The atomic habit plane (or terrace plane) of proeutectoid cementite plates in austenite had been deduced to be (1¯13)A||(101)C on the basis of transmission electron microscopy and computer-aided atom-matching. High-resolution transmission electron microscopy was used here to determine directly the atomic structure and atomic habit plane of the cementite/austenite interface; corresponding to the broad faces of cementite plates. An Fe-13Mn-1.3wt%C alloy was isothermally reacted (650C, 100s) in order to form cementite plates that were embedded in a completely retained austenite matrix. The high-resolution transmission electron microscopic observations confirmed directly the previous deductions that (1¯13)A||(101)C was the terrace plane of proeutectoid cementite plates at the atomic level, that the cementite/austenite interfaces contained ledges with a [010]C||[110]A line direction, and that the ledges resulted in an average habit plane for cementite plates that was inclined with respect to the (101)C||(1¯13)A terrace plane. The ledge plane which connected adjacent (1¯13)A||(101)C terraces was determined to be (101)C||(1¯13)A. It was therefore not orthogonal to the terrace plane. An almost perpendicular pair of edge misfit dislocations was associated with each ledge and terrace. One or both of these dislocations had to climb in order for the cementite/austenite interface, in the vicinity of the ledges, to migrate. The ledges were intrinsic features of the interface. In most cases, they did not result from the intersection of faults or other defects with the cementite/austenite interface.

Atomic Structure of the Austenite/Cementite Interface of Proeutectoid Cementite Plates. J.M.Howe, G.Spanos: Philosophical Magazine A, 1999, 79[1], 9-30