U.S. patent application number 13/995739 was filed with the patent office on 2013-10-17 for steel wire material and method for manufacturing same.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel. Ltd.). The applicant listed for this patent is Masayuki Endo, Kazuhiko Kirihara, Shohei Nakakubo, Mikako Takeda. Invention is credited to Masayuki Endo, Kazuhiko Kirihara, Shohei Nakakubo, Mikako Takeda.
Application Number | 20130272914 13/995739 |
Document ID | / |
Family ID | 46457565 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130272914 |
Kind Code |
A1 |
Takeda; Mikako ; et
al. |
October 17, 2013 |
STEEL WIRE MATERIAL AND METHOD FOR MANUFACTURING SAME
Abstract
The steel wire material of the present invention contains 0.05
to 1.2% of C (mass %; same for the chemical components hereafter),
0.01 to 0.5% of Si, 0.1 to 1.5% of Mn, 0.02% or less (but not 0%)
of P, 0.02% or less (but not 0%) of S, and 0.005% or less (but not
0%) of N, with the balance being iron and inevitable impurities.
The wire material has a scale layer that is no thicker than 7.0
.mu.m or less. The scale layer has an FeO percentage of 30 to 80
vol % and an Fe.sub.2SiO.sub.4 percentage of less than 0.1 vol %.
The scale layer that is formed will not peel when cooled after hot
rolling or during storage and transport, but will easily peel
during mechanical descaling.
Inventors: |
Takeda; Mikako; (Kobe-shi,
JP) ; Nakakubo; Shohei; (Kobe-shi, JP) ;
Kirihara; Kazuhiko; (Kakogawa-shi, JP) ; Endo;
Masayuki; (Kakogawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Takeda; Mikako
Nakakubo; Shohei
Kirihara; Kazuhiko
Endo; Masayuki |
Kobe-shi
Kobe-shi
Kakogawa-shi
Kakogawa-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel. Ltd.)
Kobe-shi ,Hyogo
JP
|
Family ID: |
46457565 |
Appl. No.: |
13/995739 |
Filed: |
January 6, 2012 |
PCT Filed: |
January 6, 2012 |
PCT NO: |
PCT/JP2012/050155 |
371 Date: |
June 19, 2013 |
Current U.S.
Class: |
420/84 ; 420/112;
420/119; 420/121; 420/125; 420/126; 420/127; 420/128; 420/89;
420/90; 420/91; 420/92; 72/201 |
Current CPC
Class: |
D07B 1/066 20130101;
C22C 38/00 20130101; C22C 38/46 20130101; C21D 9/52 20130101; C22C
38/20 20130101; C22C 38/48 20130101; C22C 38/26 20130101; C22C
38/42 20130101; D07B 2205/3025 20130101; C22C 38/04 20130101; C22C
38/28 20130101; C21D 9/525 20130101; C21D 8/06 20130101; C22C
38/002 20130101; C22C 38/12 20130101; C21D 1/76 20130101; C22C
38/02 20130101; C21D 9/561 20130101; C21D 8/065 20130101; C22C
38/50 20130101; C22C 38/54 20130101; C22C 38/06 20130101; D07B
2205/3025 20130101; C22C 38/32 20130101; C22C 38/001 20130101; C21D
9/562 20130101; D07B 2801/10 20130101; C22C 38/24 20130101; C22C
38/14 20130101; B21B 1/16 20130101; C22C 38/16 20130101; C22C 38/08
20130101; C21D 1/74 20130101 |
Class at
Publication: |
420/84 ; 420/89;
420/90; 420/91; 420/92; 420/112; 420/119; 420/121; 420/125;
420/126; 420/127; 420/128; 72/201 |
International
Class: |
C22C 38/54 20060101
C22C038/54; C22C 38/16 20060101 C22C038/16; C22C 38/20 20060101
C22C038/20; C22C 38/42 20060101 C22C038/42; C22C 38/08 20060101
C22C038/08; C22C 38/14 20060101 C22C038/14; C22C 38/12 20060101
C22C038/12; C22C 38/02 20060101 C22C038/02; C22C 38/04 20060101
C22C038/04; C22C 38/06 20060101 C22C038/06; C22C 38/24 20060101
C22C038/24; C22C 38/26 20060101 C22C038/26; C22C 38/28 20060101
C22C038/28; C22C 38/32 20060101 C22C038/32; C22C 38/46 20060101
C22C038/46; C22C 38/48 20060101 C22C038/48; C22C 38/50 20060101
C22C038/50; B21B 1/16 20060101 B21B001/16; C22C 38/00 20060101
C22C038/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2011 |
JP |
2011-002014 |
Claims
1. A steel wire material comprising, by mass % based on the total
mass of the steel wire material: C: 0.05-1.2%; Si: 0.01-0.5%; Mn:
0.1-1.5%; P: 0.02% or less (not including 0%); S: 0.02% or less
(not including 0%); and N: 0.005% or less (not including 0%); with
the remainder being iron and unavoidable impurities, wherein a
scale with 7.0 .mu.m or less thickness is included, FeO ratio
inside the scale is 30-80 vol %, and Fe.sub.2SiO.sub.4 ratio is
less than 0.1 vol %.
