Prediction of Carbon Partitioning and Austenite Stability via Non-equilibrium Thermodynamics in Quench and Partition (Q&P) Steel

Abstract

Thermodynamics-based predictive modeling for phase characteristics after the quench and partition (Q&P) process is key to the design of new alloys and processing cycles with the best combination of mechanical properties. The austenite carbon content influences its phase stability during mechanical deformation and thus determines the improvement to total elongation from transformation-induced plasticity. The current article describes a carbon partition model based on para-equilibrium simulations with the addition of a temperature-dependent effective stored energy model that predicts carbon enrichment in austenite after Q&P processing. A retained austenite stability model is also proposed that uses the predicted carbon in austenite to quantify the austenite stability in terms of the Msσ temperature. The developed models were calibrated and subsequently validated using measurements from advanced characterization techniques such as local electrode atom probe tomography, synchrotron-based x-ray diffraction and uniaxial tensile tests at varying test temperatures.