High-strength steel sheet and production method therefor

A high-strength steel sheet comprising:

• a chemical composition that contains, by mass %, C:
• 0.060% or more and 0.200% or less, Si:
• 0.50% or more and 2.20% or less, Mn:
• 1.00% or more and 3.00% or less, P:
• 0.100% or less, S:
• 0.0100% or less, Al:
• 0.010% or more and 2.500% or less, N:
• 0.0100% or less, either or both Ti:
• 0.001% or more and 0.200% or less and Nb:
• 0.001% or more and 0.200% or less, and
• at least one selected from groups (a) to (e):
• (a) at least one selected from Cr:
• 0.05% or more and 1.00% or less, Mo:
• 0.05% or more and 1.00% or less, Ni:
• 0.05% or more and 1.00% or less, and Cu:
• 0.05% or more and 1.00% or less;
• (b) B:
• 0.0003% or more and 0.0050% or less;
• (c) at least one selected from Ca:
• 0.0010% or more and 0.0050% or less, Mg:
• 0.0005% or more and 0.0100% or less, and REM:
• 0.0003% or more and 0.0050% or less;
• (d) at least one selected from Sn:
• 0.0020% or more and 0.2000% or less and Sb:
• 0.0020% or more and 0.2000% or less;
• and
• (e) Ta:
• 0.0010% or more and 0.1000% or less;
• and
• the balance consisting of Fe and incidental impurities, the chemical composition satisfying a relation of 500≤C*≤1300, where C* is determined by any one of formula (1) to (4) given below;
• and
• a microstructure that contains ferrite in an area ratio of 20% or more, martensite in an area ratio of 7% or more, and tempered martensite in an area ratio of 5% or more, the ferrite having a mean grain size of 20.0 μm or less, and an inverse intensity ratio of γ-fiber to α-fiber in the ferrite being 1.00 or more and an inverse intensity ratio of γ-fiber to α-fiber in the martensite and the tempered martensite being 1.00 or more:
• in the case of the chemical composition containing only Ti from among Ti and Nb, or both Ti and Nb, and not containing Ta,
• C*=(C−(12.0/47.9)×(Ti−(47.9/14.0)×N−(47.9/32.1)×S)−(12.0/92.9)×Nb)×10000 (1),
• in the case of the chemical composition containing only Nb from among Ti and Nb and, not containing Ta,
• C=(C−(12.0/92.9)×Nb)×1000 (2),
• in the case of the chemical composition containing only Ti from among Ti and Nb, or both Ti and Nb, and containing Ta,
• C*=(C−(12.0/47.9)×(Ti−(47.9/14.0)×N−(47.9/32.1)×S)−(12.0/92.9)×Nb−(12.0/180.9)×Ta)×10000 (3), or
• in the case of the chemical composition containing only Nb from among Ti and Nb, and containing Ta,
• C*=(C−(12.0/92.9)×Nb−(12.0/180.9)×Ta)×10000 (4),
• where each of the element symbols C, N, S, Ti, Nb, and Ta indicates content by mass % of the corresponding element in the steel sheet, and the unit of C* is mass ppm.