,430.degree. C. Each refining agent according to the
present invention was used in a form prepared by mixing and
crushing the following materials to have an average particle size
0.6 mm, or a form prepared by pelletizing them. Specifically, the
materials were flux, which was formed by combining light-burnt
dolomite (63.9 mass % CaO and 32.6 mass % MgO) having an average
particle size of 3.0 mm, lime powder having an average particle
size of 4.0 mm, and light-burnt brucite powder (83.6 mass % MgO,
3.4 mass % CaO, and 7.2 mass % SiO.sub.2) having an average
particle size of 4.1 mm, in several CaO/MgO ratios; and aluminum
dross powder (70.1 mass % Al and 3.0 mass % Mg) having an average
particle size of 0.3 mm. In the pelletized form, the mixed and
crushed powder having an average particle size of 0.6 mm was
supplied with 2.0 mass % soft pitch (a fixed carbon content of 33
mass %, and a viscosity of 4 poise at 60%) used as a binder, and
was kneaded to manufacture a refining agent in a lumped form with a
4 mm size. In the comparative examples, a refining agent, in which
the flux was lime alone, or the flux was light-burnt brucite alone
used as a MgO source, was used to perform desulfurization. TABLE 1
shows the flux composition, refining agent Al ratio, refining agent
form, refining agent unit requirement, desulfurization result, and
so forth. As shown in TABLE 1, the present invention samples Nos. 5
to 19 showed higher desulfurization rates with smaller refining
agent unit requirements, as compared to the comparative examples
Nos. 1 and 2 using a refining agent with flux formed of lime alone.
FIG. 11 shows the relationship between the CaO/MgO ratio and the
desulfurization rate, where the Al/MgO ratio of the flux was set at
0.45, and the flux unit requirement except aluminum dross was set
at 4.5 kg/t, uniformly. In the case of using light-burnt dolomite
as a base, and adding light-burnt brucite (Nos. 5 to 9), as the
CaO/MgO ratio increases, the desulfurization rate improves, and the
desulfurization rate is highest in the case of using only
light-burnt dolomite (No. 13). In the case of using light-burnt
dolomite as a base, and adding lime (Nos. 10 to 12), as the CaO/MgO
ratio increases, the desulfurization rate decreases. The
desulfurization rate is highest in the case of using light-burnt
dolomite only, and it decreases as the ratio of light-burnt
dolomite decreases. In a range of the CaO/MgO ratio of 0.5 to 10,
the desulfurization rate is not less than that in the case of
increasing the unit requirement with flux formed of lime alone (No.
1). Accordingly, it is understood that a refining agent with a
range of the CaO/MgO ratio of 0.5 to 10 is effective. Where the
CaO/MgO ratio is larger than 10, the combination rate of lime
increases, and the ratio of light-burnt dolomite relatively
decreases, whereby it is thought that the effects of light-burnt
dolomite are lowered.
[0195] Even where the CaO/MgO ratio is 2.0, there is a large
difference in desulfurization rate between the case of using only
light-burnt dolomite (No. 13) and the case of using light-burnt
brucite and lime to form an equivalent composition (No. 14), such
that the desulfurization rate is only about 55% in the case of
mixing light-burnt brucite and lime. Also from this result, it can
be said that use of dolomite is effective as a CaO source and MgO
source. Where the flux was light-burnt brucite alone used as a MgO
source (the comparative examples Nos. 3 and 4), the level of
desulfurization was low with a desulfurization rate of about
10%.
[0196] FIG. 12 shows the relationship between the Al/MgO ratio and
the desulfurization rate, where the CaO/MgO ratio was set at 2.0
only by light-burnt dolomite, and the flux unit requirement except
aluminum dross was set at 4.5 kg/t, uniformly, (No. 13, and 15 to
19). From this, the following matters were confirmed. Specifically,
as the Al/MgO ratio increased, the desulfurization rate improved,
and where the Al/MgO ratio was 0.05 or more, the desulfurization
rate was 80% or more. Accordingly, the Al/MgO ratio was preferably
set at 0.05 or more. In this respect, the same result was obtained
in both of cases where the refining agent was powdered and where
the refining agent was pelletized.
Example 2
[0197] Aluminum dross powder (52.1 mass % Al and 2.5 mass % Mg)
having an average particle size of 0.3 mm, light-burnt dolomite
(63.9 mass % CaO and 32.6 mass % MgO) having an average particle
size of 3.0 mm, seawater magnesia powder (91.0 mass % MgO, 3.2 mass
% CaO, and 1.0 mass % SiO.sub.2) having an average particle size of
0.3 mm, and coke powder (a fixed carbon content of 88%) having an
average particle size of 2.2 mm were used as raw materials. The raw
materials were combined to have ratios among Al, C, MgO, and CaO as
shown in TABLE 2, and then they were crushed and mixed to have an
average particle size of 0.5 mm. The raw materials were supplied
with 3.0 mass % soft pitch (a fixed carbon content of 33 mass %,
and a viscosity of 8 poise at 60.degree. C.) used as a binder, and
was kneaded to manufacture a refining agent in a lumped form with a
35 mm size.
[0198] The refining agent was charged into molten pig iron and the
Mg reduction rate was obtained. TABLE 2 also shows the result. As
shown in TABLE 2, the Mg reduction rate was 90% or more in every
case.
[0199] Then, each of the refining agents shown in TABLE 2 was used
to perform desulfurization. 830 kg of each of the refining agents
was charged into 230.degree. C. of molten pig iron at a temperature
of 1,350.degree. C. in a molten pig iron ladle, and the molten pig
iron was stirred by an impeller. Then, it was confirmed that, 15
minutes later, an initial S concentration of 0.032 mass % decreased
by 0.002 to 0.003 mass %, and the desulfurization rate obtained was
91 to 94%. As described above, a high desulfurization rate was
obtained with such a small refining agent quantity.
Example 3
[0200] In this example, refining agents according to the present
invention and refining agents according to comparative examples
were used to desulfurize 300 tons of molten pig iron in a ladle by
injection. As in the examples 1 and 2, the molten pig iron used in
the treatment was, in advance, subjected to desiliconization
treatment at two stages of a runner in a cast house of a blast
furnace, and a molten pig iron ladle used as a pig iron-receiving
container, following tapping from a blast furnace. With the
pre-desiliconization, the molten pig iron composition was set such
that [Si]=0.05 to 0.10 mass %, [C]=4.3 to 4.6 mass %, [Mn]=0.22 to
0.41 mass %, [P]=0.10 to 0.13 mass %, and [S] before the
treatment=0.040 to 0.42 mass %. The molten pig iron temperature was
1,330 to 1,430.degree. C. Each refining agent according to the
present invention examples was used in a form with a particle size
of 1 mm or less, prepared by mixing flux, which was formed by
combining dolomite, burnt lime, and light-burnt brucite in several
CaO/MgO ratios; and aluminum dross having an Al content of 50 mass
%. In the comparative examples, a refining agent, in which the flux
was lime alone, or the flux was light-burnt brucite alone used as a
MgO source, was used to perform desulfurization. For injection,
each refining agent was carried by nitrogen gas to blow it into
molten pig iron. For some of molten pig iron, aluminum dross was
separately added thereto in advance, and only flux was injected.
TABLE 3 shows the flux composition, refining agent Al ratio,
refining agent unit requirement, desulfurization result, and so
forth.
[0201] As shown in TABLE 3, the present invention samples Nos. 29
to 34 showed equivalent desulfurization rates with smaller refining
agent unit requirements, as compared to the comparative examples
Nos. 26 and 27 using a refining agent with flux formed of lime
alone. In the case of the comparative example No. 28 using flux
formed of light-burnt brucite alone used as a MgO source, the level
of desulfurization was low with a desulfurization rate of about
10%. Among the present invention examples, more preferable
desulfurization results were obtained with a flux CaO/MgO ratio of
1.0 to 10.
Example 4
[0202] This example considers the formula (11). Refining agents
according to the present invention and refining agents according to
comparative examples were used to desulfurize 150 tons of molten
pig iron in a ladle, by a mechanically stirring setup. The molten
pig iron used in the treatment was, in advance, subjected to
desiliconization treatment at two stages of a runner in a cast
house of a blast furnace, and a molten pig iron ladle used as a pig
iron-receiving container, following tapping from a blast furnace.
With the pre-desiliconization, the molten pig iron composition was
set such that [Si]=0.05 to 0.10 mass %, [C]=4.3 to 4.6 mass %,
[Mn]=0.22 to 0.41 mass %, [P]=0.10 to 0.13 mass %, and [S] before
the treatment=0.015 to 0.045 mass %. The molten pig iron
temperature was 1,250 to 1,400.degree. C. A refining agent
according to the present invention examples was used in a form
prepared by mixing and crushing aluminum dross and light-burnt
dolomite, having a composition and form with the highest
desulfurization efficiency, as described above, and adjusting the
mixture to have a particle size of about 1 mm or less. A refining
agent formed by combining them with burnt lime was also prepared in
the same way. In the comparative examples, a conventional refining
agent, formed of lime alone, or formed of lime and fluorite, was
used as a refining agent. The aluminum dross used had an Al content
of 70 mass %.
