Relationship Between Surface Topography and Fatigue Life of Deep Rolled AISI 4140 Steel

Abstract

Abstract Deep rolling is an effective and economically viable mechanical surface treatment that induces surface deformation by the action of a rolling tool. It is capable of reducing roughness, increasing hardness and inducing compressive residual stresses on the workpiece surface, thus increasing the fatigue strength of the component. This behavior, however, is only achieved with use of suitable parameters. This work investigates the surface topography and fatigue life of hardened AISI 4140 steel subjected to turning followed by deep rolling under distinct conditions. The findings indicates that for the turned samples, roughness increases with turning feed rate, resulting in fatigue life reduction. Deep rolling promotes a roughness reduction and an increase in fatigue life and, surprisingly, the samples with the highest surface roughness after turning achieved the longest fatigue lives after deep rolling. The areal power spectral density (APSD) analysis of the surface topography was able to identify distinct effects of deep rolling for each level of pressure used. The morphology analysis indicates an initial loss of orientation, followed by the creation of a new orientation after deep rolling under high pressures. Furthermore, the interaction between deep rolling feed and deep rolling pressure presents a significant effect on the roughness parameters, indicating that different behaviors depend on each parameter level used. Deep rolling also affects the form of the fatigue fracture, reducing the number of nucleation sites, and modifying the final overload fracture site.