5th International High Manganese Steel Conference - HMNS 2022

Segregation engineering by controlling the solute decoration state of certain interfaces has recently been proposed as a new method to tailor mechanical properties in metallic materials. Despite the advancements in thermodynamic understanding of grain boundary segregation, the segregation behaviour at phase boundary in multiphase steels has largely remained untouched. Such information is deemed to be a key to further improve the damage tolerance of multiphase steels. In this study, we aim to investigate the dominant mechanisms of phase boundary segregation, based on Gibbs adsorption theory and elemental partitioning between adjacent phases. A detailed investigation using atom probe tomography (APT) analysis was carried out on a medium Mn steel with a ferrite-austenite two phase microstructure, which was subjected to low temperature tempering at 450℃ for varying durations (2, 50 and 200 hours). While the Mn concentration at the austenite-ferrite phase boundary was consistent throughout the course of tempering, the level of C segregation showed a decreasing trend with increasing tempering time. The underlying mechanisms of the observed phase boundary segregation and its change with tempering time will be discussed in this talk. Furthermore, a detailed analysis will be presented pertaining to the effects of orientation relationship between adjacent phases on the C and Mn segregation behaviour.