1) Advantages of vacuum heat treatment. Vacuum heat treatment is a widely used non-oxidizing heat treatment technology which keeps abreast with controllable atmosphere and is also one of the main signs of advanced heat treatment production technology. Vacuum heat treatment can not only realize no oxidation and decarburization of steel parts, but also realize no pollution and less distortion of workpiece, so it also belongs to the category of clean and precision production technology. At present, it has become an irreplaceable advanced technology in the production of tools and molds.
2) Vacuum heat treatment process. Small distortion of workpiece is a very important advantage of vacuum heat treatment. According to the experience at home and abroad, the distortion of workpiece in vacuum heat treatment is only one third of that in salt bath heating and quenching. It is of great significance to popularize vacuum heat treatment technology to study the vacuum heating mode of various materials and parts of different complexity and the distortion law under various cooling conditions, and to simulate it by computer. The uniformity of air flow during vacuum heating, atmospheric or high-pressure air quenching has great influence on the quenching effect and mass dispersion of parts.
It is of great significance to study airflow circulation in furnace by computer simulation method for improving furnace structure change. Vacuum carburizing is the most possible way to realize high temperature carburizing. However, heating for a long time at high temperature will make the austenite grain size of most steel grow very large, for specific steel carburizing at high temperature, the influence of reheating and quenching on material and workpiece properties to study, to optimize the vacuum carburizing, cooling, heating and quenching process and equipment is very necessary. In recent years, there is a trend of developing combustion vacuum furnace using gas fuel. There are too many difficulties in using gas fuel for heating in vacuum furnace, although there is a claim to save energy, but it is not necessarily an important development direction.
3) Vacuum heat treatment furnace. Modern vacuum heat treatment furnace refers to the vacuum heating of components, and then quenching in oil or in atmospheric pressure and pressurized gas cold wall furnace. The research and development of this type of device is a comprehensive, interdisciplinary and technological endeavor.
The application prospect of vacuum heat treatment of die and mould materials is very great. Most die steels are currently heated in vacuum and then cooled and hardened in gas. In order to obtain satisfactory mechanical properties both on the surface and inside the workpiece, vacuum high-pressure gas quenching technology must be adopted. At present, the international pressure of true air quenching has been increased from 0.2mpa and 0.6mpa to 1 ~ 2MPa or even 3MPa. Therefore, the gradual increase of cooling gas pressure of high-pressure gas quenching vacuum furnace is an important development trend. In addition to high pressure gas quenching, convection heating after vacuumizing and filling high pressure inert gas can increase the speed more than twice than traditional vacuum radiation heating, so as to significantly improve the heating efficiency is one of the important directions of vacuum heating technology. The development of multifunctional vacuum furnace is also one of the trends.
Semi-continuous vacuum heat treatment equipment with oil quenching in the front chamber, atmospheric or high-pressure gas quenching in the back chamber, vacuum heating or plasma carburizing in the middle heating chamber is one of the typical examples. The current domestic market has reflected the demand for this type of furnace. Various continuous vacuum carburizing, high pressure, air cooling, quenching and tempering production lines can meet the needs of mass production. It can be expected that a great revolution of heat treatment of automobile parts will be brought about in the near future. In view of the characteristics of vacuum heating to achieve high temperature carburizing, the development of vacuum high temperature (1000℃ ~ 1050℃) carburizing, slow cooling, reheating, quenching in oil, cleaning, tempering production line should be put on the agenda as soon as possible.