Thermodynamic assessment of the Fe–Mn–C system

The Fe–Mn–C ternary system has been thermodynamically evaluated using the CALPHAD method. Published data on thermochemical properties and phase equilibria have been critically examined and used to optimise the model parameters. The Fe–Mn–C system has been evaluated previously by Huang [W. Huang, Metall. Trans. A 21A (1990) 2115–2123]. In comparison to that evaluation, experimental liquidus data are now considerably better described and carbide equilibria at low temperatures are also more reasonable now. The differences in equilibria involving the γ (austenite), α (ferrite), ε (hcp) and M3C (cementite) phases are very small. The improvement of carbide equilibria was possible by doing ab initio calculations of the enthalpies of formation of the metastable Fe3C, Fe23C6, Fe5C2 and Fe7C3 carbides. Calculations using the presently developed thermodynamic description are extensively compared with experimental data.