HIGH-STRENGTH COLD-ROLLED STEEL SHEET WHICH IS EXCELLENT IN WORKABILITY AND STRAIN AGE-HARDENING PROPERTY, HIGH-STRENGTH PLATED STEEL SHEET AND THEIR PRODUCTION METHODS

PROBLEM TO BE SOLVED: To provide high-strength cold-rolled steel sheet which has a high workability, is excellent in strain age-hardening property and shows little aging degradation at room temperature, and high-strength plated steel sheet. SOLUTION: Steel slab comprising, by mass, ≤0.015% C, ≤0.5% Si, 1.0-3.5% Mn, ≤0.10% P, ≤0.003% S, ≤0.02% Al and 0.0050-0.025% N is heated to ≥1,000°C, thereafter subjected to hot rolling employing a finishing mill exit temperature of ≥800°C, coiled at ≤650°C, thereafter subjected to cold rolling, subsequently subjected to continuous annealing at a temperature which is ≤950°C and yields ≥50% austenitic phase, cooled to ≤500°C at a cooling rate of ≥20°C/s and, if required, further subjected to plating treatment. COPYRIGHT: (C)2004,JPO&NCIPI