1. The chemical composition of sun gear material conforms to the requirement of chemical composition content of 42CrMo steel in alloy structural steel GB/T 3077-2015.The gear material belongs to high-quality alloy structural steel and no abnormal metallurgical quality defects have been found in the gear material.
2. Tooth fracture of solar gear material belongs to fatigue fracture caused by multiple accumulated damages, and the fatigue source is located at the root of the tooth.
3. The gear has not undergone surface hardening carburizing heat treatment, and the surface hardness of the gear does not reach HRC60+2.
4. Due to insufficient quenching and cooling, the material of sun gear has a brittle Widmanstatten structure.At the same time, there are segregation zones with large size due to uneven composition in the material, and there are structural differences between segregation zones and non-segregation zones. Therefore, large structural stresses occur in the material. The superposition of the structural stresses and working stresses is easy to induce the formation and propagation of cracks.
Recommendations:
(1) Improve the forging process of material to further improve the composition uniformity of gear material;
(2) Induction hardening or laser hardening treatment is carried out on the surface of the sun gear teeth theory. The hardening layer is 0.5~1.2mm deep to improve the surface hardness, wear resistance and fatigue strength of the gear.
(3) Improve gear installation accuracy and force distribution.