Influence of Friction Stir Processing on Wear, Corrosion, and Fracture Toughness Behavior of 2507 Super Duplex Stainless Steel

Abstract

Super duplex stainless steels (SDSS) are used in offshore applications and oil/gas plants operating under severe service conditions due to their superior mechanical and electrochemical properties. Fracture toughness, wear and corrosion resistance of a material depends largely on its microstructure and can be improved by refining the latter. Friction stir processing (FSP) can be employed to refine the microstructure of the material, resulting in superior fracture toughness, wear, and corrosion resistance. In the present research, SAF 2507 SDSS was subjected to FSP with optimized processing parameters to study the influence of FSP on fracture toughness, wear, and corrosion resistance of the material. It was observed that FSP refined alloy grains by decreasing the grain size from an average of 160 µm in the base metal to 2-30 µm in the stir zone. Refinement of grains increased the hardness of the material, which enhanced its wear resistance by more than 15%. Wear track and debris analysis revealed the change in wear mechanism of the processed material. FSP also modified the surface composition of processed material, which served to improve its corrosion resistance by more than 80%. Morphology of the corroded surfaces of base and processed material showed that the processed material was more resistant to corrosive attacks than base material. FSP enhanced the grain boundaries in the processed region which improved the fracture toughness after exposure to accelerated corrosion by about 26%. Fractographic study revealed that processed material had brittle fracture behavior while base material had ductile fracture behavior.