To provide a cold rolled steel sheet and a plated steel sheet with a composite structure having satisfactory surface properties, free from the generation of pinholes in a product after coating, also having excellent baking hardenability and cold aging resistance, and having a tensile strength of 340 MPa, and to provide methods for producing these steel sheets.
The steel sheet has a structure where the main phase is composed of a ferritic phase and the second phase is composed of a low-temperature transformation-generation phase, wherein the size of surface defects including oxide is 25 m, and preferably has a chemical composition containing, by mass, 0.0025 to 0.04% C, 0.5% Si, 0.5 to 3.0% Mn, 0.05% P, 0.01% S, 0.15% sol.Al, 0.008% N, 0.02 to 2.0% Cr, and the balance Fe with impurities.
AKIOKA KOJI
KITA KAZUAKI
| JP2006052465A | 2006-02-23 | |||
| JPS63266096A | 1988-11-02 |