Modeling of Interfacial Layer Growth Kinetics on Mn-Containing Steels during Continuous Hot-Dip Galvanizing

A kinetic model based on an oxide film growth analogy was developed to describe the continuous galvanizing Fe-Al interfacial layer growth for 0.2 – 3.0 wt% Mn-containing steels coated in 0.20 wt% and 0.30 wt% dissolved Al baths. It indicated that interfacial layer microstructural development and the presence of unreduced surface MnO had a significant influence on the interfacial layer growth rate. However, in the cases of the higher Mn steels in the 0.20 wt% Al bath, despite the more open interfacial layer microstructure the kinetic model could not predict the interfacial layer Al uptake as the Fe-Al growth rate was Al limited due to the additional Al consumed in reducing the thicker MnO layer present on these substrates. However, for the case of 0.30 wt% Al bath, the more open interfacial layer microstructures combined with the higher dissolved Al supply, resulted in the growth kinetics for the higher Mn alloys shifting significantly to interface controlled growth from the mixed diffusion mechanism observed for all other substrates and bath Al contents.