Crystallography of Eutectoid Decomposition in the FeO Oxide Layer Formed on Steel Surface

The crystallographic aspects of the 4FeO→Fe3O4+Fe eutectoid decomposition have been examined by means of transmission electron microscopy. The eutectoid decomposition product exhibits a “pearlite-like” structure comprising α-Fe and Fe3O4 lamellae. Two α-Fe/Fe3O4 orientation relationships were observed, and they are those of the Bain and the inverse Nishiyama-Wassermann types, the former showing the well-defined (100)α−Fe//(100)Fe3O4 habit plane. The formation of these two orientation relationships arises probably from the epitaxial nucleation of α-Fe on the surface of a Fe3O4 particle.