Influence of steel substrate grain size on phase layers growth kinetics and thickness of zinc hot dipped steel sheets

It has been suggested that the grain size of the substrate steel sheet affects the coating formation kinetics and growth rate in the hot dip galvanising process. In the present study, two low carbon steel samples with different grain sizes of 5 and 40 mm, were prepared and hot dipped for different immersion times from 5 to 40 s to examine the effects of steel grain size on phase layers thickness and growth rate. The microstructure of the coatings was studied using scanning electron microscopy and energy dispersive spectroscopy analysis. It was observed that due to the absence of an inhibition layer, four phase layers were obtained after galvanising. The values of growth rate time constant n were determined for the phase layers. It was concluded that a smaller steel grain size would result in relatively thicker coatings. Furthermore, it was deduced that the same possible mechanism that controls zeta and eta layer growth would also control the total coating layer growth.