U.S. patent application number 12/312166 was filed with the patent office on 2009-11-12 for steel sheet having high plane integration and method of production of same.
Invention is credited to Tooru Inaguma, Youji Mizuhara, Hiroaki Sakamoto.
Application Number | 20090280350 12/312166 |
Document ID | / |
Family ID | 39429828 |
Filed Date | 2009-11-12 |
United States Patent
Application |
20090280350 |
Kind Code |
A1 |
Inaguma; Tooru ; et
al. |
November 12, 2009 |
STEEL SHEET HAVING HIGH PLANE INTEGRATION AND METHOD OF PRODUCTION
OF SAME
Abstract
Steel sheet having a high {222} plane integration comprising
steel sheet having an Al content of less than 6.5 mass %
characterized by one or both of (1) a {222} plane integration of
one or both of an .alpha.Fe phase and .gamma.Fe phase with respect
to the steel sheet surface being 60% to 99% and (2) a {200} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 0.01% to
15%.
Inventors: |
Inaguma; Tooru; (Tokyo,
JP) ; Sakamoto; Hiroaki; (Tokyo, JP) ;
Mizuhara; Youji; (Tokyo, JP) |
Correspondence
Address: |
KENYON & KENYON LLP
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
39429828 |
Appl. No.: |
12/312166 |
Filed: |
November 21, 2007 |
PCT Filed: |
November 21, 2007 |
PCT NO: |
PCT/JP2007/072997 |
371 Date: |
April 27, 2009 |
Current U.S.
Class: |
428/609 ;
148/534; 420/103; 420/77; 427/295; 427/319; 427/360 |
Current CPC
Class: |
C21D 8/0426 20130101;
C21D 9/46 20130101; C22C 38/06 20130101; C21D 8/0473 20130101; C21D
8/0436 20130101; C23C 2/12 20130101; C21D 2201/05 20130101; C21D
2211/005 20130101; C22C 38/00 20130101; C21D 8/0226 20130101; C21D
8/0273 20130101; Y10T 428/12451 20150115; C21D 8/0236 20130101;
C21D 2211/001 20130101 |
Class at
Publication: |
428/609 ; 420/77;
420/103; 427/360; 148/534; 427/319; 427/295 |
International
Class: |
B32B 7/00 20060101
B32B007/00; C22C 38/06 20060101 C22C038/06; B05D 3/12 20060101
B05D003/12; C21D 8/02 20060101 C21D008/02; B05D 3/02 20060101
B05D003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 21, 2006 |
JP |
2006-314240 |
Claims
1. Steel sheet having a high {222} plane integration comprised of
steel sheet having an Al content of less than 6.5 mass %,
characterized by one or both of: (1) a {222} plane integration of
one or both of an .alpha.Fe phase and .gamma.Fe phase with respect
to the steel sheet surface being 60% to 99% and, (2) a {200} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 0.01% to
15%.
2. Steel sheet having a high {222} plane integration comprising
steel sheet having an Al content of less than 6.5 mass % on at
least one surface of which a second layer is deposited,
characterized by one or both of: (1) a {222} plane integration of
one or both of an .alpha.Fe phase and .gamma.Fe phase with respect
to the steel sheet surface being 60% to 99% and (2) a {200} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 0.01% to
15%.
3. Steel sheet having a high {222} plane integration comprising
steel sheet having an Al content of less than 6.5 mass % on at
least one surface of which a second layer is formed and having the
second layer and steel sheet partially alloyed, characterized by
one or both of: (1) a {222} plane integration of one or both of an
.alpha.Fe phase and .gamma.Fe phase with respect to the steel sheet
surface being 60% to 99% and (2) a {200} plane integration of one
or both of an .alpha.Fe phase and .gamma.Fe phase with respect to
the steel sheet surface being 0.01% to 15%.
4. Steel sheet having a high {222} plane integration comprising
steel sheet having an Al content of less than 6.5 mass % on at
least one surface of which a second layer is deposited and alloyed
with the steel sheet, characterized by one or both of: (1) a {222}
plane integration of one or both of an .alpha.Fe phase and
.gamma.Fe phase with respect to the steel sheet surface being 60%
to 99% and (2) a {200} plane integration of one or both of an
.alpha.Fe phase and .gamma.Fe phase with respect to the steel sheet
surface being 0.01% to 15%.
5. Steel sheet having a high {222} plane integration as set forth
in claim 1 characterized in that said {222} plane integration is
60% to 95%.
6. Steel sheet having a high {222} plane integration as set forth
in claim 2 characterized in that said second layer contains at
least one element from among Fe, Al, Co, Cu, Cr, Ga, Hf, Hg, In,
Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and
Zr.
7. Steel sheet having a high {222} plane integration as set forth
in claim 1 characterized in that the thickness of the steel sheet
is 5 .mu.m to 5 mm.
8. Steel sheet having a high {222} plane integration as set forth
in claim 2 characterized in that the thickness of the second layer
is 0.01 .mu.m to 500 .mu.m.
9. A method of production of steel sheet having a high {222} plane
integration having (a) a step of depositing a second layer on at
least one surface of steel sheet having an Al content of less than
6.5 mass % serving as a matrix, (b) a step of cold rolling the
steel sheet on which the second layer has been deposited, (c) a
step of removing the second layer from the cold rolled steel sheet,
and (d) a step of heat treating the second layer from which the
second layer has been removed to make the steel sheet
recrystallize.
10. A method of production of steel sheet having a high {222} plane
integration having (a) a step of depositing a second layer on at
least one surface of steel sheet having an Al content of less than
3.5 mass % serving as a matrix, (b) a step of cold rolling the
steel sheet on which the second layer has been deposited, and (c) a
step of heat treating the cold rolled steel sheet to make the steel
sheet recrystallize, (d) an Al content of the recrystallized steel
sheet being less than 6.5 mass %.
11. A method of production of steel sheet having a high {222} plane
integration having: (a) a step of depositing a second layer on at
least one surface of steel sheet having an Al content of less than
3.5 mass % serving as a matrix, (b) a step of cold rolling the
steel sheet on which the second layer has been deposited, and (c) a
step of heat treating the cold rolled steel sheet to alloy part of
the second layer and make the steel sheet recrystallize, (d) an Al
content of the alloyed and recrystallized steel sheet being less
than 6.5 mass %.
12. A method of production of steel sheet having a high {222} plane
integration having: (a) a step of depositing a second layer on at
least one surface of steel sheet having an Al content of less than
3.5 mass % serving as a matrix, (b) a step of cold rolling the
steel sheet on which the second layer has been deposited, and (c) a
step of heat treating the cold rolled steel sheet to alloy the
second layer and make the steel sheet recrystallize, (d) an Al
content of the steel sheet being less than 6.5 mass %.
13. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9, said method of production of
steel sheet having a high {222} plane integration characterized by
control to obtain one or both of: (1) a {222} plane integration of
one or both of an .alpha.Fe phase and .gamma.Fe phase with respect
to the steel sheet surface being 60% to 99% and (2) a {200} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 0.01% to
15%.
14. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9, said method of production of
steel sheet having a high {222} plane integration characterized by
control to obtain one or both of: (1) a {222} plane integration of
one or both of an .alpha.Fe phase and .gamma.Fe phase with respect
to the steel sheet surface being 60% to 95% and (2) a {200} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 0.01% to
15%.
15. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9, said method of production of
steel sheet having a high {222} plane integration characterized in
that the second layer contains at least one element among Fe, Al,
Co, Cu, Cr, Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn,
Ta, Ti, V, W, Zn, and Zr.
16. A method of production of steel sheet having a high {222} plane
integration, said method of production of steel sheet having a high
{222} plane integration characterized by having (a) a step of
depositing on at least one surface of steel sheet having an Al
content of less than 6.5 mass % serving as a matrix a second layer
of one or more elements among Fe, Co, Cu, Cr, Ga, Hf, Hg, In, Mn,
Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr, (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, (c) a step of removing the second layer from the
cold rolled steel sheet, and (d) a step of heat treating the second
layer from which the second layer has been removed to make the
steel sheet recrystallize.
17. A method of production of steel sheet having a high {222} plane
integration, said method of production of steel sheet having a high
{222} plane integration characterized by having (a) a step of
depositing on at least one surface of steel sheet having an Al
content of less than 6.5 mass % serving as a matrix a second layer
of one or more elements among Fe, Co, Cu, Cr, Ga, Hf, Hg, In, Mn,
Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr, (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and (c) a step of heat treating the cold rolled
steel sheet to make the steel sheet recrystallize.
18. A method of production of steel sheet having a high {222} plane
integration, said method of production of steel sheet having a high
{222} plane integration characterized by having (a) a step of
depositing on at least one surface of steel sheet having an Al
content of less than 6.5 mass % serving as a matrix a second layer
of one or more elements among Fe, Co, Cu, Cr, Ga, Hf, Hg, In, Mn,
Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr, (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and (c) a step of heat treating the cold rolled
steel sheet to alloy part of the second layer and make the steel
sheet recrystallize.
19. A method of production of steel sheet having a high {222} plane
integration, said method of production of steel sheet having a high
{222} plane integration characterized by having (a) a step of
depositing on at least one surface of steel sheet having an Al
content of less than 6.5 mass % serving as a matrix a second layer
of one or more elements among Fe, Co, Cu, Cr, Ga, Hf, Hg, In, Mn,
Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr, (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and (c) a step of heat treating the cold rolled
steel sheet to alloy the second layer and make the steel sheet
recrystallize.
20. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that the
thickness of the steel sheet serving as said matrix is 10 .mu.m to
10 mm.
21. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that the
thickness of the second layer is 0.05 .mu.m to 1000 .mu.m.
22. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized by, before
depositing said second layer, preheat treating the steel sheet.
23. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 22 characterized in that the
temperature of said preheat treatment is 700 to 1100.degree. C.
24. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 22 characterized in that an
atmosphere of said preheat treatment is at least one of a vacuum,
an insert gas atmosphere, and a hydrogen atmosphere.
25. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that said step
of depositing the second layer on the steel sheet is by
plating.
26. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that said step
of depositing the second layer on the steel sheet is by roll
cladding.
27. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that a
reduction rate in said step of cold rolling is 30% to 95%.
28. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that a heat
treatment temperature in said step of heat treatment is 600.degree.
C. to 1000.degree. C. and a heat treatment time is 30 seconds or
more.
29. A method of production of steel sheet having a high {222} plane
integration as set forth in claim 9 characterized in that a heat
treatment temperature in said step of heat treatment is over
1000.degree. C.
Description
TECHNICAL FIELD
[0001] The present invention relates to steel sheet excellent in
deep drawability, press formability, punchability, and other
workability and a method of production of that steel sheet.
BACKGROUND ART
[0002] For sheet steel for automobiles or home electrical
appliances, in addition to the needs for higher strength and
lighter weight, excellent workability enabling working in press
forming and other work processes without causing cracks or wrinkles
is required.
[0003] The workability of steel sheet depends on the texture of the
.alpha.Fe phase or the .gamma.Fe phase. In particular, by
increasing {222} plane integration of the crystals at the steel
sheet surface, it is possible to improve the workability. For this
reason, several methods have been proposed for controlling the
texture to raise the workability of the steel.
[0004] Japanese Patent Publication (A) No. 6-2069 discloses high
strength cold rolled steel sheet and hot dip galvanized steel sheet
wherein the amounts of Si, Mn, and P are controlled based on a
fixed relationship with the X-ray diffraction intensities of the
{222} planes and {200} planes parallel to the steel sheet surface
so as to secure deep drawability.
[0005] Japanese Patent Publication (A) No. 8-13081 discloses an
enameling use high strength cold rolled steel sheet and a method of
production of the same wherein the amount of Nb is defined by the
amount of C and, furthermore, the hot rolling and cold rolling
conditions are defined so as to control the (111) texture
[0006] Japanese Patent Publication (A) No. 10-18011 discloses a hot
dip galvannealed steel sheet and method of production of the same
wherein, when, among the X-ray diffraction intensities, the ratio
of the {200} plane intensity and the {222} plane intensity, that
is, I(200)/I(222), becomes less than 0.17, there are no longer
streak like defects at the plating surface and wherein when the
final rolling temperature of the hot rolling is made
A.sub.r3+30.degree. C. or more, the X-ray diffraction intensity
ratio I(200)/I(222) becomes less than 0.17.
[0007] Japanese Patent Publication (A) No. 11-350072 discloses very
low carbon cold rolled steel sheet with a content of C in the steel
of 0.01% or less which, when the particle size of the ferrite at
the surface layer part accounting for 1/10 of the total thickness
from the surface of the steel sheet is a and the particle size of
the ferrite at the inner layer part accounting for 1/2 of the total
thickness centered at the center of thickness is b, satisfies
a-b.gtoreq.0.5, a.gtoreq.7.0, and b.ltoreq.7.5 and which, if
controlling the ratio I(222)/I(200) of X-ray diffraction
intensities from the {222} plane and the {200} plane to be 5.0 or
more at the part of 1/15 the total sheet thickness from the surface
of the steel sheet and to be 12 or more at the center part of sheet
thickness of the steel sheet, it is possible to reduce the orange
skin peel state of the steel sheet at the time of press
formation.
[0008] In this way, in the past, to improve the workability of a
steel sheet, the technique has been devised of increasing the {222}
plane integration of the .alpha.Fe phase or .gamma.Fe phase. This
has been used to optimize the steel sheet ingredients, rolling
conditions, temperature conditions, etc.
[0009] Furthermore, Japanese Patent Publication (A) No. 2006-144116
discloses high Al content steel sheet having an Al content of 6.5
mass % to 10 mass % wherein the {222} plane integration of the
.alpha.Fe crystals is made 60% to 95% or the {200} plane
integration is made 0.01% to 15% so as to improve the
workability.
[0010] Furthermore, the above publication discloses a method of
raising the plane integration of specific planes in high Al content
steel sheet comprising treating the surface of matrix steel sheet
having an Al content of 3.5 mass % to less than 6.5 mass % by hot
dip Al coating to deposit Al alloy, cold rolling, then performing
diffusion heat treatment.
[0011] Further, when punching steel sheet, a small size of the
burrs formed at the cross-section is sought as one aspect of the
workability, so in the past various methods have been proposed for
suppressing the formation of burrs.
[0012] Japanese Patent Publication (A) No. 3-277739 discloses steel
sheet hardened at its surface so as to make the burrs formed at the
time of shearing extremely small and give a soft hardness
distribution inside the steel sheet so as to prevent reduction of
the press formability. Specifically, steel sheet having an r value
(Rankford value) of 1.7 to 2 and having a burr height at the time
of punching of 12 to 40 .mu.m is disclosed.
[0013] Japanese Patent Publication (A) No. 8-188850 discloses cold
rolled steel sheet comprised of very low carbon steel to which S is
added in an amount of 0.003 to 0.03% so as to satisfy a fixed
formula and raised in deep drawability and punchability.
Specifically, steel sheet having an r value of 2.2 to 2.6 and a
burr height at the time of punching of 30 to 80 .mu.m is
disclosed.
DISCLOSURE OF THE INVENTION
[0014] As explained above, in the past, techniques have been
devised for optimizing the steel sheet ingredients, rolling
conditions, temperature conditions, etc. so as to raise the {222}
plane integration of the .alpha.Fe phase or .gamma.Fe phase. These
have met the needs for improvement of the workability of steel
sheet.
[0015] However, meeting more sophisticated requirements is
difficult with the prior art. A new perspective is required.
[0016] That is, in steel sheet with a {222} plane integration of
the conventional extent, the punchability becomes poor in the
working process. Further, the plastic flowability required in
complicated press forming is insufficient. It has not been possible
to meet the needs for more sophisticated working or higher
efficiency of the working process.
