| 摘要 |
PURPOSE:To enhance strain age-hardenability by a method wherein a steel containing specified amounts of C, Mn, Al together with one or more selected from Zr, Ca, Mg and rare earth elements is hot rolled, cold rolled and subjected to recrystallizing annealing in specified conditions. CONSTITUTION:A steel containing 0.03-0.2wt% of C, 1-2wt% of Mn, less than 0.1wt% of Al and one or more elements selected from Zr, Ca, Mg and rare earth elements in a total amount of less than 0.1wt% is hot rolled, followed by cold rolling with a draft of at least 30%. Then, after heating the steel with an average heating rate of 1 deg.C/sec at the range from 600 deg.C to 760 deg.C and maintaining the steel in the temperature range of 760-900 deg.C for 30sec-30min, the steel is cooled with the cooling rate of at least 30 deg.C/sec at the range from 700 deg.C to 200 deg.C to effect recrystallizing annealing. Accordingly, the high-strength cold- rolled steel sheet can be obtained with a 0.2% offset yield stress of 15-55kg/mm.<2>, a tensile strength of 50-100kg/mm.<2> and a ratio of 0.2% offset yield stress to tensile strength of less than 0.6. |
