Investigating the difference in mechanical stability of retained austenite in bainitic and martensitic high-carbon bearing steels using in situ neutron diffraction and crystal plasticity modeling

TL;DR

This study compares the stability and transformation behavior of retained austenite in bainitic versus martensitic high-carbon steels using in situ neutron diffraction and crystal plasticity modeling, revealing microstructure-dependent transformation characteristics.

Contribution

It provides new insights into how microstructure influences austenite stability and transformation kinetics in high-carbon steels through combined experimental and modeling approaches.

Findings

Retained austenite transforms at lower strain in bainitic microstructures.

Transformation rate of austenite is higher in martensitic microstructures.

Austenite stability is greater in martensitic matrices under identical loading.

Abstract

In situ neutron diffraction of the uniaxial tension test was used to study the effect of the surrounding matrix microstructure on the mechanical stability of retained austenite in high-carbon bearing steels. Comparing the samples with bainitic microstructures to those with martensitic ones it was found that the retained austenite in a bainitic matrix starts transforming into martensite at a lower strain compared to that within a martensitic matrix. On the other hand, the rate of transformation of the austenite was found to be higher within a martensitic microstructure. Crystal plasticity modeling was used to analyze the transformation phenomenon in these two microstructures and determine the effect of surrounding microstructure on elastic, plastic and transformation components of the strain. The results showed that the predominant difference in the deformation accumulated was from the transformation strain and the critical transformation driving force within the two microstructures. The retained austenite was more stable for identical loading conditions in case of martensitic matrix compared to the bainitic one. It was also observed that the initial volume fraction of retained austenite within the bainitic matrix would alter the onset of transformation to martensite but not the rate of transformation.