Effect of Al and Mo on interplay of stacking fault energy and carbide formation in high-Mn steels for cryogenic applications

To develop cost-effective, nickel-free steels suitable for cryogenic applications, present study investigated the effects of Mo and Al on the microstructure and mechanical behavior of V-containing high-manganese austenitic steels. All alloys maintained austenitic phase after deformation at both room and cryogenic temperatures. Mo addition promoted grain refinement and elevated dislocation density, thereby enhancing strength but decreased ductility and impact toughness at low temperatures. In contrast, the Al-induced increase in SFE slowed the twinning rate, and the relatively lower carbide fraction elevated the matrix carbon content, thereby improving elongation and Charpy impact energy under cryogenic conditions. The combined Mo and Al addition resulted in intermediate mechanical properties, indicating the competing influences of carbide formation and SFE modification. Although Mo had a negligible effect on SFE, it promoted the formation of V-Mo-rich MC type carbides, which influenced work hardening and fracture behavior through solute drag and precipitation strengthening. These findings highlight the distinct roles of Mo and Al and provide insight into the design strategy for Ni-free steels with enhanced cryogenic performance.