Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 33: Phase Transitions I

MM 33.6: Talk

Wednesday, March 25, 2009, 16:00–16:15, IFW B

An atomistic study of low-C tetragonal Fe-C states — •Alexander Udyansky, Johann von Pezold, Martin Friák, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Strasse 1, 402 37, Düsseldorf, Germany

The tetragonal states of interstitial Fe-C solid solutions are known as martensite, a metastable product obtained by quenching high-temperature austenitic fcc solutions with high C content. Along such a processing route, the tetragonality is proposed to be due to Bain’s fcc–bcc diffusionless transformation. It has been long speculated that the tendency towards tetragonal distortions is an inherent property of the Fe matrix, i.e., it should manifest itself also at low C concentrations, independently on the processing route. To address this issue we calculated the chemical contributions of the interatomic interactions using EAM-potentials [1] and the strain-induced long-range interactions within the microscopic elasticity theory. Our study predicts tetragonal states to be preferred also at low C concentrations due to thermodynamically driven [2] orientational ordering of carbon interstitials. These states are found stable only below their order-disorder transition temperature. Above this temperature the loss of the orientational ordering results in the experimentally observed cubic ferritic phase.

1. T.T. Lau, C.J. Först, et al., PRL 98, 215501 (2007).

2. M.S. Blanter, A.G. Khachaturyan, Phys. Stat. Sol. A 51 291 (1979).