What is vacuum heat treatment technology
It mainly refers to the new heat treatment technology which combines vacuum technology with heat treatment technology. The vacuum environment of vacuum heat treatment refers to the atmospheric environment below 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 all and part of the heat treatment process carried out in vacuum. Vacuum heat treatment can achieve almost all the heat treatment processes involved in conventional heat treatment, but the quality of heat treatment is greatly improved.
Compared with conventional heat treatment, vacuum heat treatment technology can achieve non-oxidation, no decarburization, no carburization at the same time, remove the phosphorus chips on the surface of the workpiece, and degrease and degassing, so as to achieve the effect of surface brightness and purification.
1. Vacuum Heat Treatment Technology Application
In fact, the technology of vacuum heat treatment has been applied earlier abroad. In 1968, Hayes Corporation of the United States and Japan Vacuum Research Institute developed vacuum quenching oil and water quenching medium successively. As a result, 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 and vacuum water quenching. Vacuum carburizing, vacuum carbonitriding and multicomponent carburizing, 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 instead of imported vacuum equipment has gradually increased, which reduces the production costs of users and expands the application scope of vacuum heat treatment rapidly.
2. Vacuum Heat Treatment Technology of Processing Principle
The thermodynamics and kinetics of solid-state phase transformation do not change in vacuum with a difference of only 0.1 MPa from atmospheric pressure. In formulating the process rules of vacuum heat treatment, it is entirely possible to refer to the data of various types of microstructural transformation under atmospheric pressure, based on the principle of solid phase transformation under atmospheric pressure. At the same time, under the action of vacuum degassing, the physical properties and mechanical properties of metal materials can be improved. When heated in vacuum, the surface elements of metal workpieces will evaporate. The vacuum degree and surface purifying function of metal for non-oxidation heating are realized, and less oxidation and less detachment are realized.
3. Vacuum Heat Treatment Processing Technology Characteristics
(1) Vacuum Heat Treatment Processing Advantages
Vacuum heat treatment is a widely used non-oxidizing heat treatment technology, which can keep pace with controlled atmosphere. It is also one of the main indicators of the advanced degree of heat treatment production technology. Vacuum heat treatment can not only realize the non-oxidation and decarbonization of steel parts, but also realize the non-pollution of production and less distortion of workpieces. Therefore, it belongs to the category of clean and precise production technology. At present, it has become an irreplaceable advanced technology in the production of tools and dies.
(2) Small distortion of workpiece in vacuum heat treatment process
According to experience at home and abroad, the distortion of vacuum heat treatment of workpiece is only one third of that of salt bath quenching. It is of great significance to study the vacuum heating mode of various materials and parts with different complexity and the distortion law under various cooling conditions, and to simulate them by computer for popularizing the vacuum heat treatment technology. When vacuum heating, atmospheric pressure or high pressure air-cooled quenching, the uniformity of air flow has a great influence on the hardening effect and quality dispersion of parts. It is of great significance to study the law of gas flow circulation in furnace by means of computer simulation for improving furnace structure.
(3) Vacuum heat treatment furnace
Modern vacuum heat treatment furnace refers to a cold wall furnace which can be heated in vacuum and then quenched in oil or in atmospheric pressure and pressurized gas. Research and development of this type of equipment is a comprehensive, interdisciplinary work involving many scientific and technological fields.
The application prospects of vacuum heat treatment of tool and die materials are great. Most die steels are heated in vacuum and then cooled and quenched in gas. In order to obtain satisfactory mechanical properties both on the surface and inside of the workpiece, vacuum high pressure gas quenching technology must be adopted. At present, the pressure of vacuum gas quenching has increased from 0.2 MPa, 0.6 MPa to 1-2 MPa or even 3 MPa in the world. Therefore, the gradual increase of the pressure of cooling gas in high pressure gas quenching vacuum furnace is an important development trend.