U.S. patent application number 10/513186 was filed with the patent office on 2005-09-15 for nozzle for continuous casting of aluminum killed steel and continuous casting method.
Invention is credited to Asano, Keisuke, Hokii, Toshiyuki, Ogata, Koji, Shimizu, Koichi, Yoshitomi, Joki.
Application Number | 20050200057 10/513186 |
Document ID | / |
Family ID | 29397265 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050200057 |
Kind Code |
A1 |
Ogata, Koji ; et
al. |
September 15, 2005 |
Nozzle for continuous casting of aluminum killed steel and
continuous casting method
Abstract
The present invention provides a technique of applying a
CaO-containing material to a nozzle unit for casting of
aluminum-killed steel, in such a manner that the amount of
large-size alumina inclusions in slabs can be reduced irrespective
of nozzle type, such as single-part type or multi-part type. The
amount of large-size alumina inclusions in slabs obtained using a
single-part type or multi-part type nozzle unit, which has an inner
hole to be used for pouring molten steel from a tundish to a mold
therethrough and CaO-containing refractories applied to a surface
of the inner hole, has a strong correlation with the entire surface
area of the inner hole of the nozzle unit and the amount of CaO
contained in the employed refractories. According to the present
invention, 50% or more of the entire surface area of the inner hole
of the nozzle unit is formed of refractories containing 20 mass %
or more of CaO to allow the amount of large-size alumina inclusions
to be reduced.
Inventors: |
Ogata, Koji;
(Kitakyushu-shi, JP) ; Shimizu, Koichi;
(Kitakyushu-shi, JP) ; Asano, Keisuke;
(Kitakyushu-shi, JP) ; Hokii, Toshiyuki;
(Kitakyushu-shi, JP) ; Yoshitomi, Joki;
(Kitakyushu-shi, JP) |
Correspondence
Address: |
JORDAN AND HAMBURG LLP
122 EAST 42ND STREET
SUITE 4000
NEW YORK
NY
10168
US
|
Family ID: |
29397265 |
Appl. No.: |
10/513186 |
Filed: |
January 5, 2005 |
PCT Filed: |
April 30, 2003 |
PCT NO: |
PCT/JP03/05558 |
Current U.S.
Class: |
266/280 |
Current CPC
Class: |
B22D 41/54 20130101 |
Class at
Publication: |
266/280 |
International
Class: |
C21B 007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2002 |
JP |
2002-128337 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. A method for providing to a continuous casing nozzle unit a
function of preventing the attachment of alumina and a function of
reducing large-size inclusions in slabs, comprising applying
CaO-containing refractories to a surface of an inner hole of said
continuous casting nozzle unit, while correlating said function of
preventing the attachment of alumina and said function of reducing
large-size inclusions in slabs, with the ratio of a surface area of
said inner hole to be defined by said CaO-containing refractories
to the entire surface area of said inner hole and the amount of CaO
to be contained in said CaO-containing refractories, wherein
according to said correlation, said amount of CaO to be contained
in said CaO-containing refractories is set at 20 mass % or more,
and said ratio of a surface area of said inner hole to be defined
by said CaO-containing refractories to the entire surface area of
said inner hole is set at 50% or more.
7. The method as defined in claim 6, wherein said CaO-containing
refractories are sleeve-shaped sintered refractories, wherein said
method includes inserting said sleeve-shaped sintered refractories
into said inner hole.
8. A continuous casting nozzle unit comprising CaO-containing
refractories applied to a surface of an inner hole of said
continuous casting nozzle unit so as to provide a function of
preventing the attachment of alumina and a function of reducing
large-size inclusions in slabs, wherein said function of preventing
the attachment of alumina and said function of reducing large-size
inclusions in slabs are provided in correlation with the ratio of a
surface area of said inner hole to be defined by said
CaO-containing refractories to the entire surface area of said
inner hole, and the amount of CaO to be contained in said
CaO-containing refractories, wherein according to said correlation,
said amount of CaO to be contained in said CaO-containing
refractories is set at 20 mass % or more, and said ratio of a
surface area of said inner hole to be defined by said
CaO-containing refractories to the entire surface area of said
inner hole is set at 50% or more.