[0203] For the present invention examples, the addition quantity of
a refining agent was determined, using the formula (11), and
compared with the addition quantity in the case of using a
conventional refining agent formed of lime and fluorite under the
same conditions. In the case of the present invention examples,
since the used manufacture method and mechanically stirring setup
were the same, the stirring power .omega. and Al contribution rate
c in the formula (11) could be consider to be the same among them
in determining the addition quantity. Accordingly, in determining
the addition quantity of a refining agent, only the molten pig iron
temperature before the treatment, and the S concentration before
the treatment need to be considered. TABLE 4 shows the used
refining agent composition, addition quantity, molten pig iron
temperatures before the treatment, S concentration before the
treatment, and desulfurization results. In TABLE 4, the addition
quantity of a refining agent is shown on the provision that the
necessary quantity of a refining agent (Nos. 35 and 36) formed of
lime and fluorite is 1 when it is used for desulfurization.
[0204] As shown in TABLE 4, in the present invention samples Nos.
39 to 48, the following matters were confirmed. Specifically, an
optimum addition quantity could be determined in accordance with
various conditions in the molten pig iron temperature before the
treatment and the S concentration before the treatment, in
desulfurization with a refining agent basically formed of dolomite
and aluminum dross according to the present invention. Furthermore,
the desulfurization was performed to cause the S concentration to
be 0.003 mass % or less after the treatment.
[0205] In the case of the comparative examples (Nos. 37 and 38) in
which a refining agent formed of lime alone without adding fluorite
in consideration of F-less was used to perform desulfurization, the
following matters were confirmed. Specifically, the addition
quantity was 1.3 to 1.4 times that of the case of using lime and
fluorite. Furthermore, the present invention examples, in which a
refining agent was added at a charge quantity calculated from the
formula (11), could reduce the addition quantity by about 25% in
average, as compared to the comparative examples, on the assumption
that the addition quantity of the two refining agents of the
comparative examples were averaged and used as a reference. If a
lot of desiliconization slag is left on the molten metal surface
before the treatment, a refining agent may be set to have a
composition with a high lime ratio. In this case, the addition
quantity can be determined similarly on the basis of the formula
(11), thereby causing the S concentration to be 0.003 mass % or
less after the treatment.
Example 5
[0206] This example considers the formulas (12) and (13). Refining
agents according to the present invention and refining agents
according to comparative examples were used to desulfurize 200 tons
of molten pig iron in a ladle, by a mechanically stirring setup.
The molten pig iron used in the treatment was, in advance,
subjected to desiliconization treatment at two stages of a runner
in a cast house of a blast furnace, and a molten pig iron ladle
used as a pig iron-receiving container, following tapping from a
blast furnace. At this time, the desiliconization slag quantity
carried into the desulfurization treatment was changed. The
desiliconization slag was analyzed in advance to determine the
representative values of each composition, so as to use them in
calculating the refining agent charge quantity. TABLE 5 shows the
representative composition of desiliconization slag at this
time.
[0207] With the pre-desiliconization, the molten pig iron
composition was set such that [Si]=0.05 to 0.10 mass %. [C]=4.3 to
4.6 mass % [Mn]=0.22 to 0.41 mass %, [P]=0.10 to 0.13 mass %, and
[S] before the treatment=0.040 to 0.42 mass %. The molten pig iron
temperature was 1,330 to 1,430.degree. C. There were prepared
refining agents made within the range of the present invention, and
refining agents according to the comparative examples made out of
the range.
[0208] Each refining agent made within the range of the present
invention was used in a form prepared by combining light-burnt
dolomite, burnt lime, and light-burnt brucite in suitable CaO/MgO
ratios, and adding aluminum dross thereto. Each refining agent
according to the comparative example was used in a form using lime
alone, or a form using combination of light-burnt brucite (84 mass
% MgO) used as a MgO source with aluminum dross. For the
desulfurization treatment, each refining agent was prepared by
mixing and crushing all the raw materials, and adjusting the
mixture to have a particle size of about 1 mm or less, and then it
was added at a constant quantity of 5 kg/T to molten pig iron. In
the desulfurization treatment, slag sampling was preformed. The
aluminum dross used had a content of about 50 mass % Al and 0.15
mass % F. TABLE 6 shows the refining agent composition, pre-process
slag quantity,
Q(.alpha..sub.cao+.alpha..sub.MgO)/W(.alpha..sub.SiO2+.alpha..sub.Al2O3)
value, (CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value of treatment
slag, and desulfurization rate.
[0209] FIG. 13 shows the relationship between the
Q(.alpha..sub.CaO+.alpha-
..sub.MgO/W(.alpha..sub.siO2+.alpha..sub.Al2O3) value and the
desulfurization rate, in the case of setting Al/MgO=0.45 to be
constant, and setting the CaO/MgO value of flux at 0, 0.88, 2
(dolomite), 4.5, and .infin..
[0210] As shown in TABLE 6 and FIG. 13, where a refining agent
(Nos. 49 to 53) with CaO/MgO=0 or CaO/MgO=.infin. according to the
comparative examples was used, a desulfurization rate of 70% likely
defining the acceptable range was not ensured without reference to
the
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.alpha..sub.siO2+.alpha..sub.Al2O3)
value. On the other hand, where a refining agent with CaO/MgO=0.88,
CaO/MgO=2 (dolomite), or CaO/MgO=4.5 in the range of the present
invention was used, a desulfurization rate of 70% was ensured if
the
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.alpha..sub.siO2+.alpha..sub.Al2O3)
value was 4 or more, but the desulfurization rate decreased with an
decrease in the value, and became less that 70% if the value was
less than 4. Accordingly, it was confirmed that, even where a
refining agent in the range of the present invention was used, if
pre-process slag was present, it was necessary to satisfy
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W
(.alpha..sub.siO2+.alpha..sub.Al2O3) value .gtoreq.4, in order to
obtain a result not less than a desulfurization rate of 70% likely
defining the acceptable range.
[0211] FIG. 14 shows the relationship between the
(CaO+MgO)/(SiO.sub.2+Al.- sub.2O.sub.3) value and the
desulfurization rate, in the case of setting Al/MgO=0.45 to be
constant, and setting the CaO/MgO value of flux at 0, 0.88, 2
(dolomite), 4.5, and .infin..
[0212] As shown in TABLE 6 and FIG. 14, where a refining agent with
CaO/MgO=0 or CaO/MgO=.infin. according to the comparative examples
was used, a desulfurization rate of 70% likely defining the
acceptable range was not ensured without reference to the
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.s- ub.3) value.
[0213] On the other hand, where a refining agent with CaO/MgO=0.88,
CaO/MgO=2 (dolomite), or CaO/MgO=4.5 in the range of the present
invention was used, a desulfurization rate of 70% was ensured if
the (CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value was 3 or more, but
the desulfurization rate decreased with an decrease in the value,
and became less that 70% if the value was less than 3.
[0214] Accordingly, it was confirmed that, even where a refining
agent in the range of the present invention was used, if
pre-process slag was present, it was necessary to satisfy
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3- ) value .gtoreq.3, in order
to obtain a result not less than a desulfurization rate of 70%
likely defining the acceptable range.
[0215] Furthermore, it was confirmed that, in every case, the F
concentration in slag was 0.1 mass % or less after the
desulfurization treatment, and thus, where the F content in the Al
source was set at 0.15% or less, the F concentration in slag became
sufficiently low.
Example 6
[0216] This example considers the formulas (12) and (13), as in the
example 5. Refining agents according to the present invention and
refining agents according to comparative examples were respectively
injected into 300 tons of molten pig iron in a ladle to perform
desulfurization treatment. As in the example 5, the molten pig iron
used in the treatment was, in advance, subjected to
desiliconization treatment at two stages of a runner in a cast
house of a blast furnace, and a molten pig iron ladle used as a pig
iron-receiving container, following tapping from a blast furnace.
At this time, the desiliconization slag quantity carried into the
desulfurization treatment was changed.
[0217] With the pre-desiliconization, the molten pig iron
composition was set such that [Si]=0.05 to 0.10 mass %, [C]=4.3 to
4.6 mass %, [Mn]=0.22 to 0.41 mass %, [P]=0.10 to 0.13 mass %, and
[S] before the treatment=0.040 to 0.42 mass %. The molten pig iron
temperature was 1,330 to 1,430.degree. C. There were prepared
refining agents made within the range of the present invention, and
refining agents according to the comparative examples made out of
the range.
