Phase equilibria and thermal analysis in the Fe-Mn-Ni system Based on the critical review of the experimental data available in the literature, 7 decisive ternary alloys were prepared. New phase transition temperatures and phase equilibria at 800 8C in the Fe -Mn -Ni system were measured. An effective method to accurately determine phase transition temperatures from differential thermal analysis curves with overlapped peaks and nonlevel baselines within a narrow temperature range was developed. A massive transformation was observed in one quenched Fe-rich alloy. In order to make the fcc_A1 phase always in the fully disordered state in the ternary system, the effect of the binary reciprocal parameter on the Gibbs energy of ternary ordered L1 2 phase was considered. It was found that the introduction of only one parameter could describe all reliable experimental data in the Fe -Mn -Ni system satisfactorily. The presently obtained parameters were successfully applied in two practical cases.