HIGH STRENGTH COLD ROLLED STEEL SHEET EXCELLENT IN DEEP DRAWABILITY, CHEMICAL CONVERSION TREATING PROPERTY, SECONDARY WORKING BRITTLENESS RESISTANCE, AND SPOT WELDABILITY AND ITS PRODUCTION

摘要

PURPOSE:To produce a cold rolled high strength steel sheet excellent in deep drawability, chemical conversion treating property, secondary working brittleness resistance, and spot weldability by preparing a cold rolled sheet of a steel having a specific composition in which respective contents of Si, Ni, B, P, Al, etc., are specified. CONSTITUTION:A cold rolled sheet of a steel having a composition consisting of, by weight, 0.0005-0.0050% C, 0.30-1.20% Si, 0.05-0.30% Mn, 0.02-0.20% Ni, Ti in an amount of 0.010-0.30% expressed in terms of effective Ti computed by [effective Ti (%)]=Ti(%)-48/32S(%)-48/14N(%), 0.0003-O.0020% B, 0.040-0.150% P, 0.060-0.150% Al, =0.010% S, =0.0040% Ni, and the balance iron with inevitable impurities is prepared. By this method, the cold rolled high strength steel sheet having =about 40kgf/mm2 tensile strength can be obtained.