Steel sheet and producing method therefor

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

• C:
• 0.14 to 0.60%,
• Si:
• more than 0% to less than 3.00%,
• Al:
• more than 0% to less than 3.00%,
• Mn:
• 5.00% or less,
• P:
• 0.030% or less,
• S:
• 0.0050% or less,
• N:
• 0.015% or less,
• B:
• 0 to 0.0050%,
• Ni:
• 0 to 5.00%,
• Cu:
• 0 to 5.00%,
• Cr:
• 0 to 5.00%,
• Mo:
• 0 to 1.00%,
• W:
• 0 to 1.00%,
• Ti:
• 0 to 0.20%,
• Zr:
• 0 to 0.20%,
• Hf:
• 0 to 0.20%,
• V:
• 0 to 0.20%,
• Nb:
• 0 to 0.20%,
• Ta:
• 0 to 0.20%,
• Sc:
• 0 to 0.20%,
• Y:
• 0 to 0.20%,
• Sn:
• 0 to 0.020%,
• As:
• 0 to 0.020%,
• Sb:
• 0 to 0.020%,
• Bi:
• 0 to 0.020%,
• Mg:
• 0 to 0.005%,
• Ca:
• 0 to 0.005%, and
• REM:
• 0 to 0.005%,
• with the balance:
• Fe and impurities, and
• satisfying following formulas (i) to (v), wherein
• a value of Ms expressed by a following formula (vi) is 200 or more,
• a steel micro-structure contains, in volume %:
• martensite:
• 85% or more, and
• retained austenite:
• 15% or less,
• with the balance:
• bainite,
• an average block size of martensite and bainite:
• 3.0 μm or less,
• an average axial ratio of martensite and bainite:
• 1.0004 to 1.0100, and
• a yield stress is 1000 MPa or more:
• Si+Al≤3.00 (i)
• C×Mn 0.80 (ii)
• Mn+Ni+Cu+1.3Cr+4(Mo+W)≥0.80 (iii)
• 0.003≤Ti+Zr+Hf+V+Nb+Ta+Sc+Y≤0.20 (iv)
• Sn+As+Sb+Bi≤0.020 (v)
• Ms=546 ×exp(−1.362 x C)−11 ×Si−30 ×Mn−18 ×Ni−20 ×Cu−12×Cr −8(Mo+W) (vi)
• where symbols of elements represent contents (mass %) of the elements in the steel sheet, and in a case where an element is not contained, zero is assigned to its symbol.