The Fe–Cr–Zn System in Relation with the Galvanizing Process in Chromium-Added Zinc Bath

Abstract

Taking into account new experimental measurements, the Fe-Zn-Cr ternary system is critically modified at 460 °C. A continuous solid solution between (-FeZn 13 and CrZn 13 compounds is shown but is shared at 460 °C by the stable CrZn 17 compound containing about 2 wt.% Fe. This ternary system is assessed with the CALPHAD method using the PARROT modulus of the Thermo-Calc software. The liquid and solid solution phases are modeled with Redlich-Kister-Muggianu equations. The intermetallic compounds ζ-(Fe,Cr)Zn 13 and CrZn 17 are treated as stoichiometric compounds in the binary systems. The experimental Fe and Cr solubilities at various temperatures modify the shape of the liquidus curve and are satisfying for industrial applications. A set of parameters consistent with most of the available experimental data on both phase diagram and solubility measurements is obtained by optimization. A comparison with previous experimental work is also presented and a reactional model between iron substrate and Zn-Cr bath is proposed. This optimization allows to interpret the growth of intermetallic layers and the formation of dross when galvanizing in Cr-added Zn bath.