[0017] Specifically, the above steel sheet had the problem of
formation of burrs at the cross-section at the time of punching and
the need for a chamfering process to remove the formed burrs.
[0018] Further, the above steel sheet had the problem of
insufficient slip of the steel sheet with the die surface at the
time of press formation by a complicated die and therefore the
inability to form shapes more complicated than in the past.
[0019] The steel sheet disclosed in Japanese Patent Publication (A)
No. 2006-144116 has a {222} plane integration for raising the
workability higher than the past and has workability enough for
forming foil for forming a honeycomb structure, but has a large Al
content, so cannot be used as usual processing use steel sheet for
sophisticated working or for higher efficiency of the working
process.
[0020] Further, the methods disclosed in Japanese Patent
Publication (A) No. 6-2069, Japanese Patent Publication (A) No.
8-13081, Japanese Patent Publication (A) No. 10-18011, and Japanese
Patent Publication (A) No. 11-350072 enable integration of the
{222} planes up to a certain ratio, but there are limits to the
improvement of the plane integration with just setting the
ingredient conditions and conditions in the annealing and other
conventional processes.
[0021] In the method disclosed in Japanese Patent Publication (A)
No. 2006-144116, the conventional process is augmented by a step of
deposition of an Al alloy on the matrix surface by hot dip Al
coating so as to raise the {222} plane integration.
[0022] However, the above method is a method improving the {222}
plane integration only when using a matrix having an Al content of
3.5 mass % to less than 6.5 mass %. If just applying this method to
steel sheet with a low Al content, it is difficult to raise or
lower the integration of specific planes.
[0023] Furthermore, the methods disclosed in Japanese Patent
Publication (A) No. 3-277739 and Japanese Patent Publication (A)
No. 8-188850 succeed in reducing the formation of burrs
accompanying punching to a certain extent, but have not reached the
point of enabling elimination of the chamfering step for removing
the burrs.
[0024] Therefore, the inventors studied art for plating or
otherwise treating the surface of steel sheet to control the
texture further. The present invention has as its object the
provision of "less than 6.5 mass % Al content steel sheet"
excellent in workability having an unprecedentedly high level of
{222} plane integration and free from formation of burrs at the
cross-section at the time of punching.
[0025] Further, the present invention has as its object the
provision of a method of production for producing a "less than 6.5
mass % Al content steel sheet" having an unprecedentedly high {222}
plane integration.
[0026] The inventors discovered that in steel sheet with an Al
content of less than 6.5 mass %, if (x1) making the {222} plane
integration of the Fe crystals a high specific range and/or (x2)
making the {200} plane integration of the Fe crystals a low
specific range, no burrs form at the cross-section at the time of
punching and unprecedentedly excellent workability is obtained.
[0027] Furthermore, the inventors discovered that, as techniques
for effectively integrating specific crystal planes by a high ratio
in steel sheet having an Al content of less than 6.5 mass %, (y1)
depositing a second layer on the surface of a matrix steel sheet
having an Al content of less than 3.5 mass % (the matrix steel
sheet being referred to as the "first layer" and the layer provided
on its surface being referred to as the "second layer"), then heat
treating this to integrate specific crystal planes to a high level,
by making the content of Cr in the matrix steel sheet 12 mass % or
less and, further, (y2) depositing a second layer on a matrix steel
sheet having an Al content of less than 6.5 mass %, then cold
rolling, then removing the second layer and performing heat
treatment were effective.
[0028] Below, the gist of the present invention will be
described.
[0029] (1) Steel sheet having a high {222} plane integration
comprised of steel sheet having an Al content of less than 6.5 mass
%, characterized by one or both of: [0030] (1) a {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 60% to 99% and,
[0031] (2) a {200} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
being 0.01% to 15%. [0032] (2) Steel sheet having a high {222}
plane integration comprising steel sheet having an Al content of
less than 6.5 mass % on at least one surface of which a second
layer is deposited, characterized by one or both of: [0033] (1) a
{222} plane integration of one or both of an .alpha.Fe phase and
.gamma.Fe phase with respect to the steel sheet surface being 60%
to 99% and [0034] (2) a {200} plane integration of one or both of
an .alpha.Fe phase and .gamma.Fe phase with respect to the steel
sheet surface being 0.01% to 15%.
[0035] (3) Steel sheet having a high {222} plane integration
comprising steel sheet having an Al content of less than 6.5 mass %
on at least one surface of which a second layer is formed and
having the second layer and steel sheet partially alloyed,
characterized by one or both of: [0036] (1) a {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface being 60% to 99% and
[0037] (2) a {200} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
being 0.01% to 15%.
[0038] (4) Steel sheet having a high {222} plane integration
comprising steel sheet having an Al content of less than 6.5 mass %
on at least one surface of which a second layer is deposited and
alloyed with the steel sheet, characterized by one or both of:
[0039] (1) a {222} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
being 60% to 99% and [0040] (2) a {200} plane integration of one or
both of an .alpha.Fe phase and .gamma.Fe phase with respect to the
steel sheet surface being 0.01% to 15%.
[0041] (5) Steel sheet having a high {222} plane integration as set
forth in any of (1) to (4) characterized in that said {222} plane
integration is 60% to 95%.
[0042] (6) Steel sheet having a high {222} plane integration as set
forth in any of (2) to (5) characterized in that said second layer
contains at least one element from among Fe, Al, Co, Cu, Cr, Ga,
Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W,
Zn, and Zr.
[0043] (7) Steel sheet having a high {222} plane integration as set
forth in any of (1) to (6) characterized in that the thickness of
the steel sheet is 5 .mu.m to 5 mm.
[0044] (8) Steel sheet having a high {222} plane integration as set
forth in any of (2) to (7) characterized in that the thickness of
the second layer is 0.01 .mu.m to 500 .mu.m.
[0045] (9) A method of production of steel sheet having a high
{222} plane integration having [0046] (a) a step of depositing a
second layer on at least one surface of steel sheet having an Al
content of less than 6.5 mass % serving as a matrix, [0047] (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, [0048] (c) a step of removing the second layer from
the cold rolled steel sheet, and [0049] (d) a step of heat treating
the second layer from which the second layer has been removed to
make the steel sheet recrystallize.
[0050] (10) A method of production of steel sheet having a high
{222} plane integration having [0051] (a) a step of depositing a
second layer on at least one surface of steel sheet having an Al
content of less than 3.5 mass % serving as a matrix, [0052] (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and [0053] (c) a step of heat treating the cold
rolled steel sheet to make the steel sheet recrystallize, [0054]
(d) an Al content of the recrystallized steel sheet being less than
6.5 mass %.
[0055] (11) A method of production of steel sheet having a high
{222} plane integration having: [0056] (a) a step of depositing a
second layer on at least one surface of steel sheet having an Al
content of less than 3.5 mass % serving as a matrix, [0057] (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and [0058] (c) a step of heat treating the cold
rolled steel sheet to alloy part of the second layer and make the
steel sheet recrystallize, [0059] (d) an Al content of the alloyed
and recrystallized steel sheet being less than 6.5 mass %.
[0060] (12) A method of production of steel sheet having a high
{222} plane integration having: [0061] (a) a step of depositing a
second layer on at least one surface of steel sheet having an Al
content of less than 3.5 mass % serving as a matrix, [0062] (b) a
step of cold rolling the steel sheet on which the second layer has
been deposited, and [0063] (c) a step of heat treating the cold
rolled steel sheet to alloy the second layer and make the steel
sheet recrystallize, [0064] (d) an Al content of the steel sheet
being less than 6.5 mass %.
[0065] (13) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (12), said
method of production of steel sheet having a high {222} plane
integration characterized by control to obtain one or both of:
[0066] (1) a {222} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
being 60% to 99% and [0067] (2) a {200} plane integration of one or
both of an .alpha.Fe phase and .gamma.Fe phase with respect to the
steel sheet surface being 0.01% to 15%.
[0068] (14) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (12), said
method of production of steel sheet having a high {222} plane
integration characterized by control to obtain one or both of:
[0069] (1) a {222} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
being 60% to 95% and [0070] (2) a {200} plane integration of one or
both of an .alpha.Fe phase and .gamma.Fe phase with respect to the
steel sheet surface being 0.01% to 15%.
[0071] (15) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (12), said
method of production of steel sheet having a high {222} plane
integration characterized in that the second layer contains at
least one element among Fe, Al, Co, Cu, Cr, Ga, Hf, Hg, In, Mn, Mo,
Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr.
[0072] (16) A method of production of steel sheet having a high
{222} plane integration, said method of production of steel sheet
having a high {222} plane integration characterized by having
[0073] (a) a step of depositing on at least one surface of steel
sheet having an Al content of less than 6.5 mass % serving as a
matrix a second layer of one or more elements among Fe, Co, Cu, Cr,
Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V,
W, Zn, and Zr, [0074] (b) a step of cold rolling the steel sheet on
which the second layer has been deposited, [0075] (c) a step of
removing the second layer from the cold rolled steel sheet, and
[0076] (d) a step of heat treating the second layer from which the
second layer has been removed to make the steel sheet
recrystallize.
[0077] (17) A method of production of steel sheet having a high
{222} plane integration, said method of production of steel sheet
having a high {222} plane integration characterized by having
[0078] (a) a step of depositing on at least one surface of steel
sheet having an Al content of less than 6.5 mass % serving as a
matrix a second layer of one or more elements among Fe, Co, Cu. Cr,
Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V,
W, Zn, and Zr, [0079] (b) a step of cold rolling the steel sheet on
which the second layer has been deposited, and [0080] (c) a step of
heat treating the cold rolled steel sheet to make the steel sheet
recrystallize.
[0081] (18) A method of production of steel sheet having a high
{222} plane integration, said method of production of steel sheet
having a high {222} plane integration characterized by having
[0082] (a) a step of depositing on at least one surface of steel
sheet having an Al content of less than 6.5 mass % serving as a
matrix a second layer of one or more elements among Fe, Co, Cu, Cr,
Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V,
W, Zn, and Zr, [0083] (b) a step of cold rolling the steel sheet on
which the second layer has been deposited, and [0084] (c) a step of
heat treating the cold rolled steel sheet to alloy part of the
second layer and make the steel sheet recrystallize.
[0085] (19) A method of production of steel sheet having a high
{222} plane integration, said method of production of steel sheet
having a high {222} plane integration characterized by having
[0086] (a) a step of depositing on at least one surface of steel
sheet having an Al content of less than 6.5 mass % serving as a
matrix a second layer of one or more elements among Fe, Co, Cu, Cr,
Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V,
W, Zn, and Zr, [0087] (b) a step of cold rolling the steel sheet on
which the second layer has been deposited, and [0088] (c) a step of
heat treating the cold rolled steel sheet to alloy the second layer
and make the steel sheet recrystallize.
[0089] (20) A method of production of steel sheet having a high
{222} plane integration as set forth in any one of (9) to (19)
characterized in that the thickness of the steel sheet serving as
said matrix is 10 .mu.m to 10 mm.
[0090] (21) A method of production of steel sheet having a high
{222} plane integration as set forth in any one of (9) to (19)
characterized in that the thickness of the second layer is 0.05
.mu.m to 1000 .mu.m.
[0091] (22) A method of production of steel sheet having a high
{222} plane integration as set forth in any one of (9) to (19)
characterized by, before depositing said second layer, preheat
treating the steel sheet.
[0092] (23) A method of production of steel sheet having a high
{222} plane integration as set forth in (22) characterized in that
the temperature of said preheat treatment is 700 to 1100.degree.
C.
[0093] (24) A method of production of steel sheet having a high
{222} plane integration as set forth in (22) or (23) characterized
in that an atmosphere of said preheat treatment is at least one of
a vacuum, an insert gas atmosphere, and a hydrogen atmosphere.
[0094] (25) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (19)
characterized in that said step of depositing the second layer on
the steel sheet is by plating.
[0095] (26) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (19)
characterized in that said step of depositing the second layer on
the steel sheet is by roll cladding.
[0096] (27) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (19)
characterized in that a reduction rate in said step of cold rolling
is 30% to 95%.
[0097] (28) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (19)
characterized in that a heat treatment temperature in said step of
heat treatment is 600.degree. C. to 1000.degree. C. and a heat
treatment time is 30 seconds or more.
[0098] (29) A method of production of steel sheet having a high
{222} plane integration as set forth in any of (9) to (19)
characterized in that a heat treatment temperature in said step of
heat treatment is over 1000.degree. C.
[0099] The steel having a high {222} plane integration of the
present invention (the present invention steel sheet) sheet is an
unprecedented steel sheet excellent in workability which has an Al
content of less than 6.5 mass % and a high {222} plane integration
and has a low {200} plane integration, so not being formed with
burrs at the cross-section at the time of punching.
[0100] For this reason, the present invention steel sheet can
easily be worked to various shapes including conventional shapes to
special shapes and for example are useful for outer panels for auto
parts, home electrical appliance parts, etc. requiring
complicatedly shaped press formation and other various structural
materials, functional materials, etc.
[0101] In the method of production of the present invention, in
steel sheet having an Al content of less than 6.5 mass %, it is
possible to increase the {222} plane integration or to lower the
{200} plane integration easily and effectively. Further, the method
of production of the present invention enables the production of
the present invention steel sheet having a high {222} plane
integration without production of new facilities by just switching
processes of existing facilities easily and at low cost.
BEST MODE FOR CARRYING OUT THE INVENTION
[0102] Below, the present invention will be explained in
detail.
[0103] The inventors discovered that by making the Al content of
the steel sheet less than 6.5 mass % and (x1) raising the {222}
plane integration of the Fe crystal phase to 60% to 99% and/or (x2)
lowering the {200} plane integration to 0.01% to 15%, it is
possible to provide unprecedented steel sheet excellent in
workability free from the occurrence of burrs at the cross-section
at the time of punching.
[0104] The inventors disclosed "high Al content steel sheet having
an Al content of 6.5 mass % to 10 mass %" having a {222} plane
integration of an .alpha.Fe phase of 60% to 95% and/or a {200}
plane integration of an .alpha.Fe phase of 0.01% to 15% in Japanese
Patent Publication (A) No. 2006-144116.
[0105] The above method of production of steel sheet is
characterized by depositing an Al alloy on at least one surface of
steel sheet containing Al in 3.5 mass % to 6.5 mass %, applying
working strain by cold working, then applying heat treatment for
making the Al diffuse.
[0106] The inventors, after this, tackled the development of
technology for further raising the {222} plane integration in steel
sheet having an Al content of less than 6.5 mass % and ran various
experiments.
[0107] As a result, regarding the method for integrating specific
crystal planes, the inventors found that by using a matrix steel
sheet having an Al content of less than 3.5 mass %, making the
content of Cr of the matrix steel sheet 12 mass % or less,
depositing a second layer comprised of not only Al, but also
another metal on the steel sheet, then heat treating this to make
the steel sheet recrystallize, it is possible to raise the {222}
plane integration.
[0108] This is based on the discovery disclosed in Japanese Patent
Publication (A) No. 2006-144116 that "at the time of cold rolling,
the special dislocation structures to be formed in the steel sheet
are effectively formed and that due to the heat treatment,
recrystallization nuclei are efficiently formed for making the
dislocation structures grow to a {222} plane texture.
[0109] That is, according to the present invention, even if the
ingredients of the steel sheet are ingredients where the Al content
after recrystallization becomes less than 6.5 mass %, the frequency
of occurrence of the above recrystallization nuclei tends to become
higher and as a result steel sheet having a higher {222} plane
integration can be obtained.
[0110] Note that, in the present invention, the content of Cr in
the matrix steel sheet is preferably less than 10 mass %. With such
a Cr content, it is possible to more easily raise the {222} plane
integration.
