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 steel sheet, method for producing steel sheet, and method for producing coated steel sheet

A method for producing a hot-rolled steel sheet, the method comprising:

• heating a steel slab having a composition that contains, in terms of mass %
• C:
• 0.048% or more and 0.200% or less,
• Si:
• 0.40% 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;
• rough-rolling the heated steel slab;
• in subsequent finish-rolling, hot-rolling the rough-rolled steel slab under conditions of a finish-rolling inlet temperature of 1060° C. or higher and 1180° C. or lower, a rolling reduction in a final pass of the finish rolling of 5% or more and 15% or less, a rolling reduction in a pass before the final pass of 15% or more and 25% or less, and a finish-rolling delivery temperature of 800° C. or higher and 1000° C. or lower;
• after the hot-rolling, cooling the hot-rolled steel sheet under a condition of an average cooling rate of 5° C./s or more and 90° C./s or less;
• and coiling the cooled steel sheet under a condition of a coiling temperature of 300° C. or higher and 700° C. or lower;
• heating the coiled steel sheet under conditions of a maximum attained temperature of a T1 temperature or higher and a T2 temperature or lower and an average heating rate of 50° C./s or less in a temperature range of 450° C. to [T1 temperature−10° C.], wherein the T1 temperature is 770° C. and the T2 temperature is 855° C.;
• and
• after the heating, performing cooling and pickling to produce a product having a microstructure containing, in terms of area fraction, 20% or more of ferrite and 7% or more of martensite.