Patent ID: 7687152
Filing Date: 2010-03-30
Classification: C22C,C23C,Y10S,Y10T

Abstract:
1. A high strength molten zinc plated steel sheet characterized by comprising a steel sheet including, by wt %, C: 0.05 to 0.40%, Si: 0.2 to 3.0%, Mn: 0.1 to 2.5%, and including at least one or two or more types of: P: 0.001 to 0.05%, S: 0.001 to 0.05%, Al: 0.0 1% to 2%, B: 0.0005% to less than 0.01%, Ti: 0.01 to less than 0.1%, V: 0.01 to less than 0.3%, Cr: 0.01% to less than 1%, Nb: 0.01% to less than 0.1%, Ni: 0.01% to less than 2.0%, Cu: 0.01% to less than 2.0%, Co: 0.01% to less than 2.0%, Mo: 0.01% to less than 2.0%, with a balance of Fe and unavoidable impurities, further containing a steel sheet structure including at least 2% to 20% by vol % of an austenite phase in a ferrite phase, having on its surface a Zn plating layer containing Al in a concentration of 0.01 to 1 wt % and a balance of Zn and unavoidable impurities, and containing inside the steel sheet within 2.0 μm from the interface of the plating layer and the steel sheet at least one type of internal oxide particles selected from Al oxide, Si oxide, Mn oxide, or a complex oxide composed of at least two of Al, Si, and Mn, wherein the oxide particle has an average diameter of 0.001 to 1 μm in a density of not more than 1×10 wherein said zinc plated steel sheet is produced by the steps comprising; heating the steel sheet without forming an external oxide layer and Fe oxides on the surface of the steel sheet by means of a radiant tube heating system in a continuous molten zinc plating step, heating the steel sheet at a heating a temperature T of 650° C. to 900° C. in the dual phase region during recrystallization annealing for 30 sec. to 10 min., reducing the steel sheet through a reducing atmosphere where a ratio PH forming inside the steel sheet wherein 2.0 μm from the interface of the plating layer and the steel sheet at least one type of internal oxide particles selected from Al, oxide, Si oxide, Mn oxide, or a complex oxide composed of at least two of Al, Si and Mn, wherein the oxide particle has an average diameter of 0.001 to 1 μm in a density of not more than 1×10 cooling the steel sheet to a temperature range of 350 to 500° C., and maintaining the cooled steel sheet for 5 sec. to 20 min., performing molten zinc plating treatment in a molten zinc bath, containing Al:0.01to 1 wt % and a remainder of Zn, having a temperature of 450° C. to 500° C., then cooling the zinc plated steel sheet to a temperature of below 250° C. with a cooling rate of more than 5° C./sec.