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Vacuum Heat Treatment Furnace

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Vacuum heat treatment process of steel bearing parts

High temperature bearing is a kind of bearing that can withstand high temperature, which is widely used in metallurgy, kiln, glass, blast furnace, painting equipment and other high temperature operation machinery. This type of bearing must undergo a good heat treatment process, and its strength can be improved by quenching and tempering process to ensure that it will not be deformed or damaged during use, and has a good service life.

When quenching high-temperature steel bearing parts, in order to prevent oxidation and decarburization, the traditional process is to use barium chloride high-temperature salt bath furnace with good deoxidation for heating. This heating method has many problems:

(1) The working environment of heat treatment is harsh, and the gas generated during heating is harmful to the operator’s body and pollutes the environment.

(2) For some parts with complex structure, such as ferrules with oil grooves and oil holes, the residual salt left in the salt bath after heating is difficult to remove in the subsequent processing, and it is easy to produce rust and corrosion pitting.

In recent years, vacuum heat treatment technology has developed rapidly. With the rapid development of science and technology and aerospace, aviation, and weapon industries, the requirements for metal materials are getting higher and higher. Vacuum heat treatment can make metal materials obtain good results that other heat treatments cannot. Vacuum pressurized gas quenching furnace can perform related heat treatment on high temperature bearing steel and stainless steel bearing parts, and has the following advantages:

(1) Non-polluting, automatic control, the operator’s labor environment improvement intensity is greatly reduced.

(2) The workpiece has no oxidation and no decarburization in vacuum heating, and can achieve bright heat treatment, which can degrease and degas the parts and avoid surface pollution.

(3) It can realize controlled heating and cooling, and improve the heat treatment quality of parts.

Process flow:

Loading method of workpiece

The furnace loading method of the workpiece also has a great influence on the heat treatment quality of the workpiece. Because the heating method of vacuum heat treatment mainly relies on radiation rather than convection heating, the excessive density or mutual shielding of workpieces will significantly affect the heating speed and uniform heating of the workpiece. Therefore, the amount of furnace should be properly controlled when loading the furnace, and special attention should be paid to the binding and placement of the workpieces to avoid mutual blocking as much as possible.

Determination of heating temperature

The typical three-stage vacuum heating is one preheating at about 650°C; secondary preheating at about 850°C; through firing and alloying above 1000°C. For Cr4Mo4V steel, two-stage heating can be used. Convective heating is used at 850 °C to improve the uniformity of low-temperature heating, shorten the heating time, and reduce the temperature difference of the workpiece, which is beneficial to reduce deformation. 1110 °C adopts vacuum heating.

Determination of heating time

After many tests, comprehensively considering the advantages and disadvantages of hardness and structure, it was finally determined that the holding time in the convection heating stage was 75 minutes, and the holding time in the vacuum heating stage was 35 minutes.

Determination of vacuum degree

In the convection heating stage, vacuum is firstly carried out to make the vacuum degree in the furnace reach 50Pa, and then nitrogen with a pressure of 1×10°Pa is charged, and the nitrogen purity is 99.999%. The convection heating device at the front of the vacuum furnace can make the furnace The temperature remains uniform. Vacuum heating mainly relies on radiation heat transfer, and determining a relatively stable vacuum degree is an important part of determining other parameters in the entire vacuum heating process. At this stage, if the vacuum is too high, some elements on the surface of the workpiece will be seriously evaporated, such as Mn and Co. Therefore, controlling the vacuum degree to 100Pa can not only ensure the surface quality of the workpiece, so that it will not be oxidized, but also prevent Alloying elements in steel evaporate when heated at high temperatures.

Determination of cooling pressure

Since the shortest austenite incubation period of Cr4Mo4V steel is 18 min, this steel can be hardened by air cooling, so the requirement of cooling rate can be fully met by pressurized gas quenching. Usually, the selected gas quenching pressure is 5 × 10Pa, and the workpiece is cooled to about 40 ℃ and released. If the furnace load is particularly large, the quenching pressure can be appropriately increased.

Vacuum tempering process

Tempering is also carried out in this vacuum furnace, using (550 ± 10) ℃ × 2h three times tempering, convection heating, the heating rate is 10 ℃/min, and the workpiece is cooled to about 40 ℃ after each tempering. The Cr4Mo4V steel bearing parts have a bright surface after the above quenching and tempering process, and there is no oxidation and decarburization. The deformation is checked by sampling, and the deformation is within the qualified range, which meets the design requirements.

Selection of vacuum heat treatment equipment: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tooling, mold and bearing. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.