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

Abstract

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.