PRODUCTION OF BAKING HARDENING TYPE HIGH STRENGTH COLD ROLLED STEEL SHEET FOR DEEP DRAWING

摘要

PURPOSE: To produce a baking hardening type high strength cold rolled steel sheet excellent in deep drawability by subjecting a low carbon steel stock in which the contents of P, Ti and Nb are specified to hot rolling, coiling and cold rolling under specified conditions and furthermore subjecting it to continuous annealing at a specified temp. rising rate. ;CONSTITUTION: A dead soft steel having a compsn. contg., by mass, 0.05 to 0.15% P and contg. Ti and Nb so as to satisfy the inequalities I and II in the relationships of C, N and S is used. This steel is subjected to hot rolling so as to regulate the finishing temp. to the Ar₃ point or above, is coiled at 500 to 600°C and is thereafter subjected to cold rolling at ≥60% draft. Next, this steel is subjected to continuous annealing in such a manner that it is heated at 700 to 800°C at ≥5°C/sec temp. rising rate and is heated so as to regulate the temp. rising rate till the temp. of 800°C to the Ac₁ point to the one slower than the temp. rising rate in the former. Moreover, in this dead soft steel, the content of C is suppressed to 0.001 to 0.008%, N to ≤0.005% and S to ≤0.02%. Furthermore, in the inequalities, N, S and CNb respectively show mass %.;COPYRIGHT: (C)1996,JPO