A Descriptive Model on the Grain Size Dependence of Deformation and Martensitic Transformation in Austenitic Stainless Steel

A descriptive model is presented on the austenite grain size dependence of deformation and martensitic transformation upon tensile loading of a metastable 301L grade austenitic stainless steel. Cold rolling and subsequent short-duration annealing of the as-received coarse-grained material at 973 K to 1023 K (700 °C to 750 °C) resulted in a mixed microstructure consisting of fine and ultra-fine grains (UFG) that showed a more pronounced γ → ε-martensite and γ → twin formation (precursors of α′-martensitic transformation) and finally more α′-martensite in the tensile-tested specimen. Whereas their coarse-grained (CG) counterpart facilitates only the former reaction, which eventually leads to less severe martensitic transformation in CG than that in UFG. The evolution of texture under tensile deformation is simulated using visco-plastic self-consistent (VPSC) model and compared with the experimental data obtained from interrupted tensile tests. Besides a thermodynamic approach, microstructural characterization using optical and electron microscopy (scanning and transmission), electron backscattered diffraction, nanoindentation, and transmission Kikuchi diffraction studies were realized to establish a mechanistic explanation on the grain size dependence of austenite stability against deformation-induced martensitic transformation.