Carbon Clustering in Low-Temperature Bainite

The bainitic ferrite phase formed at temperatures below 573 K (300 degrees 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. (C) The Minerals, Metals & Materials Society and ASM International 2018