Vacuum heat treatment is a comprehensive technology combining vacuum technology and heat treatment, which means that all and part of the heat treatment process are carried out in vacuum state. Vacuum heat treatment can realize almost all heat treatment processes, such as quenching, annealing, tempering, carburizing, chromizing and nitriding. In the quenching process, air quenching, oil quenching, nitrate quenching and water quenching can be realized. Compared with ordinary heat treatment, it has the following advantages.
1. No oxidation, no decarburization and no carburization can protect the internal and surface of the workpiece
Oxidation makes the metal surface lose metallic luster, the surface roughness increases, and the accuracy decreases. Moreover, the oxide skin on the steel surface is often the source of quenching soft spot and quenching crack. Oxidation makes the strength of steel parts decrease, and other mechanical properties decrease. Decarburization (see Figure 1) refers to the phenomenon that the carbon content on the surface of steel decreases when it is heated.
Generally, the decarburization of steel is carried out at the same time. Due to the oxidation of decarburized layer, the reduction of carbon content will significantly reduce the quenching hardness, wear resistance and fatigue performance of steel, and the decarburization of high-speed steel will reduce the red hardness.
Because the metal is heated in a certain degree of vacuum, the work piece avoids contact with oxygen, there is no oxidation and decarburization of the work piece, so the bright surface and better heat treatment quality can be obtained. At the same time, in the vacuum state, there will be no reduction reaction and no carbon increase. The advantage of vacuum heat treatment can be seen clearly by comparing the metallographic diagram of the workpiece surface after adding protective agent with that of vacuum quenching.
2. Improve overall mechanical properties, degassing and promote metal surface purification
Vacuum has an obvious degassing effect on liquid metal, and it also has a good effect on the gas dissolved in solid metal. The harmful gas Z * in metals is hydrogen. When vacuum heating is used, the hydrogen in metals and alloys can be rapidly reduced to a low level of Z * to eliminate hydrogen embrittlement, so as to improve the plasticity, toughness and fatigue strength of materials and improve the overall mechanical properties of workpieces. When metals and alloys are heated in vacuum, if the vacuum degree is lower than the decomposition pressure of corresponding oxides, the oxides will decompose, and the formed free oxygen will be discharged out of the vacuum chamber immediately, making the metal surface quality further improved, even making the surface reach the activation state, playing a role of purification.
3. Small deformation of workpiece
Generally speaking, the workpiece to be processed is heated by thermal radiation in the furnace. The temperature difference between the inside and outside is small and the thermal stress is small, which determines that the deformation of the parts to be processed by the vacuum heat treatment process is small. At the same time, the parts to be heated and quenched in the vacuum are automatically completed to avoid the handling of the workpiece in the air under the hot state (although the salt bath treatment and atmosphere protection treatment are heated in the oxygen free environment, they are still Air or quenching medium containing oxygen molecules is used to complete quenching, which reduces the artificial processing deformation. For example, Cr12MoV wire roller is treated by vacuum heat treatment and salt bath respectively. The deformation of vacuum heat treatment is 70% less than that of salt bath treatment, and the product qualification rate is high.
4. It can reduce the volatility of gold elements in workpieces
The vacuum heat treatment can be heated and quenched in a controlled atmosphere, thus reducing the volatility of gold elements in the workpiece and ensuring the quality of heat treatment.
5, others
The vacuum heat treatment furnace has the advantages of high thermal efficiency, fast temperature rise and drop, good stability and repeatability. Good working environment, safe operation, no pollution and public hazards.
On 2018-08-08 11:45:46