[0111] When using matrix steel sheet having an Al content of less
than 6.5 mass %, it is possible to deposit a second layer on the
steel sheet surface, cold roll the sheet, then remove the second
layer to obtain, by subsequent heat treatment, a high {222} plane
integration.
[0112] This phenomenon is basically also considered to arise based
on the mechanism of formation of recrystallization nuclei.
[0113] Below, details of the present invention will further
described.
[0114] The present invention steel sheet, at ordinary temperature,
is comprised or one or both of an .alpha.Fe phase and .gamma.Fe
phase. The Al content is less than 6.5 mass %.
[0115] If the Al content becomes 6.5 mass % or more, it is not
possible to easily obtain a high {222} plane texture. Not only
this, the tensile elongation at break falls. Even if having a high
{222} plane integration, sufficient workability cannot be
obtained.
[0116] That is, in steel sheet having an Al content of 6.5 mass %
or more, no matter how one raises the {222} plane integration and,
further, no matter how one lowers the {200} plane integration,
burrs end up forming at the cross-section at the time of punching.
Therefore, in the present invention steel sheet, the Al content was
made less than 6.5 mass %.
[0117] The Al content of the present invention steel sheet is
preferably 0.001 mass % or more. If the Al is 0.001 mass % or more,
the yield at the time of production will rise. More preferably, it
is 0.11 mass % or more. If Al becomes 0.11 mass % or more, the
{222} plane integration becomes higher and as a result a higher
workability can be obtained.
[0118] The inventors discovered that by depositing a second layer
on at least one side of a matrix steel sheet having an Al content
of less than 3.5 mass % and then heat treating this to make the
steel sheet recrystallize, it is possible to raise the {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface very high.
[0119] The steel sheet having a high {222} plane integration of the
present invention (the present invention steel sheet) is excellent
in deep drawability, punchability, and other workability.
[0120] Since the Al content of the matrix steel sheet is less than
3.5 mass %, even if the second layer contains Al, in the production
process, the steel sheet is resistant to shrinkage and other
deformation. The Al content of the matrix steel sheet is preferably
0.001 mass % or more. If the Al is 0.001 mass % or more, the
production yield of the matrix steel sheet is improved.
[0121] The present invention steel sheet is comprised of one or
both of an .alpha.Fe phase and .gamma.Fe phase.
[0122] The .alpha.Fe phase is an Fe crystal phase of a structure of
a body centered orientation, while the .gamma.Fe phase is an Fe
crystal phase of a structure of a face centered orientation. The Fe
crystal phase includes phases where other atoms replace part of the
Fe or enter between the Fe atoms.
[0123] The present invention steel sheet has an Al content of less
than 6.5 mass % and is characterized in that a {222} plane
integration of one or both of the .alpha.Fe phase and .gamma.Fe
phase is 60% to 99% and a {200} plane integration of one or both of
the .alpha.Fe phase and .gamma.Fe phase is 0.01% to 15%.
[0124] If the above plane integration is in the range of the
present invention, the value for evaluation of the drawability,
that is, the average r value (Rankford value), becomes 2.5 or more.
Furthermore, at the time of punching, excellent workability free of
formation of burrs at the cross-section can be obtained.
[0125] The plane integration was measured by X-ray diffraction
using MoK.alpha. rays. The {222} plane integration of the .alpha.Fe
phase and the {200} plane integration of the .alpha.Fe phase were
found as follows.
[0126] The integrated intensities of the 11 .alpha. crystal planes
of Fe parallel to a sample surface, that is, {110}, {200}, {211},
{310}, {222}, {321}, {411}, {420}, {332}, {521}, and {442}, were
measured. The measurement values were respectively divided by the
theoretical integrated intensities of a sample of random
orientation, then the ratios with the {200} intensity or {222}
intensity were found by percentages.
[0127] For example, the ratio with the {222} intensity is expressed
by the following formula (1).
{222} plane
integration=[{i(222)/I(222)}/{.SIGMA.i(hkl)/I(hkl)}].times.100
(1)
[0128] where the symbols are as follows: [0129] i(hkl): measured
integrated intensity of {hkl} plane at measured sample [0130]
I(hkl): theoretical integrated intensity of {hkl} plane at sample
having random orientation [0131] .SIGMA.: sum for 11 .alpha.-Fe
crystal planes
[0132] In the same way, the {222} plane integration of the Fe phase
and the {200} plane integration of the .gamma.Fe phase were found
as follows:
[0133] The integrated intensities of the 6 .gamma. crystal planes
of Fe parallel to the sample surface, that is, {111}, {200}, {220},
{311}, {331}, and {420}, were measured. The measurement values were
respectively divided by the theoretical integrated intensities of a
sample of a random orientation, then the ratios with the {200}
intensity or {222} intensity were found by percentages.
[0134] For example, the ratio with the {222} intensity is expressed
by the following formula (2).
{222} plane
integration=[{i(111)/I(111)}/{.SIGMA.i(hkl)/I(hkl)}].times.100
(2)
[0135] where the symbols are as follows: [0136] i(hkl): measured
integrated intensity of {hkl} plane at measured sample [0137]
I(hkl): theoretical integrated intensity of {hkl} plane at sample
having random orientation [0138] .SIGMA.: sum for 6 .gamma.-Fe
crystal planes
[0139] For .alpha.Fe crystal grains, separately, the EBSP (Electron
Backscattering Diffraction Pattern) method may also be used to find
the {222} plane integration.
[0140] The area rate of the {222} planes with respect to the total
area of the crystal planes measured by the EPSP method becomes the
{222} integration. Therefore, even by the EBSP method, in the
present invention steel sheet, the {222} plane integration becomes
60% to 99%.
[0141] In the present invention, it is not necessary that the
values obtained by all analysis methods satisfy the range
prescribed by the present invention. The effect of the present
invention is obtained if the value obtained by one analysis method
satisfies the range of the present invention.
[0142] Further, in the EPSP method, the {222} plane deviates from
the steel sheet surface. This deviation is preferably within
30.degree..
[0143] The deviation of the {222} plane is observed by the L
cross-section. The area ratio of the crystal grains with deviation
of the {222} plane of 30.degree. or less is preferably 80 to
99.9%.
[0144] Furthermore, the area ratio of the crystal grains with
deviation of the {222} plane in the L cross-section of 0 to
10.degree. is more preferably 40 to 98%.
[0145] The "average r value" means the average plastic strain ratio
found by JIS Z 2254 and is a value calculated by the following
formula:
Average r value=(r0+2r45+r90)/4 (3)
[0146] Here, r0, r45, and r90 are the plastic strain ratios
measured when taking test samples in directions of 0.degree.,
45.degree., and 90.degree. with respect to the rolling direction of
the sheet surface.
[0147] Note that the integrated intensity of the sample having a
random orientation may also be found by measurement using a sample
prepared in advance.
[0148] In the present invention steel sheet, (i) a {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface is 60% to 99% and/or
(ii) a {200} plane integration of one or both of an .alpha.Fe phase
and .gamma.Fe phase with respect to the steel sheet surface is
0.01% to 15%.
[0149] If the {222} plane integration is less than 60% and the
{200} plane integration is over 15%, cracks and breakage easily
occur at the time of drawing, bending, and rolling. Further, burrs
occur at the cross-section at the time of punching.
[0150] If the {222} plane integration is over 99% and the {200}
plane integration is less than 0.01%, the effect of the present
invention becomes saturated and production also becomes
difficult.
[0151] Therefore, the texture of the present invention steel sheet
was defined as in the above.
[0152] Note that the {222} plane integration of one or both of an
.alpha.Fe phase and .gamma.Fe phase with respect to the steel sheet
surface is preferably 60% to 95%. If the {222} plane integration is
in the above range, production becomes easier and the yield is
improved.
[0153] The {200} plane integration of one or both of an .alpha.Fe
phase and .gamma.Fe phase with respect to the steel sheet surface
is preferably 0.01% to 10%. If the {200} plane integration is in
the above range, burrs will not occur at the cross-section at the
time of punching.
[0154] One method for producing the present invention steel sheet
is comprised of a step of depositing a second layer on at least one
surface of a matrix steel sheet having an Al content of less than
6.5%, a step of cold rolling the steel sheet on which the second
layer is deposited, a step of removing the second layer from the
cold rolled steel sheet, and a step of heat treating the steel
sheet from which the second layer has been removed to make the
steel sheet recrystallize.
[0155] To obtain a high {222} plane integration, it is essential to
cold roll the matrix steel sheet in the state with the second layer
deposited on it.
[0156] At this time, if the second layer is not deposited on at
least one surface of the matrix steel sheet, a high {222} plane
integration cannot be obtained. If making the second layer deposit
on both surfaces of the steel sheet and then cold rolling, the
effect of the present invention can be improved more.
[0157] At the time of heat treatment to make the steel sheet
recrystallize, the second layer does not necessarily have to be
deposited. The second layer deposited on the steel sheet may
therefore be removed before heat treatment.
[0158] For example, when the elements forming the second layer
would diffuse into the steel sheet at the time of heat treatment
and have a detrimental effect on the mechanical properties etc., if
removing the second layer before heat treatment, it would be
possible to obtain only the effect of improvement of the {222}
plane integration.
[0159] A steel sheet on at least one surface of which a second
layer is deposited and having one or both of a {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface of 60% to 99% and a
{200} plane integration of one or both of an .alpha.Fe phase and
.gamma.Fe phase with respect to the steel sheet surface of 0.01% to
15% is included in the present invention steel sheet.
[0160] If the {222} plane integration is less than 60% and the
{200} plane integration is over 15%, cracks and breakage will
easily occur at the time of drawing, bending, and rolling and,
further, burrs will form at the cross-section at the time of
punching.
[0161] If the {222} plane integration is over 99% and the {200}
plane integration is less than 0.01%, the effect of the present
invention becomes saturated and production further becomes
difficult.
[0162] Here, if the second layer is deposited on the steel sheet,
it is possible to prevent internal oxidation, corrosion, etc. of
the steel sheet and possible to make the steel sheet more
sophisticated in functions.
[0163] The method of production of this steel sheet includes a step
of depositing the second layer on at least one surface of a matrix
steel sheet having an Al content of less than 3.5 mass %, a step of
cold rolling the sheet in the state with the second layer
deposited, and a step of heat treating the steel sheet to make the
steel sheet recrystallize.
[0164] To obtain a higher {222} plane integration, it is preferable
to cold roll the matrix steel sheet in a state with the second
layer deposited.
[0165] When heat treating the steel sheet to make it recrystallize
in the subsequent steps, even if the second layer is deposited on
at least one surface, the effects of the present invention can be
obtained. If the second layer is deposited on both surfaces of the
matrix steel sheet, the effect of the present invention is further
improved.
[0166] Steel sheet wherein the second layer and the steel sheet are
partially alloyed and having one or both of a {222} plane
integration of one or both of an .alpha.Fe phase and .gamma.Fe
phase with respect to the steel sheet surface of 60% to 99% and a
{200} plane integration of one or both of an .alpha.Fe phase and
.gamma.Fe phase with respect to the steel sheet surface of 0.01% to
15% is also included in the present invention steel sheet.
[0167] If the {222} plane integration is less than 60% and the
{200} plane integration is over 15%, cracks and breakage will
easily occur at the time of drawing, bending, and rolling and,
further, burrs will form at the cross-section at the time of
punching.
[0168] If the {222} plane integration is over 99% and the {200}
plane integration is less than 0.01%, the effect of the present
invention becomes saturated and production further becomes
difficult.
[0169] If the second layer is deposited on the steel sheet surface
and part of the second layer is alloyed with the steel sheet,
internal oxidation, corrosion, etc. of the steel sheet can be
prevented, peeling of the second layer can be prevented, and the
steel sheet can be made more sophisticated in function.
[0170] To obtain a higher {222} plane integration, it is preferable
to cold roll the matrix steel sheet in a state with the second
layer deposited on at least one surface. If the second layer is
deposited on both surfaces of the matrix steel sheet, the effect of
the present invention is further improved.
[0171] In the steps after this, the steel sheet has to be heat
treated to make it recrystallize. At this time, if part of the
second layer deposited on one or both surfaces is alloyed with the
matrix steel sheet, a higher {222} plane integration can be
obtained.
[0172] Here, the second layer and the steel sheet partially
alloying means, for example, the second layer and the steel sheet
partially alloying near their boundary by mutual diffusion.
[0173] Steel sheet where the second layer and steel sheet are
alloyed and having one or both of a {222} plane integration of one
or both of an .alpha.Fe phase and .gamma.Fe phase with respect to
the steel sheet surface of 60% to 99% and a {200} plane integration
of one or both of an .alpha.Fe phase and .gamma.Fe phase with
respect to the steel sheet surface of 0.01% to 15% is also included
in the present invention steel sheet.
[0174] If the {222} plane integration is less than 60 and the {200}
plane integration is over 15%, cracks and breakage will easily
occur at the time of drawing, bending, and rolling and, further,
burrs will form at the cross-section at the time of punching.
[0175] If the {222} plane integration is over 99% and the {200}
plane integration is less than 0.01%, the effect of the present
invention becomes saturated and production further becomes
difficult.
[0176] If the second layer is deposited on the steel sheet surface
and the second layer alloys with the steel sheet, the mechanical
properties or functionality of the steel sheet will be improved in
accordance with the elements making up the second layer. For
example, when the element forming the second layer is Al, the high
temperature oxidation resistance and corrosion resistance of the
steel sheet will be improved.
[0177] To obtain a higher {222} plane integration, it is preferable
to cold roll the matrix steel sheet in a state with the second
layer deposited, then heat treat the steel sheet to make it
recrystallize.
[0178] At the time of cold rolling, the second layer has to be
deposited on at least one surface of the matrix steel sheet,
preferably both surfaces. After this, after the heat treatment
step, the second layer completely alloys with the steel sheet
whereby a higher {222} plane integration can be obtained.
[0179] In the present invention steel sheet having the second
layer, the second layer is preferably a metal.
[0180] The preferable elements forming the second layer are at
least one element among Fe, Al, Co, Cu, Cr, Ga, Hf, Hg, In, Mn, Mo,
Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr.
[0181] The above elements have the common feature of being alloying
elements with Fe. Particularly preferably, the elements are at
least one element among Al, Cr, Ga, Mo, Nb, P, Sb, Si, Sn, Ti, V,
W, and Zn which become solid solute in .alpha.Fe and tend to
stabilize the a phase.
[0182] Further, more preferably, the elements are at least one
element among Al, Cr, Mo, Si, Sn, Ti, V, W, and Zn which become
solid solute in .alpha.Fe and tend to stabilize the a phase
more.
[0183] For example, as the second layer, it is possible to select
an Al alloy, Zn alloy, Sn alloy, etc.
[0184] Further, in the method of production of the present
invention steel sheet, the second layer applied to the surface of
the matrix steel sheet is, in the same way as the above, preferably
a metal.
[0185] The preferable elements forming the second layer are at
least one element among Fe, Al, Co, Cu, Cr, Ga, Hf, Hg, In, Mn, Mo,
Nb, Ni, Pb, Pd, Pt, Sb, Si, Sn, Ta, Ti, V, W, Zn, and Zr.
[0186] The above elements have the common feature of being alloying
elements with Fe. Particularly preferably, the elements are at
least one element among Al, Cr, Ga, Mo, Nb, P, Sb, Si, Sn, Ti, V,
W, and Zn which become solid solute in .alpha.Fe and tend to
stabilize the .alpha. phase.
[0187] Further, more preferably, the elements are at least one
element among Al, Cr, Mo, Si, Sn, Ti, V, W, and Zn which become
solid solute in .alpha.Fe and tend to stabilize the .alpha. phase
more.
