The impact of annealing temperature on the microstructure - Properties relationship of reversion-induced austenitic stainless steels

This study investigates the impact of annealing temperature on the microstructure and mechanical properties of reversion-induced, fine grain strengthened austenitic stainless steels (ASSs). Commercial Cr–Mn–N metastable ASS was cold-rolled at room temperature to a thickness reduction of 60% and then annealed at 700 °C and 1000 °C, respectively. The microstructural evolution of the annealed samples was characterized by optical and transmission electron microscopy (TEM); and by the scanning electron microscopy (SEM) techniques of electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The results indicated that at 700 °C, reversion of deformation-induced martensite (DIM) to austenite occurred via a combination of diffusion and shear mechanisms, while at 1000 °C, it occurred solely through a shear mechanism. The alterable DIM reversion behavior and controllable recrystallization process resulted in bimodal microstructure in specimens annealed at 700 °C and unimodal microstructure in specimens annealed at 1000 °C. Tensile test results revealed that specimens with a unimodal structure had higher yield strength, while specimens with a bimodal structure had larger elongation for the same average grain size. Comprehensive analysis reveals that the strength-plasticity combination for bimodal specimens was higher than for unimodal specimen. This superior plasticity is related to the formation of more geometrically necessary dislocations (GNDs), deformation twins (DTs), and DIM during tension.