[0218] Each refining agent made within the range of the present
invention was used in a form prepared by combining light-burnt
dolomite, burnt lime, and light-burnt brucite in suitable CaO/MgO
ratios, and adding aluminum dross thereto. Each refining agent
according to the comparative examples was used in a form using lime
alone, or a form using combination of light-burnt brucite (84 mass
% MgO) used as a MgO source with aluminum dross. For the
desulfurization treatment, each refining agent was prepared by
mixing and crushing all the raw materials, and adjusting the
mixture to have a particle size of about 1 mm or less, and then it
was added at a constant quantity of 5 kg/T to molten pig iron. In
the desulfurization treatment, slag sampling was performed. The
aluminum dross used was the same as that of the example 5. TABLE 7
shows the refining agent composition, pre-process slag quantity,
Q(.alpha..sub.cao+.alpha..sub.MgO)/W(.alpha..sub.SiO2+.alpha..sub.Al2O3)
value, (CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value of treatment
slag, and desulfurization rate.
[0219] As shown in TABLE 7, where a refining agent with CaO/MgO=0
or CaO/MgO=.infin. according to the comparative examples was used,
a desulfurization rate of 70% likely defining the acceptable range
was not ensured without reference to the
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.al-
pha..sub.siO2+.alpha..sub.Al2O3) value. On the other hand, where a
refining agent with CaO/MgO=0.88 to 4.5 in the range of the present
invention was used, a desulfurization rate of 70% was ensured if
the
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.alpha..sub.siO2+.alpha..sub.Al2O3)
value was 4 or more, but the desulfurization rate became less that
70% if the value was less than 4. Accordingly, it was confirmed
that, even where a refining agent in the range of the present
invention was used, if pre-process slag was present, it was
necessary to satisfy
Q(.alpha..sub.CaO+.alpha..sub.MgO)/W(.alpha..sub.siO2+.alpha..sub.Al2O3)
value .gtoreq.4, in order to obtain a result not less than a
sulfurization rate of 70% likely defining the acceptable range.
[0220] Furthermore, where a refining agent with Cao/MgO=0 or
CaO/MgO=.infin. according to the comparative examples was used, a
desulfurization rate of 70% likely defining the acceptable range
was not ensure without reference to the
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value. On the other hand,
where a refining agent with CaO/MgO=0.88 to 4.5 in the range of the
present invention was used, a desulfurization rate of 70% was
ensured if the (CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3) value was 3 or
more, but became less that 70% if the value was less than 3.
Accordingly, it was confirmed that, even where a refining agent in
the range of the present invention was used, if pre-process slag of
the present, it was necessary to satisfy
(CaO+MgO)/(SiO.sub.2+Al.sub.2O.sub.3- ) value .gtoreq.3, in order
to obtain a result not less than a desulfurization rate of 70%
likely defining the acceptable range. As a result, it was confirmed
that, where desulfurization was preformed by injection, it was
preferable to satisfy the formulas (12) and (13), as in the
mechanically stirring method.
[0221] Furthermore, it was confirmed that, in every case, the F
concentration in slag was 0.1 mass % or less after the
desulfurization treatment, and thus, where the F content in the Al
source was set at 0.15% or less, the F concentration in slag became
sufficiently low.
Example 7
[0222] This example will be explained in cases where a series of
treatment of molten pig iron, which includes desulfurization
treatment using refining agents according to the present invention
and refining agents according to comparative examples, is performed
after tapping from blast furnace.
[0223] After the tapping, 150 tons of molten pig iron in a ladle
was sequentially subjected to pig iron pre-treatments. The
treatments was performed in the following three cases or orders:
(a) molten pig iron desiliconization--molten pig iron
desulfurization, (b) molten pig iron desiliconization--molten pig
iron dephosphorization--molten pig iron desulfurization, and (c)
molten pig iron dephosphorization--molten pig iron desulfurization.
In tapping, the molten pig iron composition was that [Si]=0.21 mass
%, [C]=5.0 mass %, [P]=0.10 mass %, and [S]=0.033 mass %, and the
molten pig iron temperature was 1,495.degree. C.
[0224] In the molten pig iron desulfurization, a mechanically
stirring type (KR) desulfurization setup was used. Each refining
agent according to the present invention was used in a form
prepared by crushing and mixing a combination of light-burnt
dolomite with aluminum dross having a metal Al content of 50 mass
%. The combination ratio was set at 88:12 in mass ratio. The grain
size of each refining agent was set to be under 200 .mu.m, and the
addition quantity was changed to perform the desulfurization
treatment. In the comparative examples, a refining agent, formed of
lime alone, or formed of a combination of lime with 5% fluorite,
was used to perform desulfurization.
[0225] In the molten pig iron desiliconization, oxygen was fed at a
rate of 2,500 Nm.sup.3/hr to molten pig iron in a ladle by a top
blowing method, and nitrogen gas was blown therein at a rate of 2
Nm.sup.3/min from a refractory immersion lance, to perform the
desiliconization with stirring. Lime was used as a refining agent,
and the refining agent addition quantity was set such that the slag
basicity was 1.2, this level being a ratio of the CaO content in
the refining agent relative to SiO.sub.2 production quantity
determined by the desiliconization quantity.
[0226] In the dephosphorization treatment, a treatment manner the
same as the desiliconization treatment was used, but oxygen was fed
at a rate of 5,000 Nm.sup.3/hr to molten pig iron in a ladle by a
top blowing method, and nitrogen gas was blown therein at a rate of
2 Nm.sup.3/min from a refractory immersion lance, for stirring. A
refining agent containing lime and 20% fluorite was used at a
predetermined quantity in accordance with the silicon concentration
and the temperature before the treatment.
[0227] In the series of treatment Qf molten pig iron, the slag
mixture quantity from the blast furnace was about 5 kg/T. When each
of the treatments was finished, the ladle was inclined and the
generated slag was removed by a mechanical type slag removing
apparatus.
[0228] TABLE 8 shows the treatment conditions and the treatment
results. TABLE 9 shows the total of refining agent quantity and the
total of slag generation quantity in the series of treatment
according to the present invention examples and the comparative
examples, in terms of the average value of each process.
[0229] As shown in TABLE 9, it was confirmed that, in the present
invention examples using a refining agent according to the present
invention to perform desulfurization treatment, the refining agent
quantity used and the slag quantity generated in the series of
treatment of molten pig iron were lower than those of the
comparative examples.
Example 8
[0230] This example will be explained in cases where molten pig
iron treatment was performed in the treatment order (c) of the
example 7, i.e., molten pig iron dephosphorization--molten pig iron
desulfurization, and molten pig iron temperature at the end of the
dephosphorization was changed.
[0231] In tapping, the molten pig iron composition was that
[Si]=0.21 mass %, [C]=5.0 mass %, [P]=0.10 mass %, and [S]=0.033
mass %, and the molten pig iron temperature was 1,495.degree.
C.
[0232] In the molten pig iron desulfurization, a mechanically
stirring type (KR) desulfurization setup was used. Each refining
agent according to the present invention was used in a form
prepared by crushing and mixing a combination of light-burnt
dolomite with aluminum dross having a metal Al content of 50 mass
%, as in a refining agent according to the present invention used
in the example 7.
[0233] The treatment manner of the dephosphorization treatment was
also the same, but sintered ore was added to molten pig iron in a
ladle along with oxygen feed as described above. The ratio of gas
oxygen relative to the sintered ore oxygen source was changed to
control the end point temperature.
[0234] TABLE 10 shows the treatment conditions and the treatment
results.
[0235] As shown in TABLE 10, the following matters were confirmed.
Specifically, even where the molten pig iron temperature was
1,280.degree. C. before the desulfurization treatment, it was
possible to perform the desulfurization. However, with an increase
in the molten pig iron temperature before the desulfurization
treatment, the refining agent quantity and the generated slag
quantity were lowered in the desulfurization treatment. The molten
pig iron temperature was preferably 1,300.degree. C. or more before
the desulfurization treatment.
Example 9
[0236] This example will be explained in cases where a series of
treatment of molten pig iron, which includes desulfurization
treatment using refining agents according to the present invention
and refining agents according to comparative examples, is performed
after tapping from blast furnace.
[0237] After the tapping, 150 tons of molten pig iron in a ladle
was sequentially subjected to pig iron pre-treatments. The
treatments was performed in the following four cases or orders: (d)
molten pig iron desiliconization--molten pig iron
desulfurization--molten pig iron dephosphorization, (e) molten pig
iron desiliconization--molten pig iron dephosphorization--molten
pig iron desulfurization, (f) molten pig iron
desulfurization--molten pig iron desiliconization--molten pig iron
dephosphorization, and (g) molten pig iron desulfurization--molten
pig iron dephosphorization.
[0238] In tapping, the molten pig iron composition was that
[Si]=0.22 mass %, [C]=5.0 mass %, [P]=0.11 mass %, and [S]=0.035
mass %, and the molten pig iron temperature was 1,490.degree.
C.
