HIGH-STRENGTH COLD-ROLLED STEEL SHEET EXCELLENT IN STRETCH-FLANGE FORMABILITY AND IMPACT ENERGY ABSORPTION CHARACTERISTIC AND ITS PRODUCTION METHOD

摘要

PROBLEM TO BE SOLVED: To provide a high-strength cold-rolled steel sheet excellent in stretch-flange formability and impact energy absorption characteristic, and a production method thereof.;SOLUTION: The high-strength cold-rolled steel sheet comprises, by mass%, 0.05-0.14% C, ≥0.001% and 0.60% Si, ≥1.3% and 1.9% Mn, ≥0.001% and 0.03% P, 0.0001-0.01% S, 0.010% Al, ≥0.0005% and 0.0040% N, 0.014-0.032% Nb, ≥0.009% and 0.025% Ti, 0.002-0.011% O and the balance being Fe and unavoidable impurities and has a structure essentially comprising ferrite and pearlite and/or iron carbide. The steel sheet contains ≥90 pieces of Nb-containing compounds with a particle size of 1-20 nm per 1 mm², has a tensile strength TS of ≥490 MPa and 720 MPa and has a yield ratio of 0.70 and 0.92.;COPYRIGHT: (C)2008,JPO&INPIT