Steel sheet, member, and methods for manufacturing same

A steel sheet having a chemical composition comprising, in mass %:

• C:
• 0.06 to 0.25%,
• Si:
• 0.4 to 2.5%,
• Mn:
• 1.5 to 3.5%,
• P:
• 0.02% or less,
• S:
• 0.01% or less,
• sol. Al:
• less than 1.0%,
• N:
• less than 0.015%,
• and optionally,
• one or two or more selected from the following groups A to C:
• group A:
• one or two selected from:
• Ti:
• 0.1% or less, and
• B:
• 0.01% or less,
• group B:
• one, or two or more selected from:
• Cu:
• 1% or less,
• Ni:
• 1% or less,
• Cr:
• 1.0% or less,
• Mo:
• 0.5% or less,
• V:
• 0.5% or less,
• Nb:
• 0.1% or less,
• Zr:
• 0.2% or less, and
• W:
• 0.2% or less,
• group C:
• one, or two or more selected from:
• Ca:
• 0.0040% or less,
• Ce:
• 0.0040% or less,
• La:
• 0.0040% or less,
• Mg:
• 0.0030% or less,
• Sb:
• 0.1% or less, and
• Sn:
• 0.1% or less,
• the balance being Fe and incidental impurities,
• the steel sheet being such that:
• the steel sheet comprises a steel microstructure including, in area fraction,
• polygonal ferrite:
• 10% or less,
• tempered martensite:
• 40% or more,
• fresh martensite:
• 20% or less,
• bainitic ferrite having 20 or less internal carbides per 10 μm2:
• 3 to 40%, and, in volume fraction,
• retained austenite:
• 5 to 20%, and
• the steel sheet has a proportion SC≥0.5/SC≥0.3×100 of 20% or more wherein SC≥0.5 is the area of a region having a C concentration, in mass %, of 0.50% or more and SC≥0.3 is the area of a region having a C concentration, in mass %, of 0.30% or more.