Thermodynamic Modeling of the Fe-Mn-C and the Fe-Mn-Al Systems Using the Modified Quasichemical Model for Liquid Phase

Thermodynamic modeling of Fe-Mn-C and Fe-Mn-Al ternary systems was performed in order to develop a thermodynamically consistent database of a Fe-Mn-Al-C quaternary system. The system is a core system of high Mn-high Al steels for various applications including automotive, cryogenic, electrical steels, etc., and ferromanganese alloy production. Most previous thermodynamic modeling results were reviewed. In order to treat strong chemical interaction between metals (Fe and Mn) and non-metal (C), the modified quasichemical model in the pair approximation was employed for the liquid phase. A number of solid solutions were modeled using the compound energy formalism. Gibbs energy descriptions in sub-binary systems were taken from previous literatures, except for the Mn-Al binary system. Liquid phase in the Mn-Al system was re-optimized in the present study, while the model parameters for other solid phases were adopted from a literature. By merging the Gibbs energies for relevant phases in sub-binary systems, thermodynamic calculations were carried out for each ternary system. Optimization results of the Fe-Mn-C system in the present study showed improved descriptions for both liquid and solid phases. Solubilities of C in the liquid and the fcc phases were reproduced well, and phase diagram information (liquidus, invariant reactions) was also in good agreement with the experimental data. Thermodynamic assessment of the Fe-Mn-Al system with consideration of A2/B2 order-disorder transition for the bcc phase also showed satisfactory representations for the experimental data. The model parameters derived in the present study can be utilized for further thermodynamic modeling of the Fe-Mn-Al-C quaternary system.