| 摘要 |
PROBLEM TO BE SOLVED: To produce a cold rolled steel sheet in which two characteristics of surface roughening resistance and press formability required for an automo tive steel sheet are compatible and furthermore excellent in chemical convertibil ity and to provide a method for producing the same. SOLUTION: This steel sheet has a compsn contg., by weight, <=0.005% C, <=0.1% Si, <=0.5% Mn, <=0.1% P, 0.003 to 0.02% S, 0.02 to 0.1% Sol.Al, <=0.01% N, 0.03 to 0.08% Ti and 0.0001 to 0.0015% B, in which the average grain size of ferrite within 10% sheet thickness from the surface of the steel sheet is regulated to <=90% to the average grain size of ferrite in the center part of the steel sheet excepting <=10% sheet thickness from the surface of the steel sheet, and the average grain size of ferrite in the center part of the sheet thickness is regulated to 10 to 30μm.
|
