US 11,939,642 B2
High-strength steel sheet and method for manufacturing same
Hidekazu Minami, Tokyo (JP); Yuji Tanaka, Tokyo (JP); Junya Tobata, Tokyo (JP); and Takeshi Yokota, Tokyo (JP)
Assigned to JFE STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/283,840
Filed by JFE STEEL CORPORATION, Tokyo (JP)
PCT Filed Aug. 20, 2019, PCT No. PCT/JP2019/032513
§ 371(c)(1), (2) Date Apr. 8, 2021,
PCT Pub. No. WO2020/075394, PCT Pub. Date Apr. 16, 2020.
Claims priority of application No. 2018-191618 (JP), filed on Oct. 10, 2018.
Prior Publication US 2021/0381075 A1, Dec. 9, 2021
Int. Cl. C21D 9/46 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C23C 2/02 (2006.01); C23C 2/06 (2006.01); C23C 2/12 (2006.01); C23C 2/28 (2006.01); C23G 1/00 (2006.01); C25D 3/22 (2006.01); C25D 3/44 (2006.01)
CPC C21D 9/46 (2013.01) [C21D 8/0226 (2013.01); C21D 8/0236 (2013.01); C21D 8/0273 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C23C 2/02 (2013.01); C23C 2/0224 (2022.08); C23C 2/024 (2022.08); C23C 2/06 (2013.01); C23C 2/12 (2013.01); C23C 2/28 (2013.01); C23G 1/00 (2013.01); C25D 3/22 (2013.01); C25D 3/44 (2013.01); C21D 2211/001 (2013.01); C21D 2211/008 (2013.01)] 24 Claims
 
1. A high-strength steel sheet having a tensile strength of 1,180 MPa or more, the high-strength steel sheet having a chemical composition comprising, by mass %:
C: 0.09% or more and 0.37% or less;
Si: more than 0.70% and 2.00% or less;
Mn: 2.60% or more and 3.60% or less;
P: 0.001% or more and 0.100% or less;
S: 0.0200% or less;
Al: 0.010% or more and 1.000% or less;
N: 0.0100% or less; and
the balance being Fe and incidental impurities,
wherein the steel sheet has a steel structure in which an area fraction of martensite having a C concentration in a range of more than 0.7×[% C] and less than 1.5×[% C] is 55% or more,
an area fraction of tempered martensite having a C concentration of 0.7×[% C] or less is in a range of 5% or more and 40% or less,
a ratio of a C concentration in retained austenite to a volume fraction of retained austenite is in a range of 0.05 or more and 0.40 or less, and
the martensite and the tempered martensite each have an average grain size of 5.3 μm or less, where [% C] represents the content, by mass %, of compositional element C in the steel sheet.