Cold-rolled steel sheet, which deposits invigoration effect type composite construction, has excellent elongation, the characteristic of flange and its manufacturing method

摘要

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet with a precipitation strengthening type composite structure excellent in elongation flange properties, and a method for producing the same.SOLUTION: Provided is a cold rolled steel sheet with a precipitation strengthening type composite structure excellent in elongation flange properties being a steel comprising, by mass, 0.050 to 0.200% C, 0.050 to 2.000% Si, 1.00 to 2.50% Mn,≤0.020% P,≤0.0100% S, 0.005 to 0.500% Al,≤0.0060% N and 0.80 to 2.00% Cu, and the balance Fe with inevitable impurities, having a microstructure, being a composite structure in which a hard structure consisting of one or more selected from retained austenite, martensite, tempered martensite and bainite is used as the main phase, and ferrite of 10 to below 50% in an area fraction is used as the second phase, and the average grain size of the grains composed only of Cu in the ferrite being above 2 to 10 nm.SELECTED DRAWING: None