Effect of ultrasonic nanocrystal surface modification on surface and fatigue properties of quenching and tempering S45C steel

Abstract

Ultrasonic nanocrystal surface modification (USNM) utilizing ultrasonic vibration energy is a method which induces severe plastic deformation to a material's surface and an enhanced surface layer in order to produce a nano-structured surface. In this paper, USNM was performed to enhance the surface properties of quenched and tempered S45C steel by producing a nanostructured surface layer. Various processing parameters, such as static loading (50N, 60N and 70N) and processing density (34,000mm−2 and 68,000mm−2), were applied in the surface treatment. The microstructure, hardness and residual stress of the material were analyzed. A rotating bending fatigue test was used to investigate the fatigue properties of the enhanced surface layer. A maximum static load of about 50N was found for S45C steel process. As the strike number increased, a deeper refined grain layer and higher compressive residual stress was produced on the material's surface. The fatigue strength can be improved from 464Mpa to about 550Mpa through this process. Surface cracks, formed due to a heightened processing density of 68,000mm−2, were found on the top surface layer of the material and large processing density was the reason of the formation of cracks.