PURPOSE: To prevent deterioration in the adhesion of a hot dip galvanizing layer with time in a steel sheet and its blackening by hot dip-galvanizing the surface of a steel sheet with Zn contg. a small amount of Al and Pb and thereafter subjecting the plating layer to remelting and rapid cooling.
CONSTITUTION: A steel sheet to be plated is immersed in a hot dip galvanizing bath at 430 to 500°C contg., by weight, 0.06 to 0.20% Al and 0.001 to 0.01% Pb to form a hot dip galvanizing layer on the surface of the steel sheet. This hot dip-galvanized steel sheet is immediately heated to the melting temp. of Zn or above to remelt the galvanizing layer. After that, it is rapidly cooled at ≥20°C/sec cooling rate to prevent the intergranular segregation of Al and Pb in the galvanizing layer, thereby, the peeling of the plating layer caused by deterioration in its adhesion with time and defective appearance of the surface caused by its blackening can be prevented.
KATO CHIAKI
MOCHIZUKI KAZUO