2. The steel wire material according to claim 1, further
comprising, by mass % based on the total mass of the steel wire
material, at least one selected from the group of (1) (2), (3),
(4), (5), and (6): (1) Cr: 0.3% or less (not including 0%) and/or
Ni: 0.3% or less (not including 0%); (2) Cu: 0.2% or less (not
including 0%); (3) At least one element selected from a group
consisting of Nb, V, Ti, Hf and Zr by 0.1% or less (not including
0%) in total; (4) Al: 0.1% or less (not including 0%); (5) B:
0.005% or less (not including 0%); and (6) Ca: 0.01% or less (not
including 0%) and/or Mg: 0.01% or less (not including 0%).
3. A method for manufacturing a steel wire material, the method
comprising: hot rolling steel of the chemical composition according
to claim 1, to obtain a hot rolled steel; thereafter winding up the
hot rolled steel at 750-880.degree. C., to obtain a wound steel;
and cooling the wound steel while injecting a gas mixture of oxygen
and an inert gas whose oxygen fraction is less than 20 vol % or an
inert gas.
4. The method for manufacturing according to claim 3, wherein the
inert gas is nitrogen.
Description
TECHNICAL FIELD
[0001] The present invention relates to a steel wire material and a
method for manufacturing the same, and relates more specifically to
a hot rolled steel wire material (hereinafter simply referred to as
"wire material") formed with a thin scale not peeling off during
cooling after hot rolling and at the time of storage and
transportation and easily removable by mechanical descaling, and a
method for manufacturing the same.
BACKGROUND ART
[0002] A scale is formed normally on the surface of a wire material
manufactured by hot rolling, and it is required to remove the scale
before subjecting the wire material to secondary work such as
drawing and the like. As such a scale removing method before
secondary work, a batch type acid cleaning method was employed in
prior arts, however, in recent years, from the viewpoints of the
environmental pollution and cost reduction, a mechanical descaling
(hereinafter referred to as MD) method has come to be employed.
Therefore, the wire material is required to be formed with a scale
with excellent MD performance.
[0003] As methods for manufacturing a wire material formed with a
scale with excellent MD performance, Patent Literatures 1-5 can be
cited for example. In Patent Literatures 1, 2, the scale amount
remaining in the wire material after MD is reduced by forming a
scale which is high in FeO ratio and thick. In Patent Literature 3,
by lowering the boundary face roughness, propagation of the crack
occurring on the boundary face of the scale is promoted, and the
remaining scale amount is reduced. In Patent Literatures 4, 5, by
controlling the area ratio of the holes inside the scale, the
peeling performance of the scale is improved.
[0004] However, Patent Literatures 1-5 described above have
problems as described below. According to the method of forming the
scale thick as Patent Literatures 1, 2, drop of the yield is
caused, the scale peels off during the cooling step and at the time
of storage and transportation, and the rust is generated. Also,
when the scale is thick, even when a bending strain is applied to
the wire material by the MD method and the wire material surface is
subjected to brushing, it is difficult to perfectly remove the
scale. More specifically, according to the MD method, unlike the
batch type acid cleaning method, it is difficult to remove the
entire scale evenly and stably, and even when the wire material
formed with thick scale is subjected to MD, the surface of the wire
material may occasionally be spotted with finely crushed scale
powder. When the remaining scale remaining locally thus increases,
in the secondary work such as drawing and the like, problems such
as occurrence of a flaw due to the defective lubrication, lowering
of the lifetime of the dice and the like are caused.
[0005] Also, it is difficult to stably lower the boundary face
roughness by the method of lowering the boundary face roughness
such as Patent Literature 3, it is difficult to stably form the
holes even by the method of forming holes inside the scale such as
Patent Literatures 4, 5, and it is difficult to stably reduce the
remaining scale amount according to either of these
technologies.
[0006] Further, in these Patent Literatures 1-5, peeling off of the
scale due to the compression stress generated during cooling is not
considered at all, and there was a problem that the rust was
generated in the wire material before MD by peeling off of the
scale during cooling and at the time of storage and
transportation.
CITATION LIST
Patent Literature
[0007] [Patent Literature 1] Japanese Unexamined Patent Application
Publication No. H4-293721 [0008] [Patent Literature 2] Japanese
Unexamined Patent Application Publication No. H11-172332 [0009]
[Patent Literature 3] Japanese Unexamined Patent Application
Publication No. H8-295992 [0010] [Patent Literature 4] Japanese
Unexamined Patent Application Publication No. H10-324923 [0011]
[Patent Literature 5] Japanese Unexamined Patent Application
Publication No. 2006-28619
SUMMARY OF INVENTION
Technical Problems
[0012] The present invention has been developed in view of the
circumstances described above, and its object is to provide a wire
material formed with a scale not peeling off during cooling after
hot rolling and at the time of storage and transportation and
easily peeling off at the time of MD, and a method for
manufacturing the same.
