MANUFACTURING METHOD OF COLD ROLLED STEEL SHEET FOR AUTOMOBILE WITHOUT SURFACE STRIPE DEFECTS

摘要

PURPOSE: A manufacturing method of superior cold rolled steel sheet without surface defects when performing forming process, washing process after degreasing and electrostatic painting process is provided. CONSTITUTION: In a method for manufacturing the cold rolled steel sheet for automobile in which the work is continuously annealed after degreasing a work for cold rolled steel sheet for automobile in a continuous annealing furnace, the manufacturing method of the cold rolled steel sheet for automobile without surface stripe defects is characterized in that the continuous annealing is performed at a temperature of 750 to 850 deg.C for 20 to 30 seconds, tension is maintained in the annealing furnace in such a way that the minimum required tension is differently applied to respective sections of heating section, soaking section, slow cooling section, rapid cooling section and over-aging section to prevent stripe defects from forming on the surface of the steel sheet, and reduction elongation in the skin pass rolling process is varied according to type and thickness of the steel sheet in such a way that the reduction elongation is set to 0.6 to 1.4% if thickness of the steel sheet is 0.6 to 2.3 mm.