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 αFe phase or the γFe
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 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
r3+30°C or more, the X-ray diffraction intensity ratio I(200)/I(222) becomes less than
0.17.
[0006] 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≥0.5, a≥7.0,
and b≤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.
[0007] 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 αFe phase or γFe
phase. This has been used to optimize the steel sheet ingredients, rolling conditions,
temperature conditions, etc.
[0008] 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 αFe crystals is made 60% to 95% or the
{200} plane integration is made 0.01% to 15% so as to improve the workability.
[0009] 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.
[0010] 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.
[0011] 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 µm is disclosed.
[0012] 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 µm is disclosed.
DISCLOSURE OF THE INVENTION
[0013] 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 αFe phase or γFe phase. These have met the
needs for improvement of the workability of steel sheet.
[0014] However, meeting more sophisticated requirements is difficult with the prior art.
A new perspective is required.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] Below, the gist of the present invention will be described.
- (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 αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 99% and,
(2) a {200} plane integration of one or both of an αFe phase and γFe 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 αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 99% and
(2) a {200} plane integration of one or both of an αFe phase and γFe 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 αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 99% and
(2) a {200} plane integration of one or both of an αFe phase and γFe 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 αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 99% and
(2) a {200} plane integration of one or both of an αFe phase and γFe 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 any of (1) to
(4) characterized in that said {222} plane integration is 60% to 95%.
- (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.
- (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 µm to 5 mm.
- (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 µm to 500 µm.
- (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 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:
- (1) a {222} plane integration of one or both of an αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 99% and
- (2) a {200} plane integration of one or both of an αFe phase and γFe 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 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:
- (1) a {222} plane integration of one or both of an αFe phase and γFe phase with respect
to the steel sheet surface being 60% to 95% and
- (2) a {200} plane integration of one or both of an αFe phase and γFe 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 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.
- (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 any one of (9) to (19) characterized in that the thickness of the steel
sheet serving as said matrix is 10 µm to 10 mm.
- (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 µm to 1000 µm.
- (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.
- (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°C.
- (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.
- (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.
- (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.
- (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%.
- (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°C to 1000°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 any of (9) to (19) characterized in that a heat treatment temperature
in said step of heat treatment is over 1000°C.
[0028] 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.
[0029] 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.
[0030] 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
[0031] Below, the present invention will be explained in detail.
[0032] 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.
[0033] 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 αFe phase of 60% to 95%
and/or a {200} plane integration of an αFe phase of 0.01% to 15% in Japanese Patent
Publication (A) No.
2006-144116.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] This phenomenon is basically also considered to arise based on the mechanism of formation
of recrystallization nuclei.
[0042] Below, details of the present invention will further described.
[0043] The present invention steel sheet, at ordinary temperature, is comprised or one or
both of an αFe phase and γFe phase. The Al content is less than 6.5 mass%.
[0044] 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.
[0045] 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%.
[0046] 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.
[0047] 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 αFe phase and γFe phase with respect to the steel
sheet surface very high.
[0048] 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.
[0049] 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.
[0050] The present invention steel sheet is comprised of one or both of an αFe phase and
γFe phase.
[0051] The αFe phase is an Fe crystal phase of a structure of a body centered orientation,
while the γFe 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.
[0052] 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 αFe phase and
γFe phase is 60% to 99% and a {200} plane integration of one or both of the αFe phase
and γFe phase is 0.01% to 15%.
[0053] 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.
[0054] The plane integration was measured by X-ray diffraction using MoKα rays. The {222}
plane integration of the αFe phase and the {200} plane integration of the αFe phase
were found as follows.
[0055] The integrated intensities of the 11 α 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.
[0056] For example, the ratio with the {222} intensity is expressed by the following formula
(1).
where the symbols are as follows:
i(hkl): measured integrated intensity of {hkl} plane at measured sample
I(hkl): theoretical integrated intensity of {hkl} plane at sample having random orientation
Σ: sum for 11 α-Fe crystal planes
[0057] In the same way, the {222} plane integration of the Fe phase and the {200} plane
integration of the γFe phase were found as follows:
The integrated intensities of the 6 γ 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.
[0058] For example, the ratio with the {222} intensity is expressed by the following formula
(2).
where the symbols are as follows:
i(hkl): measured integrated intensity of {hkl} plane at measured sample
I(hkl): theoretical integrated intensity of {hkl} plane at sample having random orientation
Σ: sum for 6 γ-Fe crystal planes
[0059] For αFe crystal grains, separately, the EBSP (Electron Backscattering Diffraction
Pattern) method may also be used to find the {222} plane integration.