Solution to Problems
[0013] The steel wire material of the present invention which
solved the problems described above is a steel wire material
containing C: 0.05-1.2% ("%" means "% by mass", hereinafter the
same for chemical components), Si: 0.01-0.5%, Mn: 0.1-1.5%, P:
0.02% or less (not including 0%), S: 0.02% or less (not including
0%), and N: 0.005% or less (not including 0%), with the remainder
being iron and unavoidable impurities, in which a scale with 7.0
.mu.m or less thickness is included, FeO ratio inside the scale is
30-80 vol %, and Fe.sub.2SiO.sub.4 ratio is less than 0.1 vol
%.
[0014] According to the necessity, the steel wire material of the
present invention may also contain (a) Cr: 0.3% or less (not
including 0%) and/or Ni: 0.3% or less (not including 0%), (b) Cu:
0.2% or less (not including 0%), (c) at least one element selected
from a group consisting of Nb, V, Ti, Hf and Zr by 0.1% or less
(not including 0%) in total, (d) Al: 0.1% or less (not including
0%), (e) B: 0.005% or less (not including 0%), and (f) Ca: 0.01% or
less (not including 0%) and/or Mg: 0.01% or less (not including
0%).
[0015] Further, the present invention also includes a method for
manufacturing a steel wire material including a step of hot rolling
steel of any of the chemical compositions described above, a step
of thereafter winding up the hot rolled steel at 750-880.degree.
C., and a step of cooling the wound steel while injecting a gas
mixture of oxygen and an inert gas whose oxygen fraction is less
than 20 vol % or an inert gas. It is preferable that the inert gas
is nitrogen.
Advantageous Effects of Invention
[0016] In the steel wire material of the present invention, the FeO
ratio is appropriately controlled to a predetermined range (30-80
vol %), and a thin (7 .mu.m or less) scale is included.
Accordingly, the scale does not peel off during cooling after hot
rolling and at the time of storage and transportation, and
generation of the rust can be prevented. Further, according to the
present invention, because the scale easily peels off at the time
of MD, sufficient peeling performance can be secured with a simple
descaling device, adverse effects (a flaw on the surface of the
wire material, defective lubrication and the like due to leaving
the scale unremoved) are not exerted in secondary work such as
drawing and the like, and the steel wire material of high quality
can be provided. Also, because the scale loss is less, high yield
can be maintained.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a graph showing the relation between the FeO ratio
inside the scale and the remaining scale area ratio after MD.
[0018] FIG. 2 is a graph showing the relation between the scale
thickness and the scale peeling ratio of the rolled material.
DESCRIPTION OF EMBODIMENTS
[0019] In a cooling step during a manufacturing process of a wire
material, normally, a compression stress is generated inside the
scale due to the difference in the coefficient of thermal expansion
between the base iron and the scale. As a result, the scale
naturally peels off during the cooling step or at the time of
storage and transportation of the wire material thereafter, which
became the cause of generation of the rust. Also, the scale is
removed by MD before executing secondary work such as drawing and
the like, and the lifetime of the dice is shortened when the scale
remains after MD. Therefore, the wire material having a scale that
does not peel off in the cooling step during the manufacturing
process and at the time of storage and transportation and easily
peels off at the time of MD has been desired.
[0020] The MD method is a method for making the scale peel off by
applying strain to the wire material to generate cracks inside the
scale or in the boundary face of the base iron and the scale.
Conventionally, increase of the FeO ratio inside the scale has been
executed in order to improve the peeling performance of the scale.
This is because the increase of the FeO ratio inside the scale is
considered to be effective in improving the peeling performance of
the scale at the time of MD because the strength of FeO is weaker
than Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4. In order to increase the
FeO ratio inside the scale, it is normally required to form a scale
(a secondary scale formed in or after descaling before finish
rolling) at a high temperature, however there was a problem that,
when the scale was formed at a high temperature, the thickness of
the scale increased, the scale loss increased, and the thick scale
peeled off during the cooling step and at the time of storage and
transportation. In other words, it was extremely difficult to make
the thickness of the scale thin and to secure the FeO ratio inside
the scale.
[0021] So, as a result of studies by the present inventors, it was
found out that, when the winding temperature after the hot rolling
was made comparatively low temperature and cooling was thereafter
executed while injecting a gas mixture of oxygen and an inert gas
whose oxygen fraction was comparatively low or an inert gas, the
scale could be made thin and the FeO ratio inside the scale could
be secured by a predetermined ratio or more.
[0022] When the thickness of the scale was studied in more detail,
it was found out that, if the thickness of the scale was 7.0 .mu.m
or less, adhesiveness against the base iron was excellent, and the
scale did not peel off in the middle of cooling and at the time of
storage and transportation. The scale thickness is preferably 6.5
.mu.m or less, more preferably 6.0 .mu.m or less (particularly 5.5
.mu.m or less). Although the lower limit of the scale thickness is
not particularly limited, it is approximately 0.9 .mu.m
normally.
