The fatigue damage of automobile gear tooth surface is caused by the repeated action of automobile gear on the tensile stress generated when the tooth surface contact stress and the relative sliding speed of tooth surface meshing are different. The damage forms are mainly surface damage, pitting and peeling. Figure 1 shows an example of gear pitting damage.
The fatigue pitting life of automobile gear tooth surface is directly proportional to the surface temperature, roughness and friction coefficient of automobile gear tooth surface during gear meshing, and inversely proportional to the dynamic viscosity of lubricating oil. Generally, improving the hardness and tempering softening resistance of materials at high temperature can effectively increase the fatigue life of automobile gear tooth surface. The test shows that increasing the carbon mass fraction of automobile gear tooth surface from 0.8% ~ 1.0% to 2.0% ~ 3.0% can inhibit the high-temperature softening of material surface. However, due to the large precipitation of micro carbides during high concentration carburizing, the carburizing time and diffusion time need to be strictly controlled. Figure 2 shows the relationship between hardness, surface distance and surface temperature of high concentration carburizing and ordinary carburizing.
Another method is to appropriately increase the content of Si, Cr and other alloy elements in the material and implement the carbonitriding heat treatment method, which can greatly improve the contact fatigue life of automobile gear tooth surface. As shown in Figure 3, the pitting fatigue test results of gear steel with different alloy composition on the power cycle test bench are compared (CQT: carburizing, cnqt: carbonitriding).
