Fatigue behavior improvement of hardened parts using sequential hard turning, grinding, and ball burnishing operations

One of the major problems encountered in hardened components such as roller bearings, which work under fatigue loading conditions, is that the requirement of higher surface finishes (≈0.15 µm Ra) cannot be achieved by the sequential hard turning and ball burnishing processes. Such high surface qualities can be generated by additional finishing operations such as grinding. However, despite the improvement in the surface roughness, the grinding process increases both the tensile surface residual stresses and crack initiation sites on the ground surface; therefore, the fatigue behavior of the component may deteriorate. In this study, the effects of adding a grinding operation before the ball burnishing process on the fatigue behavior of AISI 4130 steel were experimentally studied. According to the achieved results, the burnished pre-ground samples show a considerable reduction in the final surface roughness and, at the same time, higher microhardness, higher endurance limit, and smaller area of the fatigue cracking zone. The burnished pre-turned and burnished pre-ground samples showed 4.24% and 10.95% improvements in the endurance limit compared to that of the turned samples, respectively.