Vacuum heat treatment technology mainly refers to a new type of heat treatment technology combining vacuum technology and heat treatment technology. The vacuum environment in which vacuum heat treatment is located refers to an atmosphere environment lower than one atmospheric pressure, including low vacuum, medium vacuum, high vacuum and ultra-high vacuum. Therefore, vacuum heat treatment actually belongs to atmosphere controlled heat treatment.
Vacuum heat treatment refers to that all or part of the heat treatment process is carried out under vacuum. Vacuum heat treatment can realize almost all the heat treatment processes that can be involved in conventional heat treatment, but the quality of heat treatment is greatly improved.
Compared with conventional heat treatment, vacuum heat treatment processing technology can realize no oxidation, no decarburization, no carburization at the same time, remove phosphorus chips on the surface of the workpiece, and have the functions of degreasing and degassing, so as to achieve the effect of bright surface purification.
1. Application of vacuum heat treatment processing technology
In fact, the vacuum heat treatment processing technology was applied in foreign countries earlier. In 1968, the American Hayes Company and the Japanese Vacuum Research Institute successively developed vacuum quenching oil and aqueous quenching medium. As a result, the vacuum quenching technology has developed rapidly in the heat treatment industry, from single chamber furnace to multi combination machine group, from general vacuum quenching to high-pressure gas quenching, vacuum water quenching, vacuum carburizing Vacuum carbonitriding and multi-element carbonitriding, etc.
After decades of efforts in China, vacuum furnace manufacturers have greatly improved their design, manufacturing level and quality. The use of domestic vacuum equipment to replace imported vacuum equipment has gradually increased, which has reduced the production cost of users and rapidly expanded the application range of vacuum heat treatment.
- Process principle of vacuum heat treatment processing technology
Taking advantage of the phase transformation characteristics of metals in vacuum state, the thermodynamics and dynamics of solid phase transition do not change much under the vacuum which is only 0.1 MPa different from atmospheric pressure. When formulating the vacuum heat treatment process specification, it can be completely based on the principle of solid phase transformation under atmospheric pressure, and can completely refer to the data of various types of structural transformation under atmospheric pressure. At the same time, the physical and mechanical properties of metal materials can be improved under vacuum degassing. When heated in vacuum, the elements on the surface of metal workpiece will evaporate. The vacuum degree required for metal to realize oxidation free heating, and the surface purification function can realize less oxidation and less dehydration.
3 Features of vacuum heat treatment processing technology
(1) Advantages of Vacuum Heat Treatment
Vacuum heat treatment processing is a widely used non oxidative heat treatment technology that keeps pace with the controlled atmosphere, and it is also one of the main signs of the advanced level of the current heat treatment production technology. Vacuum heat treatment can not only realize no oxidation and decarburization of steel parts, but also realize no pollution in production and less distortion of workpieces. Therefore, it also belongs to the category of clean and precision production technology. At present, it has become an irreplaceable advanced technology in tool and die production.
(2) Small distortion of workpiece in vacuum heat treatment process
According to the domestic and foreign experience, the distortion of workpiece in vacuum heat treatment is only one third of that in salt bath quenching. It is of great significance to study the vacuum heating methods of various materials and parts of different complexity and the distortion rules under various cooling conditions, and to simulate them with computers, for the promotion of vacuum heat treatment technology. During vacuum heating, atmospheric pressure or high-pressure air cooling quenching, the uniformity of air flow has a great influence on the hardening effect and mass dispersion of parts. It is of great significance to improve the furnace structure to study the air circulation law in the furnace by means of computer simulation.
(3) Adopt vacuum heat treatment furnace
Modern vacuum heat treatment furnace refers to a cold wall furnace that can perform vacuum heating of components, and then quenching in oil or quenching in normal pressure and pressurized gas. The research and development of this type of equipment is a comprehensive, interdisciplinary work involving many scientific and technological fields.
The application prospect of vacuum heat treatment of tool and die materials is great. At present, most tool and die steels are heated in vacuum and then cooled and quenched in gas. In order to obtain satisfactory mechanical properties on the surface and inside of the workpiece, the vacuum high-pressure gas quenching technology must be adopted. At present, the pressure of vacuum gas quenching in the world has increased from 0.2MPa, 0.6MPa to 1-2MPa or even 3MPa. Therefore, the gradual increase of the cooling gas pressure of high-pressure gas quenching vacuum furnace is an important development trend.