METHOD FOR PREVENTING BULGING FLAW IN EXTREME LOW CARBON TI KILLED COLD-ROLLED STEEL SHEET

摘要

PURPOSE:To prevent the development of bulging flaw on surface of a steel sheet at the time of annealing the cold-rolled steel sheet by executing primary cold-rolling with cold-rolling ratio having = the specific value at the time of cold-rolling the hot-rolled steel sheet of an extreme low carbon Ti killed steel. CONSTITUTION:After making the steel sheet by hot rolling a steel ingot of the extreme low carbon Ti killed steel containing 0.010wt.% C,0.01% Ti and after primary cold-rolling at =80% cold-rolling ratio, the annealing is executed. By making the cold-rolling ratio large, such as =80% at the time of executing the primary cold-rolling, hard non-metallic inclusion in matrix in the steel strip is finely broken down, and as the gap between the matrix and the inclusion is not developed, the bulging flaw expanded in the soft matrix part caused by invasion of hydrogen into the gap during annealing from gas in annealing atmosphere and raising of the partial pressure, is not developed.