Thermodynamics of Solid and Liquid MnS–CrS–FeS Phase in Equilibrium with Molten Fe–Cr–Mn–S Alloy

Abstract

Alloying elements such as Mn and Cr are widely used in steel. These two chemical elements have stronger affinity with sulfur than iron. 1) During cooling and solidification of steel, because of the decrease of sulfide solubility in steel and sulfur segregation, sulfide inclusions which consist of MnS-CrS-FeS may form in Fe-Cr-Mn-S based materials such as stainless steel. 2,3) It is very important to control the composition of MnS-CrS-FeS sulfide phase in terms of balancing properties of machinability and corrosion resistance [4][5][6][7][8] of the steel product.The mechanism of sulfide formation diagram was provided by Oikawa et al. 3) He suggested that there are three types of sulfide formation mechanism: 1). Stable eutectic reaction proceeds by nucleation of sulfide crystals by highmelting particles; 2). Metastable monotectic reaction; 3). Stable monotectic reaction which proceeds through the formation of low-melting sulfides. On knowing the different sulfide formation mechanisms, to control sulfide formation, it is fundamentally important to know the equilibria involving sulfide phase in the Fe-Cr-Mn-S system during solidification of steel. To create the equilibrium relationships, thermodynamic properties of both metal phase and sulfide phase are necessary to know.The thermodynamic information of liquid metal phase in Fe-Cr-Mn-S system, such as e