Mechanical Properties and Fracture Characteristics in High Mn Austenitic Steel for Cryogenic Applications

Material applied in low-temperature liquefied gas storage tanks is required to have sufficient toughness. In recent years, high Mn austenitic steel has attracted attention for use in this application. In this study, the basic deformation characteristics and toughness of high Mn steel containing about 25% Mn were compared with those of 9% Ni steel in order to investigate the applicability of high Mn steel to LNG tanks. The high Mn steel showed larger uniform elongation than the 9% Ni steel due to higher strain-hardening, but elongation after the maximum load was significantly smaller. The plastic flow stress of the high Mn steel increased with decreasing temperature and showed temperature dependence similar to that of 0.2% proof stress in the 9% Ni steel. The Charpy absorbed energy of the high Mn steel was about half that of the 9% Ni steel, with an average value of 86 J at 77 K. Cleavage fracture surfaces were not observed in the fracture surfaces obtained at any temperature, indicating the micro-void coalescence type of fracture. The characteristics of ductile damage in the high Mn steel were discussed based on observation of micro-voids.