Thermodynamic Modeling of Phase Equilibrium in Fe-Y-Cr-C-O Liquid Metal System

Abstract

The thermodynamic characteristics of processes in the liquid metal system Fe–Y–Cr–C–O are considered as applied to low-carbon and low-alloy metal. The critical parameters for the state diagram of the oxide system Y2O3–Cr2O3 were established based on the values quoted in literature. The temperature dependence of the melting reaction constant Y2O3·Cr2O3 was determined. The coordinates of eutectic transformation points for the system Y2O3–Cr2O3 were calculated. In accordance with subregular solution theory, the energetic parameters which are necessary to calculate the activities Cr2O3 and Y2O3 of oxide melts in the system Y2O3–Cr2O3 were determined. The energetic parameters of subregular solution theories for the oxide system FeO–Cr2O3–Y2O3 were determined based on the values for the binary systems FeO–Y2O3, FeO–Cr2O3 and Y2O3–Cr2O3. The view of this diagram, as coupled with the existence domain of liquid metal within the framework of the quaternary system Fe–Y–Cr–O–С, suggests that low-carbon chromic liquid metal when injected with yttrium can form the following non-metallic inclusions: |Cr2O3|, |Y2O3|, |FeO·Cr2O3|, |Y2O3·Cr2O3| or oxide melt (FeO, Y2O3, Cr2O3). Oxide melt may contain up to 2 % of divalent chrome (Cr2+). The equilibrium constants for the main reactions of steel deoxidation with the formation of liquid, solid and gas products of chemical reactions were also established. The activity of components dissolved in metal was calculated using interaction parameters. The set of derived expressions for the activity of components and the dependences of equilibrium constants of chemical reactions and phase transformations allowed us to diagram the surface of component solubility in liquid metal (SCSM). SCSM diagrams show the compositions of liquid metal and indicate oxide phases which are in equilibrium with liquid metal.