[0188] For example, as the second layer, it is possible to select
an Al alloy, Zn alloy, Sn alloy, etc.
[0189] Here, when the second layer includes Al, the preferable Al
content of the matrix steel sheet is less than 3.5 mass %. If the
Al concentration of the matrix steel sheet is 3.5 mass % or more,
if heat treating the sheet with the Al alloy deposited as the
second layer, shrinkage will occur during the heat treatment and
the dimensional precision will remarkably drop.
[0190] Therefore, in the present invention steel sheet, when the
second layer contains Al, the Al content of the matrix steel sheet
is made less than 3.5 mass %.
[0191] When the second layer does not contain Al, the Al content of
the matrix steel sheet is made less than 6.5 mass %.
[0192] When the production process includes a step of depositing on
at least one surface a second layer of at least one element among
Fe, Co, Cu, Cr, Ga, Hf, Hg, In, Mn, Mo, Nb, Ni, Pb, Pd, Pt, Sb, Si,
Sn, Ta, Ti, V, W, Zn, and Zr, if the Al content of the matrix steel
sheet is 6.5 mass % or more, the tensile elongation at break of the
obtained steel sheet falls and even if having a high {222} plane
integration, sufficient workability will no longer be obtained and
burrs will form at the cross-section at the time of punching.
[0193] Therefore, the Al content of the steel sheet when the second
layer does not contain Al is made less than 6.5 mass %.
[0194] Note that even if the second layer contains Al, if removing
the second layer before the heat treatment, no shrinkage will
occur. Therefore, when removing the second layer before heat
treatment, the Al content of the matrix steel sheet is preferably
less than 6.5 mass %.
[0195] In this method of production, the method of omitting the
step of removing the second layer so as to raise the work
efficiency is also included in the present invention.
[0196] Further, the method of heat treating the sheet to alloy part
or all of the second layer and produce steel sheet having a high
{222} plane integration is also included in the present
invention.
[0197] In the present invention, the alloyed region of the steel
sheet and second layer is defined as follows.
[0198] When the element of the greatest content in the second layer
is "A", the region where the Fe content is 0.5 mass % higher than
the Fe content of the second layer before alloying and the content
of A is 0.1 mass % higher than the content of A of the matrix steel
sheet before alloying is defined as an "alloyed region".
[0199] Further, the ratio of alloying is the ratio of the alloyed
region in the overall region. In the present invention steel sheet,
by forming the alloyed region in accordance with the above
definition, a more superior workability can be obtained.
[0200] Furthermore, if the Fe content and/or A content become large
and intermetallic compounds etc. are formed, a higher effect of the
present invention can be obtained.
[0201] Note that the alloying ratio for example can be found by
using EPMA etc., analyzing the distribution of contents of the Fe
and element A at the L cross-section, identifying the alloyed
region, finding that area, and finding the ratio of the area of the
identified region to the overall area.
[0202] The thickness of the steel sheet of the present invention is
preferably 5 .mu.m to 5 mm. This is the thickness including the
second layer. If the thickness of the steel sheet is less than 5
.mu.m, the production yield falls so this is not suitable for
practical application.
[0203] If the thickness of the steel sheet exceeds 5 mm, the {222}
plane integration will sometimes not fall in the range of the
present invention. Therefore, the thickness of the steel sheet is
preferably 5 .mu.m to 5 mm.
[0204] The thickness of the steel sheet is more preferably 100
.mu.m to 3 mm. If the thickness of the steel sheet is 3 mm or less,
the effect of suppression of the formation of burrs at the
cross-section at the time of punching becomes more remarkable.
[0205] If the thickness of the steel sheet is 100 .mu.m or more,
the {222} plane integration becomes higher and more easily
controlled. Similarly, the effect of suppression of formation of
burrs becomes more remarkable.
[0206] In the thickness of the steel sheet in the present
invention, the thickness of the second layer is preferably 0.01
.mu.m to 500 .mu.m. When the steel sheet and the second layer are
partially alloyed, the thickness of the alloyed part is included in
the thickness of the second layer. When the second layer is
deposited at both surfaces, this is the thicknesses of the two
surfaces in total.
[0207] The second layer has the function of improving the {222}
plane integration at the time of production and can be left after
production and used as a rust-preventive and protective coating of
the steel sheet.
[0208] If the thickness of the second layer is over 500 .mu.m, the
possibility of peeling rises, so 500 .mu.m or less is preferable.
If the thickness of the second layer is less than 0.01 .mu.m, the
coating will easily tear and the rust-preventive and protective
effect will be reduced.
[0209] Therefore, the thickness of the second layer is preferably
0.01 .mu.m or more. The case where the entire thickness of the
steel sheet is alloyed is also preferable. In this case, the second
layer may be considered to have disappeared.
[0210] In the method of production of the present invention steel
sheet, the thickness of the matrix steel sheet is 10 .mu.m to 10
mm. If the thickness of the matrix steel sheet is less than 10
.mu.m, the production yield will drop in the steps from cold
rolling on so this is not suitable for practical application in
some cases.
[0211] If the thickness of the matrix steel sheet is over 10 mm,
the {222} plane integration may not fall in the range of the
present invention.
[0212] Therefore, the thickness of the matrix steel sheet is
preferably 10 .mu.m to 10 mm.
[0213] A thickness of the matrix steel sheet of over 130 .mu.m to 7
mm is more preferable. In this range of thickness, an efficient and
sufficient increase in the {222} plane integration can be expected
and production of steel sheet able to suppress the formation of
burrs at the time of punching becomes easy.
[0214] The thickness of the second layer deposited on the matrix
steel sheet before cold rolling is preferably 0.05 .mu.m to 1000
.mu.m. When the steel sheet and the second layer are alloyed, the
thickness of the alloyed part is included in the thickness of the
second layer. When the second layer is deposited at both surfaces,
this becomes the thicknesses of the two surfaces in total.
[0215] If the thickness of the second layer is less than 0.05
.mu.m, the {222} plane integration becomes lower and may not fall
in the range of the present invention, so 0.05 .mu.m or more is
preferable.
[0216] Even when the thickness of the second layer exceeds 1000
.mu.m, the {222} plane integration becomes lower and may not fall
in the range of the present invention, so 1000 .mu.m or less is
preferable.
[0217] To express more superior effects of the present invention,
the matrix steel sheet before deposition of the second layer is
preferably given preheat treatment.
[0218] This preheat treatment causes rearrangement of the
dislocations accumulated in the process of production of the matrix
steel sheet. Therefore, causing recrystallization is preferable,
but there is not necessarily a need to cause recrystallization.
[0219] The preheat treatment temperature is preferably 700.degree.
C. to 1100.degree. C. If the preheat treatment temperature is less
than 700.degree. C., changes in the dislocation structure for
obtaining more superior effects of the present invention are hard
to occur, so the preheat treatment temperature is made 700.degree.
C. or more.
[0220] If the preheat treatment temperature exceeds 1100.degree.
C., the steel sheet surface is formed with an unpreferable oxide
film. This has a detrimental effect on the later deposition of the
second layer and the cold rolling, so the preheat treatment
temperature is made 1100.degree. C. or less.
[0221] The atmosphere of the preheat treatment may be a vacuum,
inert gas atmosphere, hydrogen atmosphere, or weak acidic
atmosphere. In any atmosphere, the effect of the present invention
can be obtained, but an atmosphere is sought of conditions not
forming on the steel sheet surface an oxide film having a
detrimental effect on the deposition of the second layer after the
preheat treatment or on the cold rolling.
[0222] The preheat treatment time does not particularly have to be
limited, but if considering the production of the steel sheet etc.,
several seconds to several hours are suitable.
[0223] The second layer may be deposited on the steel sheet by the
hot dip method, electroplating method, dry process, cladding, etc.
No matter which method is used, the effect of the present invention
can be obtained. Further, it is also possible to add desired alloy
elements to the second layer deposited and simultaneously alloy
it.
[0224] The cold rolling is performed with the second layer
deposited on the steel sheet. The reduction rate is 30% to 95%.
[0225] If the reduction rate is less than 30%, the {222} plane
integration of the steel sheet obtained after heat treatment is low
and sometimes will not reach the range of the present invention. If
the reduction rate is over 95%, the increase in plane integration
becomes saturated and the production cost increases. Therefore, the
reduction rate is made 30% to 95%.
[0226] When removing the second layer before the heat treatment, as
the method of removal, mechanical removal by polishing etc. or
chemical removal by dissolution by a strong acid or strong alkali
aqueous solution may be applied.
[0227] For example, in the case of an Al plated steel sheet, the
steel sheet is dipped in an aqueous solution of caustic soda to
remove the plating ingredient. As a result, in the heat treatment
process, the effect of the Al ingredient can be eliminated.
[0228] The heat treatment for causing the steel sheet to
recrystallize can be performed in a vacuum atmosphere, Ar
atmosphere, H.sub.2 atmosphere, or other nonoxidizing atmosphere.
At this time, preferably the heat treatment temperature is
600.degree. C. to 1000.degree. C. and the heat treatment time is 30
seconds or more.
[0229] If the heat treatment temperature is 600.degree. C. or more,
the {222} plane integration becomes higher and more easily reaches
the range of the present invention. At a heat treatment temperature
of 1000.degree. C. or less and a heat treatment time of less than
30 seconds, in the same way, the {222} plane integration becomes
higher and more easily reaches the range of the present
invention.
[0230] Therefore, preferably the heat treatment temperature is
600.degree. C. to 1000.degree. C. and the heat treatment time is 30
seconds or more.
[0231] If the heat treatment temperature is over 1000.degree. C., a
high {222} plane integration can be obtained without restriction by
the heat treatment time. In particular, if over 1000.degree. C.,
even with less than 30 seconds heat treatment time, the {222} plane
integration can be easily increased.
[0232] Note that the heat treatment temperature is more preferably
1300.degree. C. or less. If the heat treatment temperature is
1300.degree. C. or less, the flatness of the steel sheet and other
sheet properties become more superior.
[0233] The temperature rise rate at the time of the heat treatment
is preferably 1.degree. C./min to 1000.degree. C./min. If the
temperature rise rate is 1000.degree. C./min or less, a higher
{222} plane integration can be easily obtained. If the temperature
rise rate is 1.degree. C./min or more, the productivity is
remarkably improved.
[0234] Therefore, a temperature rise rate of 1.degree. C./min to
1000.degree. C./min is preferable.
[0235] The heat treatment performed in the state with the second
layer deposited is designed to make the steel sheet recrystallize
and also to make the elements included in the second layer diffuse
into the steel.
[0236] If the elements contained in the second layer diffuse into
the steel, the {222} plane integration is improved more and the
high temperature oxidation resistance and mechanical properties are
improved, so in the method of production of the present invention
steel sheet, the diffusion of elements included in the second layer
is positively utilized.
[0237] The matrix steel sheet preferably has a content of Cr of 12
mass % or less under the above Al content. A Cr content of less
than 10 mass % is more preferable.
[0238] Further, the matrix steel sheet is a steel sheet with a C
content of 2.0 mass % or less and includes as impurities slight
amounts of Mn, P, S, etc. For example, carbon steel is included in
the matrix steel sheet of the present invention. Furthermore,
alloyed steel containing alloy elements such as Ni and Cr in
addition to C is also included in the matrix steel sheet of the
present invention.
[0239] The alloy elements which the matrix steel sheet may contain
are Si, Al, Mo, W, V, Ti, Nb, B, Cu, Co, Zr, Y, Hf, La, Ce, N, O,
etc.
EXAMPLES
[0240] Below, examples will be used to explain the present
invention in more detail.
Example 1
[0241] The Al content of the matrix steel sheet was changed to
investigate the manufacturability and {222} plane integration.
[0242] Matrix steel sheets of ingredients of five different types
of Al content were produced. The Al contents were, by mass %, 3.0%
(ingredients A), 3.4% (ingredients E), 4.0% (ingredients B), 6.0%
(ingredients C), and 7.5% (ingredients D). In addition, the
ingredients included C: 0.008%, Si: 0.2%, Mn: 0.4%, Cr: 20.0%, Zr:
0.08%, La: 0.08%, and a balance of iron and unavoidable
impurities.
[0243] By each of these ingredients, ingots were produced by vacuum
melting and hot rolled to try to reduce them to 3.0 mm
thickness.
[0244] In the case of the ingredients A, B, C, and E, the ingots
could be easily hot rolled to 3.0 mm thick steel sheets, but in the
case of the ingredients D, the steel sheet frequently broke during
the hot rolling, so hot rolling could not be continued.
[0245] In this way, if the Al content of the matrix steel sheet is
over the range of the present invention at 6.5% or more, production
becomes difficult. Therefore, production of steel sheet of the
ingredients D was foregone and the steel sheets of the ingredients
A, B, C, and E were cold rolled to 0.4 mm thickness.
[0246] The main phases of the steel sheets of the ingredients A, B,
C, and E at ordinary temperature were .alpha.Fe phases. X-ray
diffraction was used to measure the texture of the .alpha.Fe phase
of each matrix steel sheet and, in the same way as above, the plane
integration was calculated.
[0247] It was confirmed that the {222} plane integration was, in
the ingredients A, 32%, ingredients B, 31%, ingredients C, 31%, and
ingredients E, 30%, while the {200} plane integration was, in the
ingredients A, 16%, ingredients B, 15%, ingredients C, 16%, and
ingredients E, 16%.
[0248] Each steel sheet was heat treated at 800.degree. C..times.10
sec in a hydrogen atmosphere before forming the second layer. After
this, the hot dip method was used to deposit Al alloy on the
surface of the matrix steel sheet.
[0249] The composition of the plating bath was, by mass %, 90%
Al-10% Si. The Al alloy was deposited on both surfaces of each
steel sheet.
[0250] The amount of deposition, for each steel sheet as a whole,
was controlled to give an Al content by mass % of 3.5% (ingredients
A), 4.5% (ingredients B), 6.4% (ingredients C), and 6.4%
(ingredients E).
[0251] With the Al alloy deposited as the second layer, each steel
sheet was cold rolled by a reduction rate of 70%. Next, it was heat
treated in a vacuum under conditions of 1000.degree. C..times.120
min to cause the steel sheet to recrystallize.
[0252] At this time, the steel sheets of the ingredients B and C
shrank during the heat treatment and remarkably dropped in
dimensional precision.
[0253] When the second layer does not include Al, if the Al content
in the matrix steel sheet is outside the range of the present
invention at 3.5% or more, it was confirmed that shrinkage occurs
during heat treatment and use for practical applications is
difficult.
[0254] On the other hand, if the Al content of the matrix steel
sheet is in the range of the present invention at less than 3.5%,
no shrinkage occurs and use is possible for practical
applications.
[0255] A second layer not containing Al was deposited on a matrix
steel sheet having an Al content of 3.5% or more and similar heat
treatment was performed. In this case, no shrinkage occurred during
the heat treatment.
[0256] When using steel sheets of the ingredients A and E as matrix
steel sheets, the {222} plane integrations of the obtained steel
sheets were respectively 82% and 83% and the {200} plane
integrations were respectively 0.5% and 0.8%. Both integrations
were in the range of the present invention.
[0257] Furthermore, these steel sheets were measured for the
average r value. It was confirmed that the average r value was a
high level of 2.5 or more. These steel sheets had excellent
drawability.
[0258] In this way, it was confirmed that steel sheets produced by
the method of production of the present invention were in the range
of the present invention with a {222} plane integration of the
.alpha.Fe phase parallel to the steel sheet surface of 60% or more
or with a {200} plane integration parallel to the steel sheet
surface of 15% or less.