[0060] 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%.
[0061] 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.
[0062] Further, in the EPSP method, the {222} plane deviates from the steel sheet surface.
This deviation is preferably within 30°.
[0063] 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° or less is preferably
80 to 99.9%.
[0064] Furthermore, the area ratio of the crystal grains with deviation of the {222} plane
in the L cross-section of 0 to 10° is more preferably 40 to 98%.
[0065] The "average r value" means the average plastic strain ratio found by JIS Z 2254
and is a value calculated by the following formula:
[0066] Here, r0, r45, and r90 are the plastic strain ratios measured when taking test samples
in directions of 0°, 45°, and 90° with respect to the rolling direction of the sheet
surface.
[0067] Note that the integrated intensity of the sample having a random orientation may
also be found by measurement using a sample prepared in advance.
[0068] In the present invention steel sheet, (i) a {222} plane integration of one or both
of an αFe phase and γFe 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 αFe phase and γFe phase
with respect to the steel sheet surface is 0.01% to 15%.
[0069] 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.
[0070] 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.
[0071] Therefore, the texture of the present invention steel sheet was defined as in the
above.
[0072] Note that the {222} plane integration of one or both of an αFe phase and γFe 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.
[0073] The {200} plane integration of one or both of an αFe phase and γFe 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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 αFe phase and γFe phase
with respect to the steel sheet surface of 60% to 99% and a {200} plane integration
of one or both of an αFe phase and γFe phase with respect to the steel sheet surface
of 0.01% to 15% is included in the present invention steel sheet.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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 αFe phase and
γFe phase with respect to the steel sheet surface of 60% to 99% and a {200} plane
integration of one or both of an αFe phase and γFe phase with respect to the steel
sheet surface of 0.01% to 15% is also included in the present invention steel sheet.
[0087] 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
[0092] 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 interdiffusion.
[0093] 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 αFe phase and γFe phase with
respect to the steel sheet surface of 60% to 99% and a {200} plane integration of
one or both of an αFe phase and γFe phase with respect to the steel sheet surface
of 0.01% to 15% is also included in the present invention steel sheet.
[0094] 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.
[0095] 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.
[0096] 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.
[0097] 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.
[0098] 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.
[0099] In the present invention steel sheet having the second layer, the second layer is
preferably a metal.
[0100] 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.
[0101] 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 αFe and tend to stabilize the
α phase.
[0102] 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 αFe and tend to stabilize the
α phase more.
[0103] For example, as the second layer, it is possible to select an Al alloy, Zn alloy,
Sn alloy, etc.
[0104] 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.
[0105] 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.
[0106] 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 αFe and tend to stabilize the
α phase.
[0107] 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 αFe and tend to stabilize the
α phase more.
[0108] For example, as the second layer, it is possible to select an Al alloy, Zn alloy,
Sn alloy, etc.
[0109] 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.
[0110] 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%.
[0111] When the second layer does not contain Al, the Al content of the matrix steel sheet
is made less than 6.5 mass%.
[0112] 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.
[0113] Therefore, the Al content of the steel sheet when the second layer does not contain
Al is made less than 6.5 mass%.
[0114] 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%.
[0115] 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.
[0116] 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.
[0117] In the present invention, the alloyed region of the steel sheet and second layer
is defined as follows.
[0118] 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".
[0119] 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.
[0120] 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.
[0121] 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.
[0122] The thickness of the steel sheet of the present invention is preferably 5 µm to 5
mm. This is the thickness including the second layer. If the thickness of the steel
sheet is less than 5 µm, the production yield falls so this is not suitable for practical
application.
[0123] 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 µm to 5 mm.
[0124] The thickness of the steel sheet is more preferably 100 µm 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.
[0125] If the thickness of the steel sheet is 100 µm or more, the {222} plane integration
becomes higher and more easily controlled. Similarly, the effect of suppression of
formation of burrs becomes more remarkable.
[0126] In the thickness of the steel sheet in the present invention, the thickness of the
second layer is preferably 0.01 µm to 500 µm. 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.
[0127] 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.
[0128] If the thickness of the second layer is over 500 µm, the possibility of peeling rises,
so 500 µm or less is preferable. If the thickness of the second layer is less than
0.01 µm, the coating will easily tear and the rust-preventive and protective effect
will be reduced.
[0129] Therefore, the thickness of the second layer is preferably 0.01 µm 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.
[0130] In the method of production of the present invention steel sheet, the thickness of
the matrix steel sheet is 10 µm to 10 mm. If the thickness of the matrix steel sheet
is less than 10 µm, the production yield will drop in the steps from cold rolling
on so this is not suitable for practical application in some cases.
