The effects of strain rate, adiabatic heating, and stress/strain state on strain-induced martensitic transformation in metastable austenitic stainless steel: Experimental and Numerical study

Abstract

In this work, the mechanical response and the transformation kinetics of metastable austenitic stainless steel were studied under uniaxial tension, simple shear, and plane strain. Simultaneous in-situ synchrotron X-ray diffraction (XRD), infrared (IR) and digital image correlation (DIC) measurements were used to investigate the effects of strain rate, adiabatic heating, and stress/strain state on the strain-induced martensitic transformation in this steel. The results indicate that the α′-martensite transformation rate is notably stress-state dependent at both strain rates of 10−3 s−1 and 1 s−1. The highest transformation rate occurred in the plane strain loading and the lowest in the simple shear state. When the strain rate was increased from 10−3 s−1 to 1 s−1, the α′-martensite volume fraction decreased for all specimens. This effect was the largest in the uniaxial specimen and was attributed to adiabatic heating and changes in microstructural evolution. The deformation behavior and transformation kinetics were accurately predicted in finite-element simulations by a combination of a continuum plasticity model and the Olson-Cohen (OC) model under uniaxial and plane strain conditions. However, the FEM simulations were less accurate under simple shear loading. It was shown that revising the parameters of the OC model improves the prediction. This adjustment suggested a new interpretation of the shear band formation in the simple shear state, i.e. a significant formation of faulted austenite (γ) with ε-martensite signature. The higher volume fraction of faulted γ in the simple shear specimen compared to that in other specimens was validated by the in-situ X-ray diffraction data.