9. The continuous casting nozzle unit as defined in claim 8,
wherein said CaO-containing refractories are sleeve-shaped sintered
refractories.
10. The continuous casting nozzle unit as defined in claim 9, which
is a multi-part type or single-part type nozzle unit for continuous
casting of aluminum-killed steel.
11. A method of continuous casting of aluminum-killed steel using a
continuous casting nozzle unit which has a function of preventing
the attachment of alumina and a function of reducing large-size
inclusions in slabs, wherein large-size inclusions in slabs to be
caused by pouring molten steel from a tundish to a mold through an
inner hole of said continuous casting nozzle unit having
CaO-containing refractories applied to a surface of said inner hole
is reduced in correlation with the ratio of a surface area of said
inner hole to be defined by said CaO-containing refractories to the
entire surface area of said inner hole, and the amount of CaO to be
contained in said CaO-containing refractories.
12. The method as defined in claim 11, wherein said amount of CaO
to be contained in said CaO-containing refractories is 20 mass % or
more, and said ratio of a surface area of said inner hole to be
defined by said CaO-containing refractories to the entire surface
area of said inner hole is 50% or more.
13. The continuous casting nozzle unit as defined in claim 8, which
is a multi-part type or single-part type nozzle unit for continuous
casting of aluminum-killed steel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a nozzle unit for
continuous casting of aluminum-killed steel, and the use of the
nozzle unit.
BACKGROUND ART
[0002] In a process for casting of aluminum-killed steel, alumina
inclusions are attached to the surface of an inner hole of a nozzle
unit for use in casting (hereinafter referred to as "nozzle unit"
for brevity), and agglomerated to form a large-size alumina
particles. The agglomerated alumina particles are mixed in the
molten steel flow, and incorporated into slabs as large-size
inclusions to cause defect or deteriorated quality in the
slabs.
[0003] In particular, as to aluminum-killed steel which is molded
as high-grade steel, such as thin sheets, it has been recently
required to strictly control the quality of steel products. To meet
this requirement, a good deal of effort has been made to prevent
alumina from being attached onto the surface of an inner hole of a
nozzle unit for use in pouring molten steel from a tundish
(hereinafter referred to as "TD") into a mold in a continuous
casting process.
[0004] As one of measures against the attachment of alumina, there
has been known a method comprising injecting argon gas from the
inner surface of a nozzle unit into molten steel to physically
prevent the attachment of alumina. In this method, if the argon gas
is injected at an excessive amount, bubbles of the injected argon
gas will be incorporated into molten steel to form pinholes in
slabs or cause defect thereof. Thus, due to the restriction in the
allowable injection amount of argon gas, this method cannot be
exactly used as a sufficient measure for preventing the attachment
of alumina.
[0005] As another measure, there has also been known a method
intended to provide a function of preventing the attachment of
alumina, to a refractory material itself constituting a nozzle
unit. This method is directed to prepare a refractory brick
containing CaO and induce the reaction between the CaO and alumina
attached onto the brick to form a low-melting-point compound so as
to prevent the attachment of alumina from further increasing. For
example, Japanese Patent Publication No. 61-44836 discloses a
casting nozzle unit using refractories which comprise a primary
component consisting of a combination of graphite, and sintered or
fused calcia or another ceramic engineering material containing a
CaO component.
[0006] Generally, a nozzle unit for use in pouring molten steel
from a TD to a mold during casting of steel includes a multi-part
type nozzle unit constructed by combining a plurality of segmental
nozzles as shown in FIG. 1, and a single-part type nozzle unit
consisting of only a single-piece nozzle as shown in FIG. 2.