[0023] Further, the present inventors investigated the relation
between the FeO ratio inside the scale and the MD performance. More
specifically, the wire material with 200 mm length having a
composition of 0.9% C-0.25% Si-0.86% Mn-0.007% P-0.0063% S-0.002% N
was used, the winding temperature condition was changed, and the
samples whose composition of the scale was adjusted were
manufactured. Also, the winding temperature was changed in the
range of 700-1,000.degree. C., and N.sub.2-10 vol % O.sub.2 gas was
used for cooling after winding. The scale was made peel off by
applying a deformation strain (6%) equivalent to MD to the
manufactured sample, and the scale amount (area ratio) remained was
measured by image analysis similarly to the example described
below. FIG. 1 is a graph showing the relation between the FeO ratio
inside the scale and the area ratio of the scale that remained
after MD.
[0024] According to FIG. 1, it is known that, when the FeO ratio
inside the scale is 30-80 vol %, the remaining scale amount after
MD can be reduced sufficiently. The FeO ratio is preferably 35 vol
% or more and 75 vol % or less, more preferably 40 vol % or more
and 70 vol % or less, and further more preferably 45 vol % or more
and 65 vol % or less.
[0025] Also, the Fe.sub.2SiO.sub.4 (fayalite) ratio inside the
scale is to be less than 0.1 vol %. When excessively formed,
Fe.sub.2SiO.sub.4 is formed unevenly on the boundary face between
the scale and the base iron, the scale unevenly peels off at the
time of MD, and therefore the MD performance deteriorates. The
Fe.sub.2SiO.sub.4 ratio is preferably 0.09 vol % or less, more
preferably 0.08 vol % or less, and further more preferably 0.07 vol
% or less. On the other hand, since Fe.sub.2SiO.sub.4 inside the
scale is an oxide that is brittle and easily peels off and is
formed evenly and thin if its amount is slight, it has an action of
improving the MD performance. In order to exert such action
effectively, it is preferable to secure Fe.sub.2SiO.sub.4 by 0.01
vol % or more, more preferably 0.02 vol % or more, and further more
preferably 0.03 vol % or more.
[0026] In the scale in the present invention, Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4 and the like are included other than FeO and
Fe.sub.2SiO.sub.4.
[0027] By making the thickness of the scale and the area ratio of
the fine holes as described above, the remaining scale amount after
MD can be made 30% or less by the area ratio relative to the scale
amount before MD. This is equivalent to approximately 0.05 mass %
or less in terms of the remaining scale amount relative to the mass
of the steel wire material. The remaining scale amount is
preferably 25% or less by area, more preferably 20% or less by
area.
[0028] In order to form the scale described above, it is important
to hot-roll the steel with the chemical composition described
below, to thereafter execute winding at a comparatively low
temperature (750-880.degree. C.), and then to execute cooling while
injecting a gas mixture of oxygen and an inert gas whose oxygen
fraction is low or an inert gas. By executing winding at a low
temperature, the scale can be made thin. Also, by injecting the gas
whose oxygen fraction is low or not including oxygen as described
above and executing cooling, FeO can be secured by a predetermined
amount or more without converting FeO formed to
Fe.sub.3O.sub.4.
[0029] When the winding temperature after hot rolling exceeds
880.degree. C., the scale thickness exceeds 7.0 .mu.m, the FeO
ratio inside the scale exceeds 80 vol %, and the MD performance
deteriorates. Also, when the winding temperature exceeds
880.degree. C., Fe.sub.2SiO.sub.4 (fayalite) possibly exceeds 0.1
vol % and is formed unevenly on the boundary surface between the
scale and the base iron, the scale peels off unevenly at the time
of MD, and the MD performance deteriorates. On the other hand, when
the winding temperature is below 750.degree. C., 30 vol % or more
of the FeO ratio cannot be secured, and the MD performance
deteriorates. The winding temperature is preferably 770.degree. C.
or above and 875.degree. C. or below, more preferably 790.degree.
C. or above and 860.degree. C. or below.
[0030] Cooling after hot rolling is executed while injecting a gas
mixture of oxygen and an inert gas whose oxygen fraction is less
than 20 vol % or an inert gas. By cooling while injecting such a
gas with low oxygen fraction or not containing oxygen, FeO already
formed can be prevented from being converted to Fe.sub.3O.sub.4,
and the FeO ratio inside the scale can be secured. The oxygen
fraction is preferably 10 vol % or less, more preferably 5 vol % or
less, and further more preferably 0 vol % (that is, the inert gas
only). Argon, nitrogen and the like can be cited as the inert gas,
and nitrogen is preferable. Although the cooling stopping
temperature in cooling executed while injecting the gas described
above is not particularly limited, cooling may be executed to
approximately 550-650.degree. C. for example while injecting the
gas described above, and cooling may be executed thereafter to the
room temperature in the atmospheric air.
[0031] Below, the chemical composition of the steel wire material
of the present invention will be described.
C: 0.05-1.2%
[0032] C is an element greatly affecting the mechanical properties
of steel. In order to secure the strength of the wire material, the
C amount was stipulated to be 0.05% or more. The C amount is
preferably 0.15% or more, more preferably 0.3% or more. On the
other hand, when the C amount is excessively high, the hot
workability in manufacturing the wire material deteriorates.
Therefore, the C amount was stipulated to be 1.2% or less. The C
amount is preferably 1.1% or less, more preferably 1.0% or
less.
