Microstructure evolution and mechanical properties of bimodal grain sized 301 stainless steel strip induced by reverse phase transformation

The sub-micron bimodal grain structure of 301 austenitic stainless steel stripe obtained by phase reversion process, and the relationship between grain size distribution and mechanical properties was described in this study. With the change of annealing heating rate under the industrial condition 10 °C/min, the bimodal grain size of submicron scale was obtained at 750 °C. By analyzing the micrograph of bimodal structure, it was found that the deformed martensite transformed to austenite through diffusion transformation, and the recovery austenite grain had obvious size distribution. It was found that the bimodal structure was easier to form under the condition of slow heating rate, and the ultra-fine grain materials with high performance were obtained by controlling the annealing parameter. The high-density grain boundary of ultrafine grain presents microvoid in the tensile fracture, and the streaks formed by the aggregation of holes can be observed, which is considered to be caused by deformation twinning. The large dimples in the coarse grain are observed, as the strain-induced martensite was formed in the large grain of the bimodal structure.