HIGH STRENGTH COLD ROLLED STEEL SHEET OR HIGH STRENGTH GALVANIZED STEEL SHEET EXCELLENT IN FACIAL STRAIN RESISTANCE AND PRESS FORMABILITY AND METHOD FOR PRODUCING SAME

摘要

PROBLEM TO BE SOLVED: To obtain a high strength cold rolled steel sheet excellent in breaking resistance in composite forming such as drawing and bulging, and small in facial strain damaging the appearance after press forming and having tensile strength of ≥440 MPa. ;SOLUTION: This high strength cold rolled steel sheet excellent in facial strain resistance and press formability has a composition containing, by weight, 0.0040 to 0.010% C, ≤0.05% Si, 1.0 to 2.5% Mn, 0.02 to 0.10% P, ≤0.02% S, 0.01 to 0.1% sol.Al, ≤0.004% N, 0.01 to 0.20% Nb, and the balance Fe with inevitable impurities, moreover contains the elements in the ranges so as to satisfy the following inequality (1) and also satisfies the following inequalities (2), (3) and (4), where (1) -0.46-0.83×logC%≤(Nb%×12)/(C %×93)≤-0.88-1.66×logC%, (2) 0.35≥0.0075×YP(MPa)-r, (3) 2.2≤r+3.0×n, and (4) 9.7≤r+54.5×n, furthermore, C% and N% denote weight %, r: (r) value, and n: (n) value (1 to 5% strain).;COPYRIGHT: (C)2001,JPO