초록 ▼

A high strength cold rolled strip having excellent deep drawability and resistance to deterioration by natural aging and to planar cracking and useful for motor vehicles, is produced by hot rolling a steel slab comprising 0.008-0.020% by weight of C, 0.01-0.45% by weight of Mn, 0.05-0.10% by weight

A high strength cold rolled strip having excellent deep drawability and resistance to deterioration by natural aging and to planar cracking and useful for motor vehicles, is produced by hot rolling a steel slab comprising 0.008-0.020% by weight of C, 0.01-0.45% by weight of Mn, 0.05-0.10% by weight of P, 0.005-0.050% by weight of acid-soluble Al, and the balance consisting of Fe and unavoidable impurities in which N is limited to a content of 40 ppm or less, at a temperature of 1200°C. or less but not lower than the Ar3 point of the steel slab; by cold rolling the resultant steel strip at a rolling reduction of 65% or more; by continuously annealing the cold rolled steel strip at a temperature of from 700°to 900°C. for 20 seconds to 3 minutes; by cooling the steel strip at a cooling rate of 5°C./sec or more; by overaging the annealed steel strip at a temperature of from 320°to 450°C. for 1 to 10 minutes; by cooling said overaged steel strip to the ambient temperature, and, finally; by temper-rolling the cooled steel strip at the ambient temperature.

대표청구항 ▼

A process for producing a high strength cold rolled steel strip useful for motor vehicles, comprising the steps of: preparing a steel slab comprising 0.008 to 0.020% by weight of carbon, 0.01 to 0.45% by weight of manganese, 0.05 to 0.10% by weight of phosphorus, 0.005 to 0.050% by weight of acid-so

A process for producing a high strength cold rolled steel strip useful for motor vehicles, comprising the steps of: preparing a steel slab comprising 0.008 to 0.020% by weight of carbon, 0.01 to 0.45% by weight of manganese, 0.05 to 0.10% by weight of phosphorus, 0.005 to 0.050% by weight of acid-soluble aluminum, and the balance consisting of iron and unavoidable impurities in which nitrogen is limited to a content of 40 ppm or less; heating said steel slab to a temperature of 1200°C. or less; hot rolling said heated steel slab at a temperature not lower than the Ar3 point of said steel; descaling said resultant hot rolled steel strip; cold rolling said descaled steel strip at a rolling reduction of 65% or more; continuously annealing said cold rolled steel strip by heating it to a temperature of from 700°to 900°C., by soaking the steel strip for 20 seconds to 3 minutes and by cooling the steel strip at a cooling rate of from 5°C./sec to 30°C./sec in the temperature range of 650°C. or more and then, at a cooling rate of more than 30°C./sec in the temperature range of below 650°C.; overaging said annealed steel strip at a temperature of from 320°to 450°C. for 1 to 10 minutes; cooling said overaged steel strip to the ambient temperature, and; temper-rolling said cooled steel strip at the ambient temperature.