Grain size dependence of hot deformation behaviors and resultant hot ductility in cryogenic high-manganese steel

As an emerging material with excellent cryogenic performance and cost advantages, high manganese steel is a promising candidate for low-temperature storage tanks. However, these high manganese steels often suffer from severe plastic damage at intermediate temperatures (700∼900 °C) during hot processing, hindering their widespread engineering application. In this study, by controlling the water toughening temperature, we have successfully controlled the grain size of high manganese steel to around 10 μm, achieving a minimum reduction of area value exceeding 70 %, effectively overcoming this critical issue. The fine original grain size is a primary factor in obtaining excellent hot ductility, with the minimum reduction of area dramatically decreasing to below 40 % when the grain size is 29.2 μm. Dynamic recrystallization (DRX) primarily occurs along the boundaries and positions with high orientation gradients. A decrease in grain size accelerates DRX kinetics by reducing the critical stress. The DRX fractions for the 10.0 μm, 15.8 μm, and 29.2 μm samples at 900 °C are 22.8 %, 13.3 %, and 0 %, respectively. Additionally, during the hot deformation process, large grains exhibit more pronounced uneven deformation behavior compared to fine grains, and with the increase in deformation temperature, the degree of softening in large grains is much smaller than that in small grains. Deformation is concentrated near the grain boundaries in large grains, while the central regions experience minimal deformation, leading to difficulty in coordinating deformation and resulting in slip failure near the grain boundaries.