Microhardness Profile and Residual Stresses Evaluation in a Shot Peened SAE 5160H Steel

Abstract

Shot peening (SP) is a surface cold hardening process used on metals to enhance life under cyclic stress. In this case, SP was applied to SAE5160H samples of steel quenched tempered in oil at 460 °C used for leaf springs. This study shows the residual surface stresses measured through X-ray diffraction (XRD) and the microhardness variation through the perpendicular-to-the-peened surface using a combination of metallographic preparation and Vickers microhardness (HVN). This combination of techniques makes possible measuring the SP effect in perpendicular-to-the-treated surface. A residual stress of -365.8 ± 78 MPa measured by XRD and a maximum microhardness of 525± at 92.7 HVN on the surface were obtained for the SP material. Alternatively, an average of 54.2 ± 54.3 MPa residual stress measured by XRD and 433 ± 39.5 HVN were obtained for the As-it-is samples. In addition, corrosion electrochemical potential tests showed that SP increases the corrosion potential, which makes this process undesirable if the SP component is exposed to aggressive environments. Moreover, the As-it-is samples presented not statistically significant HVN difference in the measured points. The combination of experimental techniques allows estimating hardness change in perpendicular-to-the treated surface separated by as little as 10 µm but with a simpler specimen preparation than other techniques such as XRD or strain gauges. Such a combination can be an alternative for estimating residual stresses through depth.