PURPOSE: To develop a cold rolled steel sheet excellent in baking hardenability at low baking finish temp. by subjecting a dead soft carbon steel containing specific amount of B and 0 to hot rolling and cold rolling.
CONSTITUTION: This cold rolled steel sheet is produced by subjecting a continuously cast slab, having a composition containing, by weight, 0.001-0.005% C, <0.3% Si, 0.1-2% Mn, <0.1% P, <0.015% S, 0.005-0.1% sol.Al, <0.0O4% N, (48/14)N to [(48/14)N+(48/32)S +16C]% Ti, 0.0003-0.0015% B, and 0.0005-0.003% O (where B≥0.5×O-0.0005 is satisfied), to hot rolling, cold rolling, and annealing. By this method, the cold rolled steel sheet, in which the low temp. baking hardenability of the steel sheet at 100°C is regulated to ≥35Mpa and also the difference in baking hardenability between the above baking hardenability and the low temp. baking hardenability of the steel sheet at 170°C is regulated to ≤5Mpa and superior baking hardenability at low baking finish temp., can be obtained.
TSUYAMA AOSHI
HOSOYA YOSHIHIRO
OKITA TOMOYOSHI
