The causes of reducer shaft fracture were analyzed using macro- and micro-morphological analysis, chemical composition analysis, mechanical property testing, and SEM micro-morphological analysis. The results showed that non-standard heat treatment process, resulting in viscous microstructure, was the main cause of reducer shaft fracture; unreasonable keyway design accelerated the fracture of the reducer shaft.
The fractured reducer shaft was cut and sampled. The surface morphology of the fracture surface was macroscopically examined, the chemical composition of the reducer shaft was analyzed using a read-only spectrometer, the microstructure of the reducer shaft from the surface to the core was studied using a metallographic microscope, the microhardness of the reducer shaft was tested using a microhardness tester, and the micromorphology of the reducer shaft fracture surface was observed using a scanning electron microscope (SEM).
The results of direct-reading spectroscopic chemical composition analysis of the reducer shaft material are shown in Table 1. The composition analysis results show that the reducer shaft material is carbon steel and does not contain other alloying elements. According to the general material selection principles for shaft parts and in combination with the chemical composition range of 45 steel specified in the national standard, except for the silicon content which is slightly excessive, the other elements meet the requirements of high-quality steel. Therefore, it can be determined that the reducer shaft material is 45 steel.