Steel sheet, member, and methods for producing the same

A steel sheet comprising a base steel sheet, wherein the base steel sheet has a chemical composition containing, on a mass percent basis,

• C:
• 0.050% or more and 0.400% or less,
• Si:
• 0.20% or more and 3.00% or less,
• Mn:
• 1.00% or more and less than 3.50%,
• P:
• 0.001% or more and 0.100% or less,
• S:
• 0.0001% or more and 0.0200% or less,
• Al:
• 0.010% or more and 2.000% or less, and
• N:
• 0.0100% or less,
• with the remainder being Fe and incidental impurities, and
• has a steel microstructure, as a microstructure at a quarter thickness position of the base steel sheet, in which
• an area fraction of ferrite:
• less than 20.0% (including 0.0%),
• an area fraction of retained austenite:
• 3.0% or more and 15.0% or less,
• an area fraction of fresh martensite:
• 10.0% or less (including 0.0%),
• a total area fraction of bainitic ferrite and tempered martensite:
• 45.0% or more and 90.0% or less, and
• a grain boundary length LF-MA in contact with fresh martensite and/or retained austenite on a ferrite grain boundary and a grain boundary length LF of ferrite satisfy LF-MA/LF:
• 0.70 or less,
• the steel sheet has a surface soft layer formed from a surface of the base steel sheet to a depth of 20 μm or more in a thickness direction, wherein for the steel microstructure, a total area fraction of a non-ferrite microstructure in the surface soft layer is ½ or less of that at the quarter thickness position, and
• the steel sheet has a tensile strength of 1180 MPa or more and less than 1470 MPa.