Example 2
[0259] The results of production of steel sheet having a high {222}
plane integration using an Al alloy as the second layer are
shown.
[0260] The ingredients of the matrix steel sheet were, by mass %,
Al: 1.5%, C: 0.008%, Si: 0.1%, Mn: 0.2%, Cr: 18%, Ti: 0.1%, and a
balance of iron and unavoidable impurities.
[0261] The matrix steel sheet was a steel sheet obtained by
producing an ingot by the vacuum melting method, hot rolling the
ingot to obtain steel sheet of 3.8 mm thickness, then cold rolling
it to obtain steel sheet of 0.8 mm thickness.
[0262] The main phase of the matrix steel sheet at ordinary
temperature was the .alpha.Fe phase. X-ray diffraction was used to
measure the texture of the .alpha.Fe phase of the matrix steel
sheet whereupon it was confirmed that the {222} plane integration
was 36% and the {200} plane integration was 20%.
[0263] Part of the matrix steel sheet was heat treated at
800.degree. C..times.10 sec in a hydrogen atmosphere before
plating. Al alloy was deposited on the surface of the matrix steel
sheet using the hot dip method.
[0264] The composition of the plating bath was, by mass %, 90%
Al-10% Si. The Al alloy was deposited on both surfaces of the steel
sheet. The thickness of the deposited Al alloy was controlled to be
uniform in the steel sheet surface.
[0265] The steel sheet with the Al alloy deposited was cold rolled.
After this, it was heat treated in a nonoxidizing atmosphere.
Before the heat treatment, if necessary, the Al alloy deposited on
the surface was removed.
[0266] The Al alloy was removed by dipping the steel sheet in
heated caustic soda 10% aqueous solution to dissolve the Al alloy
in the solution.
[0267] As comparative examples, cases where the Al alloy was
deposited, then the sheets were not cold rolled were also
studied.
TABLE-US-00001 TABLE 1 Product {222} {222} Second layer .alpha.Fe
plane plane .alpha.Fe Preheat Removal phase 0-30.degree.
0-10.degree. phase Al Eval. treat. Mat. of Rolling of Heat treat.
{222} dev. dev. {200} conc. Burr temp. second Red. second Temp.
Time Alloying plane area area plane mass height No. .degree. C.
layer rate % layer .degree. C. min ratio % integ. rate rate integ.
% .mu.m Remarks 1 800.degree. C. Al--Si 0 Yes 950 10 0 38 57 8 16
1.5 65 Comp. Ex. 1 2 800.degree. C. None 50 None 950 10 0 37 56 7
15 1.5 58 Comp. Ex. 2 3 800.degree. C. Al--Si 50 Yes 950 0.1 0 41
59 9 14 1.5 9 Inv. Ex. 4 800.degree. C. Al--Si 50 Yes 950 1 0 61 81
42 8.1 1.5 5 Inv. Ex. 1 5 800.degree. C. Al--Si 50 Yes 950 10 0 65
83 50 6.1 1.5 7 Inv. Ex. 2 6 None Al--Si 50 Yes 950 10 0 61 82 41
8.5 1.5 6 Inv. Ex. 3 7 800.degree. C. Al--Si 50 None 1000 120 100
74 89 60 5.2 3.2 5 Inv. Ex. 4 8 800.degree. C. Al--Si 50 None 1000
120 100 75 90 63 4.3 6.0 6 Inv. Ex. 5 9 800.degree. C. Al--Si 50
None 1000 120 100 58 78 38 16 7.5 23 Comp. Ex. 4 10 800.degree. C.
Al--Si 0 None 1050 0.17 20 36 53 7 17 3.2 57 Comp. Ex. 5 11
800.degree. C. Al--Si 50 None 1050 0.17 20 62 82 43 4.7 3.2 6 Inv.
Ex. 6 12 800.degree. C. Al--Si 75 None 1050 0.17 50 76 93 68 1.6
3.2 4 Inv. Ex. 7
[0268] Table 1 shows the alloying ratio, {222} plane integration of
the .alpha.Fe phase, {200} plane integration of the .alpha.Fe
phase, and Al content for steel sheets produced under various
conditions. The plane integration was obtained by measurement using
X-ray diffraction and calculation by the above-mentioned
calculation processing method.
[0269] The alloying ratio of the steel sheet was found as follows:
At the L cross-section, in a field of the L direction 1
mm.times.entire thickness, the EPMA (Electron Probe Micro-Analysis)
method was used to measure the plane distribution of the Fe content
and the plane distribution of the Al content.
[0270] Further, a region of Fe.gtoreq.0.5 mass % and Al.gtoreq.1.6
mass % was deemed an alloyed region and its area was found as the
alloyed area. The alloying ratio was calculated by dividing the
alloyed area by the L direction 1 mm.times.total thickness
area.
[0271] In No. 1 of Comparative Example 1, the amount of deposition
of the Al alloy was controlled by adjusting the plating thickness
so that the Al content of the steel sheet as a whole became 3.2%.
The Al alloy was removed without cold rolling after plating.
Furthermore, the steel sheet was heated treated under conditions of
950.degree. C..times.10 min to make the steel sheet
recrystallize.
[0272] As a result, the {222} plane integration and the {200} plane
integration were outside the range of the present invention. The Al
content of the obtained steel sheet was the same as the matrix
steel sheet, that is, 1.5%, since the Al alloy was removed.
[0273] In No. 2 of Comparative Example 2, the step of depositing an
Al alloy as the second layer was omitted. The matrix steel sheet
was cold rolled by a reduction rate of 50%, then the steel sheet
was heat treated under conditions of 950.degree. C..times.10 min to
make the steel sheet recrystallize.
[0274] In this case as well, the {222} plane integration and the
{200} plane integration were outside the range of the present
invention.
[0275] In No. 3 of an invention example, the amount of deposition
of the Al alloy was controlled by adjusting the plating thickness
to become 3.2% of the steel sheet as whole. After plating, the
steel sheet was cold rolled by a reduction rate of 50%, then the Al
alloy was removed and the steel sheet was heat treated under
conditions of 950.degree. C..times.0.1 min to make the steel sheet
recrystallize.
[0276] As a result, the {222} plane integration was outside the
range of the present invention, but the {200} plane integration was
in the range of the present invention. The Al content in the
obtained steel sheet was the same as the matrix, that is, 1.5%,
since the Al alloy was removed.
[0277] In Nos. 4 and 5 of Invention Examples 1 and 2, each steel
sheet was heat treated at 800.degree. C., then Al alloy was
deposited on the steel sheet surface so that the Al content became
3.2% at the steel sheet as a whole. After this, the steel sheet was
cold rolled at a reduction rate of 50% to make it thinner.
[0278] After the Al alloy was removed, in No. 4, the steel sheet
was heat treated under conditions of 950.degree. C..times.1 min,
while in No. 5, the steel sheet was heat treated under conditions
of 950.degree. C..times.10 min, to make the steel sheets
recrystallize.
[0279] As a result, in both Nos. 4 and 5 of Invention Examples 1
and 2, it was confirmed that the {222} plane integration and the
{200} plane integration were controlled to within the range of the
present invention and the Al content was also in the range of the
present invention. The Al content in the obtained steel sheet was
the same as the matrix, that is, 1.5%, since the Al alloy was
removed.
[0280] In No. 6 of Invention Example 3, the heat treatment before
deposition of the Al alloy was omitted from No. 5 of the invention
example, but it was confirmed that the {222} plane integration and
the {200} plane integration were both controlled to within the
range of the present invention and that the Al content was also in
the range of the present invention.
[0281] The Al content in the obtained steel sheet was the same as
the matrix, that is, 1.5%, since the Al alloy was removed.
[0282] In Nos. 7 and 8 of Invention Examples 4 and 5, before
depositing the Al alloy, the steel sheet was heat treated at
800.degree. C. then the Al alloy was deposited.
[0283] The amount of deposition of the Al alloy in No. 7 was
controlled to give an Al content of 3.2% in the steel sheet as a
whole. The amount of deposition of the Al alloy in No. 8 was
similarly controlled to give an Al content of 6.0% in the steel
sheet as a whole. After this, the two steel sheets were cold rolled
at a reduction rate of 50% to make them thinner.
[0284] The removal of the Al alloy was omitted, the rolling oil was
removed from the steel sheet surface, then the steel sheet was heat
treated under conditions of 1000.degree. C..times.120 min to make
the steel sheet recrystallize. Due to this heat treatment, the Al
alloy deposited on the steel sheet surface was completely alloyed
with the steel sheet.
[0285] It was confirmed that the obtained {222} plane integration
and the {200} plane integration were both controlled to within the
range of the present invention and that the Al content was also in
the range of the present invention.
[0286] In No. 9 of Comparative Example 4, compared with Nos. 7 and
8 of the invention examples, the amount of deposition of the second
layer was increased. The amount of deposition of the Al alloy was
controlled to give an Al content of 7.5% in the steel sheet as a
whole.
[0287] The other steps were the same as in Nos. 7 and 8 of the
invention examples. Due to the heat treatment, the Al alloy
deposited on the steel sheet surface was completely alloyed with
the steel sheet.
[0288] As a result, the Al content of the steel sheet became 7.5%
or ended up exceeding the range of the present invention. The {222}
plane integration of this steel sheet was considerably improved,
but failed to reach the range of the present invention.
[0289] Tensile tests were run. As a result, it was learned that the
elongation at break was 10% or less and the toughness was low. From
this, it was learned that the No. 9 steel sheet was not suited for
practical application.
[0290] In No. 10 of Comparative Example 5, the Al alloy was
deposited on the steel sheet surface so that the Al content became
3.2% in the steel sheet as a whole. The cold rolling after
deposition of the Al alloy was omitted. After depositing the Al
alloy, the steel sheet was heat treated under conditions of
1050.degree. C..times.0.17 min to make the steel sheet
recrystallize.
[0291] As a result, the {222} plane integration and the {200} plane
integration were both outside the range of the present
invention.
[0292] In Nos. 11 and 12 of Invention Examples 6 and 7, before
depositing the Al alloy, the steel sheet was heat treated at
800.degree. C. and Al alloy was deposited on the steel sheet
surface so that the Al content became 3.2% at the steel sheet as a
whole.
[0293] After this, in No. 11 of Invention Example 6, the steel
sheet was cold rolled by a reduction rate of 50% to make it
thinner. In No. 12 of Invention Example 7, the steel sheet was cold
rolled by a reduction rate of 75% to make it thinner.
[0294] The removal of the Al alloy was omitted and the steel sheet
was heat treated under conditions of 1050.degree. C..times.0.17 min
to make the steel sheet recrystallize.
[0295] As a result, in each steel sheet, it was confirmed that the
{222} plane integration and the {200} plane integration were both
controlled to within the range of the present invention and the Al
content was also in the range of the present invention.
[0296] Each of the above steel sheets was tested for burr
resistance. A 10.0 mm.phi. punch and a 10.3 mm.phi. die were used
for punching and the burr height around the punched hole was
measured by a point micrometer.
[0297] As a result, it was confirmed that the burr height was a
high level of 23 to 65 .mu.m in the comparative examples, but was
an extremely low level of 4 to 9 .mu.m in the invention
examples.
[0298] The steel sheets of the above examples were measured for the
average r value, whereupon it was confirmed that in the steel
sheets of the invention examples, the average r value was at a high
level of 2.5 or more, but in the steel sheets of the comparative
examples, the average r value was less than 2.5 or measurement was
not possible.
[0299] Therefore, the steel sheets of the invention examples have
excellent drawability. Further, the steel sheets of the invention
examples were subjected to Erichsen tests and the extruded surfaces
were observed whereupon excellent press workability was also
confirmed.
[0300] The steel sheet produced by the method of production of the
present invention in this way was confirmed to have a {222} plane
integration of .alpha.Fe phase parallel to the steel sheet surface
of 60% or more and a {200} plane integration of the .alpha.Fe phase
parallel to the steel sheet surface of 15% or less or both in the
range of the present invention.
[0301] As a result, it was confirmed that the steel sheet produced
by the method of production of the present invention achieved both
excellent burr resistance and drawability.
Example 3
[0302] The results of using a Zn alloy as the deposit (second
layer) to produce steel sheet having a high {222} plane integration
are shown.
[0303] The matrix steel sheet was a steel sheet obtained by using
the vacuum melting method to obtain an ingot of ingredients, by
mass %, of an Al content of 0.01% and also C: 0.005%, Si: 0.2%, Mn:
0.5%, Ti: 0.05%, and a balance of iron and unavoidable impurities,
hot rolling to a thickness of 3.2 mm, then cold rolling to a
thickness of 1.8 mm.
[0304] The main phase of the matrix steel sheet at ordinary
temperature was an .alpha.Fe phase. X-ray diffraction was used to
measure the texture of the .alpha.Fe phase of the matrix steel
sheet whereupon it was confirmed that the {222} plane integration
was 28% and the {200} plane integration was 19%.
[0305] Part of the matrix steel sheet was heat treated by
770.degree. C..times.5 sec in a hydrogen atmosphere before
plating.
[0306] On the surface of the matrix steel sheet, the electroplating
method was used to deposit an Zn alloy. For the plating bath, a
sulfuric acid type acidic solution was used. The deposited plating
was, by mass %, a 94% Zn-6% Ni alloy. The thickness of the
deposited Zn alloy was controlled to become uniform in the steel
sheet surface.
[0307] The steel sheet on which the Zn alloy was deposited was cold
rolled, then heat treated in a nonoxidizing atmosphere. Before the
heat treatment, if necessary, the Zn alloy deposited on the steel
sheet surface was removed. The Zn alloy was removed by dipping the
steel sheet into a heated hydrochloric acid 10% aqueous solution to
make the Zn alloy dissolve in the solution.
[0308] As comparative examples, the case of deposition of an Al
alloy, then not performing cold rolling was also studied.
TABLE-US-00002 TABLE 2 Products Second layer .alpha.Fe {222} {222}
.alpha.Fe Preheat Rolling Removal Heat phase plane plane phase Al
Eval. treat. Red. of treatment {222} 0-30.degree. 0-10.degree.
{200} conc. Burr temp. Mate- rate second Temp. Time Alloying plane
deviation deviation plane mass height No. .degree. C. rial % layer
.degree. C. min ratio % integ. area rate area rate integ. % .mu.m
Remarks 13 770 Zn--Ni 0 Yes 1050 0.1 0 31 45 0.5 17 0.01 98 Comp.
Ex. 6 14 770 None 70 None 1050 0.1 0 29 38 0.4 18 0.01 82 Comp. Ex.
7 15 770 Zn--Ni 70 Yes 1050 0.1 0 68 86 56 3.5 0.01 9 Inv. Ex. 8 16
None Zn--Ni 70 Yes 1050 0.1 0 63 83 42 4.7 0.01 9 Inv. Ex. 9 17 770
Zn--Ni 70 None 1050 0.1 30 64 86 51 4.2 0.01 8 Inv. Ex. 10 18 770
Zn--Ni 70 None 1050 0.1 60 65 87 53 3.8 0.01 8 Inv. Ex. 11 19 770
Zn--Ni 0 None 750 10 100 34 48 1.3 18 0.01 95 Comp. Ex. 8 20 770
Zn--Ni 30 None 750 10 100 64 85 48 5.7 0.01 9 Inv. Ex. 12 21 770
Zn--Ni 87 None 750 10 100 75 92 67 0.8 0.01 7 Inv. Ex. 13
[0309] Table 2 shows the alloying ratio, the {222} plane
integration of the .alpha.Fe phase, the {200} plane integration of
the .alpha.Fe phase, and the Al content of steel sheet produced
under various conditions. Note that the plane integration was found
by measurement using X-ray diffraction and calculation by the
above-mentioned calculation processing method.
