Patent ID: 8668789
Filing Date: 2014-03-11
Classification: C21D,C22C

Abstract:
1. A method for the manufacturing of high strength cold rolled steel sheets of excellent phosphatability, comprising continuously annealing a cold rolled steel sheet that has a composition containing: C: 0.05 to 0.3% by mass, Si: 0.6 to 3.0% by mass, Mn: 1.0 to 3.0% by mass, P: not more than 0.1% by mass, S: not more than 0.02% by mass, Al: 0.01 to 1% by mass, N: not more than 0.01% by mass, and Fe and inevitable impurities: balance, in a manner such that the cold rolled steel sheet is heated in a furnace using an oxidizing burner to a steel sheet temperature of not less than 700° C., thereafter the steel sheet is soak-annealed in a reducing atmosphere furnace at 750 to 900° C., and the steel sheet is cooled in a manner such that the average cooling rate between 500° C. and 100° C. is not less than 50° C./s.