Tensile and Charpy impact properties of heat-treated high manganese steel at cryogenic temperatures

The structural materials for the superconductor in next generation DEMO fusion reactor are in great demanded with excellent nonmagnetic and mechanical properties such as strength, toughness, and ductility at the cryogenic temperature. High-Mn steels, newly developed for application to cryogenic industry, including DEMO fusion reactor, can change its deformation mechanism by twinning, martensite transformation and dislocation slip according to the range of stacking fault energy (SFE). Therefore, it is very important to investigate the mechanism of deformation behavior at cryogenic temperatures. In this study, tensile tests and Charpy impact tests were performed to investigate the effects of heat treatment on mechanical properties of high-Mn steels at cryogenic temperatures. In addition, the deformation mechanism of high-Mn steels at room temperature and cryogenic temperature was investigated through various analysis such as microstructure, XRD, EBSD and TEM. As a result, phase transformation from austenite to ε and α'-martensite was generated in the tensile test with a slow loading rate at cryogenic temperatures, while ε and α'-martensite was not observed in the Charpy impact test with a high loading rate.