The behavior of C and N atoms in Fe-based solid solutions was studied by means of ab initio density functional theory calculations. The interaction of such a C or a N atom with a vacancy, with other C or N interstitials or with self-interstitial atoms, was compared with experimental results. The migration of these 2 foreign interstitial atoms was determined in pure Fe, or when a vacancy was present in the super-cell. According to the results, there was a strong binding energy of C or N to vacancies, whereas repulsion was observed for self-interstitial atoms. A vacancy could trap up to two C atoms, and covalent bonding formed between the atoms. The situation for N atoms was not as clear, and competition between the formation of N-V pairs and NN-V triplets was suggested to be likely.

Ab initio Study of Foreign Interstitial Atom (C,N) Interactions with Intrinsic Point Defects in α-Fe. C.Domain, C.S.Becquart, J.Foct: Physical Review B, 2004, 69[14], 144112 (16pp)