[0239] In the molten pig iron desulfurization, a mechanically
stirring type (KR) desulfurization setup was used. Each refining
agent according to the present invention was used in a form
prepared by crushing and mixing a combination of light-burnt
dolomite with aluminum dross having a metal Al content of 50 mass
%. The combination ratio was set at 88:12 in mass ratio. The grain
size of each refining agent was set to be under 200 .mu.m, and the
addition quantity was set at a constant value of 6 kg per ton of
molten pig iron to perform the desulfurization treatment. In the
comparative examples, a refining agent, formed of lime alone, or
formed of a combination of lime with 5% fluorite, was used to
perform desulfurization.
[0240] In the molten pig iron desiliconization, oxygen was fed at a
rate of 2,500 Nm.sup.3/hr to molten pig iron in a ladle by a top
blowing method, and nitrogen gas was blown therein at a rate of 2
Nm.sup.3/min from a refractory immersion lance, for stirring. Lime
alone or lime with fluorite was used as a refining agent and the
refining agent addition quantity was changed such that the slag
basicity was 2.0, this level being a ratio of the CaO content in
the refining agent relative to SiO.sub.2 production quantity
determined by the desiliconization quantity.
[0241] In the dephosphorization treatment, a treatment manner the
same as the desiliconization treatment was used, but oxygen was fed
at a rate of 5,000 Nm.sup.3/hr to molten pig iron in a ladle by a
top blowing method, and nitrogen gas was blown therein at a rate of
2 Nm.sup.3/min from a refractory immersion lance, for stirring.
Lime alone or lime with fluorite was used as a refining agent and
the refining agent addition quantity was changed such that the slag
basicity was 4.0, this level being a ratio of the CaO content in
the refining agent relative to SiO.sub.2 production quantity
determined by the desiliconization quantity.
[0242] In the series of treatment of molten pig iron, the mixture
quantity of slag with a F concentration of 0.1 mass % from the
blast furnace was about 5 kg/T. When each of the treatments was
finished, the ladle was inclined and the produce slag was removed
by a mechanical type slag removing apparatus.
[0243] TABLE 11 shows the treatment conditions and the treatment
results. In TABLE 11, Nos. 114 to 121 denote cases in each of which
a refining agent according to the present invention was used in the
molten pig iron desulfurization, and the consumption of fluorite
was set at 0.1 kg or less per ton of molten pig iron in the series
of treatment of molten pig iron. Nos. 122 to 129 denote cases in
each of which fluorite was used as a refining agent and/or the
consumption of fluorite was set to be more than 0.1 kg per ton of
molten pig iron in the series of treatment of molten pig iron.
[0244] As shown in TABLE 11, it was confirmed that, where a
refining agent according to the present invention was used to
perform the desulfurization treatment, and the total consumption of
fluorite was set at 0.1 kg or less per ton of molten pig iron, the
F concentration in slag of each treatment step fell in a
permissible range of 0.2 mass % or less.
Example 10
[0245] In this example, refining agents according to the present
invention and refining agents according to comparative examples
were added to molten steel in an electric furnace to perform
desulfurization and deoxidation of molten steel. The electric
furnace used was a 150-ton melting furnace of an alternating
current arc type. The furnace was provided with three nozzles at
the bottom, for blowing argon at a rate of 300 Nl per minute in
total. The furnace was also provided with a hopper or shooter above
it for adding a refining agent at a time. Each refining agent
according to the present invention examples was used in a form
prepared by mixing and crushing light-burnt dolomite (64 mass % CaO
and 33 mass % MgO), burnt lime (96 mass % CaO), and aluminum dross
(50 mass % Al), and adjusting the mixture to have a grain size of
10 mm or less. Each refining agent according to the comparative
examples was used in a form prepared by mixing and crushing only
burnt lime and aluminum dross without using light-burnt dolomite.
In electric furnaces, treatment is performed in the following
sequence. At first, predetermined steel scrap is introduced along
with lime into the electric furnace, using a 90-ton bucket. Oxygen
feed are started by an auxiliary burner on the wall of the furnace
or a water-cooled lance from the front gate of the furnace, while
electrode heating is performed, to perform primary melting. About
20 minutes later, the lid of the furnace is opened, and 73 tons of
steel scrap is further introduced. In 15 minutes, the introduced
raw materials melt down to complete a melting period. Then, it
comes to a refining period, in which carbon and aluminum dross are
blown along with oxygen feed from the water-cooled lance, while
electrode heating is performed, to adjust the oxidation level or
carbon concentration in slag and molten metal, thereby increasing
the temperature of the molten metal. Until the molten metal
temperature becomes 1,650% in 10 minutes, slag is caused to foam
and exhausted from the front gate of the furnace. The slag is
formed of lime initially introduced at a rate of 20 kg per ton of
introduced steel scrap, oxide, such as silica sand with steel scrap
adhered thereto, and non-oxide, such as Si, Mn, Al, Cr, and Ti,
which are components of the steel scrap. Since the slag has a high
oxidation level, and a basic component CaO in the slag cannot be
increased, its desulfurization function is not high. Where the
introduction amount of input sulfur is large, which probably
depends on the steel scrap type, the sulfur concentration at this
time reaches 0.05 mass % or more. The slag is generated at a rate
of about 50 kg or more per ton of steel scrap, but the amount of
residual slag in the furnace can be 10 kg or less by using flow
slag. The molten steel has a carbon concentration of 0.1 to 0.15
mass %, and scarcely contains Al, but adding ferro-silicon brings
about a silicon concentration of 0.1 to 0.15 mass %. After such a
treatment was performed, a predetermined refining agent was added
at a time to perform desulfurization and deoxidation, while bottom
blowing gas stirring was used, for 10 minutes. TABLE 12 shows the
refining agent arrangement, refining agent addition unit
requirement, sulfur concentration before and after the treatment,
desulfurization rate, oxygen concentration, and so forth, at this
time.
[0246] As shown in TABLE 12, the present invention samples Nos. 130
to 135 stably showed a desulfurization rate of 70% or more, with a
stably low oxygen concentration. On the other hand, the comparative
examples Nos. 136 and 137 showed a lower level of desulfurization
and deoxidation than that of the present invention examples.
Example 11
[0247] In this example, refining agents according to the present
invention and refining agents according to comparative examples
were added to molten steel in a tundish to perform deoxidation and
inclusion control of the molten steel. The molten steel used was
high carbon aluminum deoxidation molten steel for bearing steel, or
high carbon silicon deoxidation molten steel for tire cord steel.
Either molten steel was introduced from a 300-ton ladle into a
50-ton capacity tundish, and a refining agent was added to the
molten steel surface to perform the treatment. In order to prevent
the molten steel from being greatly disturbed, the molten steel was
not intentionally stirred. Each refining agent according to the
present invention examples was used in a form prepared by mixing
and crushing light-burnt dolomite (64 mass % CaO and 33 mass %
MgO), light-burnt brucite (83.6 mass % MgO, 3.4 mass % CaO, 7.2
mass % SiO.sub.2), and aluminum dross (50 mass % Al), and
pelletizing the mixture to be pellets with a diameter of about 10
mm, and then packing them in units of 20 kg. A predetermined amount
of such a refining agent was added by a method of calmly putting it
on the tundish molten metal surface. Molten steel started being
poured at 1,580.degree. C. from the ladle to the tundish, and each
refining agent was added when molten steel in the tundish reached
30 tons. Each refining agent was added in accordance with the
pouring rate of molten steel corresponding to casting rate, so that
a predetermined unit requirement was obtained. Each refining agent
according to the comparative examples was used in a form prepared
by mixing and crushing only brucite and aluminum dross without
using dolomite, and pelletizing the mixture to be pellets with a
diameter of about 10 mm. Furthermore, there were also comparative
examples in which no refining agent was added in the tundish.
[0248] Molten steel in the tundish was poured into a mold of 400-mm
square to perform continuous casting, and bloom thus obtained was
worked into a product, such as rod steel or wire, through cogging
and rolling steps. T.[O] was measured as the amount of oxide-based
inclusions in the product. Furthermore, the form of the inclusions
and the MgO concentration in the inclusions were measured, and the
product defective rate was obtained. For bearing steel, the product
defective rate was obtained on the basis of the rate of achieving a
standard of fatigue rupture strength. For tire cord material, it
was obtained on the basis of the rate of generating rupture defects
in the final working step. TABLE 13 shows the refining agent
arrangement, refining agent addition unit requirement, T.[O] before
and after the treatment, inclusion form, inclusion MgO quantity,
and product defective rate, at this time. In TABLE 13, in the
column of the inclusion form, A stands for Al.sub.2O.sub.3, M for
MgO, S for SiO.sub.2, and N for MnO.
[0249] As shown in TABLE 13, it was confirmed that the present
invention samples Nos. 138 to 143 showed a stably low T.[O] after
the treatment, and thus the cleanliness improved. The inclusion
form contained MgO, and, in the case of bearing steel, inclusion
alumina was reformed into spinel. In the case of tire cord
material, silicate contained a suitable amount of MgO, thereby
causing ductile improvement of inclusions. Accordingly, in the
present invention examples, the product defective rate was
extremely low with less than 1%. On the other hand, the comparative
examples Nos. 144 to 147 showed a T.[O] after the treatment,
slightly higher than that of the present invention examples.