[0007] The multi-part type nozzle unit is constructed by combining
an upper nozzle 2 which is attached to an opening formed in the
bottom wall of a tundish 1, a sliding nozzle 3, a lower nozzle 4,
and a submerged or immersion nozzle 5 immersed in a mold 6. The
flow rate of molten steel to the mold 6 is controlled by adjusting
the opening area of the sliding nozzle 3. The multi-part type
nozzle unit has an excellent flowrate control function, and can
stably maintain the level of molten steel. Thus, the multi-part
type nozzle unit is widely used in view of stable casting
performance under constant conditions and excellent safety.
[0008] The single-part type nozzle unit is comprised of a single
elongated immersion nozzle defining a flow path which extends from
the bottom opening of the tundish 1 to the mold 6. The flow rate of
molten steel to the mold 6 is controlled by adjusting the area of
the bottom opening of the tundish using a long stopper 7 disposed
in the tundish 1.
[0009] In experimental tests using the above two types of nozzle
units each of which has an inner hole whose surface is formed of
the aforementioned material containing CaO, the single-part type
nozzle unit as shown in FIG. 2 actually exhibited an effect of
reducing the attachment of alumina to the inner hole surface
thereof and reducing large-side alumina inclusions. On the other
hand, it was proven that when the CaO-containing material is
applied to only a part of the segmental nozzles of the multi-part
type nozzle unit as shown in FIG. 1, large-size alumina inclusions
in slabs tend to be formed at a larger amount that that in the
single-part type nozzle unit.
[0010] In a casting process using the single-part type nozzle unit,
molten steel passing through the nozzle unit has substantially no
contact with outside air. By contrast, in a casting process using
the multi-part type nozzle unit, outside air enters in the inner
hole through joints between the segmental nozzles. In particular,
outside air inevitably inflows through the joint surface between
the sliding nozzle (hereinafter referred to as "SN") and the
associated segmental nozzle, because it is difficult to completely
seal the joint surface with the SN to be slidingly moved during
use.
[0011] The molten steel for aluminum-killed steel contains aluminum
dissolved therein. When the aluminum comes into contact with air,
it is oxidized to create alumina. Then, the created alumina becomes
incorporated into slabs as alumina inclusions. In the multi-part
type nozzle unit composed of the plurality of segmental nozzles,
even if the CaO-containing refractories are applied to a part of
segmental nozzles, alumina will be attached to the remaining
segmental nozzles having no CaO-containing refractories, and then
large-sized alumina due to agglomeration will be incorporated into
slabs.
DISCLOSURE OF INVENTION
[0012] It is therefore an object of the present invention to
provide a nozzle unit for casting of aluminum-killed steel, which
employs a CaO-containing material in such a manner that the amount
of large-size alumina inclusions in slabs can be reduced
irrespective of nozzle type, such as single-part type or multi-part
type.
[0013] It is another object of the present invention to provide a
method for casting of aluminum killed steel, capable of
significantly reducing the amount of large-size alumina inclusions
in slabs to achieve a reduced quality-defect rate.
[0014] Through various research on the amount of large-size
aluminum inclusions in slabs obtained using a single-part type or
multi-part type nozzle unit which has an inner hole to be used for
pouring molten steel from a tundish to a mold therethrough and
CaO-containing refractories applied to a surface of the inner hole,
it was found that the amount of large-size aluminum inclusions in
slabs has a strong correlation with the entire surface area of the
inner hole of the nozzle unit and the amount of CaO contained in
the employed refractories. Based on this knowledge and obtained
specific numerical requirements, the present invention has been
accomplished.
[0015] Specifically, according to the present invention, 50% or
more of the entire surface area of an inner hole of a nozzle unit
to be used for pouring molten steel from a tundish to a mold is
formed of refractories containing 20 mass % or more of CaO.
