Quench Temperature-Dependent Phase Transformations During Nonisothermal Partitioning

Abstract

An attempt has been made to estimate the amount and composition of different phases formed during the simulated quenching and nonisothermal partitioning (Q&P) process in a dilatometer by matching the experimental dilation data with empirically determined dilation curve. The result highlights the carbon enrichment of austenite, as well as its partial transformation to secondary martensite and/or bainite, during the partitioning step. Also, an increase in quench temperature (QT) led to enhanced bainite or secondary martensite formation, as a result of reduced carbon enrichment of remaining austenite. Further Q&P experiments on bulk samples were carried out to understand the dependence of carbon diffusion and subsequent microstructure evolution with QT. Although the change in experimentally obtained retained austenite (RA) content with QT corroborates with the existing model predictions, the maximum amount of RA was observed at QT lower than predicted. The half-thickness of RA films increased with increasing QT, which substantiates the theoretical prediction of the diffusion distance of carbon atoms in austenite.