PRECIPITATION STRENGTHENING TYPE-LOW YIELD RATIO HIGH TENSILE STRENGTH COLD ROLLED STEEL SHEET FOR DEEP DRAWING

摘要

PURPOSE:To combinedly provide a steel sheet with high strength by precipitation strengthening and low yield ratio without damaging its deep drawability by specifying the compsn. in a precipitation hardening type steel sheet and particularly specifying the relatioship between Ti and C, S and N. CONSTITUTION:The compsn. of a cold rolled steel sheet is constituted of, by weight, 0.02 to 0.06% C, =0.02% Si, =0.20% Mn, 0.20 to 2.O0% Ni, =0.55% Ti, 0.0005 to 0.0020% B, 0.010 to 0.100% Al, =0.050% P, =0.010% S, =0.005% and the balance Fe with inevitable impurities. Furthermore, Ti is incorporated so as to satisfy the conditions expressed by the inequality. In this way, the precipitation strengthening type-low yield ratio high tensile strength cold rolled steel sheet for deep drawing provided with deep drawability and having the properties of about =70% yield ratio and about =40kgf/mm2 tensile strength can be obtd.