Carbon Clustering in Low-Temperature Bainite

The bainitic ferrite phase formed at temperatures below 573 K (300 °C) in high-carbon high-silicon steels holds an amount of carbon well above that expected from the thermodynamic paraequilibrium with austenite. Diffraction experiments have shown that the ferrite lattice is sufficiently Zener-ordered to possess a tetragonal symmetry, which allows the structures to be supersaturated in carbon. It could be expected that carbon undergoes ordering beyond that indicated by the Zener-ordering temperature as in the early stages of tempering of Fe-based martensites. This study examines the formation of cluster arrangements of carbon within bainitic ferrite and their relationship to the tetragonal distortion.This research was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) in the form of two Coordinate Projects (ENE2015-70300-C3-2-R and MAT2016-80875-C3-1-R); and the Research Fund for Coal and Steel under the Contract RFSR-CT- 2014-00019. APT was conducted as a part of a user proposal at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy Office of Science User Facility. R.R. heartfully thanks R.E. Hackenberg, who provided a good piece of history and insight that greatly assisted the course of this research.Peer Reviewe