Enhanced mechanical and anticorrosion properties in cryogenic friction stir processed duplex stainless steel

In the present work, duplex stainless steels (DSSs) SAF2507 were friction stir processed with flowing cryogenic medium mixed with liquid nitrogen and industrial ethanol. Homogeneous ultrafine grained (UFG) dual-phase structure with ferrite (α) and austenite (γ) grains with average size of around 1 μm was obtained due to the significantly lower peak temperature and shorter high-temperature duration. The developed UFG dual-phase structure enabled a dramatic enhancement of yield strength by about 22 %, while maintaining a high elongation of 55 % owing to the excellent strain hardening capacity. The grain refinement and increased number of α/γ interfaces were dominantly responsible for the significantly improved YS, while the massive development of geometrically necessary dislocations around the deformation incompatible α/γ interfaces primarily contributed to improving the strain hardening capacity. As a result, the enhanced strength-ductility synergy was achieved by cryogenic friction stir processing. Also, the obtained UFG dual-phase structure helps with enhancing corrosion resistance. This work provides a new strategy for preparing uniform UFG DSSs with outstanding mechanical properties and anticorrosion.