COLD-ROLLED STEEL SHEET WITH EXCELLENT FORMABILITY, SHAPE RETENTIVITY, AND SURFACE APPEARANCE AND PROCESS FOR PRODUCING SAME

摘要

A cold-rolled low-carbon steel sheet having excellent formability, shape retentivity, and surface appearance, the steel sheet combining processability with shape retentivity, being able to be processed by drawing, bending, or bulging and to ensure a shape required of a large part, and having such a high degree of flatness that no appearance defects generate. Provided is a process for producing the cold-rolled steel sheet. The cold-rolled steel sheet is characterized by having a composition which comprises, in terms of mass%, 0.030-0.060% C, up to 0.05% Si, 0.1-0.3% Mn, up to 0.05% P, up to 0.02% S, 0.02-0.10% Al, up to 0.005% N, and iron and incidental impurities as the remainder, having an r value of 0.7-1.4 when examined in the direction of rolling and in the direction perpendicular to the rolling direction, having an in-plane r-value anisotropy (?r) of -0.2=?r=0.2, having an average yield strength and an average elongation in three directions, i.e., the rolling direction, a direction forming an angle of 45º with the rolling direction, and the direction perpendicular to the rolling direction, of 230 MPa or lower and 40% or longer, respectively, and having a yield elongation after 60-minute holding at 170ºC of 2% or shorter in each of the three directions.