| abstract |
A high-strength cold-rolled steel sheet excellent in deep drawability and strength-ductility balance is provided. SOLUTION: In mass%, C: 0.05-0.2%, Si: 0.1-2.0%, Al: 0.005-1.5%, Mn, P, S, N are included in proper amounts, and Si + Al: 0.5-2.5% A hot-rolled coil having a composition adjusted to 1 and a structure mainly composed of bainite and martensite, a batch hot-rolled sheet annealing process for holding at least 1 h in the range of 550 ° C to Ac 1 point, a cold-rolling process, Continuous recrystallization annealing is performed by heating the steel sheet to the temperature of Ac 1 to Ac 3 at an average heating rate of Ac 1 point to (Ac 1 point + 50 ° C) of 5 ° C / s or more, and holding it for 5s or more. A recrystallization annealing step of sequentially cooling to 350 to 500 ° C. at a cooling rate of at least / s and applying an austempering treatment that maintains the temperature for 10 to 600 s is performed. Accordingly, the main phase has a composite structure composed of ferrite having a volume ratio of 70% or more and a second phase having an average particle diameter of 3 μm or less and containing at least 3% of retained austenite by volume ratio, and the r value is A high-strength cold-rolled steel sheet having a strength-ductility balance TS × EL of 22000 MPa ·% or more is 1.1 or more. [Selection figure] None |