[0131] 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.
[0132] Therefore, the thickness of the matrix steel sheet is preferably 10 µm to 10 mm.
[0133] A thickness of the matrix steel sheet of over 130 µm 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.
[0134] The thickness of the second layer deposited on the matrix steel sheet before cold
rolling is preferably 0.05 µm to 1000 µm. 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.
[0135] If the thickness of the second layer is less than 0.05 µm, the {222} plane integration
becomes lower and may not fall in the range of the present invention, so 0.05 µm or
more is preferable.
[0136] Even when the thickness of the second layer exceeds 1000 µm, the {222} plane integration
becomes lower and may not fall in the range of the present invention, so 1000 µm or
less is preferable.
[0137] To express more superior effects of the present invention, the matrix steel sheet
before deposition of the second layer is preferably given preheat treatment.
[0138] 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.
[0139] The preheat treatment temperature is preferably 700°C to 1100°C. If the preheat treatment
temperature is less than 700°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°C or more.
[0140] If the preheat treatment temperature exceeds 1100°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°C or less.
[0141] 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.
[0142] 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.
[0143] 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.
[0144] The cold rolling is performed with the second layer deposited on the steel sheet.
The reduction rate is 30% to 95%.
[0145] 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%.
[0146] 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.
[0147] 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.
[0148] The heat treatment for causing the steel sheet to recrystallize can be performed
in a vacuum atmosphere, Ar atmosphere, H
2 atmosphere, or other nonoxidizing atmosphere. At this time, preferably the heat treatment
temperature is 600°C to 1000°C and the heat treatment time is 30 seconds or more.
[0149] If the heat treatment temperature is 600°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°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.
[0150] Therefore, preferably the heat treatment temperature is 600°C to 1000°C and the heat
treatment time is 30 seconds or more.
[0151] If the heat treatment temperature is over 1000°C, a high {222} plane integration
can be obtained without restriction by the heat treatment time. In particular, if
over 1000°C, even with less than 30 seconds heat treatment time, the {222} plane integration
can be easily increased.
[0152] Note that the heat treatment temperature is more preferably 1300°C or less. If the
heat treatment temperature is 1300°C or less, the flatness of the steel sheet and
other sheet properties become more superior.
[0153] The temperature rise rate at the time of the heat treatment is preferably 1°C/min
to 1000°C/min. If the temperature rise rate is 1000°C/min or less, a higher {222}
plane integration can be easily obtained. If the temperature rise rate is 1°C/min
or more, the productivity is remarkably improved.
[0154] Therefore, a temperature rise rate of 1°C/min to 1000°C/min is preferable.
[0155] 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.
[0156] 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.
[0157] 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.
[0158] 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.
[0159] 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
[0160] Below, examples will be used to explain the present invention in more detail.
(Example 1)
[0161] The Al content of the matrix steel sheet was changed to investigate the manufacturability
and {222} plane integration.
[0162] 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.
[0163] By each of these ingredients, ingots were produced by vacuum melting and hot rolled
to try to reduce them to 3.0 mm thickness.
[0164] 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.
[0165] 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.
[0166] The main phases of the steel sheets of the ingredients A, B, C, and E at ordinary
temperature were αFe phases. X-ray diffraction was used to measure the texture of
the αFe phase of each matrix steel sheet and, in the same way as above, the plane
integration was calculated.
[0167] 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%.
[0168] Each steel sheet was heat treated at 800°C×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.
[0169] 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.
[0170] 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).
[0171] 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°C×120 min to cause the steel sheet to recrystallize.
[0172] At this time, the steel sheets of the ingredients B and C shrank during the heat
treatment and remarkably dropped in dimensional precision.
[0173] 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.
[0174] 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.
[0175] 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.
[0176] 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.
[0177] 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.
[0178] 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 αFe 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)
[0179] The results of production of steel sheet having a high {222} plane integration using
an Al alloy as the second layer are shown.
[0180] 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.
[0181] 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.
[0182] The main phase of the matrix steel sheet at ordinary temperature was the αFe phase.
X-ray diffraction was used to measure the texture of the αFe phase of the matrix steel
sheet whereupon it was confirmed that the {222} plane integration was 36% and the
{200} plane integration was 20%.
[0183] Part of the matrix steel sheet was heat treated at 800°C×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.
[0184] 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.
[0185] 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.
[0186] 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.
[0187] As comparative examples, cases where the Al alloy was deposited, then the sheets
were not cold rolled were also studied.
