Crystal plasticity modeling of 316L austenitic steel sheets and tubes: Role of multiaxial deformation and temperature on the extent of strain-induced martensitic transformations

An elasto-plastic self-consistent crystal plasticity model integrating a stress state-dependent martensitic transformations model and a hardening law based on the evolution of dislocation densities was used to model and interpret the deformation behavior of 316 L stainless steel. The deformation of constituent grains in the model involved a combination of anisotropic elasticity and plasticity via crystallographic slip and phase transformations. The steel was tested in simple tension under several strain-rates and temperatures to record the data for the identification of model parameters. The calibrated and validated EPSC model was then used as a constitutive law in implicit finite elements (FE) for solving several boundary value problems including inflation/tension of microtubes and biaxial tension of sheets. These multi-level simulations enabled the verification of the FE-EPSC model to capture the strain-path sensitive deformation of the 316 L tubes and sheets. The extent of ${\alpha }^{\prime }$-martensite volume fraction and texture evolution were measured using electron-backscattered diffraction (EBSD) and neutron diffraction, while the strain fields were measured using digital image correlation (DIC) technique for the multi-level model verification. The evolution of geometry, mechanical fields, phases, and texture were predicted to agree well with the experimental measurements. The model successfully predicted more martensite formation under biaxial tension than uniaxial tension, consistent with the experimental measurements. Favorable comparisons of the predictions and experimental measurements allowed us to rationalize the origins of the martensitic transformation trends with deformation in 316 L steel. Although the uniaxial loading evolved crystallography of the structure to favor the martensitic transformation, the biaxial loading induced stress fields in the grains to cause large separations between partial dislocation giving rise to a greater extent of the martensitic transformation in biaxial than uniaxial loading.