Steel sheet

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

• C:
• 0.18% to 0.35%,
• Si:
• 0.01% to 1.00%,
• Mn:
• 0.10% to 2.40%,
• P:
• 0.050% or less,
• S:
• 0.0050% or less,
• Al:
• 0.001% to 1.00%,
• Ti:
• 0.001% to 0.050%,
• B:
• 0.0005% to 0.0050%,
• N:
• 0.0100% or less,
• O:
• 0.0050% or less,
• Cr:
• 0% to 1.00%,
• Mo:
• 0% to 0.50%,
• Cu:
• 0% to 0.50%,
• Ni:
• 0% to 0.50%,
• Co:
• 0% to 0.50%,
• W:
• 0% to 0.50%,
• Sn:
• 0% to 0.50%,
• Sb:
• 0% to 0.50%,
• Nb:
• 0% to 0.050%,
• V:
• 0% to 0.50%,
• Ca:
• 0% to 0.0100%,
• Mg:
• 0% to 0.0100%,
• Ce:
• 0% to 0.0100%,
• Zr:
• 0% to 0.0100%,
• La:
• 0% to 0.0100%,
• Hf:
• 0% to 0.0100%,
• Bi:
• 0% to 0.0100%,
• REM:
• 0% to 0.0100%, and
• a balance consisting of Fe and impurities, and
• that satisfies the Formula:
• 0.001≤Ti−(47.88/14.01)×N≤0.040, wherein each element symbol represents mass % of the corresponding element, and
• a steel structure in a cross section in a rolling direction of a steel sheet and in a range of ⅛ thickness to ⅜ thickness centered on ¼ thickness from a surface of the steel sheet,
• that contains, in area ratio %,
• ferrite:
• 0 to 5%,
• martensite:
• 90.0 to 99.5%,
• a ratio of tempered martensite to total martensite:
• 80.0 to 100.0%, and
• retained austenite:
• 0.5 to 6.0%,
• and
• in a measurement region defined by a range of ⅛ thickness to ⅞ thickness from the surface of the steel sheet×25 mm in the cross section in the rolling direction of the steel sheet, a number density of inclusions satisfying a maximum diameter≥3 μm is 40 inclusions/mm2 or less,
• when the measurement region is divided into 100 sections obtained by dividing the measurement region into 2 sections in a thickness direction and 50 sections in a width direction, and the number density of the inclusions satisfying the maximum diameter≥3 μm in each section is calculated, the number density in a section where the number density of inclusions is in a top 10% is from 2 inclusions/mm2 to 80 inclusions/mm2,
• the following Formula (A) is satisfied, and
• a tensile strength is 1470 MPa or more:
• Vγ′/Vγ≥0.1 (A),
• wherein Vγ:
• area ratio of initial retained austenite, Vγ′:
• area ratio of retained austenite after deep cooling at −196° C.