COLD ROLLED STEEL SHEET EXCELLENT IN FORMABILITY, PANEL SHAPE CHARACTERISTIC, AND DENT RESISTANCE, HOT DIP GALVANIZED STEEL SHEET, AND THEIR MANUFACTURE

摘要

PROBLEM TO BE SOLVED: To provide a method of manufacturing a cold rolled steel sheet combining excellent steel sheet surface characteristic, natural aging resistance, and panel dent resistance which are all required of a steel sheet for automobile outer sheet, a hot dip galvanized steel sheet, and their manufacture. ;SOLUTION: The cold rolled steel sheet excellent in formability, panel shape characteristic, and dent resistance has a steel composition consisting of, by weight, 0.005-0.015% C, 0.01-0.2% Si, 0.2-1.5% Mn, 0.01-0.07% P, 0.006-0.015% S, 0.01-0.08% sol.Al, 0.004% N, 0.003% O, 0.04-0.23% Nb, and the balance essentially Fe with inevitable impurities and satisfying 1.0≤(Nb%×12)/(C%×93)≤3.0 and also satisfies expression exp(ε)(5.29 exp(ε)-4.19)≤σ/σ_0.2 exp(ε) (5.64 exp(ε)-4.49)) [where 0.002ε 0.096 is satisfied and the symbols (ε), (σ_0.2), and (σ) represent true strain, 0.2% proof stress, and true stress to (ε), respectively.;COPYRIGHT: (C)1999,JPO