Si: 0.01-0.5%
[0033] Si is an element required for deoxidizing steel. When its
content is too low, formation of Fe.sub.2SiO.sub.4 (fayalite)
becomes insufficient, and the MD performance deteriorates.
Therefore, the Si amount was stipulated to be 0.01% or more. The Si
amount is preferably 0.1% or more, more preferably 0.2% or more. On
the other hand, when the Si amount is excessively high, by
excessive formation of Fe.sub.2SiO.sub.4 (fayalite), such problems
occur that the MD performance extremely deteriorates, a surface
decarburized layer is formed, and the like. Therefore, the Si
amount was stipulated to be 0.5% or less. The Si amount is
preferably 0.45% or less, more preferably 0.4% or less.
Mn: 0.1-1.5%
[0034] Mn is an element useful in securing the quenchability of
steel and increasing the strength. In order to effectively exert
such actions, the Mn amount was stipulated to be 0.1% or more. The
Mn amount is preferably 0.2% or more, more preferably 0.4% or more.
On the other hand, when the Mn amount is excessively high,
segregation occurs in the cooling step after the hot rolling, and
super-cooled structure (martensite and the like) harmful for the
drawability and the like is liable to be generated. Therefore, the
Mn amount was stipulated to be 1.5% or less. The Mn amount is
preferably 1.4% or less, more preferably 1.2% or less.
P: 0.02% or Less (not Including 0%)
[0035] P is an element deteriorating the toughness and ductility of
steel. In order to prevent the wire breakage in the drawing step
and the like, the P amount was stipulated to be 0.02% or less. The
P amount is preferably 0.01% or less, more preferably 0.005% or
less. Although the lower limit of the P amount is not particularly
limited, it is approximately 0.001% normally.
S: 0.02% or Less (not Including 0%)
[0036] Similarly to P, S is an element deteriorating the toughness
and ductility of steel. In order to prevent the wire breakage in
the drawing step and the twisting step thereafter, the S amount was
stipulated to be 0.02% or less. The S amount is preferably 0.01% or
less, more preferably 0.005% or less. Although the lower limit of
the S amount is not particularly limited, it is approximately
0.001% normally.
N: 0.005% or Less (not Including 0%)
[0037] N is an element deteriorating the ductility of steel when
the content thereof becomes excessively high. Therefore, the N
amount was stipulated to be 0.005% or less. The N amount is
preferably 0.004% or less, more preferably 0.003% or less. Although
the lower limit of the N amount is not particularly limited, it is
approximately 0.001% normally.
[0038] The fundamental composition of the steel wire material of
the present invention is as described above, and the balance is
substantially iron. However, inclusion of unavoidable impurities
brought in due to situations of raw materials, materials,
manufacturing facilities and the like in the steel wire material is
allowed as a matter of course. Further, it is also recommended to
add elements described below according to the necessity within a
range not impeding the actions and effects of the present
invention.
Cr: 0.3% or Less (not Including 0%) and/or Ni: 0.3% or Less (not
Including 0%)
[0039] Both of Cr and Ni are elements enhancing the quenchability
of steel and contributing to increase the strength. In order to
exert such actions effectively, the Cr amount is preferably 0.05%
or more and the Ni amount is preferably 0.03% or more. Both of the
Cr amount and Ni amount are more preferably 0.10% or more, and
further more preferably 0.12% or more. On the other hand, when the
Cr amount and Ni amount are excessively high, the martensite
structure is liable to be generated, adhesiveness of the scale and
the base iron increases excessively high, and the peeling
performance of the scale at the time of MD deteriorates. Therefore,
both of the Cr amount and Ni amount are preferably 0.3% or less,
more preferably 0.25% or less, and further more preferably 0.20% or
less.
Cu: 0.2% or Less (not Including 0%)
[0040] Cu is an element having an action of promoting peeling of
the scale. In order to exert such action effectively, the Cu amount
is preferably 0.01% or more, more preferably 0.05% or more, and
further more preferably 0.10% or more. On the other hand, when the
Cu amount is excessively high, peeling of the scale is promoted
excessively, the scale peels off during rolling, other scales which
are thin and highly adhesive are generated on the peeled surface,
and the rust is generated when the wire material coil is stored and
transported. Therefore, the Cu amount is preferably 0.2% or less,
more preferably 0.17% or less, and further more preferably 0.15% or
less.
At Least One Element Selected from a Group Consisting of Nb, V, Ti,
Hf and Zr: 0.1% Or Less (not Including 0%) in Total
[0041] All of Nb, V, Ti, Hf and Zr are elements forming fine
carbonitride and contributing to increase the strength. In order to
exert such actions effectively, all of the Nb amount, V amount, Ti
amount, Hf amount and Zr amount are preferably 0.003% or more, more
preferably 0.007% or more, and further more preferably 0.01% or
more. On the other hand, when these elements are excessively high,
the ductility deteriorates, and therefore the total amount thereof
is preferably 0.1% or less, more preferably 0.08% or less, and
further more preferably 0.06% or less.