[0310] The alloying ratio of the steel sheet was found as follows:
At the L cross-section, in a field of the L direction 1
mm.times.entire thickness, the EPMA method was used to measure the
plane distribution of the Fe content and the plane distribution of
the Zn content.
[0311] Further, a region of Fe.gtoreq.0.5 mass % and Zn.gtoreq.0.1
mass % was deemed an alloyed region and its area was found as the
alloyed area. The alloying ratio was calculated by dividing the
alloyed area by the L direction 1 mm.times.total thickness
area.
[0312] Note that, the area ratios obtained by using the EBSP method
to separately observe by the L cross-section the crystal grains
with a deviation of the {222} plane with respect to the steel sheet
surface of 0 to 30.degree. and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to
10.degree. are described.
[0313] Further, the above steel sheet was tested for burr
resistance. A 30.0 mm.phi. punch and a 30.6 mm.phi. die were used
for punching and the burr height around the punched hole was
measured by a point micrometer.
[0314] In No. 13 of Comparative Example 6, Zn alloy of a thickness
of 0.8 .mu.m was deposited on the steel sheet surface. The cold
rolling was omitted and the Zn alloy was removed, then the steel
sheet was heat treated under conditions of 1050.degree.
C..times.0.1 min to make the steel sheet recrystallize.
[0315] As a result, the {222} plane integration and the {200} plane
integration of this steel sheet were both outside the range of the
present invention.
[0316] In No. 14 of Comparative Example 7, the deposition of the Zn
alloy was omitted and the steel sheet was cold rolled by a
reduction rate of 70%. After this, the steel sheet was heat treated
under conditions of 1050.degree. C..times.0.1 min to make the steel
sheet recrystallize. In this case as well, the {222} plane
integration and the {200} plane integration were both outside the
range of the present invention.
[0317] In No. 15 of Invention Example 8, after heat treatment at
770.degree. C., Zn alloy of a thickness of 0.8 .mu.m was deposited
on the steel sheet surface. After this, the steel sheet was cold
rolled by a reduction rate of 70% to make it thinner. Furthermore,
the Zn alloy was removed, then the steel sheet was heat treated
under conditions of 1050.degree. C..times.0.1 min to make the steel
sheet recrystallize.
[0318] As a result, it was confirmed that the {222} plane
integration and the {200} plane integration were in the range of
the present invention and the Al content was also in the range of
the present invention.
[0319] In No. 16 of Invention Example 9, the heat treatment before
deposition of the Zn alloy was omitted from No. 15 of the invention
examples, but it was confirmed that the {222} plane integration and
the {200} plane integration were both controlled to be within the
range of the present invention and the Al content was also in the
range of the present invention.
[0320] In Nos. 17 and 18 of Invention Examples 10 and 11, before
deposition of the Zn alloy, the steel sheet was heat treated at
770.degree. C. then the Zn alloy was deposited.
[0321] In No. 17, Zn alloy of a thickness of 0.8 .mu.m was
deposited on the steel sheet surface. In No. 18, Zn alloy of a
thickness of 0.4 .mu.m was deposited on the steel sheet surface.
After this, the two steel sheets were cold rolled by a reduction
rate of 70% to make them thinner.
[0322] The removal of the Zn alloy was omitted, the rolling oil on
the steel sheet surface was removed, then the steel sheet was heat
treated under conditions of 1050.degree. C..times.0.1 min to make
the steel sheet recrystallize. Due to this heat treatment, part of
the Zn alloy deposited on the steel sheet surface alloyed with the
steel sheet.
[0323] The alloying ratio was 30% in No. 17 and 60 in No. 18. It
was confirmed that the obtained {222} plane integration and {200}
plane integration were both controlled to within the range of the
present invention and the Al content was also in the range of the
present invention.
[0324] In No. 19 of Comparative Example 8, Zn alloy of a thickness
of 0.8 .mu.m was deposited on the steel sheet surface. The cold
rolling after deposition of the Zn alloy was omitted. After the
deposition of the Zn alloy, the steel sheet was heat treated under
conditions of 750.degree. C..times.10 min to make the steel sheet
recrystallize.
[0325] As a result, the {222} plane integration and the {200} plane
integration were both outside the range of the present
invention.
[0326] In Nos. 20 and 21 of Invention Examples 12 and 13, before
the deposition of the Zn alloy, the steel sheet was heat treated at
770.degree. C., then Zn alloy of a thickness of 0.8 .mu.m was
deposited on the steel sheet surface.
[0327] After this, in No. 20, the steel sheet was cold rolled by a
reduction rate of 30% to make it thinner. In No. 21, the steel
sheet was cold rolled by a reduction rate of 87% to make it
thinner.
[0328] The removal of the Al alloy was omitted and the steel sheet
was heat treated under conditions of 750.degree. C..times.10 min to
make the steel sheet recrystallize.
[0329] As a result, in each steel sheet, it was confirmed that the
{222} plane integration and the {200} plane integration were both
in the range of the present invention and that the Al content was
also in the range of the present invention.
[0330] It was confirmed that in the steel sheets of the comparative
examples, the burr height was a high level of 82 to 92 .mu.m, but
in the steel sheets of the invention examples, it was an extremely
low level of 7 to 9 .mu.m.
[0331] The steel sheets of the above examples were measured for the
average r value. It was confirmed that in the steel sheets of the
invention examples, the average r value was a high level of 2.5 or
more, but in the steel sheets of the comparative examples, it was
less than 2.5.
[0332] From these results, it was confirmed that in the steel
sheets produced by the method of production of the present
invention, both an excellent burr resistance and drawability are
achieved.
[0333] Therefore, the steel sheets produced by the method of
production of the present invention were examined at their extruded
surfaces in Erichsen tests and confirmed to be excellent in press
workability as well.
[0334] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present
invention.
Example 4
[0335] The results of using Cu as the deposit (second layer) to
produce steel sheet having a high {222} plane integration are
shown.
[0336] The ingredients of the matrix steel sheet were, by mass %,
ingredients including Al: 0.015%, C: 0.15%, Si: 0.1%, Mn: 1.5%, Mo:
0.5%, and a balance of iron and unavoidable impurities.
[0337] As the matrix steel sheet, steel sheets obtained by using
the vacuum melting method to produce an ingot and hot rolling the
ingot to thicknesses of 15 mm, 10 mm, and 3.8 mm were used.
[0338] Further, cold rolled sheets obtained by cold rolling 3.8 mm
steel sheet to thicknesses of 2.0 mm, 1.0 mm, 0.1 mm, 0.01 mm, and
0.005 mm were used as the matrix steel sheet.
[0339] The main phase of the matrix steel sheet at ordinary
temperature was the .alpha.Fe phase. X-ray diffraction was used to
measure the texture of the .alpha.Fe phase of the matrix steel
sheet whereupon it was confirmed that the {222} plane integration
was 36 to 40% and the {200} plane integration was 17 to 22%.
[0340] Before deposition of Cu, the matrix steel sheet was heat
treated at 850.degree. C..times.10 sec in a hydrogen atmosphere.
After this, different thicknesses of Cu were deposited on the two
surfaces of matrix steel sheets. The Cu was deposited by the
cladding method, the electroplating method, or the sputtering
method.
[0341] The thickness of the Cu was changed, in the cladding method,
by changing the thickness of the Cu sheet clad, in the plating
method, by changing the conducted current and dipping time, and,
further, in the sputtering method, by changing the sputtering time.
For the plating bath, a sulfuric acid solution was used.
[0342] The steel sheet on which the Cu was deposited was cold
rolled, then the steel sheet was heat treated in a nonoxidizing
atmosphere.
TABLE-US-00003 TABLE 3 Deposition of second layer Thick. after cold
rolling After heat treat. Second Matrix Second Steel Heat treatment
.alpha.Fe phase .alpha.Fe phase Deposition layer Cu Fe layer Cu
sheet Temp. Time {222} plane {200} plane No. method thick. .mu.m
thick. mm thick. .mu.m thick. mm .degree. C. min integ. integ.
Remarks 22 Cladding 1500 2.0 600 0.86 1020 0.3 61 18 Inv. Ex. 14 23
Cladding 1000 2.0 400 0.84 1020 0.3 70 3.5 Inv. Ex. 15 24 Cladding
100 2.0 40 0.80 1020 0.3 73 2.1 Inv. Ex. 16 25 Plating 10 2.0 4
0.80 1020 0.3 78 1.1 Inv. Ex. 17 26 Plating 0.1 2.0 0.04 0.80 1020
0.3 72 1.8 Inv. Ex. 18 27 Sputtering 0.02 2.0 0.008 0.80 1020 0.3
61 17 Inv. Ex. 19 28 Plating 2 15 1 7.5 900 60 60 18 Inv. Ex. 20 29
Plating 2 10 1 5.0 900 60 78 1.5 Inv. Ex. 21 30 Plating 2 1.0 1
0.50 900 60 81 0.2 Inv. Ex. 22 31 Plating 2 0.1 1 0.051 900 60 71
2.7 Inv. Ex. 23 32 Plating 2 0.01 1 0.006 900 60 70 3.1 Inv. Ex. 24
33 Plating 2 0.005 1 0.0035 900 60 61 19 Inv. Ex. 25
[0343] Table 3 shows the {222} plane integration of the .alpha.Fe
phase and the {200} plane integration of the .alpha.Fe phase of
steel sheets produced under various conditions. Note that the plane
integration was obtained by measurement by X-ray diffraction and
calculation by the above-mentioned calculation processing
method.
[0344] In Nos. 22 to 27 of Invention Examples 14 to 19, Cu was
deposited on matrix steel sheet having a thickness of 2.0 mm by the
cladding method, electroplating method, or sputtering method to a
thickness in the range of the present invention as shown in Table
3.
[0345] With the Cu as deposited, the steel sheet was cold rolled by
a reduction rate of 60%. Next, the removal of the second layer was
omitted and the steel sheet was heat treated under conditions of
1020.degree. C..times.0.3 min to make the steel sheet
recrystallize.
[0346] In each steel sheet, the {222} plane integration was in the
range of the present invention. In No. 22 where the thickness of
the second layer when depositing the second layer was over 1000
.mu.m and in No. 27 where the thickness of the second layer less
than 0.05 .mu.m, the {222} plane integration fell somewhat and the
{222} plane integration was over 15%.
[0347] In No. 22 of Invention Example 14, the thickness of the
second layer after production was over 500 .mu.m and peeling
occurred somewhat easily. In No. 27 of Invention Example 19, the
thickness of the second layer after production was less than 0.01
.mu.m, the coating tore easily, and there was some problem in terms
of rust prevention.
[0348] In Nos. 28 to 33 of Invention Examples 20 to 25, 2 .mu.m of
Cu was deposited on matrix steel sheet of a thickness of 0.005 to
15 mm by the electroplating method. Next, with the Cu as deposited,
the steel sheet was cold rolled by a reduction rate of 50%. The
removal of the second layer was omitted and the steel sheet was
heat treated under conditions of 900.degree. C..times.60 min to
make the steel sheet recrystallize.
[0349] In each steel sheet, the {222} plane integration was in the
range of the present invention, but in No. 28 where the thickness
of the matrix steel sheet at the time of deposition was over 10 mm
and in No. 33 where the thickness of the matrix steel sheet was
less than 10 .mu.m, the {222} plane integration fell somewhat and,
furthermore, the {222} plane integration exceeded 15%.
[0350] The steel sheets of the above invention examples were
measured for the average r value. It was confirmed that in the
steel sheets of the invention examples, the average r value was a
high level of 2.5 or more. Therefore, the steel sheets of the
invention examples had excellent drawability.
[0351] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present
invention.
Example 5
[0352] The results of using Cr as the deposit (second layer) to
produce steel sheet having a high {222} plane integration are
shown.
[0353] The ingredients of the matrix steel sheet were, by mass %,
ingredients including Al: 0.02%, C: 0.06%, Si: 0.2%, Mn: 0.4%, Cr:
13.1%, Ni: 11.2%, and a balance of iron and unavoidable
impurities.
[0354] As the matrix steel sheet, steel sheet obtained by using the
vacuum melting method to produce an ingot and hot rolling the ingot
to a thickness of 3.0 mm and, furthermore, cold rolling to a
thickness of 0.8 mm was used.
[0355] The main phase of the matrix steel sheet at ordinary
temperature was the .gamma.Fe phase. X-ray diffraction was used to
measure the texture of the .gamma.Fe phase of the matrix steel
sheet and the plane integration was calculated in the same way as
above. It was confirmed that the {222} plane integration was 24%
and that the {200} plane integration was 21%.
[0356] Part of the matrix steel sheet was heat treated at
950.degree. C..times.10 sec in a hydrogen atmosphere before Cr
plating.
[0357] Cr was deposited on the surface of the matrix steel sheet
using the electroplating method. For the plating bath, a chrome
sulfate solution was used. The thickness of the deposited Cr was
0.6 .mu.m. This was controlled to become uniform in the steel sheet
surface.
[0358] The steel sheet on which the Cr was deposited was cold
rolled, then the steel sheet was heated treated in a nonoxidizing
atmosphere. Before the heat treatment, if necessary, the Cr
deposited on the steel sheet surface was removed. The Cr was
removed by mechanical polishing.
TABLE-US-00004 TABLE 4 Second layer Product Preheat Rolling Removal
of .gamma.Fe .gamma. phase treat. Red. deposits Heat treatment
phase {222} Fe {200} Al temp. rate before Temp. Time Alloying plane
plane conc. No. .degree. C. Material % heat treat. .degree. C. min
ratio % integ. integ. mass % Remarks 34 950 Cr 0 Yes 1050 0.2 10 36
17 0.01 Comp. Ex. 9 35 950 None 75 None 1050 0.2 0 35 18 0.01 Comp.
Ex. 10 36 950 Cr 75 Yes 1050 0.2 0 70 3.1 0.01 Inv. Ex. 26 37 None
Cr 75 Yes 1050 0.2 0 68 3.9 0.01 Inv. Ex. 27 38 950 Cr 75 None 400
0.2 0 38 16 0.01 Comp. Ex. 11 39 950 Cr 75 None 1050 0.2 10 69 4.2
0.01 Inv. Ex. 28 40 950 Cr 75 None 1100 0.2 30 72 2.3 0.01 Inv. Ex.
29 41 950 Cr 75 None 1150 0.2 60 75 1.8 0.01 Inv. Ex. 30
[0359] Table 4 shows the alloying ratio, the {222} plane
integration of the .gamma.Fe phase, the {200} plane integration of
the .gamma.Fe phase, and the Al content of steel sheet produced
under various conditions. Note that the plane integration was found
by measurement using X-ray diffraction and calculation by the
above-mentioned calculation processing method.
[0360] The alloying ratio of the steel sheet was found as follows:
At the L cross-section, in a field of the L direction 1
mm.times.entire thickness, the EPMA method was used to measure the
plane distribution of the Fe content and the plane distribution of
the Cr content.
[0361] Further, a region of Fe.gtoreq.0.5 mass % and Cr.gtoreq.13.2
mass % was deemed an alloyed region and its area was found as the
alloyed area. The alloying ratio was calculated by dividing the
alloyed area by the L direction 1 mm.times.total thickness
area.
[0362] In No. 34 of Comparative Example 9, Cr of a thickness of 0.6
.mu.m was deposited on the steel sheet surface. The cold rolling
was omitted and the Cr was removed, then the steel sheet was heat
treated under conditions of 1050.degree. C..times.0.2 min to make
the steel sheet recrystallize.
[0363] As a result, the {222} plane integration and the {200} plane
integration of this steel sheet were both outside the range of the
present invention.
