Experimental Study of the Effect of Initial Surface Roughness on Ball Burnishing Forces and Endurance Limit of AISI 4130 Hardened Steel

Machining of hardened steels, which their hardness is generally higher than 45 Rockwell C, is called hard turning. These components usually work under dynamic loading conditions and require a high level of surface finish (in the order of 0.15 μm Ra) which cannot be achieved by sequential hard turning and burnishing processes. However, there are serious concerns about this complimant grinding operation; grinding process, on one hand increases tensile residual stresses and on the other hand, increases crack nucleation regions. Therefore, these two factors might decrease workpiece fatigue strength. So, in this paper, the effects of adding a grinding operation before ball burnishing process, have been experimentally studied on final surface roughness and burnishing forces; at the same time, in order to consider the possible destructive effects of grinding process, a set of experimental measurements including surface residual stresses and endurance limit measurement, have been done for AISI 4130 fatigue samples. Based on the achieved results, adding a grinding operation before burnishing process, has lead to 91.56% improvement in surface finish and 39.52% reduction in burnishing forces. In addition, surface residual stress are compressive and there is slight difference in the magnitude of compressive residual stresses in comparison to burnished hard turned samples. Due to these positive findings, endurance limit of produced samples show 10.95% improvement in comparison to burnished hard turned samples.