| 摘要 |
PROBLEM TO BE SOLVED: To produce a high ductility hot rolled steel sheet which has excellent pres formability and strain age hardening characteristics causingΔTS of >=80 MPa, and to provide a production method therefor. SOLUTION: A steel slab having a composition containing, by mass, 0.05 to 0.20% C, and in which the contents of Si, Mn, P, S, Al and N are controlled to proper ranges, and containing 0.5 to 3.0% Cu is subjected to hot rolling where finishing temperature in finish rolling is 780 to 980 deg.C. Within 2 sec after the completion of the finish rolling, the steel sheet is cooled to the temperature range of 620 to 780 deg.C at a cooling rate of >=50 deg.C/s, and is subjected to isothermal holding treatment in the above temperature range for 1 to 10 s, or slow cooling treatment at a cooling rate of <=20 deg.C/s. After that, the steel sheet is again cooled to 300 to 500 deg.C at a cooling rate of >=50 deg.C/s, and is coiled round a coil. Further, in place Cu, the steel sheet can contain one or more kinds selected from Mo, Cr and W by <=2.0% in total. Further, one or more kinds selected from Nb, Ti and V can be incorporated therein by <=2% in total.
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