Regensburg 2010 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 20: Topical Session Designing Innovative Structural Materials and Steels VI

MM 20.1: Talk

Tuesday, March 23, 2010, 11:30–11:45, H4

Ab initio analysis of the carbon solubility limits in various iron allotropes — Olga Kim, •Martin Friák, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 402 37, Düsseldorf, Germany

The solubility limits of carbon in various iron phases are of critical importance for many steel-industry applications. The actual values are difficult to measure accurately in ferrite and they have so far not be determined theoretically from first principles in austenite. The solubility limits of carbon in α, β, γ, and δ iron have been thus determined employing density functional theory calculations over the entire temperature range. The results show excellent agreement with experiment. The two-orders-of-magnitude higher solubility of carbon in austenite than in ferrite has been quantitatively analyzed and a complex interplay between two distinct phenomena has been found. First, the number of first nearest neighbors is higher in the fcc structure than in the bcc structure and the carbon atom is consequently more strongly bound, and secondly, the strain energy between the C-interstitial and the surrounding iron matrix is lower in the fcc lattice. The details of the actual magnetic state have not been found as important as the above mentioned two mechanisms.