Steel sheet and method for producing same

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

• C:
• 0.20 to 0.40%,
• Si:
• 0.01 to 0.95%,
• Mn:
• 0.10 to 4.00%,
• P:
• 0.0200% or less,
• S:
• 0.0200% or less,
• Al:
• 1.000% or less,
• N:
• 0.0200% or less,
• Co:
• 0 to 0.5000%,
• Ni:
• 0 to 1.0000%,
• Mo:
• 0 to 1.0000%,
• Cr:
• 0 to 2.0000%,
• O:
• 0 to 0.0200%,
• Ti:
• 0 to 0.500%,
• B:
• 0 to 0.0100%,
• Nb:
• 0 to 0.5000%,
• V:
• 0 to 0.5000%,
• Cu:
• 0 to 0.5000%,
• W:
• 0 to 0.1000%,
• Ta:
• 0 to 0.1000%,
• Sn:
• 0 to 0.0500%,
• Sb:
• 0 to 0.0500%,
• As:
• 0 to 0.0500%,
• Mg:
• 0 to 0.0500%,
• Ca:
• 0 to 0.0500%,
• Y:
• 0 to 0.0500%,
• Zr:
• 0 to 0.0500%,
• La:
• 0 to 0.0500%,
• Ce:
• 0 to 0.0500%, and
• a balance of Fe and impurities, and
• a microstructure containing, by area ratio,
• a total of ferrite, pearlite, and bainite:
• 0 to 10.0% and
• a total of martensite and tempered martensite:
• 80.0 to 100.0%,
• wherein in a cross-sectional structure taken in a width direction perpendicular to a rolling direction,
• a block size in a first depth region of 1 to 10 μm from a surface of the steel sheet is 5.0 μm or less,
• a block size in a second depth region of 10 to 60 μm from the surface of the steel sheet is 6.0 to 20.0 μm, and
• a block size in a third depth region of 60 μm to ¼ thickness from the surface of the steel sheet is less than 6.0 μm.