Abstract: Low pressure vacuum carburizing process was carried out on the aviation gear carburizing steel 16CrNi4MoA, followed by two high-temperature tempering, quenching, cryogenic treatment, and low-temperature tempering. The microstructure, carbide morphology, and hardness gradient distribution of the specimens after carburizing heat treatment were analyzed. The precise control of the microstructure of the carburized layer of 16CrNi4MoA steel was achieved by adjusting two key parameters: the time for introducing acetylene into the vacuum carburizing furnace, and the time for nitrogen protection diffusion. The results show that, when carburized at 920 ℃, with acetylene introducing time setting to 1355 s, nitrogen protection diffusion time setting to 24 800 s, uniform granular and fine strip carbides are formed on the surface of the specimen, and the quality of the carburized layer is better. After subsequent heat treatment, the thickness of carburized layer can be up to 1.08 mm, carburized layer surface hardness can reach 62.5 HRC, with the core hardness of 44.0 HRC, in line with the technical requirements of the 16CrNi4MoA steel aviation gears, and the hardness gradient from the surface of the carburized layer to the core shows a gentle feature.

Key words: low-pressure vacuum carburizing, 16CrNi4MoA steel, carburized layer, hardness