PURPOSE: To prevent galvanizing blister and enhance the quality of a galvanized steel sheet by reducing a steel sheet and holding it at a suitable temp. in a weakly reducing atmosphere of lowered hydrogen press. to dehydrogenate the sheet, followed by galvanizing.

CONSTITUTION: A hot rolled steel sheet is pickled, heat treated, reduced, and held at 450W550°C in a weakly reducing atmosphere consisting of 8W20% H2 and 92W 80% N2 to dehydrogenate the sheet, followed by dipping in molten zinc. By this method hydrogen occluded in the sheet is released to a low equilibrium concn. in the reducing atmosphere, so galvanizing blister can be prevented perfectly, thereby improving the quality of a galvanized steel sheet and enhancing the yield.