	US 12,454,736 B2
	Cold-rolled steel sheet and method for manufacturing same
Takuya Nishio, Tokyo (JP); Ryosuke Nakamura, Tokyo (JP); and Masafumi Azuma, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/273,950
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Mar. 1, 2022, PCT No. PCT/JP2022/008569 § 371(c)(1), (2) Date Jul. 24, 2023, PCT Pub. No. WO2022/190959, PCT Pub. Date Sep. 15, 2022.
Claims priority of application No. 2021-038716 (JP), filed on Mar. 10, 2021.
Prior Publication US 2024/0417820 A1, Dec. 19, 2024
Int. Cl. B32B 15/00 (2006.01); B32B 15/01 (2006.01); C21D 1/18 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C21D 9/46 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/08 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/16 (2006.01); C22C 38/22 (2006.01); C22C 38/38 (2006.01); C23C 2/02 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01)

CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); C21D 1/18 (2013.01); C21D 6/001 (2013.01); C21D 6/002 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0263 (2013.01); C21D 8/0278 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/005 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/08 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/16 (2013.01); C22C 38/22 (2013.01); C22C 38/38 (2013.01); C23C 2/0224 (2022.08); C23C 2/285 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)]

15 Claims

1. A cold-rolled steel sheet comprising, as a chemical composition, by mass %:

C: 0.140% or more and 0.400% or less;

Si: 0.35% or more and 1.50% or less;

Mn: 1.30% or more and 3.50% or less;

P: 0% or more and 0.100% or less;

S: 0% or more and 0.010% or less;

Al: 0% or more and 0.100% or less;

N: 0% or more and 0.0100% or less;

Ti: 0% or more and 0.050% or less;

Nb: 0% or more and 0.050% or less;

V: 0% or more and 0.50% or less;

Cu: 0% or more and 1.00% or less;

Ni: 0% or more and 1.00% or less;

Cr: 0% or more and 1.00% or less;

Mo: 0% or more and 0.50% or less;

B: 0% or more and 0.0100% or less;

Ca: 0% or more and 0.010% or less;

Mg: 0% or more and 0.0100% or less;

REM: 0% or more and 0.050% or less;

Bi: 0% or more and 0.050% or less; and

a remainder of Fe and impurities,

wherein a metallographic structure of a t/4 portion, which is at a 1/4 position of a sheet thickness t from a surface of the cold-rolled steel sheet in a sheet thickness direction, includes, by volume percentage,

retained austenite: 2.5% or more and 10.0% or less,

tempered martensite: 80.0% or more and 97.5% or less,

ferrite and bainite: 0.0% or more and 15.0% or less in total, and

martensite: 0.0% or more and 3.0% or less, and

in a surface layer area at a position 25 μm away from the surface of the cold-rolled steel sheet in the sheet thickness direction,

an amount of solute Si is 0.30% or more and 1.50% or less by mass %,

a volume percentage of ferrite in a metallographic structure is 0.0% or more and 20.0% or less,

a density of ferrite grains having a grain size of 15 μm or more is 0 grains/mm²or more and 3,000 grains/mm²or less, and

a ratio of the amount of the solute Si in the surface layer area to an amount of solute Si in the t/4 portion is 0.85 to 1.10.