Analysis of Fatigue Property of the Aviation Gear Steel 15Cr14Co12Mo5Ni2 During High-Temperature Carburizing and Quenching

15Cr14Co12Mo5Ni2, as a new type of low-carbon high-alloy aviation gear steel, has shown significant application potential in the transmission systems of aero engines due to its excellent high-temperature performance. In this paper, the aviation gear steel 15Cr14Co12Mo5Ni2 was treated by carburizing and quenching process. The microstructure distributions of the carburized and quenched aviation gear steel at different quenching temperature were analyzed by OM, SEM and EBSD. Subsequently, the axial tension-compressive fatigue tests (stress ratio R=-1) were carried out using a high-frequency fatigue testing machine after heat treatment at different quenching temperature (1020℃, 1050℃ and 1080℃), and the stress-number of cycles (S-N) curves were obtained by fitting the number of fatigue fracture cycles. The fracture morphologies were observed by SEM and the fracture mechanisms were analyzed. The research results show that the distribution of the microstructure and carbides exhibit gradient characteristics, and the carbide content decreases and the effective carburized layer depth decreases from 0.65mm to 0.45mm with increasing quenching temperature, also the main carbide types are M₂₃C₆ and M₇C₃. The fatigue life of 15Cr14Co12Mo5Ni2 gear steel decreases as the quenching temperature increases. Their fatigue strengths at a given fatigue life of 10⁶ cycles at 1020℃, 1050℃ and 1080℃ are 192 MPa, 183 MPa and 158 MPa, respectively. The cracks propagate outward from the core and the propagation rate accelerates with the increasing quenching temperature, eventually fracturing in the carburized layer. The fracture mechanism of 15Cr14Co12Mo5Ni2 gear steel at the quenching temperatures of 1020℃ was a mixed mode of intergranular and cleavage brittle fracture, while at 1050℃and 1080℃, it is mainly brittle fracture accompanied by local ductile fracture.