Coincidence structures of interfacial steps and secondary misfit dislocations in the habit plane between Widmanstätten cementite and austenite

The stepped habit plane between Widmanstatten cementite and austenite related by the Pitsch or T-H orientation relationship (OR) has been rationalized in terms of equilibrium interfacial structures using a CCSL/CDSCL model. The secondary lattice misfit in the habit plane is accommodated completely by the set of secondary edge dislocations, whose Burgers vector, a vector of the CDSCL, is inclined to the habit plane. Each dislocation core is coincident with the riser of a step, whose terrace plane contains dense CCSL points. Although the Burgers vectors of the secondary dislocations have not yet been determined experimentally, the calculated interfacial structures are consistent with the observed geometry of the linear defects and the extra planes associated with the steps. The condition for the OR to permit the coincidence structure is equivalent to the g parallelism rule applied previously, showing a direct link between the microscopic structure and the macroscopic description of the habit plane.  2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.