Modelling deformation-induced martensite transformation in high-carbon steels

The transformation behaviour of retained austenite in steels is known to differ according to chemical composition and other microstructural attributes. Earlier research indicated that austenite in high-carbon steels transforms into martensite only when the applied stress exceeds a critical value, contrary to low-carbon steels where transformation occurs in the early stages of deformation. Although transformation models have been proposed, most are optimised for low-carbon steels. Here, we propose physics-based models applied to high-carbon steels to overcome previous limitations. The models have fewer free parameters (4) compared to previous approaches (6), exhibiting improvements in the numerical and physical interpretation of the austenite transformation process. We envision the use of these models as tools for alloy design, also highlighting their scientific and technological value

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

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 the 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