High-strength cold-rolled steel sheet having excellent local deformability
This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ⅝ to ⅜ in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group is 4.0 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 μm or less.
1. A high-strength cold-rolled steel sheet having excellent local deformability comprising:
in mass %,
C: not less than 0.02% nor more than 0.20%;
Si: not less than 0.001% nor more than 2.5%;
Mn: not less than 0.01% nor more than 4.0%;
P: not less than 0.001% nor more than 0.15%;
S: not less than 0.0005% nor more than 0.03%;
Al: not less than 0.001% nor more than 2.0%;
N: not less than 0.0005% nor more than 0.01%; and
O: not less than 0.0005% nor more than 0.01%; in which Si+Al is limited to less than 1.0%, and
a balance being composed of iron and inevitable impurities, wherein
an area ratio of bainite in a metal structure is 95% or more,
at a sheet thickness center portion being a range of ⅝ to ⅜ in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group represented by respective crystal orientations of {100}<011>, {116}<110>, {114}<110>, {113}<110>, {112}<110>, {335}<110>, and {223}<110> is 4.0 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and
a mean volume diameter of crystal grains in the metal structure is 7 μm or less.
2. The high-strength cold-rolled steel sheet having excellent local deformability according to claim 1 , wherein
to crystal grains of the bainite, a ratio of the crystal grains in which a ratio of a length dL in a rolling direction to a length dt in a sheet thickness direction: dL/dt is 3.0 or less is 50% or more.
3. The high-strength cold-rolled steel sheet having excellent local deformability according to claim 1 , further comprising:
one type or two or more types of, in mass %,
Ti: not less than 0.001% nor more than 0.20%,
Nb: not less than 0.001% nor more than 0.20%,
V: not less than 0.001% nor more than 1.0%, and
W: not less than 0.001% nor more than 1.0%.
4. The high-strength cold-rolled steel sheet having excellent local deformability according to claim 1 , further comprising:
one type or two or more types of, in mass %,
B: not less than 0.0001% nor more than 0.0050%,
Mo: not less than 0.001% nor more than 1.0%,
Cr: not less than 0.001% nor more than 2.0%,
Cu: not less than 0.001% nor more than 2.0%,
Ni: not less than 0.001% nor more than 2.0%,
Co: not less than 0.0001% nor more than 1.0%,
Sn: not less than 0.0001% nor more than 0.2%,
Zr: not less than 0.0001% nor more than 0.2%, and
As: not less than 0.0001% nor more than 0.50%.
5. The high-strength cold-rolled steel sheet having excellent local deformability according to claim 1 , further comprising:
one type or two or more types of, in mass %,
Mg: not less than 0.0001% nor more than 0.010%,
REM: not less than 0.0001% nor more than 0.1%, and
Ca: not less than 0.0001% nor more than 0.010%.
6. The high-strength cold-rolled steel sheet having excellent local deformability according to claim 1 , wherein
on the surface, a hot-dip galvanized layer or an alloyed hot-dip galvanized layer is provided.