COLD ROLLED STEEL SHEET AND HOT DIPPED STEEL SHEET WITH SUPERIOR STRENGTH AND BAKE HARDENABILITY AND METHOD FOR MANUFACTURING THE STEEL SHEETS

摘要

A bake-hardenable high-strength cold-rolled steel sheet, a hot-dipped steel sheet thereof, and a method for manufacturing the same. The steel sheet comprises 0.0016~0.01% of C; 0.1% or less of Si; 0.2~1.5% of Mn; 0.05~0.15% of P; 0.01% or less of S; 0.08~0.5% of (soluble) Al; 0.0025% or less of N; 0.003~0.1% of Nb; 0.003% or less of Ti; 0.01~0.4% of Mo; 0.0005~0.005% of B; and the balance of Fe and other unavoidable impurities, in terms of weight %. The method includes the steps of heating a steel slab of the above composition to a temperature of 1,200° C. or more; and then hot rolling the steel slab with finish rolling at or above the Ar3 temperature to provide a hot rolled steel sheet; coiling the hot rolled steel sheet; cold rolling the hot rolled and coiled sheet; and continuous annealing the cold rolled sheet.