| 摘要 |
elow 0.005wt.%, Si:below 0.1wt.%, Mn:below 0.5wt.%, P:0.04-0.1wt.%, Cu:0.1-0.5wt.%, Al:0.01-0.10wt.%, inevitable impurity, and one or over two element selected from Ti, Nb and Zr to satisfy Nb+Zr+Ti-(48/32)S-(48/14)N= 0.5C in the range of Ti:0.01-0.06wt.% and Nb:0.005-0.04wt.% and Zr:0.01-0.06wt%, and also satisfies Cu/1.62+10P/1.06+mN/4.05= 1.0, Cu/0.6+P/0.09= 1.0. The cold rolled steel sheet is prepared by reheating steel slab at 1050-1250 deg.C; hot rolling steel sheet at the finishing rolled temp. of over 910 deg.C and rewinding temp. of below 550 deg.C; cold rolling it with a reduction ratio of over 60% after pickling hot rolled steel; annealing the cold rolled steel sheet at 700-900 deg.C by batch or continuous annealing method.
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