With the medium frequency induction heating power supply, there is no need to worry about the fracture defects of the spiral bevel gear shaft anymore.

The spiral bevel gear shaft is an important part of the micro-car transmission mechanism, and the workpiece material is 20CrMnTi steel. The gear is die forged, normalized after forging, 880-900℃, then machined, carburized and quenched and tempered. Pre-carburizing at 870℃, strong penetration at 830℃, diffusion at 870℃, cooling to 830℃, oil cooling quenching. Final tempering at 180-200℃. During production, it was discovered that many fracture and failure accidents occurred in the spiral bevel gear shaft, seriously affecting product quality and economic benefits. After analyzing the causes of the defects, it was found that the use of medium-frequency induction heating power for quenching heat treatment had good results and avoided the occurrence of the above defects.

The inspection found that the broken parts of the gear were mostly at the transitional fillet between the gear and the shaft, and some were broken and damaged in the middle of the gear shaft. Chemical composition analysis found that the content of impurity elements such as S, P, Si, and Cu in the workpiece steel was too high, and the content of some elements such as S and P was as high as 10 times or more than the standard value. Scanning electron microscopy fracture observation revealed that the fractures were intergranular fractures. There are a large number of large Si-A1 inclusions, A1-Si inclusions and Ca-Mg inclusions as well as Ca-A1-Si inclusions and loose hole defects in the fracture source area.

Analysis shows that the content of S, P, Si, and Cu impurities in the gear material is too high, especially the content of S and P is too high, which is segregated on the grain boundaries and is prone to intergranular fracture of the workpiece, which is the main reason for the early fracture of the gear shaft. . At the same time, there are many large non-metallic inclusions in the fracture source area, which have low strength and are equivalent to cracks on the surface of the workpiece. Under low stress, cracks initiate and expand and cause brittle fracture of the part. The presence of a large number of non-metallic inclusions in the fracture source area is An important cause of workpiece breakage. In addition, the transition fillet between the gear and the shaft is where the stress is concentrated after machining, thus causing the workpiece to break. When the external force on the gear shaft exceeds the tensile strength of the defective part of the workpiece, it is natural for the gear shaft to break.

Based on the above analysis, the following measures are proposed to prevent the fracture failure of the 20CrMnTi spiral bevel gear shaft:

(1) Strictly implement quality inspection indicators for gear steel 20CrMnTi steel rods to prevent excessive impurity elements such as P, S, Cu, Si, etc. and excessive inclusion content. Inclusions, especially S and P that seriously exceed the standard and a large number of non-metallic inclusions are the fundamental reasons for the fracture of the workpiece.

(2) Use a medium frequency induction heating power supply for quenching heat treatment at a temperature of 800°C and water cooling.

After adopting the improved technology, the fracture defects of the spiral bevel gear shaft have disappeared, and the service life has been greatly improved, meeting the needs of the work. What's even better is that this process is suitable for large-scale production and can greatly improve workers' production efficiency.