Al: 0.1% or Less (not Including 0%)
[0042] Al is an element effective as a deoxidizing agent. In order
to exert such action effectively, the Al amount is preferably
0.001% or more, more preferably 0.005% or more, and further more
preferably 0.01% or more. On the other hand, when the Al amount is
excessively high, oxide-based inclusions such as Al.sub.2O.sub.3
and the like increase, and wire breakage frequently occurs in
drawing work and the like. Therefore, the Al amount is preferably
0.1% or less, more preferably 0.08% or less, and further more
preferably 0.06% or less.
B: 0.005% or Less (not Including 0%)
[0043] B is an element suppressing formation of ferrite by being
present as free B (B that does not form the compound) solid-solved
in steel, and is an element effective particularly in a high
strength wire material which requires suppression of a longitudinal
crack. In order to exert such actions effectively, the B amount is
preferably 0.0001% or more, more preferably 0.0005% or more, and
further more preferably 0.0010% or more. On the other hand, when
the B amount is excessively high, the ductility deteriorates.
Therefore, the B amount is preferably 0.005% or less, more
preferably 0.0040% or less, and further more preferably 0.0035% or
less.
Ca: 0.01% or Less (not Including 0%) and/or Mg: 0.01% or Less (not
Including 0%)
[0044] Both of Ca and Mg are elements having an action of
controlling the form of the inclusions and enhancing the ductility.
Further, Ca also has an action of enhancing the corrosion
resistance of the steel material. In order to exert such actions
effectively, both of the Ca amount and the Mg amount are preferably
0.001% or more, more preferably 0.002% or more, and further more
preferably 0.003% or more. On the other hand, when these elements
are excessively high, the workability deteriorates. Therefore, both
of the Ca amount and the Mg amount are preferably 0.01% or less,
more preferably 0.008% or less, and further more preferably 0.005%
or less.
Example
[0045] Below, the present invention will be explained more
specifically referring to an example. The present invention is not
limited by the example described below, and it is a matter of
course that the present invention can also be implemented with
modifications being added appropriately within the scope adaptable
to the purposes described above and below, and any of them is to be
included within the technical range of the present invention.
[0046] After steel of the chemical composition shown in Tables 1, 2
was smelted according to an ordinary smelting method, a billet of
150 mm.times.150 mm was manufactured and was heated inside a
heating furnace. Thereafter, the primary scale formed inside the
heating furnace was descaled using high-pressure water, hot rolling
was executed under the conditions (the winding temperature after
hot rolling and the gas used for cooling) shown in Table 3, and the
steel wire material of .PHI.5.5 mm was obtained. Also, cooling
using the gas shown in Table 3 was executed to approximately
600.degree. C. in all cases, and the wire material was left for
cooling in the atmospheric air.
[0047] The obtained steel wire material was measured by a method
described below.
(1) Measurement of Thickness of Scale
[0048] Samples with 10 mm length were taken from the front end,
center part and rear end of the coil respectively, and the cross
sections of the scale of optional three locations from each sample
were observed using a scanning electron microscope (SEM)
(observation magnification: 5,000 times). The scale thickness was
measured for 10 points at every 100 .mu.m length in the peripheral
direction of the steel wire material on each measurement location,
the average scale thickness thereof was obtained, and the average
value of the three locations was made the scale thickness of each
sample. Further, the average value of respective samples (the front
end, center part and rear end of the coil) was calculated, and was
made the scale thickness of each test No.
(2) Measurement of Composition of Scale
[0049] Similarly to above (1), samples with 10 mm length were taken
from the front end, center part and rear end of the coil
respectively, X-ray diffraction was performed for the cross
sections of the scale of optional three locations from each sample,
and the ratios (vol %) of FeO and Fe.sub.2SiO.sub.4 were obtained
from the peak intensity ratio of FeO, Fe.sub.2SiO.sub.4,
Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4. The average values of the
three locations were made the FeO ratio and the Fe.sub.2SiO.sub.4
ratio of each sample. Further, the average value of respective
samples (the front end, center part and rear end of the coil) was
calculated, and was made the FeO ratio and the Fe.sub.2SiO.sub.4
ratio of each test No.
(3) Measurement of Scale Peeling Performance of Rolled Material
[0050] Samples with 200 mm length were taken from the front end,
center part and rear end of the coil respectively, air was blown to
the sample, and the scale on the surface of the steel wire material
was blown out. The appearance before and after blowing the air was
photographed by a digital camera, and the area ratio of the scale
having peeled off was obtained by comparing the both by image
analysis.
(3) Measurement of MD Performance
[0051] Samples with 250 mm length were taken from the front end,
center part and rear end of the coil respectively, were applied
with deformation strain of 6% by a tensile test machine, and were
taken out from the chuck. Air was thereafter blown to the sample,
and the scale on the surface of the steel wire material was blown
out. The appearance before and after application of the strain was
photographed by a digital camera, and the area ratio of the
remaining scale was calculated by comparing the both by image
analysis.
[0052] The results are shown in Tables 4, 5 and FIG. 2.