Furthermore, the inclusion form did not contain MgO, and the
product defective rate was high with 3.2 to 6.3%.
Example 12
[0250] In this example, refining agents according to the present
invention and refining agents according to comparative examples
were added to molten steel in an RH vacuum degassing setup to
perform desulfurization, deoxidation, and inclusion control of the
molten steel. Each refining agent was added by an immersion lance
to molten steel in a ladle, or added by a shooter to a vacuum
vessel, using a 300-ton RH vacuum degassing setup. Each refining
agent according to the present invention examples was used in a
form prepared by using light-burnt dolomite (64 mass % CaO and 33
mass % MgO) and aluminum dross (50 mass % Al) as essential
components, and mixing and crushing them with light-burnt brucite
(83.6 mass % MgO, 3.4 mass % CaO, and 7.2 mass % SiO.sub.2) or
burnt lime (96 mass % CaO) at a predetermined combination rate.
Then, the form was prepared by powdering the mixture with a
diameter of 1 mm or less for use, or further pelletizing the powder
to be pellets with a diameter of about 10 mm for use. The powdered
agent was used for addition from the immersion lance, while the
pelletized agent was used for addition from the shooter. Each
refining agent according to the comparative examples was used in a
form prepared by using only light-burnt brucite or burnt lime and
aluminum dross without using dolomite, and similarly powdering or
pelletizing it. Furthermore, there was also a comparative example
in which no refining agent was added in the RH vacuum degassing
setup.
[0251] Where each refining agent was added from the lance, it was
performed during vacuum treatment in which the immersion pipes of a
vacuum vessel were immersed in molten steel held in the ladle. In
order to finally adjust steel type components in the vacuum
treatment, an alloy agent, such as Mn or Si, and a deoxidation
agent Al were added, and then the refining agent was added from the
immersion lance. Before blowing, the molten steel was low carbon
steel with [C]=0.02 to 0.04 mass %, and the composition was that
[Si].ltoreq.0.02 mass %, [Mn]=0.15 to 0.25 mass %, and [Al]=0.02 to
0.04 mass %. In this case, the deoxidation form is so called
aluminum deoxidation steel, in which the inclusions in molten steel
are formed mainly of alumina in general. At this time, the molten
steel temperature was 1,625 to 1,630.degree. C. The refining agent
was blown at a blowing rate of 50 to 150 kg per minute, into a
position directly below the immersion pipe for lifting molten metal
up, and was circulated such that it entered the vacuum vessel while
being involved in an up flow of the molten steel, and returned into
the ladle through the other immersion pipe. The refining agent was
blown in until it reached a predetermined unit requirement, and,
after blowing, the immersion lance was withdrawn to a position
above the ladle. Then, the molten steel was stirred for 10 minutes
by circulating gas from the immersion pipes, so that the blown
refining agent was raised and separated from the molten steel.
After the treatment, the molten steel temperature was 1,570 to
1,585.degree. C.
[0252] Where each refining agent was added in the vacuum vessel, it
was performed on molten steel having substantially the same
composition after component adjustment and deoxidation were
performed by vacuum treatment. The molten steel temperature was
1,605 to 1,610.degree. C. The refining agent was continuously added
at a rate equivalent to the lance blowing, until it reaches a
predetermined unit requirement. After addition, the molten steel
was stirred for 10 minutes by circulating gas from the immersion
pipes. After the treatment, the molten steel temperature was 1,575
to 1,580.degree. C.
[0253] The molten steel in the ladle thus treated under the
conditions described above was subjected to continuous casting, and
a slab thus obtained was rolled to manufacture a very thin product.
T.[O] was measured as the amount of oxide-based inclusions in the
slab material. Furthermore, the form of the inclusions and the MgO
concentration in the inclusions were measured, and the product
defective rate was obtained. The defective rate was obtained on the
basis of the rate of generating surface defects in the product.
TABLE 14 shows the refining agent adding method, arrangement,
addition unit requirement, [S] and T.[O] before and after the
treatment, inclusion MgO quantity, and product defective rate, at
this time. In TABLE 14, in the column of the adding method, INJ
stands for addition by the lance blowing, and VAC for addition in
the vacuum vessel.
[0254] As shown in TABLE 14, it was confirmed that the present
invention samples Nos. 148 to 153 showed stably low [S] and T.[O]
after the treatment, and thus the cleanliness improved. The
inclusion form contained MgO, and inclusion alumina was reformed
into spinel. In the present invention examples, the product
defective rate was extremely low with 1.1% or less. On the other
hand, the comparative examples Nos. 154 to 158 showed [S] and T.[O]
after the treatment, relatively higher than those of the present
invention examples. Furthermore, the inclusion form contained less
MgO, and the product defective rate was high with 3.7 to 6.1%.
Example 13
[0255] In this example, refining agents according to the present
invention were used in an RH vacuum degassing setup to refine about
250 tons or 300 tons of non-deoxidation molten steel tapped from a
converter and having a [C] content of 0.02 to 0.06 mass %, so as to
perform making high clean molten steel. In comparative examples, no
refining agent was used in the RH vacuum degassing setup to
similarly perform the making molten steel.
[0256] At this time, the following treatment conditions were used
in the RH vacuum degassing apparatus.
[0257] Vacuum level of RH vacuum degassing apparatus: 67 to 267
Pa
[0258] Ar gas flow rate for circulation: 2 to 4 Nm.sup.3/min
[0259] After the vacuum treatment was performed for a predetermined
time under the conditions described above, [O] in the molten steel
was measured. In accordance with the measured [O] value, metal Al
was added to the molten steel to obtain an Al content of 0.01 to
0.05 mass %, and deoxidation of the molten steel was performed.
Following the Al addition, a refining agent was added into the
vacuum vessel from a raw material charge port or a water-cooled
lance. After the refining agent addition, the molten steel was
circulated for a predetermined time, and the treatment was
completed. The molten steel thus obtained was then subjected to
continuous casting. The number of cluster-like inclusions in a slab
formed by the continuous casting was examined by microscope. Also,
it was performed to measure a product defect index mainly caused by
alumina inclusions in the slab after cold rolling. TABLE 15 shows
the heat size, blowing gas flow rate, refining agent adding method,
addition quantity and composition, number of clusters in the slab,
and product defect index.
[0260] As shown in TABLE 15, in the present invention examples, in
which a refining agent according to the present invention was added
to molten steel after deoxidation, the number of cluster-like
inclusions was small, thereby extremely lowering the product defect
index. On the other hand, where no refining agent according to the
present invention was used to perform the RH vacuum degassing
treatment, the number of cluster-like inclusions was large, thereby
increasing the product defect index with 2.5 or more.
Example 14
[0261] This example will be explained in cases where molten pig
iron desulfurization slag was recycled to raw material to be
sintered for blast furnace.
[0262] After a refining agent according to the present invention
was used to perform desulfurization treatment, the desulfurization
slag was separated and collected from the molten pig iron. The slag
was cooled by an arbitrary method, and the metal content having a
large diameter was removed therefrom, thereby preparing
desulfurization slag for raw materials to be sintered.
[0263] TABLE 16 shows the chemical compositions of raw materials
conventionally used for sintered ore, and desulfurization slag
obtained in the case of using a refining agent according to the
present invention to perform desulfurization treatment.
[0264] The raw materials shown in TABLE 16 were subjected to grain
adjustment, and combined as shown in TABLE 17 to manufacture raw
materials to be sintered. It was confirmed that, according to the
present invention example, the desulfurization slag could be used
in place of serpentine, brucite, and magnesite, which were low
SiO.sub.2 ores contained in the conventional example. It was also
confirmed that, the raw material to be sintered according to the
present invention example had an increase of about 0.5 mass % in
Al.sub.2O.sub.3 concentration, but this level caused no problem in
practice.
[0265] Desulfurization slag obtained in the case of using a
refining agent according to the present invention to perform
desulfurization treatment can be used in place of dolomite in a raw
material to be sintered, although this is not shown in this
example.
[0266] Accordingly, it was confirmed that desulfurization slag
obtained in the case of using a refining agent according to the
present invention to perform desulfurization treatment can be
utilized as a raw material to be sintered.
INDUSTRIAL APPLICABILITY
[0267] As has been explained, according to the present invention,
since Al, MgO, and CaO are used as main components, the rate of MgO
changing into Mg vapor is increased. Since a material, in which MgO
and CaO are close to or in contact with each other in a minute
state, is used as a MgO source and CaO source, the reactivity is
increased. Accordingly, refining of molten iron, using a Mg source,
can be performed with an extremely high efficiency. Where dolomite,
which is inexpensive, is used as such a MgO source and CaO source,
refining of molten iron, using a Mg source, can be performed with
an extremely high efficiency and inexpensively.
