As an important part of transmitting power, gear shaft is widely used in transmission or reducer parts of heavy industrial equipment such as agricultural machinery, transportation and mining machinery. Its service environment is extremely harsh. While transmitting power, it also has to bear high-strength alternating load and impact load. Therefore, the material selection and heat treatment process of gear shaft have become one of the key issues concerned by relevant researchers. 17CrNiMo6 steel of Cr Ni Mo system is widely used in the design of gear shaft because of its excellent compressive capacity, high strength and high hardenability. Carburizing and quenching is one of the important heat treatment methods to ensure the working performance of gear shaft. However, due to the high hardenability of 17CrNiMo6 steel, 17CrNiMo6 steel gear shaft will produce serious distortion after carburizing and quenching in engineering practice. It is necessary to correct the distortion by increasing the milling amount in subsequent milling, resulting in the increase of production cost. Moreover, the distortion will also affect the manufacturing accuracy of the gear shaft, reduce the tolerance of the gear shaft and greatly shorten its service life. In actual production, the distortion of gear shaft is often reduced by preheating before carburizing. However, the current preheating process is mostly based on experience, and there is a lack of quantitative analysis between preheating process parameters and distortion. Therefore, quantitative analysis of the distortion of gear shaft after preheating carburization has become an important problem.
| Technology | Time / S | Temperature / ℃ | Carbonaceous atmosphere /% |
| Strong infiltration | 21 600 | 920 | 1.05 |
| Spread | 10 800 | 920 | 0.75 |
| Cool down | 3 600 | 840 | 0.75 |
| Air cooling | 3 600 | 30 | 0 |
| Quenching temperature rise | 10 800 | 840 | 0 |
| Quench | 3 600 | 60 | 0 |
With the rapid development of computer technology, it has become a trend to quantitatively analyze the influence of heat treatment process on the distortion and performance of core parts with the help of numerical simulation method, which can guide the actual production more effectively. Sun Siyuan and others used deform-ht software to calculate the quantitative relationship between the process parameters of gear carburizing quenching and precooling quenching and the distortion after carburizing quenching; Zhang et al. Established the finite element analysis model of phase transformation and distortion process of spiral bevel gear during carburization and quenching, and studied the relationship between hardenability, phase transformation, temperature and distortion of spiral bevel gear. Based on the finite element model, tewary et al. Numerically simulated the carburizing and quenching process of typical transmission shaft, studied the effects of raw materials, carburizing and quenching process parameters on distortion, predicted, analyzed and reduced distortion. However, there are few process optimization based on the influence of carburizing process on gear shaft distortion.
The carburizing and quenching process of 17CrNiMo6 steel gear shaft is numerically simulated by finite element method, and the preheating process applied in engineering practice is introduced. The quantitative analysis of carburizing preheating and carburizing distortion is carried out, in order to obtain the optimized heat treatment process parameters and provide technical methods and guidance for controlling the thermal treatment distortion of gear shaft and actual production.