Table 1
No. |
Second layer |
Rolling |
Removal of second layer |
Heat treat. |
Product |
Eval. |
Remarks |
Preheat treat. temp. °C |
Mat. of second layer |
Red. rate % |
Temp. °C |
Time min |
Alloying ratio % |
αFe phase {222} plane integ. |
{222} plane 0-30° dev. area rate |
{222} plane 0-10° dev. area rate |
αFe phase {200} plane integ. |
Al conc. mass% |
Burr height µm |
|
1 |
800°C |
Al-Si |
0 |
Yes |
950 |
10 |
0 |
38 |
57 |
8 |
16 |
1.5 |
65 |
Comp. Ex. 1 |
2 |
800°C |
None |
50 |
None |
950 |
10 |
0 |
37 |
56 |
7 |
15 |
1.5 |
58 |
Comp. Ex. 2 |
3 |
800°C |
Al-Si |
50 |
Yes |
950 |
0.1 |
0 |
41 |
59 |
9 |
14 |
1.5 |
9 |
Inv. Ex. |
4 |
800°C |
Al-Si |
50 |
Yes |
950 |
1 |
0 |
61 |
81 |
42 |
8.1 |
1.5 |
5 |
Inv. Ex. 1 |
5 |
800°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°C |
Al-Si |
50 |
None |
1000 |
120 |
100 |
74 |
89 |
60 |
5.2 |
3.2 |
5 |
Inv. Ex. 4 |
8 |
800°C |
Al-Si |
50 |
None |
1000 |
120 |
100 |
75 |
90 |
63 |
4.3 |
6.0 |
6 |
Inv. Ex. 5 |
9 |
800°C |
Al-Si |
50 |
None |
1000 |
120 |
100 |
58 |
78 |
38 |
16 |
7.5 |
23 |
Comp. Ex. 4 |
10 |
800°C |
Al-Si |
0 |
None |
1050 |
0.17 |
20 |
36 |
53 |
7 |
17 |
3.2 |
57 |
Comp. Ex. 5 |
11 |
800°C |
Al-Si |
50 |
None |
1050 |
0.17 |
20 |
62 |
82 |
43 |
4.7 |
3.2 |
6 |
Inv. Ex. 6 |
12 |
800°C |
Al-Si |
75 |
None |
1050 |
0.17 |
50 |
76 |
93 |
68 |
1.6 |
3.2 |
4 |
Inv. Ex. 7 |
[0188] Table 1 shows the alloying ratio, {222} plane integration of the αFe phase, {200}
plane integration of the αFe 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.
[0189] The alloying ratio of the steel sheet was found as follows: At the L cross-section,
in a field of the L direction 1 mmxentire 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.
[0190] Further, a region of Fe≥0.5 mass% and Al≥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 mmxtotal thickness area.
[0191] 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°C×10 min to make the steel
sheet recrystallize.
[0192] 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.
[0193] 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°C×10 min to make the
steel sheet recrystallize.
[0194] In this case as well, the {222} plane integration and the {200} plane integration
were outside the range of the present invention.
[0195] 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°C×0.1 min
to make the steel sheet recrystallize.
[0196] 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.
[0197] In Nos.4 and 5 of Invention Examples 1 and 2, each steel sheet was heat treated at
800°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.
[0198] After the Al alloy was removed, in No. 4, the steel sheet was heat treated under
conditions of 950°C×1 min, while in No. 5, the steel sheet was heat treated under
conditions of 950°C×10 min, to make the steel sheets recrystallize.
[0199] 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.
[0200] 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.
[0201] The Al content in the obtained steel sheet was the same as the matrix, that is, 1.5%,
since the Al alloy was removed.
[0202] In Nos. 7 and 8 of Invention Examples 4 and 5, before depositing the Al alloy, the
steel sheet was heat treated at 800°C then the Al alloy was deposited.
[0203] 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.
[0204] 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°C×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.
[0205] 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.
[0206] 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.
[0207] 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.
[0208] 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.
[0209] 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.
[0210] 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°C×0.17 min to make the steel
sheet recrystallize.
[0211] As a result, the {222} plane integration and the {200} plane integration were both
outside the range of the present invention.
[0212] In Nos. 11 and 12 of Invention Examples 6 and 7, before depositing the Al alloy,
the steel sheet was heat treated at 800°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.
[0213] 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.
[0214] The removal of the Al alloy was omitted and the steel sheet was heat treated under
conditions of 1050°C×0.17 min to make the steel sheet recrystallize.
[0215] 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.
[0216] Each of the above steel sheets was tested for burr resistance. A 10.0 mmφ punch and
a 10.3 mmφ die were used for punching and the burr height around the punched hole
was measured by a point micrometer.
