High-strength cold-rolled steel sheet with high yield ratio having excellent formability and method for producing the same

A method for producing a high-strength cold-rolled steel sheet with high yield ratio having excellent formability, the method comprising:

• hot-rolling a steel slab having a chemical composition containing 0.05% to 0.15% C, 0.10% to 0.90% Si, 1.0% to 2.0% Mn, 0.005% to 0.05% P, 0.0050% or less S, 0.01% to 0.10% Al, 0.0050% or less N, and 0.010% to 0.100% Nb, on a mass basis, the balance being Fe and unavoidable impurities, at a hot-rolling start temperature of 1,150° C. to 1,270° C. and a finishing delivery temperature of 830° C. to 950° C. to manufacture a hot-rolled steel sheet;
• cooling the hot-rolled steel sheet;
• then coiling the hot-rolled steel sheet in a temperature range of 450° C. to 650° C.;
• pickling the hot-rolled steel sheet;
• then cold rolling the hot-rolled steel sheet into a cold-rolled steel sheet;
• then annealing the cold-rolled steel sheet, wherein heating is performed to a first heating temperature in a temperature range of 710° C. to 820° C. at a first average heating rate of 3° C./s to 30° C./s,
• soaking is performed at the first heating temperature for a soaking time of 30 s to 300 s,
• then cooling is performed to a first cooling temperature in a temperature range of 400° C. to 600° C. at a first average cooling rate of 3° C./s to 25° C./s, and
• then cooling is performed from the first cooling temperature to a room temperature at a second average cooling rate of 3° C./s or less;
• and
• then temper-rolling the cold-rolled steel sheet with an elongation of 0.3% to 2.0%.