Microstructure evolution in 439 stainless steels under tensile: phase field simulation and experiment

A combination of phase-field simulations and experimental validation is utilized to examine the effect of annealing tension on the microstructure evolution of 439 ferrite stainless steel (FSS). The study reveals the competing mechanisms of texture under tensile stress. Furthermore, a phase field model that incorporates anisotropic grain boundary (GB) energy and elastic energy is established. The microstructure of 439 FSS is created using a 3D reconstruction strategy based on the 2D electron backscatter diffraction characterization proposed in this work. Elastic constants are calibrated using actual alloy data and determined through molecular dynamics simulations. Finally, simulations of the grain coarsening process in 439 FSS are successfully achieved, considering both tensile stress and anisotropic GB energy effects. The results reveal that the presence of low-angle GBs deviates from Hillert model predictions in terms of grain size distribution and slows down the average grain size evolution over time. A significant deviation in the grain size distribution, compared to Hillert predictions, is observed in the textured system under tensile stress. The results of growth kinetics indicate that tensile stress promotes grain growth more than GB energy anisotropy retards microstructure evolution. Both experiment and simulation results consistently demonstrate that grains with <111>//ND orientation experience a better growth proficiency compared to grains of other orientations under tensile stress. This investigation offers fresh insights into managing the ferritic microstructure of FSS to enhance its formability capabilities.