PRODUCTION OF HIGH TENSION STEEL PLATE FOR BAKING FINISH HAVING EXCELLENT AGING RESISTANCE

摘要

PURPOSE:To produce a high tension steel plate for baking finish having excellent aging resistance by adjusting the content of C and P in a low-carbon Al killed steel and subjecting the steel to hot rolling and cold rolling then to box annealing under specific conditions. CONSTITUTION:The low-carbon Al killed slab contg. 0.05-0.120% C, 0.10-1.0% Mn and <0.10% sol.Al in which P is incorporated in the relation with the content of C as expressed by 0.03<=P%<=0.6(C%)+0.03 is manufactured. Such slab is hot rolled to a plate material which is then coiled at <=600 deg.C. The coil is pickled and descaled and thereafter the coil is cold rolled to a cold rolled plate having 0.7mm. thickness. The cold rolled plate is subjected to box annealing in the temp. range of the crystallization temp. of the steel -700 deg.C and is slowly cooled at <=20 deg.C/hour. The high tension steel plate for baking finish which has <=1.0kgf/ mm.<2> AI value and >=35kgf/mm.<2> TS value and obviates strain aging even if the steel sheet is subjected to baking finish is obtd.