TABLE-US-00001 TABLE 1 Chemical composition (mass %) with the
remainder being iron and unavoidable impurities Steel kind C Si Mn
P S N Cr Ni Cu Al B Others A-1 0.80 0.25 0.55 0.007 0.003 0.002 --
-- -- -- -- -- A-2 0.80 0.25 0.55 0.007 0.003 0.002 0.28 -- -- --
-- -- A-3 0.80 0.25 0.55 0.007 0.003 0.002 -- 0.23 -- A-4 0.80 0.25
0.55 0.007 0.003 0.002 -- -- 0.18 -- -- -- A-5 0.80 0.25 0.55 0.007
0.003 0.002 -- -- -- 0.025 -- -- A-6 0.80 0.25 0.55 0.007 0.003
0.002 -- -- -- 0.0005 -- A-7 0.80 0.25 0.55 0.007 0.003 0.002 -- --
-- -- -- V = 0.035 A-8 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- --
-- Ca = 0.004 A-9 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- -- --
Hf = 0.052 A-10 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- -- -- Ti
= 0.038 A-11 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- -- -- Mg =
0.003 A-12 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- -- -- Nb =
0.031 A-13 0.80 0.25 0.55 0.007 0.003 0.002 -- -- -- -- -- Zr =
0.056 A-14 0.80 0.25 0.55 0.007 0.003 0.002 0.23 0.03 -- -- -- --
A-15 0.80 0.25 0.55 0.007 0.003 0.002 0.14 0.13 0.07 -- -- -- A-16
0.80 0.25 0.55 0.007 0.003 0.002 0.05 0.09 -- 0.011 -- -- A-17 0.80
0.25 0.55 0.007 0.003 0.002 0.12 0.25 -- -- 0.0011 -- A-18 0.80
0.25 0.55 0.007 0.003 0.002 0.08 0.08 -- -- -- Ti = 0.072 A-19 0.80
0.25 0.55 0.007 0.003 0.002 0.05 -- 0.05 -- -- -- A-20 0.80 0.25
0.55 0.007 0.003 0.002 0.16 -- 0.14 0.028 -- -- A-21 0.80 0.25 0.55
0.007 0.003 0.002 -- 0.15 0.09 -- -- -- A-22 0.80 0.25 0.55 0.007
0.003 0.002 -- 0.28 0.17 0.035 -- -- A-23 0.80 0.25 0.55 0.007
0.003 0.002 -- 0.12 0.06 -- 0.0009 -- A-24 0.80 0.25 0.55 0.007
0.003 0.002 -- 0.07 0.15 -- -- Hf = 0.054
TABLE-US-00002 TABLE 2 Chemical composition (mass %) with the
remainder being iron and unavoidable impurities Steel kind C Si Mn
P S N Cr Ni Cu Al B Others B 0.06 0.08 0.12 0.003 0.005 0.002 0.12
0.03 -- 0.01 -- V = 0.029 C 0.19 0.17 0.42 0.003 0.001 0.002 -- --
0.04 0.021 -- -- D 0.44 0.38 0.88 0.002 0.003 0.002 -- -- -- -- --
Ca = 0.002 E 0.69 0.45 0.76 0.002 0.004 0.002 -- 0.01 0.02 --
0.0005 Ti = 0.031, Hf = 0.027 F 0.88 0.37 0.46 0.002 0.003 0.002
0.27 -- 0.03 0.015 -- -- G 0.92 0.48 0.98 0.002 0.003 0.002 0.18
0.23 0.02 -- -- Ca = 0.003 H 1.05 0.29 1.15 0.004 0.003 0.002 0.26
0.02 0.16 0.002 0.0021 Ti = 0.026, Hf = 0.022 I 1.19 0.32 1.32
0.002 0.001 0.002 0.03 0.14 0.12 0.001 0.0034 Zr = 0.027, Nb =
0.043
TABLE-US-00003 TABLE 3 Manufac- Winding turing temperature
condition (.degree. C.) Cooling gas composition a 750 Nitrogen b
760 Atmospheric air c 800 Nitrogen + 1 vol % oxygen d 850 Nitrogen
+ 5 vol % oxygen e 875 Nitrogen + 10 vol % oxygen f 880 Atmospheric
air g 890 Nitrogen h 740 Nitrogen i 970 Atmospheric air
TABLE-US-00004 TABLE 4 MD performance Scale peeling Remaining scale
Scale ratio of rolled area ratio after Steel Manufacturing
thickness FeO ratio Fe.sub.2SiO.sub.4 ratio material applying 6%
strain No. kind condition (.mu.m) (vol %) (vol %) (area %) (%) 1
A-1 a 1.5 35 0.02 0.6 28 2 A-1 d 4.6 47 0.05 0.8 18 3 A-1 b 1.2 26
0.01 1.9 35 4 A-2 a 1.9 36 0.03 0.8 21 5 A-3 c 2.3 39 0.01 0.6 18 6
A-4 d 5.9 63 0.05 0.5 10 7 A-5 e 6.8 67 0.06 0.2 8 8 A-6 c 3.2 52
0.01 0.6 13 9 A-7 a 1.3 41 0.02 0.5 17 10 A-8 d 4.4 52 0.01 0.8 16
11 A-9 e 6.1 72 0.08 0.6 19 12 A-10 a 2.4 33 0.02 0.9 20 13 A-11 e
7.0 79 0.03 0.8 29 14 A-12 d 6.5 53 0.07 1.1 11 15 A-13 c 2.4 36
0.01 0.8 16 16 A-14 a 1.9 34 0.01 1.2 24 17 A-15 c 2.7 39 0.02 0.9
25 18 A-16 d 4.5 48 0.02 0.7 12 19 A-17 e 5.3 56 0.05 0.5 5 20 A-18
c 3.4 43 0.03 0.6 11 21 A-19 e 5.5 61 0.09 0.7 9 22 A-20 d 4.1 46
0.04 0.8 12 23 A-21 a 1.3 31 0.03 0.9 18 24 A-22 c 1.9 42 0.02 0.4
