Steel sheet, member, method of producing steel sheet, and method of producing member

A steel sheet comprising:

• a chemical composition containing, in mass %,
• C:
• 0.09% or more and 0.20% or less,
• Si:
• 0.3% or more and 1.5% or less,
• Mn:
• 1.5% or more and 3.0% or less,
• P:
• 0.001% or more and 0.100% or less,
• S:
• 0.050% or less,
• Al:
• 0.005% or more and 1.000% or less, and
• N:
• 0.010% or less,
• with the balance being Fe and inevitable impurities;
• the steel microstructure comprising:
• area ratio of ferrite:
• 5% or more and 65% or less,
• area ratio of martensite:
• 10% or more and 60% or less,
• area ratio of bainite:
• 10% or more and 60% or less, and
• area ratio of retained austenite:
• 5% or more, wherein
• Formula (1) is satisfied,
• average solute C concentration of the retained austenite [C]γ is 0.5 mass % or more, and standard deviation of C concentration distribution in the retained austenite is 0.250 mass % or less, and
• the steel sheet has a tensile strength of 780 MPa or more,
• [
• Mn
• ]
• γ
• ⁢
• /
• [
• Mn
• ]
• ≤
• 1.2
• (
• 1
• )
• wherein
• [Mn]γ is Mn concentration, in mass %, in retained austenite, and
• [Mn] is Mn content, in mass %, in the chemical composition of the steel sheet.