Patent ID: 8864922

Claim:
A method for manufacturing a precipitation-hardening cold-rolled steel sheet, comprising: hot rolling a steel slab with finish rolling at a temperature of Ar3 transformation point or more to form a hot-rolled steel sheet, the steel slab comprising, by weight %: C: 0.07-0.10%, Mn: 1.41-1.70%, P: 0.05-0.07%, S: 0.005% or less, N: 0.005% or less, acid-soluble Al: 0.10-0.15%, Nb: 0.06-0.09%, B: 0.0008-0.0012%, Sb: 0.02-0.06%, and the balance comprising Fe and other unavoidable impurities; cold rolling the hot-rolled steel sheet at a reduction ratio of 50% or more; and recovery-recrystallization annealing the cold-rolled steel sheet at a line speed of 150-200 mpm and at a temperature of 780-820° C. in a continuous annealing furnace, wherein a yield ratio of the cold-rolled steel sheet is 85% or more.