Patent ID: 8257517
Filing Date: 2012-09-04
Classification: B32B,C21D,C22C,C23C

Abstract:
1. A method of producing a cold-rolled steel sheet comprising: (a) producing a hot-rolled steel sheet comprising: wherein C and Mn represent the contents (in % by mass) of the respective elements in the steel; (b) pickling the hot-rolled steel sheet; (c) cold-rolling at a reduction of 40 to 90%; and (d) heat-treating at a temperature of not higher than 900° C., to yield: and, further, that, at the depth of ¼ of the sheet thickness from the steel sheet surface, the area percentage of ferrite crystal grains the crystal grain diameter d (μm) of which satisfies the relation defined by the formula (4) given below is at least 80%: wherein C, Cr and Mn represent the contents (in % by mass) of the respective elements in the steel.