Microstructural evolution of cast super austenitic stainless steel during hot compression

Abstract

In the present paper, the effect of strain on the microstructure evolution of 7Mo-0.42N contained cast super austenitic stainless steel (SASS) during compression deformation at 1200 °C was systematically studied to optimize the hot working process. The dynamic recrystallization (DRX) grains size, recrystallization mechanism, annealing twin characteristics, and dislocation evolution during high-temperature deformation at varied strains were examined. Results show that the recrystallization behavior of the SASS during high-temperature compression can be divided into three stages. In stage I, the parent grain boundaries were gradually replaced by recrystallized grains, and observed both cyclic grain refinement and coarsening of grains. In stage II, the recrystallized grains elongated into the parent grain interior from the boundaries until the parent grain was completely covered. Meanwhile, the DRX and abnormal grain growth occurred simultaneously and developed rapidly at this stage. At stage III, the recrystallized grains abnormally grew to ∼76 μm and was deformed again because of the increased strain. The nucleation mechanism also changed during deformation. The discontinuous dynamic recrystallization (DDRX) dominated at stage I and II (ε = 0.1–0.6) with relatively low deformation strain. While in the high strain range of stage III (ε = 0.7–1.0), the continuous dynamic recrystallization (CDRX) took over. These quantitative statistics and analyses of data were carried out in terms of recrystallization grain size and nucleation mechanism under different strain variables, providing experimental basis and theoretical guidance for the production of SASS.