[0268] Where Al, MgO, and CaO are used as main components, while
the Al used as a reducing agent is partly replaced with C, which is
inexpensive, refining of molten iron can be also performed
inexpensively. In this case, a refining agent having a material,
typically dolomite, in which MgO and CaO are close to or in contact
with each other in a minute state, is used as a MgO source and CaO
source, the effect described above can be also obtained.
[0269] A refining agent according to the present invention has an
extremely high industrial value, because it exerts an excellent
refining effect, where it is applied to desulfurization of molten
pig iron, or desulfurization or deoxidation of molten steel, and
because it allows inclusion control after deoxidation of molten
steel to reduce the number of product defects.
1 TABLE 1 Comparative Example Present Invention Example No. 1 2 3 4
5 6 7 8 9 10 Raw Light-burnt -- -- -- -- 22 34 51 59 72 65 Material
Dolomite Arrangement Lime 96 96 -- -- -- -- -- -- -- 22 (mass %)
Light-burnt -- -- 65 64 48 38 25 18 9 -- Brucite Al dross 4 4 35 34
30 28 24 21 20 14 Binder -- -- -- 2 -- -- -- 2 -- -- Composition
CaO 96 96 -- -- 17 26 38 43 51 67 (mass %) MgO -- -- 54 54 57 51 43
39 34 22 Al 2.8 2.8 24 24 26 23 19 18 15 10 Al/MgO -- -- 0.45 0.45
0.45 0.45 0.45 0.45 0.45 0.45 CaO/MgO .infin. .infin. 0 0 0.3 0.5
0.88 1.11 1.5 3.0 Refining Agent Unit- 10.0 4.7 6.9 7.1 6.5 6.2 5.9
5.8 5.6 5.2 requirement (kg/T) Refining Agent Form Powder Powder
Powder Lump Powder Powder Powder Lump Powder Powder Result
Desulfurization 62.0 38.5 11.9 12.5 39.6 61.0 71.9 73.4 85.9 91.0
Rate (%) Present Invention Example No. 11 12 13 14 15 16 17 18 19
Raw Light-burnt 26 22 83 -- 77 87 90 92 98 Material Dolomite
Arrangement Lime 68 73 -- 52 -- -- -- -- -- (mass %) Light-burnt --
-- -- 31 -- -- -- -- -- Brucite Al dross 5 5 17 17 21 13 10 6 2
Binder -- -- -- -- 2 -- -- 2 -- Composition CaO 87 89 53 58 50 56
58 59 62 (mass %) MgO 9 7 27 27 25 28 29 30 32 Al 4 3 12 12 15 9 7
5 2 Al/MgO 0.45 0.45 0.45 0.45 0.6 0.31 0.23 0.16 0.05 CaO/MgO 10
12 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Refining Agent Unit- 4.8 4.7 5.4 5.4
5.8 5.2 5.0 4.8 4.6 requirement (kg/T) Refining Agent Form Powder
Powder Powder Powder Lump Powder Powder Lump Powder Result
Desulfurization 62.3 55.2 94.5 54.4 95.0 95.0 93.0 90.0 79.0 Rate
(%)
[0270]
2 TABLE 2 No. 20 21 22 23 24 25 Raw Light-burnt 53.7 52.0 57.6 71.2
79.4 77.9 Material Dolomite Arrangement Seawater 23.0 22.3 14.4 7.9
0.0 0.0 (mass %) Magnesia Al dross 18.3 17.7 24.2 14.5 17.2 20.5
Coke Powder 4.9 7.9 3.8 6.5 3.3 1.6 Binder 3.0 3.0 3.0 3.0 3.0 3.0
Composition Al 10.5 10.1 14.3 8.1 9.8 11.8 (mass %) C 4.7 7.7 3.8
6.1 3.2 1.6 MgO 43.2 41.8 37.2 33.4 29.1 29.2 CaO 38.5 37.3 42.2
49.3 55.4 55.2 Al/MgO 0.24 0.24 0.38 0.24 0.34 0.41 C/MgO 0.11 0.18
0.10 0.18 0.11 0.05 CaO/MgO 0.89 0.89 1.13 1.47 1.91 1.89 Mg
Reduction Rate (%) 90.1 91.1 93.3 93.2 92.1 92.9 Desulfrization
Rate (%) 91 92 94 93 93 93
[0271]
3 TABLE 3 Refining Agent Pre-charged Refining Al Ratio Result Al
Unit- Al Unit- Agent Unit- (Al dross/flux Desulfurization Flux
Composition Requirement requirement requirement Ratio) Rate No.
CaO/MgO (kg/T) (kg/T) (kg/T) (wt %) (%) Comparative 26 .infin. 0.45
No 11.0 8.2 82.5 Examlpe (Lime Alone) 27 .infin. 0.45 0.1 11.0 10.0
85.4 (Lime Alone) 28 0 0.45 No 11.0 8.2 7.5 (MgO Source Alone)
Present 29 0.8 0.3 No 7.3 8.2 48.8 Invention 30 1.67 0.3 No 7.3 8.2
85.3 Examlpe 31 8 0.3 No 7.3 8.2 73.2 32 1.2 0.3 No 7.3 8.2 71.0 33
12 0.3 No 7.3 8.2 53.7 34 1.67 0.3 0.2 7.3 13.7 90.2
[0272]
4 TABLE 4 Treatment Conditions Result Addition Desulfrization No.
Refining Agent Composition Quantity Temperature [S]i Rate (%)
Comparative 35 Lime and Flourite 1.00 1290 0.024 87.5 Example 36
Lime and Flourite 1.00 1350 0.035 94.3 37 Lime Only 1.38 1290 0.024
87.5 38 Lime Only 1.30 1340 0.034 94.1 Present 39 Dolomite and Al
dross 0.78 1350 0.035 94.3 Invention 40 Dolomite and Al dross 0.91
1280 0.019 89.5 Example 41 Dolomite and Al dross 0.65 1400 0.040
95.0 42 Dolomite and Al dross 0.77 1360 0.026 92.3 43 Dolomite and
Al dross 0.98 1290 0.024 91.7 44 Dolomite and Al dross 0.99 1250
0.015 86.7 45 Dolomite and Al dross 0.94 1310 0.045 95.6 46
Dolomite and Al dross 0.83 1330 0.030 93.3 47 Dolomite, Lime and Al
dross 1.08 1290 0.025 92.2 48 Dolomite, Lime and Al dross 0.85 1350
0.028 92.9
[0273]
5TABLE 5 Desiliconization Slag Composition (%) SiO.sub.2
Al.sub.2O.sub.3 CaO MgO T.Fe 52 5 12 1 10
[0274]
6 TABLE 6 Pretreatment (CaO + MgO)/ Refining Agent Slag
Q(.alpha..sub.CaO + .alpha..sub.MgO)/ (SiO.sub.2 + Al.sub.2O.sub.3)
Desulfurization CaO MgO Quantity W(.alpha..sub.SiO2 +
.alpha..sub.Al2O3) Value of Slag Rate No. CaO/MgO Source Source
Al/MgO (T) Value in Treatment (%) 49 .infin. Lime -- -- 0.1 17.5
6.5 60 50 .infin. Lime -- -- 0.3 5.8 3.8 53 51 0 -- Brucite 0.45
0.1 17.5 6.4 10 52 0 -- Brucite 0.45 0.3 5.8 3.7 9 53 0 -- Brucite
0.45 0.5 3.5 2.6 6 54 0.88 Dolomite and Brucite 0.45 0.5 3.4 2.5 45
55 1.11 Dolomite and Brucite 0.45 0.5 3.6 2.7 50 56 1.5 Dolomite
and Brucite 0.45 0.5 3.5 2.8 55 57 2 Dolomite alone 0.45 0.5 3.3
2.6 63 58 3 Dolomite and Lime 0.45 0.5 3.7 2.4 60 59 4.5 Dolomite
and Lime 0.45 0.5 3.5 2.3 57 60 0.88 Dolomite and Brucite 0.45 0.1
16 6.7 72 61 0.88 Dolomite and Brucite 0.45 0.3 5.5 3.6 70 62 1.11
Dolomite and Brucite 0.45 0.1 15.3 6.9 74 63 1.11 Dolomite and
Brucite 0.45 0.3 5.2 3.4 71 64 1.5 Dolomite and Brucite 0.45 0.1
15.8 7.2 85 65 1.5 Dolomite and Brucite 0.45 0.3 5.7 3.7 81 66 2
Dolomite alone 0.45 0.1 16.4 7.4 95 67 2 Dolomite alone 0.45 0.3
5.6 3.5 93 68 3 Dolomite and Lime 0.45 0.1 17.3 6.8 92 69 3
Dolomite and Lime 0.45 0.3 5.7 3.3 90 70 4.5 Dolomite and Lime 0.45
0.1 17.5 6.7 85 71 4.5 Dolomite and Lime 0.45 0.3 5.9 3.5 82
[0275]
7 TABLE 7 Pretreatment (CaO + MgO)/ Refining Agent Slag
Q(.alpha..sub.CaO + .alpha..sub.MgO)/ (SiO.sub.2 + Al.sub.2O.sub.3)
Desulfurization CaO MgO Quantity W(.alpha..sub.SiO2+
.alpha..sub.Al2O3) Value of Slag Rate No. CaO/MgO Source Source
Al/MgO (T) Value in Treatment (%) 72 .infin. Lime -- -- 0.15 11.7
5.4 58 73 .infin. Lime -- -- 0.35 5.0 3.3 52 74 0 -- Brucite 0.45
0.15 11.3 5.2 10 75 0 -- Brucite 0.45 0.35 4.9 3.5 9 76 0 --
Brucite 0.45 0.6 3.2 2.4 6 77 0.88 Dolomite and Brucite 0.45 0.6
3.0 2.4 44 78 1.11 Dolomite and Brucite 0.45 0.6 2.9 2.4 48 79 1.5
Dolomite and Brucite 0.45 0.6 2.8 2.3 53 80 2 Dolomite alone 0.45
0.6 3.0 2.3 61 81 3 Dolomite and Lime 0.45 0.6 2.9 2.5 59 82 4.5
Dolomite and Lime 0.45 0.6 3.1 2.3 56 83 0.88 Dolomite and Brucite
0.45 0.15 11.6 5.3 73 84 0.88 Dolomite and Brucite 0.45 0.35 5.1
3.3 71 85 1.11 Dolomite and Brucite 0.45 0.15 11.5 5.2 75 86 1.11
Dolomite and Brucite 0.45 0.35 5.0 3.2 72 87 1.5 Dolomite and
Brucite 0.45 0.15 11.7 5.1 85 88 1.5 Dolomite and Brucite 0.45 0.35
5.3 3.3 81 89 2 Dolomite alone 0.45 0.15 11.8 5.5 95 90 2 Dolomite
alone 0.45 0.35 5.2 3.6 93 91 3 Dolomite and Lime 0.45 0.15 11.8
5.3 92 92 3 Dolomite and Lime 0.45 0.35 5.1 3.2 90 93 4.5 Dolomite
and Lime 0.45 0.15 12.0 5.6 85 94 4.5 Dolomite and Lime 0.45 0.35
5.3 3.4 82
[0276]
8 TABLE 8 Desiliconization Dephosphorization Refining Generated Si
Temperature Refining Generated P Temperature Agent Slag after after
Agent Slag after after Quantity Quantity Treatment Treatment
Quantity Quantity Treatment Treatment No. Kg/T Kg/T % .degree. C.
