High-strength steel sheet and method for manufacturing same

A high-strength steel sheet comprising:

• a component composition including:
• by mass %, C:
• 0.030% to 0.250%;
• Si:
• 0.01% to 3.00%;
• Mn:
• 3.10% to 4.20%;
• P:
• 0.001% to 0.100%;
• S:
• 0.0001% to 0.0200%;
• N:
• 0.0005% to 0.0100%;
• Al:
• 0.001% to 1.200%;
• and balance Fe and inevitable impurities;
• and
• a steel structure with:
• ferrite being 35% to 80%, martensite being 5% to 35%, and tempered martensite being 0.1% to 5% in terms of area fraction;
• retained austenite being 8% or more in terms of volume fraction and 60% or less in terms of area fraction;
• an average grain size of the ferrite being 6 μm or less;
• an average grain size of the retained austenite being 3 μm or less;
• a value obtained by dividing an area fraction of blocky austenite by a sum of area fractions of lath-like austenite and the blocky austenite being 0.6 or more;
• a value obtained by dividing an average Mn content, by mass %, in the retained austenite by an average Mn content, by mass %, in the ferrite being 1.5 or more;
• and
• a value obtained by dividing an average C content, by mass %, in the retained austenite by an average C content, by mass %, in the ferrite being 3.0 or more, wherein the high-strength steel sheet has a tensile strength of 980 MPa or more.