14 25 A-23 d 3.8 47 0.02 0.5 12 26 A-24 e 5.4 55 0.05 1.1 7
TABLE-US-00005 TABLE 5 MD performance Scale peeling Remaining scale
Scale ratio of rolled area ratio after Steel Manufacturing
thickness FeO ratio Fe.sub.2SiO.sub.4 ratio material applying 6%
strain No. kind condition (.mu.m) (vol %) (vol %) (area %) (%) 27 B
a 1.1 39 0.02 0.8 16 28 B c 1.8 44 0.03 1 13 29 B b 1.5 21 0.02 1.8
41 30 C c 2.4 42 0.04 0.8 15 31 C d 3.6 58 0.04 0.5 11 32 D e 5.5
71 0.05 0.7 22 33 D g 8.8 82 0.16 0.03 32 34 E c 2.5 32 0.03 0.9 27
35 E e 5.6 44 0.04 0.7 19 36 E f 6.1 25 0.04 1.9 31 37 F d 3.4 45
0.02 0.9 17 38 F a 1.5 31 0.01 0.8 24 39 F e 4.1 54 0.02 0.6 10 40
F b 1.6 14 0.01 1.9 52 41 G a 1.5 44 0.01 1 14 42 G d 3.2 57 0.04
0.5 7 43 G f 6.0 27 0.05 1.8 35 44 H a 0.9 31 0.01 0.7 18 45 H e
4.5 61 0.03 0.6 10 46 H b 1.8 8 0.02 1.8 56 47 H f 6.7 19 0.08 1.9
43 48 I d 4.8 68 0.05 0.8 14 49 I h 0.8 6 0.01 1.8 59 50 A-1 i 7.1
41 0.02 2.9 10 51 B i 7.5 38 0.01 3.5 11 52 E i 8.2 45 0.03 5.7 9
53 G i 7.8 42 0.02 4.2 12 54 I i 8.5 35 0.01 6.1 4
[0053] Nos. 1, 2, 4-28, 30-32, 34, 35, 37-39, 41, 42, 44, 45, 48 of
Tables 4, 5 are examples satisfying the requirements of the present
invention, the scale thickness and the composition of the scale are
appropriate, and therefore the MD property is excellent.
[0054] On the other hand, in Nos. 3, 29, 33, 36, 40, 43, 46, 47,
49, the MD property deteriorated, because the manufacturing
condition did not satisfy the requirements of the present
invention.
[0055] Nos. 3, 29, 36, 40, 43, 46, 47 are examples cooling was
executed by injecting the atmospheric air after hot rolling, the
FeO fraction could not be secured because FeO was converted to
Fe.sub.3O.sub.4 during cooling, and the MD property deteriorated.
No. 33 is an example the winding temperature after hot rolling was
high, the scale thickness became thick, the FeO ratio increased
excessively, the Fe.sub.2SiO.sub.4 ratio was also high, and
therefore the MD property deteriorated. No. 49 is an example the
winding temperature after hot rolling was low, the FeO ratio could
not be secured, and the MD property deteriorated. Nos. 50-54 are
examples the winding temperature after hot rolling was further
high, the scale thickness exceeded 7.0 .mu.m, the scale peeling
ratio of the rolled material increased, and the rust was generated.
More specifically, in Nos. 50-54, it is considered that the scale
drops during cooling after hot rolling and at the time of storage
and transportation, and the rust is generated.
[0056] Also, the relation between the scale thickness and the scale
peeling ratio of the rolled material is shown in FIG. 2. It is
known that the scale peeling ratio of the rolled material increases
when the scale thickness becomes thick exceeding 7.0 .mu.m.
[0057] The present invention has been described in detail and
referring to a specific embodiment, however, it is clear for a
person with an ordinary skill in the art that a variety of
alterations and modifications can be added without departing from
the spirit and scope of the present invention.
[0058] The present application is based on the Japanese Patent
Application No. 2011-002014 applied on Jan. 7, 2011, and the
contents thereof are hereby incorporated by reference.
INDUSTRIAL APPLICABILITY
[0059] The steel wire material of the present invention is
excellent in the mechanical descaling performance after hot rolling
(before drawing work), and is therefore useful as a raw material
for a tire cord (steel cord, bead wire) for an automobile, hose
wire, a saw wire and the like used for cutting a silicon for a
semiconductor and the like.
* * * * *