PRODUCTION OF HIGH STRENGTH STEEL HAVING LOW YIELD FOR STEEL TOWER

摘要

PURPOSE: A process for preparing the titled steel having a yield ratio of 80% or less by comprising a matrix structure of ferrite and bainite and heat treating is provided. Whereby, the obtained steel has the advantage of preventing crack of a weld zone of low yield steel sheet having plating crack resistance. CONSTITUTION: The titled steel is prepared by the process consisting of: hot rolling a steel ingot; heat treating at a cooling speed of 12deg.C/sec or more after heating at 880deg.C; heat treating at a cooling speed of 12deg.C/sec or more after reheating in the range of Ac1+(Ac1-Ac3)x0.5 to Ac1+(Ac1-Ac3)x0.8; and post heat treating at 600 to 700deg.C for 15 min or less.