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:
• 0.05% to 0.30%,
• Si:
• 0.10% to 2.00%,
• Mn:
• 1.00% to 3.50%,
• P:
• 0.001% to 0.100%,
• S:
• 0.0001% to 0.0200%,
• sol. Al:
• 0.005% to 2.000%, and
• N:
• 0.010% or less,
• with the remainder being Fe and incidental impurities, and
• has a steel microstructure, in which area fractions at a quarter thickness position of the base steel sheet are
• ferrite:
• 20.0% or more and 70.0% or less,
• a total of bainitic ferrite and tempered martensite:
• 20.0% or more and 70.0% or less,
• retained austenite:
• 3.0% or more and 20.0% or less, and
• fresh martensite:
• 20.0% or less (including 0.0%),
• an area fraction of the bainitic ferrite is 40% or more of a total area fraction of the bainitic ferrite and the tempered martensite, and
• a hard second phase present in the bainitic ferrite and containing the retained austenite and the fresh martensite has an average grain size of 3.0 μm 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 780 MPa or more and less than 1180 MPa.