Patent ID: 11939642
Assignee: JFE STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
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.