[0217] As a result, it was confirmed that the burr height was a high level of 23 to 65 µm
in the comparative examples, but was an extremely low level of 4 to 9 µm in the invention
examples.
[0218] 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.
[0219] 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.
[0220] 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 αFe phase parallel to
the steel sheet surface of 60% or more and a {200} plane integration of the αFe phase
parallel to the steel sheet surface of 15% or less or both in the range of the present
invention.
[0221] 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)
[0222] The results of using a Zn alloy as the deposit (second layer) to produce steel sheet
having a high {222} plane integration are shown.
[0223] 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.
[0224] The main phase of the matrix steel sheet at ordinary temperature was an αFe phase.
X-ray diffraction was used to measure the texture of the αFe phase of the matrix steel
sheet whereupon it was confirmed that the {222} plane integration was 28% and the
{200} plane integration was 19%.
[0225] Part of the matrix steel sheet was heat treated by 770°Cx5 sec in a hydrogen atmosphere
before plating.
[0226] 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.
[0227] 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.
[0228] As comparative examples, the case of deposition of an Al alloy, then not performing
cold rolling was also studied.
Table 2
No. |
Second layer |
Rolling |
Removal of second layer |
Heat treatment |
Products |
Eval. |
Remarks |
Preheat treat. temp. °C |
Material |
Red. rate % |
Temp. °C |
Time min |
Alloying ratio% |
αFe phase {222} plane integ. |
{222} plane 0-30° deviation area rate |
{222} plane 0-10° deviation area rate |
αFe phase {200} plane integ. |
Al conc. mass% |
Burr height µm |
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 |
[0229] Table 2 shows the alloying ratio, the {222} plane integration of the αFe phase, the
{200} plane integration of the αFe 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.
[0230] The alloying ratio of the steel sheet was found as follows: At the L cross-section,
in a field of the L direction 1 mmxentire thickness, the EPMA method was used to measure
the plane distribution of the Fe content and the plane distribution of the Zn content.
[0231] Further, a region of Fe≥0.5 mass% and Zn≥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×total thickness area.
[0232] 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° and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to 10° are described.
[0233] Further, the above steel sheet was tested for burr resistance. A 30.0 mmφ punch and
a 30.6 mmφ die were used for punching and the burr height around the punched hole
was measured by a point micrometer.
[0234] In No. 13 of Comparative Example 6, Zn alloy of a thickness of 0.8 µm 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°C×0.1 min to make the
steel sheet recrystallize.
[0235] 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.
[0236] 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°C×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.
[0237] In No. 15 of Invention Example 8, after heat treatment at 770°C, Zn alloy of a thickness
of 0.8 µm 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°C×0.1
min to make the steel sheet recrystallize.
[0238] 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.
[0239] 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.
[0240] 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°C then the Zn alloy was deposited.
[0241] In No. 17, Zn alloy of a thickness of 0.8 µm was deposited on the steel sheet surface.
In No. 18, Zn alloy of a thickness of 0.4 µm 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.
[0242] 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°C×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.
[0243] 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.
[0244] In No. 19 of Comparative Example 8, Zn alloy of a thickness of 0.8 µm 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°C×10 min to make the steel sheet recrystallize.
[0245] As a result, the {222} plane integration and the {200} plane integration were both
outside the range of the present invention.
[0246] 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°C, then Zn alloy of a thickness of
0.8 µm was deposited on the steel sheet surface.
[0247] 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.
[0248] The removal of the Al alloy was omitted and the steel sheet was heat treated under
conditions of 750°C×10 min to make the steel sheet recrystallize.
[0249] 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.
[0250] It was confirmed that in the steel sheets of the comparative examples, the burr height
was a high level of 82 to 92 µm, but in the steel sheets of the invention examples,
it was an extremely low level of 7 to 9 µm.
[0251] 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.
[0252] 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.
[0253] 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.
[0254] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe phase parallel to the steel sheet surface of 15% or less or in the range of
the present invention.
(Example 4)
[0255] The results of using Cu as the deposit (second layer) to produce steel sheet having
a high {222} plane integration are shown.
[0256] 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.
[0257] 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.
[0258] 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.
[0259] The main phase of the matrix steel sheet at ordinary temperature was the αFe phase.
X-ray diffraction was used to measure the texture of the αFe 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%.
[0260] Before deposition of Cu, the matrix steel sheet was heat treated at 850°C×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.
[0261] 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.
[0262] The steel sheet on which the Cu was deposited was cold rolled, then the steel sheet
was heat treated in a nonoxidizing atmosphere.
