ULTRA-HIGH STRENGTH STEEL SHEET WITH EXCELLENT BENDING WORKABILITY AND METHOD FOR MANUFACTURING THE SAME

摘要

A method of manufacturing a high-strength steel sheet excellent in bending workability according to one aspect is, (a) in weight %, carbon (C): 0.05 to 0.25%, silicon (Si): 0.1% to 3.0%, manganese (Mn): 2.0% Prepare a hot-rolled steel sheet containing ~5.0%, phosphorus (P): more than 0 and less than 200 ppm, sulfur (S): more than 0 and less than or equal to 50 ppm, aluminum (Al): 0.001% to 1.000%, remaining iron (Fe) and unavoidable impurities to do; (b) cold-rolling the hot-rolled steel sheet after pickling; (c) performing a flash plating process on the cold rolled steel sheet to form a flash plating layer on the surface of the steel sheet; (d) primary heat treatment by heating the steel sheet having the flash plating layer formed thereon to 750 to 900° C. in a heating furnace; (e) maintaining the primary heat-treated steel sheet in a holding furnace at 750 to 900° C. and performing secondary heat treatment; and (f) cooling the secondary heat-treated steel sheet.