Austenite microstructure effect on martensitic transformation in TRIP steel: A phase-field study

Abstract

Martensitic transformation (MT) in steels has been issued in various industrial applications due to its high strength. However, despite of the numerous theoretical and experimental studies, the rapid diffusionless transformation and the complex microstructure left the further understandings.

A two dimensional phase-field model coupled with a microelasticity theory is proposed to investigate the MT. Paying attention to the initiation of the MT, an energy barrier model for the MT is introduced by taking into account the effect of the alloying elements. In this study, two parts of the MT were investigated, prediction of the martensite start (Ms) temperature and interpretation of the MT behaviors during deformation.

Simulations predict the Ms temperature with a good agreement with the experimental data and the previous model. In addition, Ms temperature decreases as prior austenite grain size (pAGS) decreases due to the strain energy, so the microstructure evolution of the martensite is demonstrated. The MT under the external load is also investigated depending on the stability of retained austenite under the elasticity regime only. The chemical composition in the retained austenite was assumed using the thermodynamic scheme. The phase-field simulation indicates that the carbon enrichment in the retained austenite stabilizes it by restricting the increase of the Ms temperature from the external load, so the MT rate during deformation varies with the heat treatments.