Investigation of Carbon, Manganese and Silicon Solubility in α-Iron of Fe-Mn-Si-C Alloys

In this work, we studied iron-based alloys with a carbon content of 0.37-0.57% (wt.), silicon of 0.23-0.29% (wt.), and manganese 0.7-0.86% (wt.). The phase composition was determined using structural, compositional, and X-ray diffraction analysis. We found that after crystallization and phase transformations, the alloy phase structure included two phases: $\alpha$-iron and carbides Fe2.7Mn0.3C and Fe0.25Mn1.4C0.6 and Fe9SiC0.4. For the first time, by using a quasi-chemistry approach, we derived expression of the free energy of a solid solution of $\alpha$-iron alloyed with Si and Mg and determined the solubility limits of carbon, manganese, and silicon. We found that the solubility limits in $\delta$-iron phase are 0.09% (wt.), 3.5% (wt.) and 0.25% (wt.) for C, Mn, and Si, respectively, and 0.017% (wt.), 21% (wt.), and 1.3% (wt.) for $\alpha-$iron phase.