[0016] In the multi-part type nozzle unit as shown in FIG. 1, even
if CaO-containing refractories are applied to a part of the
segmental nozzles or to define a portion of the entire surface area
of the inner hole, alumina will be attached onto the inner hole
surface of the remaining segmental nozzles having no CaO-containing
refractories, and large-sized alumina due to agglomeration will be
undesirably incorporated into slabs.
[0017] When the refractories containing 20 mass % or more of CaO
are applied to the inner hole of the nozzle unit for allowing
molten steel to flow down therethrough, in such a manner that the
CaO-containing refractories occupy 50% or more of the entire
surface area of the inner hole, the amount of large-size alumina
inclusions in obtained slabs is drastically reduced. This effect is
derived from a synergistic effect of the actions, of which the
CaO-containing refractories act to absorb alumina, a
low-melting-point compound created through the reaction between CaO
and alumina in the form of a liquid phase acts to smooth the inner
hole surface, as well as prevention of the attachment of alumina
and prevention of the agglomeration of alumina.
[0018] Such a synergistic effect can be obtained only if the
CaO-containing refractories are applied to the surface of the inner
hole of the nozzle unit, in such a manner that they occupy 50% or
more of the entire surface area of the inner hole. If the ratio is
less than 50%, the action of reducing the amount of alumina flowing
into the mold is deteriorated to provide only an insufficient
effect of reducing the amount of large-size alumina inclusions in
the slabs. The ratio should preferably be set at 60% or more. While
100% of the entire surface area of the inner hole of the nozzle
unit may be formed of the CaO-containing refractories, the
CaO-containing refractories should be selectively applied to an
appropriate region of the nozzle unit in consideration of its use
conditions. For example, if a certain region has the risk of
causing a problem, such as fusion damage or abrasion, in
conjunction with the use of the CaO-containing refractories,
suitable conventional refractories for such a region should be
used.
[0019] The present invention can be applied to any multipart type
nozzle unit composed of either one of a combination of an upper
nozzle and an immersion nozzle, a combination of a SN and an
immersion nozzle, a combination of an upper nozzle, a SN and an
immersion nozzle, and a combination of an upper nozzle, a SN, an
lower nozzle and an immersion nozzle as shown in FIG. 1, and to any
single-part type nozzle unit composed of a single-piece immersion
nozzle as shown in FIG. 2, in such a manner that the CaO-containing
refractories occupy 50% or more of the entire surface area of the
inner hole of the nozzle unit. Further, the present invention can
also be applied to a multi-part type nozzle unit in which a SN is
integrated with an upper or lower nozzle in a single piece. Even in
case where the CaO-containing refractories are applied to only a
portion of the surface of the inner hole of the single-part type
nozzle unit, if they are applied to occupy or define 50% or more of
the entire surface area of the inner hole of the nozzle unit, the
quality of slabs can be significantly improved.
[0020] If the amount of CaO to be contained in the refractories for
defining a surface of the inner hole is less than 20 mass %, the
refractories have deteriorated abilities of absorbing alumina and
preventing the attachment of alumina to provide only an
insufficient effect of reducing the amount of large-size alumina
inclusions in slabs. Thus, the amount of CaO must be 20 mass % or
more.
[0021] While there is no upper limit of the amount of CaO to be
contained in the refractories in terms of the effect of reducing
the amount of large-size inclusions in slabs, a large amount of CaO
is likely to cause the increased risk of fusion damage or wearing.
Thus, the upper limit of the amount of CaO should be appropriately
adjusted depending on its use conditions. In usual casting
conditions, the amount of CaO may be set at about 60 mass % to
obtained sufficient effects.
[0022] The refractories may include MgO--CaO based refractories,
MgO--CaO--C based refractories, ZrO.sub.2--CaO based refractories,
and ZrO.sub.2--CaO--C based refractories. In particular, the
MgO--CaO based refractories and MgO--CaO--C based refractories are
preferable in view of their excellent ability of absorbing
alumina.
