| 摘要 |
PROBLEM TO BE SOLVED: To provide a mother sheet for a high strength extra-thin cold rolled steel sheet with a sheet thickness of ≤0.3 mm, excellent in baking hardenability in which the baking hardening quantity is ≥50 MPa, and yield stress after coating/baking treatment is ≥550 MPa and to provide a method for producing the same. SOLUTION: A hot rolled sheet (mother sheet for a high strength extra-thin cold rolled steel sheet) having a composition containing, by mass, ≤0.02% C, ≤0.10% Si, ≤1.5% Mn, ≤0.20% P, ≤0.01% S, ≤0.01% Al and 0.0050 to 0.0250% N and containing solid solution N by ≥80% of the N content is cold-rolled, is thereafter, in a continuous annealing stage, soaked in the temperature range of ≥500°C to the one at which the recrystallization ratio reaches <90%, is subsequently subjected to rapid cooling treatment at a cooling rate of ≥150°C/s to the temperature range of ≤250°C and, within 5 min after the completion of the soaking to 40°C, is cooled. After the cooling, cold rolling at a draft of ≤10% may be performed. COPYRIGHT: (C)2009,JPO&INPIT
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