COLD ROLLED STEEL SHEET HAVING EXCELLENT PRESS FORMABILITY AND VIVIDNESS AFTER PAINTING AND ITS PRODUCTION

摘要

PURPOSE:To provide a cold rolled steel sheet which has excellent vividness and the excellent press formability to have the resistance to breakdown and rupture even in the section to be subjected to severe working by specifying the flatness range in the projecting parts on the surface of a steel sheet and the average height of the valleys at the central surface. CONSTITUTION:The titled cold rolled steel sheet which is so formed that the flatness P in the projecting part on the surface of the steel sheet expressed by the equation satisfies 0<=P<=0.20 and the average height Rv of the valleys at the surface center is Rv>=0 is provided. The surface roughness of the steel sheets at the final stand of cold rolling or before the final temper rolling is increased and thereafter the cold rolling or the temper rolling is ended with the rolls of the small surface roughness in order to obtain the cold rolled steel sheet mentioned above. The cold rolled steel sheet having the die galling property at the time of pressing and the vividness after painting in compatibility which heretofore were considered to be in diametrically opposite relations is thereby obtd. while the deterioration in the material quality after the temper rolling is suppressed.