PRODUCTION OF COATING/BAKING HAREDENING TYPE COLD ROLLED STEEL SHEET EXCELLENT IN STRAIN AGING RESISTANCE

摘要

PROBLEM TO BE SOLVED: To obtain a coating/baking hardening type cold rolled steel sheet excellent in aging resistance, to a steel stock having a specified compsn. in which the contents of C, Ti, N and S and the heating temp. are specified, by specifying the finishing temp. in finish rolling, the coiling temp., the draft in cold rolling and the recrystallization annealing temp. ;SOLUTION: A steel stock having a compsn. contg., by weight, 0.0007 to 0.0050% C, ≤0.5% Si, ≤2.0% Mn, ≤0.10% P, ≤0.008% S, 0.01 to 0.20% Al, ≤0.01% N and 0.005 to 0.08% Ti, in which the contents of C, Ti, N and S also satisfy the formula I, and the balance Fe with inevitable impurities is prepd. This steel stock is subjected to hot rolling in which it is heated to a temp. TSR satisfying the formula II [S: the content (ppm) of sulfur and TSR: the heating temp. (°C) of the steel stock], after that, finish rolling is finished at 960 to 650°C, and it is coiled in the range of 750 to 400°C coiling temp., and this hot rolled sheet is subjected to cold rolling at 50 to 95% draft and is thereafter subjected to recrystallization annealing at 700 to 920°C to produce the coating/baking hardening type cold rolled steel sheet.;COPYRIGHT: (C)1998,JPO