Investigation on wear behavior for SUS420 steel gear based on discrete laser surface melting

Abstract

Gears are critical components that ensure the stable operation of a gearbox. In the era of mechanical equipment advancing towards higher speeds and heavier loads, more stringent requirements have been set for the wear performance of existing gears. Drawing inspiration from observations of natural organisms, particularly scallops, which have developed unique microstructure and excellent wear properties through long-term evolution, this paper focuses on the application of discrete laser surface melting (DLSM for short) technology to prepare units on the surface of SUS420 steel gears, simulating the radial rib structures found on scallop surfaces. The laser processing was carried out with varying defocusing amount and distribution types of discrete laser surface melted (DLSMed for short) units. The study encompassed microstructure observations, microhardness and residual stress testing, and bench wear experiments on DLSMed gears. The experimental findings reveal that a crack-free and porous-free hardened layer has formed on the tooth surface. The hardened layer consisted of the melting zone, heat-affected zone, and substrate, resulting in a surface structure characterized by alternating soft and hard phases. Comparing the wear behavior of as-received gear to DLSMed gears, it is evident that the wear damage on DLSMed gears is less pronounced. The DLSM treatment had altered the wear mechanism of the gears. During the wear test, the quantity of wear debris and iron (Fe) concentration in DLSMed gears consistently remained lower than that of as-received gears, indicating superior wear resistance in DLSMed gears. Furthermore, an increase in the defocus amount led to a deterioration in the wear performance of DLSMed gears. Notably, transverse units exhibited better efficacy in enhancing the wear resistance of gears compared to longitudinal units. There exists a positive correlation between the percentage of DLSMed unit area on the gear surface and the wear behavior of the gear.