Theoretical modeling of interstitial carbon impurities in paramagnetic Fe-Mn alloys

Abstract

We present a generalization of a model that takes into account the magnetic disorder of paramagnetic host with interstitial point defects towards the case of alloy hosts. In the framework of disordered local moment approach combined with magnetic sampling method, we calculate solution enthalpy of carbon impurity in the paramagnetic fcc Fe-Mn steels. First, we use the magnetic special quasirandom structure (M-SQS) method for simulation of the paramagnetic state in Fe-Mn alloys without impurity. Here, Fe and Mn atoms are randomly distributed at the sites of a supercell following the chemical SQS method. Next, to calculate the energies for various magnetic realizations around the interstitial carbon impurity, we vary the position of the impurity within the SQS. Our calculations show that in alloys containing $\ensuremath{\sim}20$ at. % Mn, the solution enthalpy of carbon reduces compared to the pure fcc-Fe. By analyzing the local and global effects of impurity on the properties of the matrix, we discuss various factors that could increase the carbon solubility in high-manganese austenitic steels.