On the Unified Interaction Parameter Formalism and Its Application in Critical Reassessment of Pearlitic Transformation in Fe-C-Mn System

Abstract

The significance of local equilibria (LE) models in understanding phase transformations in multicomponent steels has been revisited and the necessity for a firsthand computational tool capable of estimating metastable ferrite–austenite and cementite-austenite phase boundaries along with possible LE modes has been realized. For this purpose, thermodynamically consistent Unified Interaction Parameter Formalism (UIPF) has been adopted owing to its computational simplicity. All the necessary parameters required for UIPF-based simulations in Fe–C–Mn system, have been evaluated in the present work. The UIPF-based framework has been shown to be a computationally simple yet an efficient tool for prediction of metastable phase boundaries at low temperatures and wide composition range in the Fe–C–Mn system, where most of the available commercial thermodynamic simulation packages have prediction limitation. The phase boundaries predicted using UIPF have been validated with those predicted by ThermoCalc®, wherever possible/available. Additionally, existing experimental data on growth rates, interlamellar spacing, and partitioning coefficients prevalent during pearlitic transformation in Fe–C–Mn systems have been used to validate the predictions by different LE models adopting UIPF, which in turn affirms the potential of UIPF in predicting thermodynamics and kinetics of phase transformation in Fe–C–Mn systems.