Patent ID: 8741078

Claim:
A method for manufacturing an ultrahigh strength hot dip galvanized steel sheet, the method comprising: providing a steel sheet including C of 0.05 wt % to 0.30 wt %, Mn of 0.5 wt % to 3.5 wt %, Si of 0.1 wt % to 0.8 wt %, Al of 0.01 wt % to 1.5 wt %, Cr of 0.01 wt % to 1.5 wt %, Mo of 0.01 wt %, to 1.5 wt %, Ti of 0.001 wt %, to 0.10 wt %, N of 5 ppm to 120 ppm, B of 29 ppm to 50 ppm, an impurity, and the remainder of Fe; maintaining the steel sheet at a temperature in a range of 750° C. to 950° C. by heating to form an austenite microstructure; dipping the heated steel sheet into a hot dip galvanizing bath to hot dip galvanize the steel sheet; and quenching the hot dip galvanized steel sheet at a quenching rate of 10° C./s to 100° C./s to transform the austenite microstructure to a martensite microstructure, wherein the martensite microstructure comprises greater than 60 vol % and less than 100 vol % of total microstructure in which a bainite structure comprises greater than 0 vol % and less than 40 vol %.