Patent ID: 8182621
Filing Date: 2012-05-22
Classification: B21B,C21D,C22C

Abstract:
1. A method of manufacturing a hot-rolled thin steel sheet having a structure of a bainitic ferrite single phase having an area ratio fraction of 95% or more, a tensile strength of 440 to 640 MPa, a thickness of less than 6 mm, high strength and excellent formability, and excellent strength and toughness after heat treatment, including: hot-rolling a steel base material having a composition containing, as mass %, the balance of Fe, and unavoidable impurities at a finishing temperature of finish rolling of 820 to 880° C. to produce a hot-rolled steel sheet with a thickness of less than 6 mm; cooling the hot-rolled steel sheet to a temperature range on a surface of the hot-rolled steel sheet to 550 to 650° C. at a surface cooling rate of 15 to 50° C. per second; and coiling the hot-rolled steel sheet at the temperature range.