Cold-rolled steel sheet
View Patent ↗A cold-rolled steel sheet satisfies that an average pole density of an orientation group of {100}<011> to {223}<110> is 1.0 to 5.0, a pole density of a crystal orientation {332}<113> is 1.0 to 4.0, a Lankford-value rC in a direction perpendicular to a rolling direction is 0.70 to 1.50, and a Lankford-value r30 in a direction making an angle of 30° with the rolling direction is 0.70 to 1.50. Moreover, the cold-rolled steel sheet includes, as a metallographic structure, by area %, a ferrite and a bainite of 30% to 99% in total and a martensite of 1% to 70%.
1. A cold-rolled steel sheet treated via an annealing processing line, the cold-rolled steel sheet comprising, as a chemical composition, by mass %,
C: 0.01% to 0.4%,
Si: 0.001% to 2.5%,
Mn: 0.001% to 4.0%,
Al: 0.001% to 2.0%,
P: limited to 0.15% or less,
S: limited to 0.03% or less,
N: limited to 0.01% or less,
O: limited to 0.01% or less, and
a balance consisting of Fe and unavoidable impurities,
wherein: an average pole density of an orientation group of {100}<011> to {223}<110>, which is a pole density represented by an arithmetic average of pole densities of each crystal orientation {100}<011>, {116}<110>, {114}<110>, {112}<110>, and {223}<110>, is 1.0 to 5.0 and a pole density of a crystal orientation {332}<113> is 1.0 to 4.0 in a thickness central portion which is a thickness range of ⅝ to ⅜ based on a surface of the steel sheet;
a Lankford-value rC in a direction perpendicular to a rolling direction is 0.70 to 1.50 and a Lankford-value r30 in a direction making an angle of 30° with the rolling direction is 0.70 to 1.50; and
the steel sheet includes, as a metallographic structure, plural grains, and includes, by area %, a ferrite and a bainite of 30% to 99% in total and a martensite of 1% to 70%.
2. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 , further comprising, as the chemical composition, by mass %, at least one selected from the group consisting of
Ti: 0.001% to 0.2%,
Nb: 0.001% to 0.2%,
B: 0.0001% to 0.005%,
Mg: 0.0001% to 0.01%,
Rare Earth Metal: 0.0001% to 0.1%,
Ca: 0.0001% to 0.01%,
Mo: 0.001% to 1.0%,
Cr: 0.001% to 2.0%,
V: 0.001% to 1.0%,
Ni: 0.001% to 2.0%,
Cu: 0.001% to 2.0%,
Zr: 0.0001% to 0.2%,
W: 0.001% to 1.0%,
As: 0.0001% to 0.5%,
Co: 0.0001% to 1.0%,
Sn: 0.0001% to 0.2%,
Pb: 0.0001% to 0.2%,
Y: 0.001% to 0.2%, and
Hf: 0.001% to 0.2%.
3. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein a volume average diameter of the grains is 5 μm to 30 μm.
4. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein the average pole density of the orientation group of {100}<011> to {223}<110> is 1.0 to 4.0, and the pole density of the crystal orientation {332}<113> is 1.0 to 3.0.
5. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein a Lankford-value rL in the rolling direction is 0.70 to 1.50, and a Lankford-value r60 in a direction making an angle of 60° with the rolling direction is 0.70 to 1.50.
6. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein an area fraction of the martensite is defined as fM in unit of area %, an average grain size of the martensite is defined as dia in unit of μm, an average distance between the martensite grains is defined as dis in unit of μm, and a tensile strength of the steel sheet is defined as TS in unit of MPa, a following Expression 1 and a following Expression 2 are satisfied,
dia≦13 μm (Expression 1),
TS/ fM ×dis/dia≧500 (Expression 2).
7. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein an area fraction of the martensite is defined as fM in unit of area %, a major axis of the martensite grain is defined as La, and a minor axis of the martensite grain is defined as Lb, an area fraction of the martensite satisfying a following Expression 3 is 50% to 100% as compared with the area fraction fM of the martensite,
La/Lb≦ 5.0 (Expression 3).
8. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein the steel sheet includes, as the metallographic structure, by area %, the bainite of 5% to 80%.
9. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein the steel sheet includes a tempered martensite in the martensite.
10. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein an area fraction of coarse grain having grain size of more than 35 μm is 0% to 10% among the grains in the metallographic structure of the steel sheet.
11. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein, when a hardness of the ferrite or the bainite which is a primary phase is measured at 100 points or more, a value dividing a standard deviation of the hardness by an average of the hardness is 0.2 or less.
12. The cold-rolled steel sheet treated via an annealing processing line according to claim 1 or 2 ,
wherein a galvanized layer or a galvannealed layer is arranged on the surface of the steel sheet.