Vacuum heat treatment and traditional heat treatment

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Vacuum heat treatment is a combination of vacuum technology and heat treatment, which means that all and part of the heat treatment process are carried out under vacuum. Vacuum heat treatment can almost achieve all heat treatment processes, such as quenching, annealing, tempering, carburizing, chromizing, nitride, in the quenching process can achieve gas quenching, oil quenching, nitre quenching, water quenching, it has the following advantages compared with ordinary heat treatment.

1, no oxidation, no decarburization, no carburization of the internal and surface of the workpiece has a good protective effect

Oxidation makes the metal surface lose metallic luster, surface roughness increases, precision decreases, and steel surface oxide scale is often the root cause of quenching soft point and quenching cracking, oxidation reduces the strength of steel, other mechanical properties decline. Decarburization (see Figure 1 for typical decarburization of steel) refers to the phenomenon that the surface carbon content of steel decreases when heated.

Typical decarbonization of steel

Under normal conditions, the oxidation of steel decarburization at the same time, the decarburization layer due to oxidation, carbon content will significantly reduce the quenching hardness, wear resistance, and fatigue properties of steel, high speed steel decarburization will reduce the red hardness.

W6Mo5Cr4V2 furnace quenching figure has decarburization phenomenon, the depth of 0.23㎜

The vacuum heat treatment because the metal is heated under a certain vacuum degree, the workpiece avoids contact with oxygen, the workpiece has no oxidation, no decarburization, can get a bright surface and better heat treatment quality, at the same time in the vacuum state, there will be no reduction reaction, there will be no carburization phenomenon.

Vacuum quenching diagram of W6Mo5Cr4V2 shows uniform carbide distribution, and the grain size can be rated as 10.5

Compared with the metallographic diagram of vacuum quenching after adding protective agent on the surface of the workpiece below, the advantages of vacuum heat treatment can be clearly seen.

After 40Cr carburizing, quenching and tempering treatment, martensite level 3, residual austenite level 2, a small amount of granular carbide level 1 surface and subsurface martensite structure thickness is different

The microstructure of 40Cr vacuum quenching is medium carbon martensite and a small amount of black strip tempered martensite. Heating uniform, no surface oxidation decarburization

2, improve the overall mechanical properties, degassing and promote the purification of metal surface

Vacuum has obvious degassing effect on liquid metal, and it also has good degassing effect on dissolved gas in solid metal. The most harmful gas in metals is hydrogen. When vacuum heating is used, hydrogen in metals and alloys can be rapidly reduced to a minimum, eliminating hydrogen embrittlement, thus 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 vacuum, if the vacuum degree is lower than the decomposition pressure of the corresponding oxide, the oxide will decompose, and the free oxygen formed will be immediately discharged from the vacuum chamber, so that the quality of the metal surface can be further improved, and even the surface can reach the activation state and play a purification role.

3, the workpiece deformation is small

In general, be processed workpiece by thermal radiation heat within the furnace, the internal and external temperature difference is small, the thermal stress is small, thus determines the components of the vacuum heat treatment processing deformation is small, at the same time under the vacuum heating and quenching under vacuum, automatically, to avoid the workpiece under the thermal state in the air handling (salt bath treatment and the protection of the atmosphere is heating in anaerobic environment, but it is still in the air or complete quenching) containing oxygen quenching medium, reduces the machining deformation. For example, the roller made of Cr12MoV material is subjected to vacuum heat treatment and salt bath treatment respectively. The deformation amount of vacuum heat treatment is 70% less than that of salt bath treatment, and the qualified rate of the product is higher.

4, can reduce the workpiece containing gold element volatility

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

5, other

Vacuum heat treatment furnace has high thermal efficiency, which can realize rapid heating and cooling. Good stability and repeatability. Good working environment, safe operation, no pollution and public hazard.

Learn More : Vacuum Heat Treatment Furnace