PRODUCING METHOD OF AL KILLED COLD ROLLED HIGH TENSILE STEEL PLATE

摘要

PURPOSE:To provide an excellent baking hardenability and resistance to dent in batch type annealing process by a method wherein the quantity of Mn, P, Al, Si, and C contents in Al killed steel is limited to specific values and annealing condition after cold rolling is properly adjusted. CONSTITUTION:Al killed steel material contg. Mn: 0.2-0.6%, P: 0.04-0.15%, Al: 0.02-0.08%, C=0.10%, Si0.04% is made to steel plate by hot rolling at a finish temperature higher than Ar3 transformation temperature, then the steel plate is wound loose at a temperature less than 600 deg.C. The steel plate is processed by surface pickling, scale removal, and cold-rolling at reduction ratio of 40% or more. This is charged in a batch type annealing furnace, rapidly heated at a rate of 50-100 deg.C/hr., then is annealed at a temperature between recrystallization temperature and 750 deg.C for a specified period of time. Next, the plate is cooled at a rate of 0.15-0.6T deg.C/hr., where T deg.C represents any temperature during cooling operation. Although batch type annealing is used, this process provides a high tensile steel plate for automobile having good surface property, press workability, tensile strength, baking hardenability, and antident property.