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AssigneeKawasaki Steel Corporation
InventorsToshio Irie, Susumu Sato, Osamu Hashimoto
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Non-ageing cold rolled steel sheets having a very excellent formability are produced by hot rolling a steel consisting of not more than 0.008% of C, not more than 0.20% of Si, 0.04-0.30% of Mn, not more than 0.03% of P, 0.01-0.10% of Al, a content of Al being more than N%.times.4, not more than 0.02% of S, not more than 0.01% of N, 0.01-0.07% of Nb, a content of Nb being C%.times.3-{C%.times.8+0.02}%, and the remainder being substantially Fe, at a total reduction of not less than 90%, a rolling speed of not less than 40 m/min in the finishing rolling and a finishing temperature of not lower than 830.degree. C., coiling the hot rolled strip at a temperature of 600.degree.-800.degree. C., cold rolling the coiled strip following a conventional manner to obtain a cold rolled strip having final gauge and then continuous annealing or hot-dip galvanizing the cold rolled strip within a temperature range of 700.degree.-900.degree. C. for 10 seconds-5 minutes.
A method for producing cold rolled steel sheets having a noticeably excellent formability, comprising preparing a steel consisting of not more than 0.008% of C, not more than 0.20% of Si, 0.04-0.30% of Mn, not more than 0.03% of P, 0.01-0.10% of Al, a content of Al being more than N%.times.4, not more than 0.02% of S, not more than 0.01% of N, 0.01-0.07% of Nb, a content of Nb being C%.times.3-{C%.times.8+0.02}%, and the remainder being substantially Fe, hot rolling the steel at a total reduction of not less than 90%, a rolling speed of not less than 40 m/min in finishing rolling and a finishing temperature of not lower than 830.degree. C., coiling the hot rolled strip at a temperature of 600.degree.-800.degree. C., cold rolling the coiled strip to obtain a cold rolled strip having final gauge and then continuous annealing the cold rolled strip within a temperature range of 700.degree.- 900.degree. C. for 10 seconds-5 minutes.
A method for producing cold rolled steel sheets having a noticeably excellent formability, comprising preparing a steel consisting of not more than 0.008% of C, not more than 0.20% of Si, 0.04-0.30% of Mn, not more than 0.03% of P, 0.01-0.10% of Al, a content of Al being more than N%.times.4, not more than 0.02% of S, not more than 0.01% of N, 0.01-0.07% of Nb, a content of Nb being C%.times.3-{C%.times.8+0.02}%, and the remainder being substantially Fe, hot rolling the steel at a total reduction of not less than 90%, a rolling speed of not less than 40 m/min in finishing rolling and a finishing temperature of not lower than 830.degree. C., coiling the hot rolled strip at a temperature of 600.degree.-800.degree. C., cold rolling the coiled strip to obtain a cold rolled strip having final gauge and then continuous annealing the cold rolled strip within a temperature range of 700.degree. -900.degree. C. for 10 seconds-5 minutes and hot-dip galvanizing the thus treated strip continuously.
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