Role of ultrasonic shot peening on microstructure, hardness and corrosion resistance of nitrogen stabilised stainless steel without nickel

Abstract

The influence of Ultrasonic Shot Peening (USP) was investigated on microstructure, hardness and corrosion behavior of nitrogen stabilised stainless steel without nickel in simulated body fluid (SBF). Specimens of 11.5 mm diameter and 4.5 mm thickness were subjected to USP with 2 and 3 mm diameter shots of hard steel, for time periods of 30, 60, and 120 s, separately. The hardness and roughness of the surface were found to increase from the USP treatment. The microstructure of the specimens in the Un-USP and different USP treated conditions was examined using optical microscope, SEM and TEM. There was a drastic reduction in the size of initial grains of 36-micron to fine grains of 15 nm in the surface region from the USP treatment. There is a progressive change in microstructure, from multidirectional slip to single direction which ultimately disappears, from the USP treated surface towards interior, up to certain depth, depending on the shot diameter and the duration of USP. Corrosion resistance of the specimens in different USP treated conditions was studied in SBF and was found to increase from USP with shots of 3 mm diameter for 30 s and with shots of 2 mm diameter for 60 s. There was decrease in corrosion resistance from longer duration of the USP treatment due to localised surface damage. © 2019 IOP Publishing Ltd.