[0023] In the single-part type or multipart type nozzle unit, the
CaO-containing refractories are essentially applied to at least a
surface of the inner hole to be in contact with molten steel. Any
region of the nozzle unit other than the inner hole surface may be
made of the same material as that of the inner hole surface, or may
be made of any suitable refractories used in a conventional nozzle
unit.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a schematic sectional view showing a multi-part
type nozzle unit composed of a plurality of segmental nozzles
including a SN, which is one example of a nozzle unit to which the
present invention is applicable.
[0025] FIG. 2 is a schematic sectional view showing a single-part
type nozzle unit which is another example of a nozzle unit to which
the present invention is applicable.
[0026] FIG. 3 is a graph showing the relationship between the ratio
of a surface area of an inner hole of a nozzle unit to be defined
by CaO-containing refractories to the entire surface area of the
inner hole, and large-size alumina inclusions in obtained
slabs.
[0027] FIG. 4 is a graph showing the relationship between the
average amount of CaO in refractories defining a surface area of an
inner hole of a nozzle unit, and large-size alumina inclusions in
obtained slabs.
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] The present invention will be described in conjunction with
one embodiment in which the present invention is applied to the
multi-part type nozzle unit as shown in FIG. 1.
1 TABLE 1 Material A B C D Composition CaO 40 50 -- -- (mass %) MgO
30 46 -- -- Al.sub.2O.sub.3 -- -- 70 96 C 30 4 30 4
[0029] In the above Table 1, the respective compositions of
materials applied to the segmental nozzles of the multi-part type
nozzle in FIG. 1. Each of the materials A and B in Table 1 is a
CaO-containing material according to the present invention, and
each of the materials C and D is a comparative example containing
no CaO.
[0030] Each of the materials A to D was shaped, burnt and machined
to prepare sleeve-shaped refractories having a thickness of 10 mm.
The sleeve-shaped refractories were inserted into the respective
inner holes of the segmental nozzles, and bonded thereto with
mortar to form the segmental nozzles as shown in FIG. 1. The
refractories made of the material A or C were applied to the
immersion nozzle, and the refractories made of the material B or D
were applied to the upper nozzle, the sliding nozzle (SN) and the
lower nozzle.
[0031] Table 2 shows a surface area of the inner hole of each of
the segmental nozzles having the CaO-containing refractories
applied thereto.
2 TABLE 2 Surface Area of Inner Hole (cm.sup.2) Upper Nozzle 393
Sliding Nozzle 438 Lower Nozzle 368 Immersion Nozzle 915
[0032] A plurality of multi-part type continuous casting nozzle
units were prepared by variously combining the prepared segmental
nozzles serving as the upper nozzle 2, SN 3, lower nozzle 4 and
immersion nozzle in FIG. 1.
[0033] The influence of the materials used in the nozzle unit on
the quality of slabs was experimentally checked to clarify effects
derived from the use of the CaO-containing refractories. In the
experimental tests, the casting of aluminum-killed steel was
performed while changing a combination of the segmental nozzles
under the casting conditions of a ladle volume: 250 ton, a TD
volume: 45 ton, and a drawing speed of slabs: 1.0 to 1.3 m/min, and
the effects were checked in accordance with the number per area of
large-size alumina inclusions having a particle size of 50 .mu.m or
more, which were contained in obtained slabs.
3 TABLE 3 Comparative Example Inventive Example 1 2 3 4 5 6 7 1 2 3
4 5 6 7 Material Upper nozzle D B D D D B D B D D B B B B applied
Sliding nozzle D D B D D B B D B B B B D B to Lower nozzle D D D B
D D B D D B B D B B Inner Immersion nozzle C C C C A C C A A A C A
A A Hole Ratio of CaO in inner hole 0 19 21 17 43 39 38 62 64 61 57
83 79 100 surface Area (%) *1 Number of inclusions *2 100 90 87 92
75 80 82 15 13 16 22 6 7 3 *1 The ratio of a surface area of the
inner hole defined by the CaO-containing material to the entire
surface area of the inner hole *2 The number of large-size alumina
inclusions (Index Number on the basis that the number of large-size
alumina inclusions in Comparative Example 1 is 100)
[0034] Table 3 shows the test result. In Table 3, the number of
large-size alumina inclusions in each example is shown by an index
number on the basis that the number of large-size alumina
inclusions in slabs obtained using the multi-part type nozzle unit
in Comparative Example 1 is 100. This means that the nozzle unit
having a smaller index number can provide slabs having better
quality or a smaller number of large-size alumina inclusions.
