METHOD FOR MANUFACTURING GALVANNEALED STEEL SHEET, CHARACTERISTIC AS ITS CORROSION RESISTANCE, WITH EXCELLENT PAINTABILITY

摘要

PURPOSE: To provide a method for manufacturing galvannealed steel sheet with excellent paintability, wherein corrosion resistance of the galvannealed steel sheet after painting is improved by forming a Zn-Cr alloy layer on a surface of plating layer and forming a Zn-Fe alloy layer on a lower part of the plating layer. CONSTITUTION: The method comprises the steps of performing hot dip galvanizing on a base steel sheet in a hot dip galvanizing pot containing 0.12 wt.% of aluminum so that 20 to 30 g/m¬2 of plating solution is coated on the base steel sheet; injecting an aqueous chrome solution into which 1 to 50 g/L of Cr¬6+ is dissolved onto the hot dip galvanized base steel sheet; and performing alloy heat treatment on the aqueous chrome solution coated galvanized steel sheet in an alloying heat treatment furnace at a temperature of 400 to 450 deg.C for 5 to 10 seconds.