[0364] In No. 35 of Comparative Example 10, the deposition of Cr
was omitted and the steel sheet was cold rolled by a reduction rate
of 75% without any deposit. After this, the steel sheet was heat
treated under conditions of 1050.degree. C..times.0.2 min to make
the steel sheet recrystallize.
[0365] In this case as well, the {222} plane integration and the
{200} plane integration were both outside the range of the present
invention.
[0366] In No. 36 of Invention Example 26, the sheet was heat
treated at 950.degree. C., then Cr of a thickness of 0.6 .mu.m was
deposited on the steel sheet surface. After this, the steel sheet
was cold rolled by a reduction rate of 75% to make it thinner.
[0367] Furthermore, the Cr was removed, then the steel sheet was
heat treated under conditions of 1050.degree. C..times.0.2 min to
make the steel sheet recrystallize.
[0368] As a result, it was confirmed that the {222} plane
integration and the {200} plane integration were both controlled to
within the range of the present invention and that the Al content
was also in the range of the present invention.
[0369] Further, using a tensile test, it was confirmed that the
steel sheet of Invention Example 26 has a high toughness.
[0370] In No. 37 of Invention Example 27, the heat treatment before
deposition of Cr was omitted from No. 36 of the invention example,
but it was confirmed that the {222} plane integration and the {200}
plane integration were both controlled to within the range of the
present invention and the Al content was also in the range of the
present invention.
[0371] In No. 38 of Comparative Example 11, before deposition of
Cr, the steel sheet was heat treated at 950.degree. C., then Cr was
deposited and the sheet was cold rolled by a reduction rate of 75%
to make it thinner.
[0372] The removal of the Cr was omitted and the rolling oil on the
steel sheet surface was removed, then the steel sheet was heat
treated under conditions of 400.degree. C..times.0.2 min. At this
time, the steel sheet was not made to recrystallize.
[0373] As a result, neither the obtained {222} plane integration
and the {200} plane integration were in the range of the present
invention.
[0374] In Nos. 39 to 41 of Invention Examples 28 to 30, before
depositing the Cr, the steel sheet was heat treated at 950.degree.
C., then Cr was deposited. In each case, the steel sheet was cold
rolled by a reduction rate of 75% to make it thinner.
[0375] Removal of the Cr was omitted, then rolling oil on the steel
sheet surface was removed, then, in No. 39, the steel sheet was
heat treated under conditions of 1050.degree. C..times.0.2 min, in
No. 40, it was heat treated under conditions of 1100.degree.
C..times.0.2 min, and, further, in No. 41, it was heat treated
under conditions of 1150.degree. C..times.0.2 min to make the steel
sheet recrystallize.
[0376] Part of the deposited Cr alloyed with the steel sheet. The
ratio of alloying was, in No. 39, 10%, in No. 40, 30%, and in No.
41, 60%.
[0377] It was confirmed that the obtained {222} plane integration
and the {200} plane integration were both controlled to within the
range of the present invention and that the Al content was also in
the range of the present invention.
[0378] The steel sheets of the above examples were measured for the
average r value. It was confirmed that in the steel sheets of the
invention examples, the average r value was a high level of 2.5 or
more, but in the steel sheets of the comparative examples, it was
less than 2.5.
[0379] From these results, it was learned that the steel sheets
produced by the method of production of the present invention had
excellent drawability.
[0380] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present
invention.
Example 6
[0381] The results of using Al alloy as the second layer and
changing the thickness of the second layer to produce steel sheet
having a high {222} plane integration are shown.
[0382] The ingredients of the matrix steel sheet were, by mass %,
ingredients including Al: 0.039%, C: 0.0019%, Si: 0.011%, Mn:
0.13%, N: 0.002%, Ti: 0.061%, Cr: 0.002% or less and a balance of
iron and unavoidable impurities.
[0383] The matrix steel sheet was steel sheet obtained by using the
vacuum melting method to produce an ingot and hot rolling the ingot
to a thickness of 3.0 mm. Note that pickling was used to remove the
scale from the steel sheet surface.
[0384] The main phase of the matrix steel sheet at ordinary
temperature was the .alpha.Fe phase. X-ray diffraction was used to
measure the texture of the .alpha.Fe phase of the matrix steel
sheet and the plane integration was calculated in the same way as
above. It was confirmed that the {222} plane integration was 19%
and that the {200} plane integration was 17%.
[0385] This matrix steel sheet was heat treated at 780.degree.
C..times.10 sec in a hydrogen atmosphere before plating. On the
surface of the matrix steel sheet, Al alloy was deposited by the
hot dip method. The composition of the plating bath was, by mass %,
90% Al-10% Si. The alloy was deposited on the two surfaces of the
steel sheet.
[0386] The amount of plating deposition was controlled by, before
the plating solidified, using a wiping gas to blow nitrogen over
the steel sheet surface to blow off unnecessary plating.
[0387] The steel sheet on which the Al alloy was deposited was cold
rolled to reduce it to a thickness of 0.8 mm. After this, this
steel sheet was heat treated in a nonoxidizing atmosphere to make
the steel sheet recrystallize and promote diffusion of Al.
TABLE-US-00005 TABLE 5 Production Heat treatment Product Deposition
of second layer Reduc- Temp. .alpha.Fe phase {222} .alpha.Fe
Preheat tion rise 0-30.degree. 0-10.degree. phase Al Eva. treat.
Total rate at rate Holding dev. dev. {200} conc. Burr temp. Mate-
thick. rolling .degree. C./ Temp. time Alloying Plane area area
Plane mass height No. .degree. C. rial .mu.m % min .degree. C. sec
ratio % integ. rate rate integ. % .mu.m Remarks 42 780 None 0 73
100 700 20 -- 42 57 13 18 0.039 51 Comp. Ex. 12 43 780 None 0 73
100 950 20 -- 32 45 2 21 0.039 53 Comp. Ex. 13 44 780 None 0 73 100
1010 20 -- 24 30 0.5 22 0.039 57 Comp. Ex. 14 45 780 Al--Si 5 73
100 700 20 100 61 81 41 9.7 0.063 12 Inv. Ex. 31 46 780 Al--Si 5 73
100 950 20 100 63 82 45 8.5 0.063 13 Inv. Ex. 32 47 780 Al--Si 5 73
100 1010 20 100 67 84 52 2.5 0.063 14 Inv. Ex. 33 48 780 Al--Si 10
73 100 700 20 100 70 87 58 1.2 0.114 5 Inv. Ex. 34 49 780 Al--Si 10
73 100 950 20 100 76 92 66 0.8 0.114 6 Inv. Ex. 35 50 780 Al--Si 10
73 100 1010 20 100 81 95 72 0.5 0.114 7 Inv. Ex. 36 51 780 Al--Si
40 73 100 700 20 100 76 92 67 0.9 0.510 7 Inv. Ex. 37 52 780 Al--Si
40 73 100 950 20 100 83 96 72 0.7 0.510 8 Inv. Ex. 38 53 780 Al--Si
40 73 100 1010 20 100 89 97 81 0.3 0.510 6 Inv. Ex. 39 54 780
Al--Si 40 73 1 1010 20 100 95 99 91 0.05 0.510 6 Inv. Ex. 37 55 780
Al--Si 40 73 10 1010 20 100 99 99.8 98 0.01 0.510 7 Inv. Ex. 38 56
780 Al--Si 40 73 1000 1010 20 100 78 93 70 0.9 0.510 5 Inv. Ex. 39
57 780 Al--Si 40 73 2000 1010 20 100 72 90 61 1.1 0.510 6 Inv. Ex.
40 58 650 Al--Si 40 73 100 1010 20 100 63 82 50 12 0.510 14 Inv.
Ex. 41 59 1150 Al--Si 40 73 100 1010 20 100 60 80 41 14 0.510 14
Inv. Ex. 42
[0388] Table 5 shows the alloying ratio of the produced steel
sheet, the {222} plane integration of the .alpha.Fe phase, the
{200} plane integration of the .alpha.Fe phase, and the Al content
of steel sheet produced under various conditions. Note that the
plane integration was found by measurement using X-ray diffraction
and calculation by the above-mentioned calculation processing
method.
[0389] The alloying ratio of the steel sheet was found as follows:
At the L cross-section, in a field of the L direction 1
mm.times.entire thickness, the EPMA method was used to measure the
plane distribution of the Fe content and the plane distribution of
the Al content.
[0390] Further, a region of Fe.gtoreq.0.5 mass % and
Al.gtoreq.0.139 mass % was deemed an alloyed region and its area
was found as the alloyed area. The alloying ratio was calculated by
dividing the alloyed area by the L direction 1 mm.times.total
thickness area.
[0391] Note that, the area ratios obtained by using the EBSP method
to separately observe by the L cross-section the crystal grains
with a deviation of the {222} plane with respect to the steel sheet
surface of 0 to 30.degree. and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to
10.degree. are described.
[0392] Further, the above steel sheet was tested for burr
resistance. A 10.0 mm.phi. punch and a 10.3 mm.phi. die were used
for punching and the burr height around the punched hole was
measured by a point micrometer.
[0393] In Nos. 42 to 44 of Comparative Examples 12 to 14, the step
of deposition of the Al alloy was omitted and the steel sheet was
cold rolled by a reduction rate of 73% without any deposits. After
this, the steel sheet was heat treated under conditions of 700 to
1010.degree. C. to make the steel sheet recrystallize.
[0394] In this case, the {222} plane integration and the {200}
plane integration were both outside the range of the present
invention. The burr height was a large value of 51 to 57 .mu.m.
[0395] In No. 45 to 47 of Invention Examples 31 to 33, Al alloy of
5 .mu.m thickness in total of the front and back was deposited.
Further, the steel sheet was cold rolled to a thickness of 0.8 mm,
then the steel sheet was heat treated under conditions of 700 to
1010.degree. C. to make the steel sheet recrystallize.
[0396] In this case, the {222} plane integration and the {200}
plane integration were both in the range of the present invention.
The burr height was 12 to 14 .mu.m or remarkably lower than the
comparative examples.
[0397] In Nos. 48 to 57 of Invention Examples 34 to 40, Al alloy of
10 to 40 .mu.m thickness in total of the front and back was
deposited. Further, the steel sheet was cold rolled to a thickness
of 0.8 mm, then the steel sheet was heat treated under conditions
of 700 to 1010.degree. C. to make the steel sheet recrystallize. At
this time, the temperature rise rate was changed.
[0398] In each case, the {222} plane integration and the {200}
plane integration were both in the range of the present invention.
The burr height was 5 to 8 .mu.m or a remarkably small value.
[0399] The steel sheets of the above examples were measured for the
average r value. It was confirmed that in the steel sheets of the
invention examples, the average r value was a high level of 2.5 or
more, but in the steel sheets of the comparative examples, it was
less than 2.5.
[0400] From these results, it was learned that the steel sheets of
the invention examples have excellent drawability.
[0401] Further, an Erichsen test was performed and the extruded
surfaces were examined whereupon it was confirmed that the steel
sheets of the invention examples are also excellent in press
formability.
[0402] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present invention and
that both excellent burr resistance and drawability were
achieved.
Example 7
[0403] The results of changing the Cr content of the matrix steel
sheet to examine the manufacturability and the {222} plane
integration are shown.
[0404] The matrix steel sheet was produced by four types of
ingredients with different Cr content. The Cr content was, by mass
%, 13.0% (ingredients F), 11.9% (ingredients G), 6.0% (ingredients
H), and 0.002% or less (detection limit or less) (ingredients I).
In addition, C: 0.083%, Si: 0.11%, Mn: 0.23%, Al: 0.002%, N: 0.003,
and a balance of iron and unavoidable impurities were included in
the ingredients.
[0405] By each of these ingredients, vacuum melting was used to
produce an ingot and the ingot was hot rolled to reduce it to a
thickness of 3.5 mm. Next, the four types of steel sheets were cold
rolled to a thickness of 1.3 mm.
[0406] The main phases of the steel sheets of the ingredients F, G,
H, and I at ordinary temperature were the .alpha.Fe phases. X-ray
diffraction was used to measure the texture of the .alpha.Fe phase
of the matrix steel sheet and the plane integration was calculated
in the same way as above.
[0407] It was confirmed that the {222} plane integration was, with
the ingredients F, 8%, the ingredients G, 9%, the ingredients H,
9%, and the ingredients I, 8%, while the {200} plane integration
was, with the ingredients F, 28%, the ingredients G, 30%, the
ingredients H, 31%, and the ingredients I, 29%.
[0408] The electroplating method was used to deposit Sn on the
surface of the matrix steel sheet as the second layer. The plating
bath was a sulfuric acid acidic solution. The process was
controlled to give a basis weight per side of 1 g/m.sup.2. Both
surfaces were plated. Before the electroplating, no preheat
treatment was applied.
[0409] With the Sn deposited as the second layer in this way, each
steel sheet was cold rolled by a reduction rate of 40% to obtain
steel sheet of a thickness of 0.78 mm. For comparison, steel sheets
of the ingredients F, G, H, and I with no Sn deposited were also
cold rolled by a reduction rate of 40%.
[0410] Next, each steel sheet was heat treated in vacuum at a
temperature rise rate of 100.degree. C./min under conditions of
1100.degree. C..times.60 min to make the steel sheet recrystallize.
At this time, at each steel sheet, the Sn of the steel sheet
surface diffused in the steel and was completely alloyed.
[0411] For comparison, steel sheet without Sn deposited was
similarly heat treated.
[0412] The obtained eight types of steel sheets were measured for
the {222} plane integration and the {200} plane integration. The
{222} area integration of the steel sheets on which Sn was
deposited was, for the ingredients F, 65%, the ingredients G, 75%,
the ingredients H, 79%, and the ingredients I, 85%, while the {200}
plane integration was, for the ingredients F, 12%, the ingredients
G, 4%, the ingredients H, 2.5%, and the ingredients I, 1.4.
[0413] In each case, the plane integration was within the range of
the present invention, but it was learned that if the Cr contained
is, by mass %, less than 12.0%, a particularly high {222} plane
integration can be obtained.
[0414] On the other hand, the plane integration of the steel sheets
on which Sn was not deposited was, for the ingredients F, 21%, the
ingredients G, 12%, the ingredients H, 11%, and the ingredients I,
12 and the {200} plane integration was, for the ingredients F, 16%,
the ingredients G, 17%, the ingredients H, 16%, and the ingredients
I, 16%.
[0415] The burr resistance was evaluated by using 10.0 mm.phi.
punch and a 10.3 mm.phi. die for punching and measuring the burr
height around the punched hole by a point micrometer.
[0416] The burr height of the steel sheets on which Sn was
deposited was, for the ingredients F, 9 .mu.m, the ingredients G, 7
.mu.m, the ingredients H, 6 .mu.m, and the ingredients I, 5 .mu.m.
It was confirmed that each steel sheet had excellent
properties.
[0417] The burr height of the steel sheets on which Sn was not
deposited was, for the ingredients F, 46 .mu.m, the ingredients G,
52 .mu.m, the ingredients H, 63 .mu.m, and the ingredients I, 68
.mu.m. It was confirmed that each steel sheet suffered from large
burrs.
[0418] Furthermore, each steel sheet was measured for the average r
value, whereupon it was confirmed that the average r value of a
steel sheet on which Sn was deposited was a high level of 2.5 or
more. The average r value for a steel sheet on which Sn was not
deposited was about 1.1.
[0419] From this, it was learned that steel sheet on which Sn was
deposited has excellent drawability. Further, an Erichsen test was
performed and the extruded surface was examined. As a result, it
was confirmed that steel sheet on which Sn was deposited is
excellent in press formability as well.
[0420] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present
invention.
