MANUFACTURING METHOD OF HOT DIP GALVANNEALED STEEL(GA) HAVING GOOD SURFACE PROPERTY FOR AUTOMOBILE

摘要

PURPOSE: A manufacturing method of a hot dip galvannealed steel(GA) for automobile in CGL(Continuous Galvanizing Line) is provided, which can produce a hot dip galvannealed steel with minimized sink roll mark and dross defect by regulating Al concentration in plating bath. CONSTITUTION: The method is characterized in that in the case of converting GI mode to GA mode, a hot dip galvannealed steel(GA) is produced within the time range of 18 to 24 hours while keeping Al concentration in plating bath higher than 0.125% after aluminium concentration in plating bath is lowered less than 0.15%.