Table 3
No. |
Deposition of second layer |
Thick. after cold rolling |
Heat treatment |
After heat treat. |
Remarks |
Deposition method |
Second layer Cu thick. µm |
Matrix Fe thick. mm |
Second layer Cu thick. µm |
Steel sheet thick. mm |
Temp. °C |
Time min |
αFe phase {222} plane integ. |
αFe phase {200} plane integ. |
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 |
[0263] Table 3 shows the {222} plane integration of the αFe phase and the {200} plane integration
of the αFe 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.
[0264] 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.
[0265] 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°C×0.3 min to make the steel sheet recrystallize.
[0266] 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 µm and in No. 27 where the thickness of the second layer less
than 0.05 µm, the {222} plane integration fell somewhat and the {222} plane integration
was over 15%.
[0267] In No. 22 of Invention Example 14, the thickness of the second layer after production
was over 500 µm 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 µm, the
coating tore easily, and there was some problem in terms of rust prevention.
[0268] In Nos. 28 to 33 of Invention Examples 20 to 25, 2 µm 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°Cx60 min to make the steel sheet recrystallize.
[0269] 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 µm, the {222} plane integration fell somewhat and, furthermore,
the {222} plane integration exceeded 15%.
[0270] 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.
[0271] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe phase parallel to the steel sheet surface of 15% or less or in the range of
the present invention.
(Example 5)
[0272] The results of using Cr as the deposit (second layer) to produce steel sheet having
a high {222} plane integration are shown.
[0273] 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.
[0274] 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.
[0275] The main phase of the matrix steel sheet at ordinary temperature was the γFe phase.
X-ray diffraction was used to measure the texture of the γFe 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%.
[0276] Part of the matrix steel sheet was heat treated at 950°C×10 sec in a hydrogen atmosphere
before Cr plating.
[0277] 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 µm. This was controlled to become uniform in the steel sheet
surface.
[0278] 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 4
No. |
Second layer |
Rolling |
Removal of deposits before heat treat. |
Heat treatment |
Product |
Remarks |
Preheat treat. temp. °C |
Material |
Red. rate % |
Temp. °C |
Time min |
Alloying ratio% |
γFe phase {222} plane integ. |
γ phase Fe {200} plane integ. |
Al conc. mass% |
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 |
[0279] Table 4 shows the alloying ratio, the {222} plane integration of the γFe phase, the
{200} plane integration of the γFe 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.
[0280] The alloying ratio of the steel sheet was found as follows: At the L cross-section,
in a field of the L direction 1 mmxentire thickness, the EPMA method was used to measure
the plane distribution of the Fe content and the plane distribution of the Cr content.
[0281] Further, a region of Fe≥0.5 mass% and Cr≥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 mmxtotal thickness area.
[0282] In No. 34 of Comparative Example 9, Cr of a thickness of 0.6 µm 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°C×0.2 min to make the steel
sheet recrystallize.
[0283] 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.
[0284] 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°C×0.2 min to make the steel
sheet recrystallize.
[0285] In this case as well, the {222} plane integration and the {200} plane integration
were both outside the range of the present invention.
[0286] In No. 36 of Invention Example 26, the sheet was heat treated at 950°C, then Cr of
a thickness of 0.6 µm 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.
[0287] Furthermore, the Cr was removed, then the steel sheet was heat treated under conditions
of 1050°C×0.2 min to make the steel sheet recrystallize.
[0288] 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.
[0289] Further, using a tensile test, it was confirmed that the steel sheet of Invention
Example 26 has a high toughness.
[0290] 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.
[0291] In No. 38 of Comparative Example 11, before deposition of Cr, the steel sheet was
heat treated at 950°C, then Cr was deposited and the sheet was cold rolled by a reduction
rate of 75% to make it thinner.
[0292] 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°C×0.2 min.
At this time, the steel sheet was not made to recrystallize.
[0293] As a result, neither the obtained {222} plane integration and the {200} plane integration
were in the range of the present invention.
[0294] In Nos. 39 to 41 of Invention Examples 28 to 30, before depositing the Cr, the steel
sheet was heat treated at 950°C, then Cr was deposited. In each case, the steel sheet
was cold rolled by a reduction rate of 75% to make it thinner.
[0295] 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°C×0.2 min,
in No. 40, it was heat treated under conditions of 1100°C×0.2 min, and, further, in
No. 41, it was heat treated under conditions of 1150°C×0.2 min to make the steel sheet
recrystallize.
[0296] 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%.
[0297] 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.
[0298] 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.
[0299] From these results, it was learned that the steel sheets produced by the method of
production of the present invention had excellent drawability.
