Effect of Microstructure of Base Steel on Fe-Zn Alloy Growth during Galvanizing of an Interstitial Free Steel

摘要

The effect of the microstructure of the base steel on the formation and growth behavior of intermetallics on interstitial free steel during galvanizing under various processing conditions (substrate entry temperature, Al content in galvanizing bath) was investigated from the viewpoint of the surface morphology of the intermetallics. In addition, the surface morphology of galvannealed coating was also examined. The dependency of Fe-Zn intermetallics growth behavior on the crystal orientation of the base steel was observed clearly in galvanizing in 0.10 mass% or less Al bath, especially at low entry temperatures. In general, ζ crystals are precipitated orderly on (111 )α, whereas those are precipitated disorderly on (001 )α and (101 )α at the outset of the formation of Fe-Zn intermetallics, and the growth rate of Fe-Zn intermetallics on (001 )α and (101 )α is larger than that on (111 )α. As an exception, the formation of Fe-Zn intermetallics on (001 )α and (101 )α at the outset of Fe-Zn interaction is suppressed at the entry temperature of 673 K in 0.10mass%. Al bath, although the clump of orderly precipitated ζ is formed on (111)α. The growth of Fe-Zn intermetallics during galvannealing also depends on crystallographic orientation of the αFe grain of the base steel, being retarded on (111 )α. A large αFe grain with (111)α on the surface is thought to cause a concave portion on the galvannealed surface. Consequently, it is thought that the formation and growth behavior of Fe-Zn intermetalfics on IF steel is affected not only by the αFe grain boundary but also by the crystallographic orientation of the αFe grain of the base steel.