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Application of low pressure vacuum carburizing

In the heat treatment production process, the traditional carburizing process has the problems of long cycle, high energy consumption, and the quality needs to be further improved. To this end, heat treatment workers are very concerned, and have been working hard to study better carburizing technology to thoroughly improve and enhance.
The low-pressure vacuum carburizing process technology can adopt a higher process temperature, and the control of each process parameter relies on the computer to implement process monitoring and adjustment. The process technology is mature, showing obvious advantages in solving carburizing problems, improving product quality and saving energy. At present, low-pressure vacuum carburizing has been recognized and accepted by the heat treatment industry as a high-quality carburizing technology. In recent years, it has been popularized and applied at a relatively fast speed, and good technical effects and economic benefits have been achieved.
Environmental impact and economic analysis
The traditional carburizing process exhaust gas emission and cleaning after oil quenching have certain pollution to the environment. Poor operating conditions greatly restrict the development or progress of the enterprise. The vacuum low-pressure carburizing process technology has successfully solved the technical problems that have plagued enterprises for a long time, and realized pollution-free emissions. High-pressure nitrogen quenching has a controllable cooling rate and no pollution, the heat treatment deformation is smaller, and the internal oxidation problem can be completely solved, the carburizing quality is greatly improved, and the service life of the parts is doubled. Since the surface is still clean after vacuum low pressure carburizing quenching and high pressure gas quenching, the post-cleaning process can be omitted and pollution-free green production can be realized.
In addition, the low-pressure vacuum carburizing temperature can be higher than the traditional carburizing temperature, which can increase the carburizing rate and shorten the production cycle, which can greatly save energy and reduce production costs.
In terms of economy, the purchase price of vacuum carburizing equipment is high. Although the one-time investment cost is relatively large, the product quality is significantly improved. The change of processing method can optimize the production process, reduce the process and reduce the overall production cost. At the same time, the adverse impact on the environment and the shortening of the production cycle are reduced, which is beneficial to the comprehensive and social benefits of the product, and the rate of return is satisfactory.

Application effect and influence on subsequent processing
Low pressure vacuum carburizing is a so-called pure carburizing and pure diffusion method, that is, during vacuum carburizing, the process of carbon infiltration into the steel surface is not affected by some external factors (such as chemical reaction of gas and surface contamination of parts, etc.). The main advantages and disadvantages are summarized as follows.
1. Advantages
(1) There is no intergranular oxidation.
(2) Due to the characteristics of the vacuum carburizing equipment and process, a higher carburizing temperature can be adopted.
(3) Due to the flexibility of the vacuum carburizing process, many kinds of materials can be allowed to be vacuum carburized.
(4) The vacuum carburizing process can produce a relatively uniform carburized layer and produce a relatively uniform carbon distribution on the entire gear (tooth tip-pitch diameter-tooth root).
(5) The vacuum carburizing equipment can be connected with the cold processing equipment to form a production line. The carburizing process is clean, safe, easy to operate and easy to maintain. Excellent working conditions (no open flames, heat and pollution).
(6) Full automation of heat treatment process and mass production of parts can be realized.
(7) Accurate process control is realized by computer simulation, and the existing heat treatment process can be adjusted.
(8) The characteristics of the vacuum furnace determine that energy is only consumed when the carburizing of the parts is required, and if the carburizing of the parts is not required, the furnace can be stopped without energy consumption.
(9) Measure the parts after vacuum carburizing, and the deformation can be controlled to the minimum extent.
2. Disadvantages
(1) Compared with atmospheric carburizing equipment, higher initial fixed equipment investment is required.
(2) In order to achieve the desired carburizing results, the parts require more stringent cleaning.
(3) The time of the heating stage should be determined according to experience. It is necessary to determine the best way to charge the furnace and adjust and optimize the simulation process before processing various parts.
Because the surface of the parts can still maintain the bright color of the metal after carburizing, eliminate the occurrence of internal oxidation, the quality is stable, and the performance is more superior. Compared with traditional carburizing, the service life of parts is doubled (currently high-end car gears must be produced by low-pressure vacuum carburizing technology). The practical application shows that the advantages of low-pressure vacuum carburizing technology applied to workpieces with deep layers are very significant, which can greatly reduce the time used in the process (each increase of the process temperature by 50 °C is equivalent to reducing the process time by half), The energy-saving effect is extremely significant, the production efficiency is significantly improved, and the investment in equipment can obtain greater economic benefits.

Equipment Features
The low-pressure vacuum carburizing furnace is a furnace type developed on the basis of the vacuum heat treatment furnace. Compared with the traditional carburizing furnace, the low-pressure vacuum carburizing furnace has simple and flexible operation, completely avoiding the adverse effects of human beings, and the carburizing process can be fully monitored by the computer. Unmanned operation ensures stable and reliable quality of carburized parts. The low-pressure vacuum carburizing furnace can use high-pressure pure nitrogen to realize the quenching process, which is pollution-free, and the surface of the parts keeps the original color of the metal, which can save the subsequent cleaning process, reduce the high-investment cleaning and post-processing operations, and save more than 50% of the cost.
The performance advantages of vacuum carburizing
The test results show that carburizing or carbonitriding under low pressure can not only obtain the same impact strength and hardness as atmospheric carbonitriding, but also obtain higher bending fatigue strength (about 30% increase).
and surface residual compressive stress. Under the condition of low-pressure vacuum carburizing, heat treatment deformation can be controlled to a minimum degree, which greatly reduces the amount of subsequent grinding, reduces production costs, ensures the optimal distribution of layers, and improves the fatigue strength of parts. Due to the carburizing under vacuum and low pressure conditions, internal oxidation is avoided and the high quality requirements of the carburized layer are ensured.
Practical application shows that every 50 ℃ increase in carburizing process temperature is equivalent to reducing the process time by half, and it is obvious to increase the carburizing temperature to speed up the carburizing speed. The advantages of low pressure vacuum carburizing technology applied to carburizing layer are obvious. For the test and comparison of the gear shaft of the heavy-duty truck requiring a carburizing depth of 1.60mm: using the low-pressure vacuum carburizing technology, the total time of carburization and diffusion is about 6.5h; The time required is 12h, the production cycle is shortened by about 50%, and the energy saving and production efficiency are quite significant.
The maturity of vacuum low pressure carburizing technology has been unanimously recognized by the heat treatment industry. An effective method with good prospects for development.