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Vacuum carburizing of aviation gear steel

At present, the accessory systems of aviation turbojet and turbofan engines all adopt gear transmission. With the increase of thrust and thrust-to-weight ratio of aero-engines, it is required that aero-engine gears must be able to withstand the comprehensive effects of various complex stresses, strains, fatigue and wear under high-temperature and high-speed conditions. As a key technology to improve the surface properties of gears, the vacuum carburizing process has been widely used in the heat treatment of aero-engine materials.

The materials used to make aero-engine gears are mainly 12Cr2Ni4A and 18Cr2Ni4WA high-grade high-quality steel. However, these two steels are low-temperature materials with poor heat resistance, and the service temperature is lower than 170°C. 16Cr3NiWMoVNbE steel is a high-performance gear steel with good hardenability, high toughness and plasticity and high fatigue strength. After vacuum carburizing treatment, the surface has high hardness and strength, the core has good toughness and plasticity, good heat resistance, the service temperature can reach 350°C, and the comprehensive performance is good. It has been used to manufacture turbofan engines.

Schematic diagram of vacuum carburizing process:

The quality and hardness gradient distribution of the surface carburized layer of gear steel after vacuum carburizing determine the fatigue and wear of the gear surface, which directly affects the life of the aeroengine gear. Vacuum low pressure carburizing is currently the most advanced carburizing process. Compared with traditional atmosphere carburizing, vacuum low-pressure carburizing can achieve no intergranular oxidation and precisely control the depth of carburizing through the pulsed cycle of strong infiltration and diffusion, satisfying the reproducibility and surface carbon concentration within a low error range Optional, and has the advantages of high efficiency, energy saving and environmental protection.

Change law of carburized layer structure: The microstructure of 16Cr3NiWMoVNbE steel after vacuum carburizing process is shown in the figure.

Effect of vacuum heat treatment on mechanical properties: The structure of the material surface determines the hardness distribution of the infiltrated layer, and the hardness and gradient distribution of the infiltrated layer have an important impact on the fatigue and wear of the material surface, which is related to the performance and life of the gear. The hardness curve of 16Cr3NiWMoVNbE steelized layer after vacuum carburizing heat treatment is shown in the figure.

From the surface to the core of the gear steel after vacuum carburizing, the hardness distribution increases first and then decreases with the decrease of carbon concentration, and the depth of the carburized layer is 0.95mm. The ice-cooling treatment further transformed the retained austenite into martensite in the experimental steel structure, which greatly increased the overall hardness.

Vacuum carburizing equipment selection: The vacuum carburizing furnace produced by SIMUWU company overcomes the blind hole carburizing problem that cannot be solved by traditional atmosphere thermal carburizing, avoids internal oxidation, shortens the process time, combines with gas quenching, and controls the cooling rate during the quenching process. improve product quality. Excellent quality and reliable. SIMUWU company focuses on the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.