Adding C to the thermodynamic description of the Cr–Fe–Ni–O system

The Cr–Fe–Ni–O system has been studied in an earlier work with the intention to thermodynamically describe the influence of oxygen in highly alloyed steels. The aim of this study was to also include carbon in this description, with an emphasis on the modelling of the liquid phase. The liquid phase is assessed using the ionic two-sublattice model and good agreement between calculated and experimental data is achieved in the C–Fe–O system. In the C–Ni–O system the calculated solubility of oxygen in the liquid phase is about two orders of magnitude lower than the experimental data. Due to the very low oxygen solubility in liquid C–Ni, no ternary parameter could have any effect on the calculated solubility. By comparing with other oxide bearing ternary systems, it is suggested that the thermodynamic calculations probably give more reliable results than the experimental measurements when the oxygen solubility is very low. For the C–Cr–O system, no experimental information is available. The interaction parameters in the liquid phase were therefore set to zero.