An original unified approach for the description of phase tranformations in steel during cooling : first application to binary Fe-C

TL;DR

This paper introduces a unified theoretical framework based on Landau's theory to describe phase transformations in steel during cooling, providing a comprehensive classification and predicting transformation behaviors.

Contribution

It presents a novel, unified approach for describing steel phase transformations using Landau's theory, including a new classification and predictions of cooling rate effects.

Findings

Unified description of ferrite, bainite, martensite formation

Prediction of bainite start temperature dependence on cooling rate

New thermodynamic classification of transformation conditions

Abstract

Exploiting Landau's theory of phase transformations, defining an original order parameter and using the phenomenological transformation temperatures, it is reported that it is possible to describe in a global approach the conditions for the formation of each phase (ferrite, bainite, martensite) from austenite during cooling in steel. It allowed to propose a new rigorous classification of the different thermodynamic conditions controlling each phase tranformation. In a second step, the approach predicts naturally the effect of cooling rate on the bainite start temperature. Finally perspectives are assessed to extend the approach in order to take into account the effect of an external field such as applied stress.