Olga Kim, Martin Friák, Jörg Neugebauer

The difference in solubility of carbon between the austenite and ferrite is the basis for solid solution hardening of steels. The C-solubility is determined by the C-C interaction energy that influences the distribution of carbon atoms in both phases. The interaction energy in austenite is easily measurable and well known. However, in ferrite it hardly can be deduced experimentally due to the very low solubility of carbon in ferrite. Several experimental results have been reported in the literature, with the large repulsive interaction energy 1.56 eV [1-4]. Evidences of a clustering tendency have been discussed [5-7]. All studies reported large and unsystematic variations in the value of interaction energy as a function of distance between carbon atoms. In order to gain a detailed insight into this issue we determine theoretically the dependence of the C-C interaction energy in ferrite as function of the C-C separation by employing density functional theory (DFT) in the generalized gradient approximation (GGA).