Example 8
[0421] The results of changing the Al content of the matrix steel
sheet to examine the manufacturability and the {222} plane
integration are shown.
[0422] The matrix steel sheet was produced by four types of
ingredients with different Al content. The Al content was, by mass
%, 7.5% (ingredients J), 6.4% (ingredients K), 3.4% (ingredients
L), and 0.002% or less (ICP detection limit or less) (ingredients
M). In addition, C: 0.083%, Si: 0.11%, Mn: 0.23%, Cr: 0.002% or
less (ICP analysis detection limit or less), N: 0.003, and a
balance of iron and unavoidable impurities were included in the
ingredients.
[0423] By each of these ingredients, vacuum melting was used to
produce an ingot and the ingot was hot rolled to reduce it to a
thickness of 2.8 mm.
[0424] The ingots of the ingredients K, L, and M could be easily
hot rolled to steel sheets, but the ingot of the ingredients J
frequently broke during hot rolling so hot rolling could not be
continued.
[0425] In this way, if the Al content of the matrix steel sheet is
over the range of the present invention at 6.5% or more, production
is difficult, so production of steel sheet of the ingredients J was
foregone. Next, the steel sheets of the ingredients K, L, and M
were cold rolled to 1.6 mm thicknesses.
[0426] The main phases of the steel sheets of the ingredients K, L,
and M at ordinary temperature were the .alpha.Fe phases. X-ray
diffraction was used to measure the texture of the .alpha.Fe phase
of the matrix and the plane integration was calculated in the same
way as above. It was confirmed that the {222} plane integration
was, for the ingredients K, 11%, the ingredients L, 12%, and the
ingredients M, 12%, while the {200} plane integration was, for the
ingredients K, 8%, the ingredients L, 7%, and the ingredients M,
8%.
[0427] Each matrix steel sheet, before formation of the second
layer, was heat treated at 750.degree. C..times.10 sec in a
hydrogen atmosphere. After this, the hot dip method was used to
deposit Zn on the surface of the matrix steel sheet.
[0428] The composition of the plating bath was 95% Zn-5% Fe. The Zn
alloy was deposited on both surfaces of the steel sheet. The amount
of deposition, in total for the front and back, was made 80
g/m.sup.2. The amounts of deposition on the front and back were
made as uniform as possible.
[0429] With the Zn alloy deposited as the second layer, each steel
sheet was cold rolled by a reduction rate of 50% to obtain steel
sheet of a thickness of 0.80 mm.
[0430] For comparison, steel sheets of the ingredients K, L, and M
with no Zn alloy deposited were also cold rolled by a reduction
rate of 50% to a thickness of 0.80 mm.
[0431] Next, each steel sheet was heat treated in a vacuum at a
temperature rise rate of 10.degree. C./min under conditions of
1100.degree. C..times.60 min to make the steel sheet recrystallize.
At this time, in each steel sheet, the Zn alloy of the steel sheet
surface diffused in the steel and was completely alloyed.
[0432] For comparison, steel sheet without Zn alloy deposited was
similarly heat treated.
[0433] The obtained eight types of steel sheets were measured for
the {222} plane integration and the {200} plane integration. The
{222} area integration of the steel sheets on which Zn alloy was
deposited was, for the ingredients K, 78%, the ingredients L, 85%,
the ingredients M, 90%, and the ingredients I, 85%, while the {200}
plane integration was, for the ingredients K, 1.4%, the ingredients
L, 0.6%, and the ingredients M, 0.4%.
[0434] In each case, the plane integration was within the range of
the present invention, but it was learned that if the Al contained
is, by mass %, less than 3.5%, a particularly high {222} plane
integration can be obtained.
[0435] On the other hand, the plane integration of the steel sheets
on which Zn alloy was not deposited was, for the ingredients K,
36%, the ingredients L, 32%, and the ingredients M, 25%, and the
{200} plane integration was, for the ingredients K, 17%, the
ingredients L, 19%, and the ingredients M, 16%.
[0436] The burr resistance was evaluated by using 10.0 mm.phi.
punch and a 10.3 mm.phi. die for punching and measuring the burr
height around the punched hole by a point micrometer.
[0437] The burr height of the steel sheets on which Zn was
deposited was, for the ingredients K, 7 .mu.m, the ingredients L, 5
.mu.m, and the ingredients M, 5 .mu.m. It was confirmed that each
steel sheet had excellent properties.
[0438] The burr height of the steel sheets on which Zn alloy was
not deposited was, for the ingredients K, 52 .mu.m, the ingredients
L, 57 .mu.m, and the ingredients M, 65 .mu.m. It was confirmed that
each steel sheet suffered from large burrs.
[0439] Furthermore, each steel sheet was measured for the average r
value, whereupon it was confirmed that the average r value of a
steel sheet on which Zn alloy was deposited was a high level of 2.5
or more. The average r value for a steel sheet on which Zn alloy
was not deposited was about 1.1.
[0440] From this, it was learned that steel sheet on which Zn alloy
was deposited has excellent drawability.
[0441] Further, an Erichsen test was performed on each steel sheet
and the extruded surface was examined. As a result, it was
confirmed that steel sheet on which Zn alloy was deposited is
excellent in press formability as well.
[0442] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present
invention.
Example 9
[0443] The results of using Mo, Cr, Ge, Si, Ti, W, and V metal as
the deposits of the second layer to produce steel sheet having a
high {222} plane integration are shown.
[0444] The hot rolled sheets of the thicknesses of 2.8 mm of the
ingredients K, L, and M used in Example 8 were used as the matrix
steel sheets. Steel sheets of the ingredients K, L, and M were cold
rolled to 0.4 mm thickness.
[0445] The main phases of the steel sheets of the ingredients K, L,
and M at ordinary temperature were .alpha.Fe phases. X-ray
diffraction was used to measure the texture of the .alpha.Fe phase
of each matrix steel sheet and the plane integration was calculated
in the same way as above.
[0446] It was confirmed that the {222} plane integration was, for
the ingredients K, 15%, the ingredients L, 17%, and the ingredients
M, 16%, while the {200} plane integration was, for the ingredients
K, 7%, the ingredients L, 6%, and the ingredients M, 8%.
[0447] Before sputtering for depositing the second layer, each
matrix steel sheet was heat treated at 620.degree. C..times.60 sec
in an Ar atmosphere. The sputtering method was used to deposit on
the surface of the matrix steel sheet a second layer of Mo, Cr, Ge,
Si, Ti, W, and V metal.
[0448] Metal target materials of purities of 99.9% or more were
prepared and the thicknesses per side were controlled to 1 .mu.m to
form coatings on the two surfaces.
[0449] With the second layer comprised of each metal as deposited,
each steel sheet was cold rolled by a reduction rate of 62.5% to
obtain steel sheet of a thickness of 0.15 mm.
[0450] For comparison, steel sheets of the ingredients K, L, and M
on which no second layer comprised of a metal is deposited were
also cold rolled by a reduction rate of 62.5% to a thickness of
0.15 mm.
[0451] Next, each steel sheet was heat treated in vacuum at a
temperature rise rate of 500.degree. C./min under conditions of
1150.degree. C..times.15 sec to make the steel sheet
recrystallize.
[0452] At this time, in each steel sheet, the second layer metal at
the steel sheet surface diffused in the steel and was completely
alloyed. For comparison, steel sheets on which no second layer
metal was deposited were similarly heat treated.
TABLE-US-00006 TABLE 6 Production Product Deposition .alpha.Fe of
second Heat treatment .alpha.Fe phase {222} phase layer Red. Temp.
Alloy- 0-30.degree. 0-10.degree. {200} Al Eval. Total rate at rise
Holding ing Plane dev. dev. Plane conc. Burr thick. rolling rate
Temp. time ratio integ. area area integ. mass height No. Matrix
Material .mu.m % .degree. C./min .degree. C. sec % % rate rate % %
.mu.m Remarks 60 K None 0 60 500 1150 15 -- 38 55 8 16 6.4 42 Comp.
Ex. 15 61 L None 0 60 500 1150 15 -- 24 30 0.4 18 3.4 53 Comp. Ex.
16 62 M None 0 60 500 1150 15 -- 18 18 0.1 19 <0.002 63 Comp.
Ex. 17 63 K Mo 2 60 500 1150 15 100 63 82 47 7.6 6.4 9 Inv. Ex. 43
64 L Mo 2 60 500 1150 15 100 68 87 57 3.8 3.4 8 Inv. Ex. 44 65 M Mo
2 60 500 1150 15 100 74 92 63 1.8 <0.002 8 Inv. Ex. 45 66 K Cr 2
60 500 1150 15 100 61 81 46 8.5 6.4 8 Inv. Ex. 46 67 L Cr 2 60 500
1150 15 100 66 85 53 5.4 3.4 7 Inv. Ex. 47 68 M Cr 2 60 500 1150 15
100 73 91 62 2.3 <0.002 7 Inv. Ex. 48 69 K Si 2 60 500 1150 15
100 66 86 55 4.7 6.4 8 Inv. Ex. 49 70 L Si 2 60 500 1150 15 100 69
89 60 3.0 3.4 7 Inv. Ex. 50 71 M Si 2 60 500 1150 15 100 78 93 73
1.2 <0.002 8 Inv. Ex. 51 72 K Ge 2 60 500 1150 15 100 63 82 47
6.7 6.4 9 Inv. Ex. 52 73 L Ge 2 60 500 1150 15 100 67 88 56 4.1 3.4
8 Inv. Ex. 53 74 M Ge 2 60 500 1150 15 100 75 92 69 2.1 <0.002 8
Inv. Ex. 54 75 K Ti 2 60 500 1150 15 100 67 86 57 5.2 6.4 8 Inv.
Ex. 55 76 L Ti 2 60 500 1150 15 100 69 89 59 3.4 3.4 7 Inv. Ex. 56
77 M Ti 2 60 500 1150 15 100 77 92 70 1.3 <0.002 7 Inv. Ex. 57
78 K W 2 60 500 1150 15 100 62 81 47 10.2 6.4 9 Inv. Ex. 58 79 L W
2 60 500 1150 15 100 65 83 50 8.5 3.4 7 Inv. Ex. 59 80 M W 2 60 500
1150 15 100 73 91 63 2.3 <0.002 8 Inv. Ex. 60 81 K V 2 60 500
1150 15 100 64 83 51 6.4 6.4 8 Inv. Ex. 61 82 L V 2 60 500 1150 15
100 67 88 57 5.8 3.4 6 Inv. Ex. 62 83 M V 2 60 500 1150 15 100 75
92 68 1.7 <0.002 8 Inv. Ex. 63
[0453] Table 6 shows the alloying ratio, the {222} plane
integration of the .alpha.Fe phase, the {200} plane integration of
the .alpha.Fe phase, and the Al content of steel sheet produced
under various conditions. The plane integration was found by
measurement using X-ray diffraction and calculation by the
above-mentioned calculation processing method.
[0454] The alloying ratio of the steel sheet was found as follows:
At the L cross-section, in a field of the L direction 1
mm.times.entire thickness, the EPMA method was used to measure the
plane distribution of the Fe content and the plane distribution of
the content of the deposited metal elements among Mo, Cr, Ge, Si,
Ti, W, and V.
[0455] Further, a region of Fe.gtoreq.0.5 mass % and a content of
the deposited metal element among Mo, Cr, Ge, Si, Ti, W, and
V.gtoreq.0.1 mass % was deemed an alloyed region and its area was
found as the alloyed area. The alloying ratio was calculated by
dividing the alloyed area by the L direction 1 mm.times.total
thickness area.
[0456] Note that, the area ratios obtained by using the EBSP method
to separately observe by the L cross-section the crystal grains
with a deviation of the {222} plane with respect to the steel sheet
surface of 0 to 30.degree. and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to
10.degree. are described.
[0457] Further, the above steel sheet was tested for burr
resistance. A 10.0 mm.phi. punch and a 10.3 mm.phi. die were used
for punching and the burr height around the punched hole was
measured by a point micrometer.
[0458] In Nos. 60 to 62 of Comparative Examples 15 to 17, the
deposition of the metal of the second layer was omitted. In this
case, the {222} plane integration and the {200} plane integration
were both outside the range of the present invention. The burr
height was a large value of 42 to 63 .mu.m.
[0459] In Nos. 63 to 65 of Invention Examples 43 to 45, Mo was
deposited as the second layer. The {222} plane integration and the
{200} plane integration were both in the range of the present
invention. The burr height was 8 to 9 .mu.m or much lower than the
comparative examples.
[0460] In Nos. 66 to 68 of Invention Examples 46 to 48, Cr metal
was deposited as the second layer. The {222} plane integration and
the {200} plane integration were both in the range of the present
invention. The burr height was 7 to 8 .mu.m or much lower than the
comparative examples.
[0461] In Nos. 69 to 71 of Invention Examples 49 to 51, Si metal
was deposited as the second layer. The {222} plane integration and
the {200} plane integration were both in the range of the present
invention. The burr height was 7 to 8 .mu.m or much lower than the
comparative examples.
[0462] In Nos. 72 to 74 of Invention Examples 52 to 54, Ge metal
was deposited as the second layer. The {222} plane integration and
the {200} plane integration were both in the range of the present
invention. The burr height was 8 to 9 .mu.m or much lower than the
comparative examples.
[0463] In Nos. 75 to 77 of Invention Examples 55 to 57, Ti metal
was deposited as the second layer. The {222} plane integration and
the {200} plane integration were both in the range of the present
invention. The burr height was 7 to 8 .mu.m or much lower than the
comparative examples.
[0464] In Nos. 78 to 80 of Invention Examples 58 to 60, W metal was
deposited as the second layer. The {222} plane integration and the
{200} plane integration were both in the range of the present
invention. The burr height was 7 to 9 .mu.m or much lower than the
comparative examples.
[0465] In Nos. 81 to 83 of Invention Examples 60 to 63, V metal was
deposited as the second layer. The {222} plane integration and the
{200} plane integration were both in the range of the present
invention. The burr height was 6 to 8 .mu.m or much lower than the
comparative examples.
[0466] The steel sheets of the above examples were measured for the
average r value. It was confirmed that in the steel sheets of the
invention examples, the average r value was a high level of 2.5 or
more, but in the steel sheets of the comparative examples, it was
less than 2.5.
[0467] Therefore, it was learned that the steel sheets of the
invention examples have excellent drawability.
[0468] In this way it was confirmed that the steel sheet produced
by the method of production of the present invention had a {222}
plane integration of the .alpha.Fe phase parallel with respect to
the steel sheet surface of 60% or more and a {200} plane
integration of the .alpha.Fe phase parallel to the steel sheet
surface of 15% or less or in the range of the present invention and
that excellent burr resistance and drawability were both
achieved.
INDUSTRIAL APPLICABILITY
[0469] As explained above, the present invention steel sheet has
the unprecedented superior workability of absence of formation of
burrs at the cross-section at the time of punching, so can be
easily worked into various shapes including everything from
conventional shapes to special sheets.
[0470] Therefore, the present invention steel sheet is for example
useful for outer panels of auto parts, home electrical appliances,
etc. requiring press formation into complicated shapes and other
various structural materials and functional materials.
[0471] Further, the method of production of the present invention
enables the {222} plane integration to be raised and/or the {200}
plane integration to be lowered easily and effectively even in
steel sheet having an Al content of less than 6.5 mass %.
[0472] Therefore, according to the method of production of the
present invention, it is possible to produce steel sheet having a
high {222} plane integration (the present invention steel sheet)
without production of new facilities by just switching processes of
existing facilities easily and at low cost.
[0473] Therefore, the present invention is high in industrial
applicability in the manufacturing industries utilizing the various
structural materials and functional materials.
* * * * *