The center of carburized gear is required to have a certain hardness. When the hardness is low, the yield point of the gear material is reduced, which is easy to produce plastic deformation in the center, which reduces the anti peeling performance of the gear surface hardening layer and the bending fatigue performance of the tooth root.
1. Cause analysis
(1) The hardenability of gear material is poor, the gear material is poor, and the banded structure inside the steel is serious.
(2) After carburizing, the pre cooling temperature before direct quenching is too low or when re quenching after carburizing, the quenching temperature is too low.
(3) The cooling rate is not enough. According to metallographic observation, it is not low-carbon martensite, but sorbite.
(4) A large amount of insoluble ferrite exists in the heart, which is caused by low heating temperature or insufficient heating time.
2. Preventive measures
(1) The cooling medium with good cooling performance is selected for quenching to obtain low-carbon martensite in the heart.
(2) Proper quenching temperature and heating time are selected to obtain uniform austenite in the core, so as to obtain martensite after quenching.
(3) Steel with good hardenability and good material is selected as carburized gear material.