| 摘要 |
PURPOSE:To obtain a cold rolled steel sheet having good deep drawability by limiting the contents of C, N, S, Ti and Nb of a specifically composed dead soft steel added with Ti and Nb in combination and limiting strictly the cooling conditions for hot rolling and the heating conditions for continuous annealing. CONSTITUTION:The cooling of the steel contg., by weight, <=0.0050% C, <=1.0% Si, <=1.0% Mn, formula I (X is the larger value of either formula II or III) Ti, formula IV Nb, 0.005-0.10% Al, <=0.15% P, <=0.0050% N and <=0.015% S is started within 2sec from the completion of the finish rolling in hot rolling. The steel is then cooled at >=10 deg.C/s average cooling rate up to coiling and is coiled at <=710 deg.C. The steel sheet is thereafter subjected to cold rolling at >=50% draft and is continuously annealed at the heat cycle consisting of heating at >=5 deg.C/s heating rate up to 400-600 deg.C and holding for >=1sec in the temp. region of 700 deg.C - Ac3 point. The cold rolled steel sheet having the good deep drawability is thus obtd. while maintaining the advantages intrinsic to the steel.
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