Experimental investigation of the Fe-Mn-Al-C system
The contemporary car producers have tackled the task of energy saving and weight reduction, retaining high specific strength and ductility . The answer to these challenges could be the lightweight steels, which are produced on the basis of the Fe-Mn-Al-C system. This system forms the basis for high-manganese austenitic twinning induced plasticity (TWIP) steels, two-phase transformation induced plasticity (TRIP) steels or steels, reinforced with nanosized κ-carbides (Fe,Mn)3AlC . One of the most important research studies of the phase equilibria in the Fe-Mn-Al-C system was done by Ishida et al. . In  the phase equilibria at different contents of manganese (20-30 wt.%) and Al (0-10 wt.%) in the system at temperatures between 900 and 1200 °C were studied by experimentally. Extensive computational works [2-4] for the thermodynamic description of the Fe-Mn-Al-C system have been made. However, the data are very contradictory. Therefore, the goal of the present research is to study the phase equilibria in the Fe-Mn-Al-C system at crystallization and at temperatures 1100 and 1000 °C using the methods of (DTA), (SEM), (EPMA) and (XRD).
The liquidus surface is characterized by primary crystallization regions of (γFe), (aFe), graphite (C), cementite (M3C) and ternary compound (Fe,Mn)3AlC (κ-carbide). The isothermal sections at 1100 and 1000 °C of the Fe-10Mn-Al-C system in the Fe-rich region is defined by the co-existence of the κ-carbide with almost all phases of the binary subsystems, except cementite (M3C): (γFe), (aFe) and graphite (С). The isothermal sections at 1100 and 1000°C of the Fe-20Mn-Al-C system in the Fe-rich region is defined by the co-existence of the κ-carbide with all phases of the binary subsystems: graphite (С), (γFe), (aFe) and cementite (M3C).
The ternary compound (Fe,Mn)3AlC (κ-carbide) (antiperovskite structure CaTiO3-type, сР5-Pm-3m) shows significant changes in the lattice parameter depending on the composition, which indicates the presence of a region of homogeneity of this phase. Therefore, the κ-carbide cannot be modeled as a stoichiometric compound.
Differential scanning calorimetry (DSC) method was used to investigate thermodynamic properties of κ-carbide.
The experimental results from this study have been used as input for the CALPHAD modeling of data for this system.