Kg/T Kg/T % .degree. C. Present 95 3.8 15.0 0.05 1440 -- -- -- --
Invention 96 1.4 8.1 0.15 1410 -- -- -- -- Example 97 3.8 15.2 0.06
1435 -- -- -- -- 98 3.8 14.7 0.05 1430 7.0 12.4 0.008 1370 99 1.4
8.3 0.15 1415 12.0 20.8 0.015 1350 100 3.8 14.9 0.07 1420 8.0 14.1
0.011 1360 101 -- -- -- -- 10.5 23.7 0.029 1350 102 -- -- -- --
13.8 26.9 0.021 1345 103 -- -- -- -- 15.5 29.1 0.014 1350
Comparative 104 3.8 15.3 0.06 1445 -- -- -- -- Example 105 1.4 8.0
0.15 1415 -- -- -- -- 106 3.8 14.8 0.05 1430 7.0 12.5 0.009 1370
107 1.4 8.4 0.14 1420 11.8 20.5 0.013 1350 108 -- -- -- -- 10.7
23.1 0.030 1350 109 -- -- -- -- 13.5 26.7 0.020 1345
Desulfurization Decarburization Series of Treatment Refining
Generated S Temperature Refining Generated C Refining Generated
Agent Slag after after Agent Slag after Agent Slag Quantity
Quantity Treatment Treatment Quantity Quantity Treatment Quantity
Quantity No. Kg/T Kg/T % .degree. C. Kg/T Kg/T % Kg/T Kg/T Process
Present 95 5.0 6.5 0.002 1420 15.0 41.0 0.018 23.2 62.5 a Invention
96 4.0 5.2 0.002 1390 17.0 44.5 0.019 22.4 57.8 a Example 97 3.5
4.6 0.005 1410 15.5 43.2 0.017 22.8 63.0 a 98 5.0 6.5 0.005 1350
4.1 7.1 0.007 19.9 40.7 b 99 6.0 7.8 0.002 1330 5.0 8.7 0.010 17.5
45.0 b 100 5.0 6.5 0.004 1340 3.9 6.9 0.009 20.6 42.4 b 101 6.0 7.8
0.002 1330 11.2 17.3 0.012 27.7 48.2 c 102 4.0 5.2 0.005 1325 9.6
14.7 0.010 27.4 46.8 c 103 4.0 5.2 0.004 1330 4.0 6.5 0.013 23.5
40.8 c Com- 104 10.2 13.3 0.003 1415 15.5 41.9 0.020 29.5 70.5 a
parative 105 9.5 12.4 0.005 1385 17.5 45.2 0.021 28.4 66.4 a
Example 106 10.2 13.4 0.003 1405 5.6 8.3 0.008 26.0 49.0 b 107 9.5
12.3 0.004 1380 6.5 9.1 0.011 28.6 50.3 b 108 11.5 15.1 0.003 1320
12.2 18.8 0.012 34.4 57.0 c 109 10.5 13.8 0.005 1320 10.1 14.6
0.009 34.1 54.5 c
[0277]
9 TABLE 9 Average Consumption of Generated Refining Agent (kg/T)
Slag Quantity (kg/T) Com- Com- Proc- Present parative Differ-
Present parative Differ- ess Invention Example ence Invention
Example ence a 22.8 29.0 -6.2 60.9 68.5 -7.6 b 19.3 27.3 -8.0 42.7
49.7 -7.0 c 26.2 34.3 -8.1 45.3 55.8 -10.5
[0278]
10 TABLE 10 Dephosphorization Desulfurization Refining Generated P
Temp. Temp. Refining Generated S Temp. Agent Slag after after
before Agent Slag after after Quantity Quantity Treatment Treatment
Treatment Quantity Quantity Treatment Treatment No. Kg/T Kg/T %
.degree. C. .degree. C. Kg/T Kg/T % .degree. C. Process 110 15.5
29.1 0.012 1290 1280 7.2 10.2 0.003 1255 c 111 15.5 28.8 0.013 1340
1320 6.4 8.7 0.002 1305 c 112 15.5 29.0 0.013 1350 1345 5.2 6.9
0.002 1330 c 113 15.5 29.1 0.012 1370 1360 4.2 5.4 0.002 1340 c
[0279]
