| 摘要 |
PROBLEM TO BE SOLVED: To obtain a cold rolled steel sheet reduced in inplane anisotropy and excellent in formability by adding specific amounts of Ti to a low C aluminum killed steel and specifying hot rolling, cold rolling rate, and conditions in annealing, etc., respectively. SOLUTION: A steel, having a composition consisting of, by weight, 0.02-0.06% C, <=0.5% Si, 0.05-2.0% Mn, <=0.10% P, <=0.02% S, 0.005-0.1% Al, <=0.01% N, Ti in an amount satisfying Ti-48×(N/14+S/32)>=0.02 and Ti<=0.1%, and the balance essentially Fe is used. This steel is hot-rolled at >=800 deg.C and coiled at <=750 deg.C. After acid pickling, cold rolling is performed at 70-95% rolling rate. The resultant steel sheet is heated at >=5 deg.C/sec temp.-rise rate up to a temp. between the recrystallization temp. and the Ac3 point and held at this temp. for <=5min. The steel sheet is cooled at >=5 deg.C/sec cooling rate down to 250-500 deg.C and subjected to overaging treatment in this temp. region for <=10min. The degree of elongation of annealed recrystallized grains in the cross section parallel to a rolling direction is regulated to >=1.5, and the indexΔr of inplane anisotropy using r-value is regulated to <=0.1 absolute value.
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