US 12,331,379 B2
Cold-rolled steel sheet and manufacturing method thereof
Takuya Nishio, Tokyo (JP); Masafumi Azuma, Tokyo (JP); Yoshimasa Narita, Tokyo (JP); and Shintaro Okura, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/273,884
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Mar. 1, 2022, PCT No. PCT/JP2022/008567
§ 371(c)(1), (2) Date Jul. 24, 2023,
PCT Pub. No. WO2022/190958, PCT Pub. Date Sep. 15, 2022.
Claims priority of application No. 2021-038717 (JP), filed on Mar. 10, 2021.
Prior Publication US 2024/0309482 A1, Sep. 19, 2024
Int. Cl. C21D 6/00 (2006.01); B32B 15/01 (2006.01); B32B 15/04 (2006.01); B32B 15/18 (2006.01); C21D 1/18 (2006.01); C21D 1/19 (2006.01); C21D 1/25 (2006.01); C21D 1/26 (2006.01); C21D 1/74 (2006.01); C21D 1/76 (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 38/18 (2006.01); C22C 38/20 (2006.01); C22C 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C22C 38/38 (2006.01); C22C 38/40 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01); C22C 38/58 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/28 (2006.01); C23C 2/40 (2006.01); C23C 28/02 (2006.01); C23C 30/00 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (2013.01); B32B 15/04 (2013.01); B32B 15/043 (2013.01); B32B 15/18 (2013.01); C21D 1/18 (2013.01); C21D 1/19 (2013.01); C21D 1/25 (2013.01); C21D 1/26 (2013.01); C21D 1/74 (2013.01); C21D 1/76 (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 8/0242 (2013.01); C21D 8/0263 (2013.01); C21D 8/0273 (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 38/18 (2013.01); C22C 38/20 (2013.01); C22C 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/38 (2013.01); C22C 38/40 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C22C 38/58 (2013.01); C23C 2/022 (2022.08); C23C 2/0224 (2022.08); C23C 2/06 (2013.01); C23C 2/28 (2013.01); C23C 2/285 (2013.01); C23C 2/29 (2022.08); C23C 2/40 (2013.01); C23C 28/025 (2013.01); C23C 30/00 (2013.01); C23C 30/005 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); Y10T 428/12799 (2015.01); Y10T 428/12951 (2015.01); Y10T 428/12972 (2015.01)] 18 Claims
 
1. A cold-rolled steel sheet comprising, as a chemical composition, by mass %:
C: 0.180% or more and 0.350% or less;
Mn: 2.00% or more and 4.00% 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;
Si: 0% or more and 1.00% 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 0.0500% 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 ¼ position of a sheet thickness t from a surface of the cold-rolled steel sheet in a sheet thickness direction, in a longitudinal section parallel to a rolling direction of a center portion, which is a center position in a width direction, includes, by volume percentage,
retained austenite: 2.0% or more and 8.0% or less,
tempered martensite: 80.0% or more and 98.0% or less,
ferrite and bainite: 0.0% or more and 15.0% or less in total, and
martensite: 0.0% or more and 5.0% or less, and
in both a longitudinal section of an edge portion, which is at a position 50 mm away from an end portion of the cold-rolled steel sheet in a width direction, and the longitudinal section of the center portion of the cold-rolled steel sheet in the width direction,
a metallographic structure of a 20 μm portion, which is at a position 20 μm away from the surface in the sheet thickness direction, includes, by volume percentage,
ferrite and bainite: 75.0% or more and 100.0% or less in total, and
martensite and tempered martensite: 0.0% or more and 25.0% or less in total,
an average grain size of the martensite and the tempered martensite, when either is present or both are present, in the metallographic structure of each of the 20 μm portions is 5.0 μm or less, and
a metallographic structure of a 75 μm portion, which is at a position 75 μm away from the surface in the sheet thickness direction, in the longitudinal sections of each of the center portion and the edge portion, includes, by volume percentage,
ferrite and bainite: 0.0% or more and 15.0% or less in total.