11 TABLE 11 Desulfurization Desiliconization Present Si Temp.
Invention S Lime Fluorite after after Slag Lime Fluorite Refining
after Quantity Quantity Treatment Treatment (F) Quantity Quantity
Agent Treatment No. Kg/T Kg/T % .degree. C. % Kg/T Kg/T Kg/T % 114
6.0 -- 0.05 1430 0.03 -- -- 6.0 0.003 115 6.0 0.02 0.05 1420 0.10
-- -- 6.0 0.002 116 6.0 0.02 0.05 1430 0.10 -- -- 6.0 0.005 117 4.0
0.02 0.10 1400 0.14 -- -- 6.0 0.004 118 6.0 -- 0.05 1420 0.01 -- --
5.2 0.002 119 6.0 0.02 0.05 1420 0.07 -- -- 5.0 0.002 120 -- -- 5.0
0.002 121 -- -- 5.0 0.002 122 6.0 -- 0.05 1435 0.04 7.6 0.4 --
0.003 123 6.0 0.5 0.05 1430 1.73 6.0 0.002 124 6.0 -- 0.05 1430
0.03 7.6 0.4 -- 0.005 125 4.0 0.4 0.10 1400 1.65 -- -- 6.0 0.004
126 6.0 -- 0.05 1400 0.49 7.6 0.4 -- 0.002 127 6.0 0.5 0.05 1420
1.79 -- -- 6.0 0.002 128 7.6 0.4 -- 0.002 129 -- -- 6.0 0.002
Desulfurization Dephosphorization Temp. P Temp. after Slag Lime
Fluorite after after Slag Treatment (F) Quantity Quantity Treatment
Treatment (F) No. .degree. C. % Kg/T Kg/T % .degree. C. % Process
114 1360 0.01 6.0 -- 0.012 1320 0.01 d 115 1350 0.02 10 0.03 0.009
1320 0.05 d 116 1295 0.01 6.0 -- 0.010 1320 0.03 e 117 1300 0.02 10
0.01 0.012 1330 0.06 e 118 1390 0.03 6.0 -- 0.013 1360 0.01 f 119
1410 0.02 10 -- 0.012 1350 0.02 f 120 1400 0.02 6.0 0.05 0.008 1340
0.17 g 121 1405 0.02 10 0.08 0.009 1330 0.20 g 122 1340 1.35 6.0 --
0.010 1340 0.45 d 123 1360 0.58 6.0 -- 0.009 1325 0.21 d 124 1295
0.67 8.0 0.8 0.012 1335 2.15 e 125 1300 0.21 6.0 -- 0.009 1315 0.52
e 126 1385 1.38 6.0 -- 0.011 1375 0.23 f 127 1410 0.02 13 -- 0.010
1335 0.39 f 128 1410 1.29 6.0 -- 0.012 1370 0.43 g 129 1415 0.02 10
0.2 0.011 1320 0.46 g
[0280]
12 TABLE 12 Refining Agent Arrangement (mass %) Addition Unit [S] %
T.[O] ppm Burnt Burnt Requirement Before After Desulfrization
Before After No. Dolomite Lime Al dross (kg/T) Treatment Treatment
Rate (%) Treatment Treatment Presennt 130 90 0 10 10 0.062 0.016 74
45 18 Invention Example Presennt 131 50 40 10 10 0.059 0.012 80 47
17 Invention Example Presennt 132 10 80 10 10 0.063 0.018 71 44 15
Invention Example Presennt 133 50 40 10 20 0.060 0.008 87 49 13
Invention Example Presennt 134 44 36 20 10 0.058 0.013 78 48 16
Invention Example Presennt 135 39 31 30 10 0.062 0.015 76 45 12
Invention Example Comparative 136 0 90 10 10 0.058 0.024 59 44 29
Example Comparative 137 0 90 10 20 0.059 0.022 63 45 27 Example
[0281]
13 TABLE 13 Refining Agent Arrangement (mass %) Addition Unit T.[O]
ppm Inclusion Defective Steel Burnt Al Requirement Before After
Inclusion MgO Rate No. Type Dolomite Brucite dross (kg/T) Treatment
Treatment Form (mass %) (%) Presennt 138 Bearing 45 15 40 3 8.2 4.5
A--M 24 0.6 Invention Example Presennt 139 Bearing 60 20 20 3 8.9
4.7 A--M 19 0.9 Invention Example Presennt 140 Tire 67 23 10 3 21
13 S--N--M 8 0.5 Invention Example Presennt 141 Tire 70 25 5 6 23
16 S--N--M 11 0.2 Invention Example Presennt 142 Tire 49 41 10 3 22
15 S--N--M 11 0.3 Invention Example Presennt 143 Tire 90 0 10 3 20
14 S--N--M 6 0.7 Invention Example Comparative 144 Bearing 0 90 10
3 8.1 6.5 A 4 3.5 Example Comparative 145 Bearing -- -- -- 0 8.3
7.1 A 0 6.3 Example Comparative 146 Tire 0 90 10 3 20 18 S--N 2 3.2
Example Comparative 147 Tire -- -- -- 0 20 19 S--N 0 5.9
Example
[0282]
14 TABLE 14 Addition Refining Agent Unit Arrangement (mass %)
Require- [S] ppm T.[O] ppm Defective Adding Burnt Burnt Al ment
Before After Before After MgO Rate No. Method Dolomite Brucite Lime
dross (kg/T) Treatment Treatment Treatment Treatment (mass %) (%)
Presennt 148 INJ 90 -- -- 10 4 48 19 21 9 11 0.8 Invention Example
Presennt 149 INJ 50 -- 40 10 4 51 18 20 10 9 0.9 Invention Example
Presennt 150 INJ 45 15 -- 40 4 47 21 19 7 18 0.2 Invention Example
Presennt 151 INJ 60 20 -- 20 4 49 19 20 8 15 0.4 Invention Example
Presennt 152 VAC 50 -- 40 10 5 48 17 19 11 7 1.1 Invention Example
Presennt 153 VAC 45 15 -- 40 5 50 22 21 9 13 0.7 Invention Example
Comparative 154 INJ 0 -- 90 10 4 45 30 18 14 0 5.5 Example
Comparative 155 INJ 0 90 -- 10 4 49 47 20 13 4 3.7 Example
Comparative 156 VAC 0 -- 90 10 5 46 31 19 15 0 6.1 Example
Comparative 157 VAC 0 90 -- 10 5 48 45 18 13 3 4.0 Example
Comparative 158 No -- -- -- -- 0 47 47 18 15 0 5.9 Example
[0283]
15 TABLE 15 Blowing Refining Agent Number of Heat Gas Flow Addition
Clusters in Product Size Rate Adding Quantity Slab Defect No. (ton)
(Nm.sup.3/min) Method (kg/T) Al/MgO CaO/MgO (index) Index Presennt
159 250 2.5 Water-cooled 1.8 0.05 0.75 2.1 0.2 Invention Lance
Example Presennt 160 250 2.5 Water-cooled 2.1 0.05 1.00 1.5 0.0
Invention Lance Example Presennt 161 250 2.5 Water-cooled 6.1 0.05
5.00 3.1 0.5 Invention Lance Example Presennt 162 250 4.0
Water-cooled 0.8 0.30 1.00 2.1 0.0 Invention Lance Example Presennt
163 250 4.0 Water-cooled 2.1 0.30 5.00 0.8 0.0 Invention Lance
Example Presennt 164 250 4.0 Water-cooled 3.1 0.30 8.00 2.6 0.1
Invention Lance Example Presennt 165 300 3.0 Raw Material 0.9 0.10
0.75 1.9 0.3 Invention Charge Port Example Presennt 166 300 3.0 Raw
Material 1.1 0.10 1.00 0.7 0.0 Invention Charge Port Example
Presennt 167 300 3.0 Raw Material 3.1 0.10 5.00 1.2 0.0 Invention
Charge Port Example Presennt 168 300 3.0 Raw Material 2.1 0.08 1.00
1.5 0.3 Invention Charge Port Example Presennt 169 300 3.0 Raw
Material 6.1 0.08 5.00 2.4 0.4 Invention Charge Port Example
Presennt 170 300 3.0 Raw Material 9.1 0.08 8.00 1.1 0.1 Invention
Charge Port Example Comparative 171 250 4.0 No 10.0 2.7 Example
Comparative 172 250 4.0 No 8.0 3.1 Example Comparative 173 300 3.0
No 12.0 3.0 Example Comparative 174 300 3.0 No 11.0 2.5 Example
[0284]
16 TABLE 16 Chemical Component Composition (mass %) T.Fe FeO
SiO.sub.2 CaO Al.sub.2O.sub.3 MgO Ig. loss Ore Hamersley 62.8 0.3
3.7 0.1 2.3 0.05 3.4 Mixture 60.5 4.7 4.4 3.1 1.7 0.5 4 Powder A
Mixture 62.1 5.3 3.2 1.5 1.4 0.5 4 Powder B Magnesite 0.5 0.3 0.9
0.6 0.02 45.7 50.5 Brucite 0.8 0.2 2.2 0.6 0.4 64.8 30.6 Dolomite
0.3 0.1 1 33.7 0.2 19.0 47.0 Serpentine 5.3 2.5 38.3 1.0 0.9 38.3
13.2 Silica Rock 1.3 0.5 92.2 0.1 2.6 0 2.6 Powder Coke 0.5 0 6.4
0.4 3.6 0.1 88.0 Return 57.8 5.0 5 9.4 1.9 1.1 0 Quick Lime 0.1 0.0
0.7 81.2 1.4 1.1 13.3 Lime Stone 0.3 0.15 0.9 55.8 1.1 0.4 42
Desulfurization 8.0 0.5 10.0 44.2 7.5 19.3 -- Slag
[0285]
17 TABLE 17 Conventional Present Invention Example Example No. 175
176 177 178 179 180 Arrangement Ore Hamersley 10 10 10 10 10 10
(mass%) Mixture 90 90 90 90 90 90 Powder A Mixture 0 0 0 0 0 0
Powder B Magnesite 0 2.45 0 0 0 0 Brucite 0 0 1.72 0 0 0 Dolomite 0
0 0 0 0 0 Serpentine 3 0 0 0 0 0 Silica Rock 0 0 0 0.5 0.3 0.3
Powder Coke 3.5 3.5 3.5 3.5 3.5 3.5 Return 15 15 15 15 15 15 Quick
Lime 1.5 1.5 1.5 1.5 1.5 1.5 Lime Stone 13.6 9.4 9.5 8.9 4.7 4.7
Desulfurization Slag 0 0 0 6 6 6 Sintered Ore SiO.sub.2 (mass %)
5.3 4.5 4.5 5.3 4.5 4.5 Sintered Ore MgO (mass %) 1.5 1.5 1.5 1.5
1.5 1.5 Sintered Ore Al.sub.2O.sub.3 (mass %) 2.3 2.3 2.3 2.8 2.8
2.8
* * * * *