Structure and stability of Fe2C phases from density-functional theory calculations

Fe2C plays a crucial role in the precipitation of iron carbides. Jack's structural models for epsilon-Fe2C, and non-stoichiometric epsilon-Fe2.4C, are analyzed using first-principles calculations. Several new configurations of epsilon-Fe2C with even higher stability are found. We show how epsilon-Fe2C transforms into eta-Fe2C, and address the structural relationships with the chi-Fe5C2, theta-Fe3C and Fe7C3 phases. The relative occurrence of these phases in steel, as well as their probable evolution during tempering of quenched steels, is discussed. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.