High-strength steel sheet and method for producing same

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:
• 2.2 to 3.5%,
• P:
• 0.003% to 0.015%,
• 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 and bainite in total, 5 to 70% ferrite phase, and less than 3% (and 0% or greater) austenite phase, and
• the high-strength steel sheet has a tensile strength of 980 MPa or greater.