Patent ID: 11898230
Assignee: JFE STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A high-strength steel sheet comprising: a chemical composition containing, in mass %,
C: 0.13% or more and less than 0.40%,
Si: 0.01% or more and 1.0% or less,
Mn: 1.7% or less (excluding 0%),
P: 0.030% or less,
S: 0.010% or less,
Al: 0.20% or less (excluding 0%),
N: 0.010% or less, and the balance being Fe and incidental impurities; and
a steel structure in which a total area fraction of martensite and bainite in a position of ¼ of a sheet thickness is 95% or more and 100% or less, the balance in a case where the total area fraction is not 100% contains retained austenite, and an area fraction of ferrite in a region extending up to 10 μm in a sheet thickness direction from a surface is 13% or more and 40% or less,
wherein a tensile strength is 1320 MPa or more, and
a Vickers hardness in a position of 15 μm in the sheet thickness direction from the surface satisfies a formula (1) below,

Hv≥0.294×σ  (1)

where Hv represents a Vickers hardness in the position of 15 μm in the sheet thickness direction from the surface, and a represents a tensile strength (MPa).