Influence of Ultrasonic Shot Peening on Microstructure, Mechanical, and Electrochemical Behavior of 316 Stainless Steel

The influence of severe plastic deformation induced by ultrasonic shot peening (USP) on evolution of microstructure and the resulting properties of 316 austenitic stainless steel is evaluated. Microstructural characterization was carried out by using optical, scanning, and transmission electron microscopies in addition to electron backscattered diffraction, x-ray diffraction and x-ray photoelectron spectroscopy. Mechanical properties were evaluated using hardness and sliding wear tests. USP resulted in high dislocation density and refined microstructure that led to significant increase in hardness. Although no strain induced martensite formed after USP at room temperature, USP carried at cryogenic temperatures led to martensite formation indicating the importance of temperature in USP on strain induced martensite development. Contrary to this, sliding wear at room temperature led to martensite development suggesting dominant role of deformation mode on martensite development during sliding wear. Sliding wear mechanism involved abrasion of steel accompanied by plastic deformation. Localized corrosion resistance improved due to nanostructured surface produced after USP enhancing the diffusional transport of chromium to surface. XPS analysis revealed higher Cr: Fe ratio in the oxide film after USP. Simultaneous enhancement of wear and corrosion resistance of stainless steels by the application of USP is discussed.