Excellent in shape and processability properties, method for producing a cold rolled steel sheet small anisotropy

摘要

PROBLEM TO BE SOLVED: To provide a manufacturing method in which cold rolled steel sheets having an extra low carbon and nitrogen content and excellent in formability, processability and having reduced anisotropy can be stably obtained, and also to provide a manufacturing method in which cold rolled steel sheets having uniform quality along longitudinal direction in addition to the above characteristics can be stably obtained.;SOLUTION: In manufacturing the cold rolled steel sheet by subjecting a steel slab having an extra low carbon/nitrogen type composition to heating, hot rolling, cold rolling and annealing, finish rolling is applied under the following conditions: 25-45% total draft at two passes before the final pass; 5-25% draft at the final pass; and finishing temperature between the Ar3 transformation point and (Ar3 transformation point + 50°C). Subsequently, within 1 s or 0.5-1 s after the completion of the finish rolling, rapid cooling is started at (200 to 2,000)°C/s cooling rate. The amount of temperature fall during this rapid cooling from the finishing temperature at the above finish rolling is regulated to 50-250°C, and cooling finish temperature of this rapid cooling is regulated to 650-850°C. Successively, slow cooling at a rate of ≤100°C/s or air cooling is carried out, followed by coiling.;COPYRIGHT: (C)2001,JPO