Steel sheet, coated steel sheet, method for producing hot-rolled steel sheet, method for producing cold-rolled full hard steel sheet, method for producing heat-treated sheet, method for producing steel sheet, and method for producing coated steel sheet

A steel sheet comprising:

• a composition that contains, in terms of mass %,
• C:
• 0.03% or more and 0.20% or less,
• Si:
• 0.70% or less,
• Mn:
• 1.50% or more and 3.00% or less,
• P:
• 0.001% or more and 0.100% or less,
• S:
• 0.0001% or more and 0.0200% or less,
• Al:
• 0.001% or more and 1.000% or less,
• N:
• 0.0005% or more and 0.0100% or less, and
• the balance being Fe and unavoidable impurities;
• a steel structure containing ferrite and a secondary phase, in which an area fraction of the ferrite is 50% or more, the secondary phase contains 1.0% or more and 25.0% or less of martensite in terms of area fraction with respect to the entirety, the ferrite has an average crystal grain size of 3 μm or more, a difference in hardness between the ferrite and the martensite is 1.0 GPa or more and 8.0 GPa or less, and, in a texture of the ferrite, an inverse intensity ratio of γ-fiber to α-fiber is 0.8 or more and 7.0 or less;
• and, a tensile strength of 540 MPa or more.