Patent ID: 8646301

Claim:
A method of manufacturing a high strength hot rolled steel sheet comprising: heating a slab to a temperature in the range of 1150 to 1300° C.; hot rolling the slab with a finishing rolling temperature in the range of 800 to 1000° C.; cooling the steel sheet at a mean cooling rate of 30° C/s or higher to a cooling termination temperature in the range of 525 to 625° C.; suspending cooling for a time period in the range of 3 to 10 seconds; after suspending cooling, cooling the steel sheet such that cooling of the steel sheet is nucleate boiling; and coiling the steel sheet at a temperature in the range of 400 to 550° C., wherein the slab contains the following elements at the following content ratios by weight percent: C: 0.05 to 0.15% Si: 0.1 to 1.5% Mn: 0.5 to 2.0% P: 0.06% or lower S: 0.005% or lower Al: 0.10% or lower; and Fe and unavoidable impurities as the balance, and wherein the steel sheet contains ferrite at a volume fraction of 80% or more and bainite at a volume fraction of 3-20%.