Direct evidence for the formation of ordered carbides in a ferrite-based low-density Fe-Mn-Al-C alloy studied by transmission electron microscopy and atom probe tomography

We study the structure and chemical composition of the kappa-carbide formed as a result of isothermal transformation in an Fe-3.0Mn-5.5Al-0.3C alloy using transmission electron microscopy and atom probe tomography. Both methods reveal the evolution of kappa-particle morphology as well as the partitioning of solutes. We propose that the kappa-phase is formed by a eutectoid reaction associated with nucleation growth. The nucleation of kappa-carbide is controlled by both the ordering of Al partitioned to austenite and the carbon diffusion at elevated temperatures. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.