METHOD FOR MANUFACTURING GALVANNEALED STEEL SHEET WITH IMPROVED SURFACE CHARACTERISTICS

摘要

PURPOSE: A method for manufacturing superior galvannealed steel sheet is provided which is capable of improving corrosion resistance even after coating by forming Zn-Cr-Mo alloy layer on the surface of galvanized layer and Zn-Fe alloy phase on coating layer. CONSTITUTION: The method comprises the processes of controlling coating weight adhered to the surface of strip(5) passing through plating pot(1) to 40 to 60 g/m¬2 in air knife(7); spraying an aqueous solution comprising chromium concentration of 1 to 25 g/L, molybdenum concentration of 5 to 30 g/L onto the strip(5) by an aqueous solution sprayer(2); and manufacturing a galvannealed steel sheet by passing a galvanized steel sheet through a heat treatment furnace(3) under the conditions that heat treatment temperature is 400 to 470 deg.C, strip passing time is 3 to 7 seconds, and Fe content in coating layer is maintained to 5 to 10 wt.%.