Effect of Ultrasonic Shot Peening on the Microstructure of Austenitic Stainless Steel 316 and Super Duplex Stainless Steel UNS S32750

摘要

Shot peening for nanocrystallization of the surface region is a good way of improving corrosion-, fatigue-, and wear-resistance, etc. of metallic parts (Lu, K., 2014. Making strong nanomaterials ductile with gradients. Science, 345 (6203), pp.1455-1456). The technique has been widely used for various materials as a method of surface modification. SUS316 has excellent corrosion and oxidation resistance with good formability. However, its application is limited by the low mechanical strength and hardness. S32750 (duplex stainless steel) is one of most used tubing materials for oil/gas delivery systems in a corrosive environment under high pressure (Nilsson, J.O., 1992. Super duplex stainless steels. Materials Science and Technology, 8(8), pp.685-700). Thus, improving corrosion resistance is a key for the wider application and better maintenance of S32750. In our study, the alloy S32750 was heat-treated at 1070 degrees C to obtain a precipitation-free microstructure (gamma and delta dual-phase structure). It was then ultrasonic shot peened and microstructures were analyzed for: (1) surface nanocrystallization, (2) effect of the treatment processing parameters, and (3) the determination of microstructural evolution and the effect of the shot peening process.