Steel sheet

A steel sheet including a steel micro-structure containing, in volume fraction,

• tempered martensite:
• 85% or more, retained austenite:
• 5% or more to less than 15%, and ferrite, pearlite, bainite, and as-quenched martensite being less than 10% in total,
• a chemical composition of the steel sheet consisting of, in mass %:
• C:
• 0.18% or more to 0.38% or less,
• Si:
• 0.80% or more to 2.50% or less,
• Mn:
• 0.6% or more to 5.0% or less,
• P:
• 0.0200% or less,
• S:
• 0.0200% or less,
• N:
• 0.0200% or less,
• O:
• 0.0200% or less,
• Al:
• 0% or more to 1.000% or less,
• Cr:
• 0% or more to 2.0% or less,
• Mo:
• 0% or more to 0.50% or less,
• Ti:
• 0% or more to 0.10% or less,
• Nb:
• 0% or more to 0.10% or less,
• B:
• 0% or more to 0.0100% or less,
• V:
• 0% or more to 0.50% or less,
• Cu:
• 0% or more to 0.50% or less,
• W:
• 0% or more to 0.100% or less,
• Ta:
• 0% or more to 0.100% or less,
• Ni:
• 0% or more to 1.00% or less,
• Co:
• 0% or more to 0.50% or less,
• Sn:
• 0% or more to 0.050% or less,
• Sb:
• 0% or more to 0.050% or less,
• As:
• 0% or more to 0.050% or less,
• Mg:
• 0% or more to 0.050% or less,
• Ca:
• 0% or more to 0.050% or less,
• Y:
• 0% or more to 0.050% or less,
• Zr:
• 0% or more to 0.050% or less,
• La:
• 0% or more to 0.050% or less,
• Ce:
• 0% or more to 0.050% or less, and
• the balance:
• Fe and unavoidable impurities,
• when a content of Mn and a content of C in the retained austenite are denoted by MnA and CA, respectively, and when a content of Mn and a content of C in a matrix are denoted by MnM and CM, respectively, following Formulas (1) to (3) are satisfied, and
• when a region measuring 20000 μm2 and centered about a t/4 point (t denotes a thickness of the steel sheet) from a surface of the steel sheet is observed, the number of carbides having an equivalent circle radius of 0.1 μm or more is 100 or less, and the steel sheet has a tensile strength of 1100 MPa or more,
• MnA/MnM≥1.2 (1)
• CA/CM≤5.0 (2)
• CA≤1.0 (3).