[0300] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe phase parallel to the steel sheet surface of 15% or less or in the range of
the present invention.
(Example 6)
[0301] 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.
[0302] 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.
[0303] 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.
[0304] The main phase of the matrix steel sheet at ordinary temperature was the αFe phase.
X-ray diffraction was used to measure the texture of the αFe 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%.
[0305] This matrix steel sheet was heat treated at 780°C×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.
[0306] 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.
[0307] 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 5
No. |
Production |
Product |
Eva. |
Remarks |
Deposition of second layer |
Reduction rate at rolling % |
Heat treatment |
Alloying ratio % |
αFe phase {222} |
αFe phase {200} |
Al conc. mass% |
Burr height µm |
Preheat treat. temp. °C |
Material |
Total thick. µm |
Temp. rise rate °C/min |
Temp. °C |
Holding time sec |
Plane integ. |
0-30° dev. area rate |
0-10° dev. area rate |
Plane integ. |
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. 33 |
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 |
[0308] Table 5 shows the alloying ratio of the produced steel sheet, the {222} plane integration
of the αFe phase, the {200} plane integration of the αFe 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.
[0309] The alloying ratio of the steel sheet was found as follows: At the L cross-section,
in a field of the L direction 1 mmxentire thickness, the EPMA method was used to measure
the plane distribution of the Fe content and the plane distribution of the Al content.
[0310] Further, a region of Fe≥0.5 mass% and Al≥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×total thickness area.
[0311] 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° and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to 10° are described.
[0312] Further, the above steel sheet was tested for burr resistance. A 10.0 mmφ punch and
a 10.3 mmφ die were used for punching and the burr height around the punched hole
was measured by a point micrometer.
[0313] 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°C to make the steel sheet recrystallize.
[0314] 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 µm.
[0315] In No. 45 to 47 of Invention Examples 31 to 33, Al alloy of 5 µm thickness in total
of the front and back was deposited. Further, the steel sheet was cold rolled to a
thickness of 0.8mm, then the steel sheet was heat treated under conditions of 700
to 1010°C to make the steel sheet recrystallize.
[0316] 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 µm or remarkably
lower than the comparative examples.
[0317] In Nos. 48 to 57 of Invention Examples 34 to 40, Al alloy of 10 to 40 µm thickness
in total of the front and back was deposited. Further, the steel sheet was cold rolled
to a thickness of 0.8mm, then the steel sheet was heat treated under conditions of
700 to 1010°C to make the steel sheet recrystallize. At this time, the temperature
rise rate was changed.
[0318] 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 µm or a remarkably
small value.
[0319] 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.
[0320] From these results, it was learned that the steel sheets of the invention examples
have excellent drawability.
[0321] 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.
[0322] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe 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)
[0323] The results of changing the Cr content of the matrix steel sheet to examine the manufacturability
and the {222} plane integration are shown.
[0324] 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.
[0325] 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.
[0326] The main phases of the steel sheets of the ingredients F, G, H, and I at ordinary
temperature were the αFe phases. X-ray diffraction was used to measure the texture
of the αFe phase of the matrix steel sheet and the plane integration was calculated
in the same way as above.
[0327] 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%.
[0328] 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
2. Both surfaces were plated. Before the electroplating, no preheat treatment was applied.
[0329] 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%.
[0330] Next, each steel sheet was heat treated in vacuum at a temperature rise rate of 100°C/min
under conditions of 1100°C×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.
[0331] For comparison, steel sheet without Sn deposited was similarly heat treated.
[0332] 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.
[0333] 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.
[0334] 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%.
[0335] The burr resistance was evaluated by using 10.0 mmφ punch and a 10.3 mmφ die for
punching and measuring the burr height around the punched hole by a point micrometer.
[0336] The burr height of the steel sheets on which Sn was deposited was, for the ingredients
F, 9 µm, the ingredients G, 7 µm, the ingredients H, 6 µm, and the ingredients I,
5 µm. It was confirmed that each steel sheet had excellent properties.
[0337] The burr height of the steel sheets on which Sn was not deposited was, for the ingredients
F, 46 µm, the ingredients G, 52 µm, the ingredients H, 63 µm, and the ingredients
I, 68 µm. It was confirmed that each steel sheet suffered from large burrs.
[0338] 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.
[0339] 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.
[0340] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe phase parallel to the steel sheet surface of 15% or less or in the range of
the present invention.
(Example 8)
[0341] The results of changing the Al content of the matrix steel sheet to examine the manufacturability
and the {222} plane integration are shown.
[0342] 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.
