1991 Volume 77 Issue 7 Pages 1184-1191
Both anti-powdering property and press-formability are the most important performances for the galvannealed steel sheet to be processed into automobile body panels successfully. The press-formability is to be strongly influenced by friction between the coating surface and the press-forming die. Because these properties depend on the coating compositions, it is meaningful to discuss the mutual relationship between these performances either in production of the material or in press-forming. The increase in Fe content of the coating deteriorated the anti-powdering property and decreased the friction resistance. The formation of Γ phase at the interface of the coating and the substrate metal fatally affected the antipowdering property and the existence of ζ phase on the coating surface increased the friction resistance. In a view point of the Fe content, therefore, the friction property is contrary to the anti-powdering property. When the galvannealed steel sheet was electroplated with Fe-P alloy, the friction property was remakably improved. The friction property did not influence the delamination of the coating by bending but the amount of the coating peeling off at the shrinking flange in the cylindrical cup forming increased with the decrease of the friction resistance. It is supposed that the decrease in friction resistance increases the compression of material at the shrinking flange and that the compression enhances the delamination of the coating.