[0035] FIG. 3 diagrammatically shows the result in Table 3 in the
form of the relationship between the ratio of a surface area of the
inner hole defined by the CaO-containing material to the entire
surface area of the inner hole, and the number of large-size
alumina inclusions.
[0036] As seen in FIG. 3, when the ratio of a surface area of the
inner hole defined by the CaO-containing refractories to the entire
surface area of the inner hole of the nozzle unit is increased up
to 50% or more, the number of large-size alumina inclusions is
sharply reduced to improve the quality of slabs. Then, the quality
of slabs is further improved as the ratio is increased, and the
best quality can be obtained when the CaO-containing refractories
are applied to the entire surface area of the inner hole of the
nozzle unit.
[0037] Further, in the nozzle unit as shown in FIG. 1, the
influence of the amount of CaO in the CaO-containing refractories
on the quality of slabs was experimentally checked.
4TABLE 4 Material A B E F G H I J K L Composition CaO 40 50 10 15
20 30 10 15 20 30 (mass %) MgO 30 46 60 55 50 40 76 71 66 56 C 30 4
30 30 30 30 4 4 4 4
[0038] As an example, Table 4 shows CaO-containing refractories
having compositions E to L in addition to the compositions A and B
in Table 1. As with the materials in Table 1, each of these
CaO-containing refractories were shaped, burnt and machined to form
sleeve-shaped refractories having a thickness of 10 mm. The
sleeve-shaped refractories were inserted into the respective inner
holes of the segmental nozzles, and bonded thereto with mortar to
form segmental nozzles for test. The refractories made of the
material A, E, F, G or H were applied to the immersion nozzle 5 in
FIG. 1, and the refractories made of the material B, I, J, K or L
were applied to the upper nozzle 2, the SN 3, and the lower nozzle
4 in FIG. 1.
[0039] A surface area of the inner hole of each of the segmental
nozzles is the same as that shown in Table 2.
[0040] In the experimental tests, the casting was performed using
each of multipart type nozzle units prepared by variously combining
these segmental nozzles in the structure as shown in FIG. 1, under
the same casting conditions as those described above to check the
quality of slabs. The test results are shown in Table 5. The
quality of slabs was evaluated in the same manner as in Table
3.
5 TABLE 5 Comparative Example Inventive Example 8 9 8 9 10 Material
Upper nozzle I J K L B applied Sliding nozzle I J K L B to Lower
nozzle I J K L B Inner Immersion nozzle E F G H A Hole Number of
inclusions *1 80 65 20 14 3 *1 The number of large-size alumina
inclusions (Index Number on the basis that the number of large-size
alumina inclusions in Comparative Example 1 is 100)
[0041] The results in Table 5 are summarized in FIG. 4 in the form
of the relationship between the average amount of CaO in the
refractories applied to the inner hole of the nozzle unit, and the
number of large-size alumina inclusions. As seen in FIG. 4, when
the average amount of CaO in the refractories applied to the inner
hole of the nozzle unit is increased up to 20 mass % or more, the
quality of slabs is significantly improved.
INDUSTRIAL APPLICABILITY
[0042] The present invention can significantly reduce the amount of
large-size inclusions in slabs during casting of aluminum-killed
steel, and can be applied to various nozzle units irrespective of
nozzle type, such as multi-part type and single-part type.
* * * * *