Patent ID: 6797410
Filing Date: 2004-09-28
Classification: C21D,C22C,C23C,Y10T

Abstract:
A high tensile strength hot-dipped steel sheet, characterized in that the hot-dipped steel sheet is obtained by subjecting a steel sheet of a composition consisting of:C: not less than 0.03 mass % and not more than 0.20 mass %, Nb: not less than 0.005 mass % and not more than 0.2 mass %, not less than 0.03 mass % and notmore than 1.5 mass % in total of one or more selected from Cu: less than 0.5 mass%, Ni: less than 1.0 mass % and Mo: less than 1.0 mass %, Al: not more than 0.10 mass %, P: not more than 0.100 mass %, S: not more than 0.010 mass %, N: not more than 0.010 mass %, and containing Si: not less than 0.5 mass % and not more than 1.5 mass %, Mn: not less than 1.2 mass % and not more than 3.5 mass % in a range satisfying 1.5Ã—Si(mass %)>Mn(mass %), and the remainder being Fe and inevitable impurities to a recrystallization annealing and forming an internal oxide layer in a reducing atmosphere having a dew point of not higher than 0Â° C. and not lower than âˆ’45Â° C. at an annealing temperature of not lower than 750Â° C., cooling, removing oxides formed on a surface of the steel sheet by pickling, reheating to a temperature of not lower than 650Â° C. and not higher than 850Â° C. in a reducing atmosphere having a dew point of not higher than âˆ’20Â° C., and subjecting to a hot-dipping treatment during the course of cooling own from the reheating temperature to provide a hot-dipping layer on a surface of the steel sheet.