Steel sheet and method for producing same

A steel sheet having a chemical composition comprising, by mass %,

• C:
• 0.15 to 0.30%,
• Si:
• 0.30 to 1.50%,
• Mn:
• 1.40 to 3.49%,
• P:
• 0.050% or less,
• S:
• 0.0100% or less,
• Al:
• 0.30 to 1.50%,
• Ti:
• 0.001 to 0.100%,
• N:
• 0.0100% or less,
• O:
• 0.0100% or less,
• Cr:
• 0 to 1.00%,
• Mo:
• 0 to 1.00%,
• Cu:
• 0 to 1.00%,
• Ni:
• 0 to 1.00%,
• Co:
• 0 to 1.00%,
• W:
• 0 to 1.00%,
• Sn:
• 0 to 1.00%,
• Sb:
• 0 to 0.50%,
• Nb:
• 0 to 0.200%,
• V:
• 0 to 1.00%,
• B:
• 0 to 0.0050%,
• Ca:
• 0 to 0.0100%,
• Mg:
• 0 to 0.0100%,
• Ce:
• 0 to 0.0150%,
• Zr:
• 0 to 0.0100%,
• La:
• 0 to 0.0150%,
• Hf:
• 0 to 0.0100%,
• Bi:
• 0 to 0.0100%,
• REM other than Ce and La:
• 0 to 0.0100%, and
• balance:
• Fe and impurities, and
• a steel microstructure in a range of ⅛ thickness to ⅜ thickness centered on ¼ thickness from the surface comprising, by vol %,
• ferrite:
• 1 to 50%,
• ratio of nonrecrystallized ferrite in the ferrite:
• 0 to 50%,
• tempered martensite:
• 1% or more,
• retained austenite:
• 5% or more,
• fresh martensite:
• 0 to 10%,
• total of pearlite and cementite:
• 0 to 5%, and
• balance:
• bainite, and
• when analyzing the surface by an EPMA, an area ratio of regions with an AlS/SiS ratio of 0.2 or less is 50% or less, and a tensile strength is 980 MPa or more,
• where AlS is a surface Al concentration (mass %), and SiS is a surface Si concentration (mass %).