| 摘要 |
PROBLEM TO BE SOLVED: To produce a cold rolled steel sheet in which precipitates essentially consisting of Ti4 C2 S2 and TiS are specifically present and excellent in burring workability and blankability by specifying the contents of C, Si, Mn, S, Ti or the like and the relations among the content of Ti and the contents of C, S and N in a steel. SOLUTION: A slab composed of a steel satisfying, by mass, 0.0010 to 0.010% C, <=0.25% Si, 0.20 to 1.0% Mn, <=0.05% P, 0.010 to <0.025% S, <=0.01% N and <=0.15% Ti, satisfying (Ti*/48)/(C/12+S/32)=0.8 to 4.0, where Ti*=Ti-(48/14)N, and the balance Fe is prepd. This slab is heated at 1100 to 1200 deg.C, and thereafter, hot rolling is finished at (the Ar3 transformation temp. +80 deg.C) to (the Ar3 transformation temp. -40 deg.C), which is next coiled at 600 to 700 deg.C, is subjected to cold rolling and is then annealed. Thus, the objective steel sheet in which precipitates with 100 to 10000Åsize essentially consisting of Ti4 C2 S2 and TiS are present in the inside by 1×10<4> to 5×10<5> pieces/ mm<2> can be obtd. Furthermore, 0.0002 to 0.0050% B may be incorporated into the above steel as well.
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