Comparison of Vacuum Heat Treatment and Traditional Heat Treatment

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Vacuum heat treatment is a comprehensive technology that combines vacuum technology and heat treatment. It means that all and part of the heat treatment process is carried out in a vacuum state. Vacuum heat treatment can almost realize all heat treatment processes, such as quenching, annealing, tempering, carburizing, chromizing, and nitriding. In the quenching process, gas quenching, oil quenching, nitrate quenching, water quenching, etc. can be realized. It is similar to ordinary heat treatment. Compared with the following advantages.

1. No Oxidation, No Decarburization, No Recarburization

Oxidation causes the metal surface to lose its metallic luster, the surface roughness increases, and the precision decreases, and the oxide scale on the steel surface is often the source of quenching softness and quenching cracking. Oxidation reduces the strength of steel parts and other mechanical properties. And decarburization (Figure 1) refers to the phenomenon that the surface carbon content of steel decreases when it is heated.

Figure 1

Under normal circumstances, the oxidative decarburization of steel is carried out at the same time. As the decarburized layer is oxidized, the reduction in carbon content will significantly reduce the quenching hardness, wear resistance, and fatigue properties of the steel, and the decarburization of high-speed steel will reduce the red hardness (Figure 2) . In vacuum heat treatment, because the metal is heated under a certain degree of vacuum, the workpiece avoids contact with oxygen, and the workpiece is not oxidized or decarburized. A bright surface and better heat treatment quality can be obtained. At the same time, it will not When a reduction reaction occurs, carbon increase will not occur. The advantages of vacuum heat treatment can be clearly seen from the metallographic diagram of vacuum quenching after adding protective agent on the surface of the workpiece below. As shown in Figure 3 and Figure 4

Figure 2

Figure 3 Quenching and tempering treatment of 40Cr after carburizing, martensite level 3, retained austenite level 2, a small amount of granular carbides level 1, and the surface layer and subsurface layer martensite are different in thickness.

Fig. 4 40Cr vacuum quenched structure is medium carbon martensite and a small amount of black strip tempered martensite. The heating is uniform, and the surface has no oxidation and decarburization.

2. Improve the Overall Mechanical Performance, Degas and Promote the Purification of the Metal Surface

Vacuum has obvious degassing effect on liquid metal, and also has a good effect on removing gas dissolved in solid metal. The most harmful gas in metals is hydrogen. When vacuum heating is used, the hydrogen in metals and alloys can be quickly reduced to a minimum, and hydrogen embrittlement can be eliminated, thereby improving the plasticity, toughness and fatigue strength of the material, and improving the overall mechanical properties of the workpiece. When metals and alloys are heated in a vacuum, if the vacuum degree is lower than the decomposition pressure of the corresponding oxides, the oxides will decompose, and the free oxygen formed will be immediately discharged from the vacuum chamber, so that the surface quality of the metal can be further improved or even made The surface reaches the activated state and plays a role of purification.

3. Small Deformation of the Workpiece

Generally speaking, the workpiece to be processed is heated by thermal radiation in the furnace, and the temperature difference between the inside and the outside is small, and the thermal stress is small, which determines the small deformation of the parts processed by the vacuum heat treatment process. At the same time, heating under vacuum and quenching under vacuum are automatically completed. , To avoid the handling of the workpiece in the air under the hot state (the salt bath treatment and the atmosphere protection treatment are heated in an anaerobic environment, but the quenching is still completed in the air or the quenching medium containing oxygen molecules), and the artificial processing deformation is reduced . For example, the rolling wheel made of Cr12MoV has vacuum heat treatment and salt bath treatment respectively. The deformation of vacuum heat treatment is 70% smaller than that of salt bath treatment, and the product qualification rate is high.

4. It can Reduce the Volatility of Gold Elements in the Workpiece

Vacuum heat treatment can be heated and vacuum quenched in a controlled atmosphere, thereby reducing the volatility of gold elements in the workpiece and ensuring the quality of the heat treatment of the workpiece.

5. Other Features

The vacuum heat treatment furnace has high thermal efficiency and can realize rapid heating and cooling; it has good stability and repeatability. The working environment is good, the operation is safe, and there is no pollution and pollution.

Shanghai Gehang Vacuum Technology Co., Ltd. currently has a number of vacuum heat treatment furnaces, the equipment is fully automated, all the process can be freely programmed and controlled, accurate temperature and process control, the uniformity of the furnace temperature can be monitored through the touch screen throughout the process; it can meet a variety of Processes such as vacuum bright quenching, vacuum quenching, vacuum annealing of tool steel and die steel.

Learn more:

Vacuum Carburizing Furnace

Vacuum Heat Treatment Furnace

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