Patent ID: 11946112
Assignee: JFE STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC C

Claim 0:
1. A high-strength steel sheet, the high-strength steel sheet having a chemical composition containing, in mass %,
C: 0.10 to 0.35%,
Si: 0.01 to 2.0%,
Mn: 1.5 to less than 2.2%,
P: 0.015% or less (and greater than 0%),
S: 0.0015% or less (and greater than 0%),
Sol. Al: 0.01 to 1.0%,
N: 0.0055% or less (and greater than 0%),
O: 0.0025% or less (and greater than 0%), and
Ca: 0.0005% or less (and 0% or greater), with a balance of Fe and incidental impurities, wherein
in a region within 100 μm of a surface of the high-strength steel sheet in a sheet thickness direction, a degree of Mn segregation is 1.5 or less,
in a region within 100 μm of the surface in the sheet thickness direction, a maximum P concentration is 0.08 mass % or less,
in a region within 100 μm of the surface in the sheet thickness direction, at least one MnS particle group formed of one or more MnS particles having a major axis of 0.3 μm or greater is present, the one or more MnS particles being elongated and/or distributed in a form of a sequence of dots in a rolling direction of the steel sheet, a distance between adjacent MnS particles being 40 μm or less in a case where the at least one MnS particle group is formed of two or more MnS particles, and a number of MnS particle groups having a longitudinal dimension of 150 μm or greater is 2.0 or fewer per 1 mm2, as viewed in a cross section in a sheet thickness direction and parallel to the rolling direction,
in a region within 100 μm of the surface in the sheet thickness direction, a number of oxide-based inclusions having a particle diameter of 5 μm or greater is 8 or fewer per 1 mm2 as viewed in a plane parallel to a sheet surface,
of all the number of the oxide-based inclusions having a particle diameter of 5 μm or greater, oxide-based inclusions having a composition in which an alumina content is 50 mass % or greater, a silica content is 20 mass % or less, and a calcia content is 40 mass % or less are present in the number ratio of 80% or greater,
the high-strength steel sheet has a microstructure that includes, in terms of a volume fraction, 30 to 95% martensite, 5 to 70% ferrite phase, less than 30% (and 0% or greater) bainite, and less than 2.0% (and 0% or greater) austenite phase, and
the high-strength steel sheet has a tensile strength of 980 MPa or greater.