Effects of temperature and grain size on the TRIP behaviour of 201LN austenitic stainless steel: Experiments and molecular dynamics simulations

We investigate the effects of temperature and grain size on the transformation-induced plasticity (TRIP) behavior of an AISI 201LN austenitic stainless steel. Three distinct microstructures with different grain sizes are produced through annealing at different temperatures. Quasi-static tensile tests are conducted at temperatures ranging from 123 K to 573 K to evaluate mechanical properties. Microstructural evolution and deformation mechanisms are characterized using electron backscatter diffraction and transmission electron microscopy. The results indicate that lowering the deformation temperature significantly promotes martensitic transformation, owing to a reduction in stacking fault energy with decreasing temperature, as confirmed by molecular dynamics (MD) simulations. Additionally, larger grain sizes reduce the extent of martensitic transformation by decreasing deformation band intersections, which act as nucleation sites for the BCC martensite. A structure-based strength model effectively describes the yield strength variation among the samples, and annealing at 1373 K providing an optimal combination of strength and ductility. The findings highlight the critical roles of thermal and microstructural conditions in controlling the TRIP effect in metastable austenitic steels.