[0343] 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.
[0344] 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.
[0345] 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.
[0346] The main phases of the steel sheets of the ingredients K, L, and M at ordinary temperature
were the αFe phases. X-ray diffraction was used to measure the texture of the αFe
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%.
[0347] Each matrix steel sheet, before formation of the second layer, was heat treated at
750°C×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.
[0348] 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
2. The amounts of deposition on the front and back were made as uniform as possible.
[0349] 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.
[0350] 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.
[0351] Next, each steel sheet was heat treated in a vacuum at a temperature rise rate of
10°C/min under conditions of 1100°C×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.
[0352] For comparison, steel sheet without Zn alloy deposited was similarly heat treated.
[0353] 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%.
[0354] 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.
[0355] 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%.
[0356] The burr resistance was evaluated by using 10.0 mmφ punch and a 10.3 mmφ die for
punching and measuring the burr height around the punched hole by a point micrometer.
[0357] The burr height of the steel sheets on which Zn was deposited was, for the ingredients
K, 7 µm, the ingredients L, 5 µm, and the ingredients M, 5 µm. It was confirmed that
each steel sheet had excellent properties.
[0358] The burr height of the steel sheets on which Zn alloy was not deposited was, for
the ingredients K, 52 µm, the ingredients L, 57 µm, and the ingredients M, 65 µm.
It was confirmed that each steel sheet suffered from large burrs.
[0359] 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.
[0360] From this, it was learned that steel sheet on which Zn alloy was deposited has excellent
drawability.
[0361] 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.
[0362] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe phase parallel to the steel sheet surface of 15% or less or in the range of
the present invention.
(Example 9)
[0363] 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.
[0364] 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.
[0365] The main phases of the steel sheets of the ingredients K, L, and M at ordinary temperature
were αFe phases. X-ray diffraction was used to measure the texture of the αFe phase
of each matrix steel sheet and the plane integration was calculated in the same way
as above.
[0366] 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%.
[0367] Before sputtering for depositing the second layer, each matrix steel sheet was heat
treated at 620°Cx60 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.
[0368] Metal target materials of purities of 99.9% or more were prepared and the thicknesses
per side were controlled to 1 µm to form coatings on the two surfaces.
[0369] 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.
[0370] 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.
[0371] Next, each steel sheet was heat treated in vacuum at a temperature rise rate of 500°C/min
under conditions of 1150°C×15 sec to make the steel sheet recrystallize.
[0372] 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 6
No. |
Production |
Product |
Eval. |
Remarks |
Matrix |
Deposition of second layer |
Red. rate at rolling % |
Heat treatment |
Alloying ratio% |
αFe phase {222} |
αFe phase {200} |
Al conc. mass% |
Burr height µm |
Material |
Total thick. µm |
Temp. rise rate °C/min |
Temp. °C |
Holding time sec |
Plane integ. % |
0-30° dev. area rate |
0-10° dev. area rate |
Plane integ. % |
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 |
[0373] Table 6 shows the alloying ratio, the {222} plane integration of the αFe phase, the
{200} plane integration of the αFe 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.
[0374] The alloying ratio of the steel sheet was found as follows: At the L cross-section,
in a field of the L direction 1 mmxentire 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.
[0375] Further, a region of Fe≥0.5 mass% and a content of the deposited metal element among
Mo, Cr, Ge, Si, Ti, W, and V ≥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×total thickness area.
[0376] 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° and the crystal grains with a deviation
of the {222} plane with respect to the steel sheet surface of 0 to 10° are described.
[0377] Further, the above steel sheet was tested for burr resistance. A 10.0 mmφ punch and
a 10.3 mmφ die were used for punching and the burr height around the punched hole
was measured by a point micrometer.
[0378] 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 µm.
[0379] 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 µm or much lower than the comparative
examples.
[0380] 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 µm or much lower than the
comparative examples.
[0381] 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 µm or much lower than the
comparative examples.
[0382] 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 µm or much lower than the
comparative examples.
[0383] 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 µm or much lower than the
comparative examples.
[0384] 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 µm or much lower than the
comparative examples.
[0385] 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 µm or much lower than the
comparative examples.
[0386] 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.
[0387] Therefore, it was learned that the steel sheets of the invention examples have excellent
drawability.
[0388] 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 αFe phase parallel with
respect to the steel sheet surface of 60% or more and a {200} plane integration of
the αFe 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
[0389] 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.
[0390] 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.
[0391] 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%.
[0392] 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.
[0393] Therefore, the present invention is high in industrial applicability in the manufacturing
industries utilizing the various structural materials and functional materials.