Very High Cycle Fatigue Behavior of SAE52100 Bearing Steel by Ultrasonic Nanocrystalline Surface Modification

In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (similar to 10 mu m) were refined to nanosize (similar to 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to similar to 400% and similar to 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by similar to 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen.