vacuum heat treatment furnace common electrothermal materials

---

With the improvement of the manufacturing level of vacuum heat treatment furnace, vacuum heat treatment gradually shows incomparable advantages. Vacuum heat treatment with its own degassing, degreasing, no oxidation and automation has been favored by people. However, there are still many problems in the electric heating elements of the vacuum heat treatment furnace, such as high temperature deformation, fracture, volatilization and so on. In order to solve these problems, graphite stands out with its unique advantages.

The commonly used electric heating materials for vacuum heat treatment furnace are as follows:

1. Alloy electric heating material: mainly refers to iron chromium aluminum alloy and nickel chromium alloy. Their common characteristics are: the resistance coefficient is larger, the resistance temperature coefficient is smaller, and the heat resistance is good. Therefore, they work stably in the heating process. But in vacuum, due to the high vapor pressure of chromium, it is easy to volatilize, so the application range is limited. Generally, it can only be used in medium, low temperature, medium and low vacuum heat treatment furnace or external heating vacuum heat treatment furnace.

Nickel lattice alloy has good machinability, easy manufacturing, not easy embrittlement after high temperature heating, easy repair and welding, good resistance to nitrogen, but poor resistance to carburization. Tiege aluminum alloy is a widely used electric heating material in China. It has strong ability of carburizing, sulfur resistance and resistance to various carbon and nitrogen gases. However, it is difficult to manufacture because of its poor processability. After high temperature heating, the crystal becomes thicker and the material becomes brittle, which is not easy to repair and weld.

2. Pure metal electrothermal materials: mainly platinum, phase, tungsten, tantalum, etc., their common characteristics are high melting point, poor oxidation resistance, can only be used in vacuum or protective atmosphere. Because of their small resistance coefficient and large resistance temperature coefficient, the power of the furnace changes greatly with the change of temperature. In order to stabilize the power, the regulator must be used.

3. Non metallic electric heating materials: mainly silicon carbide, disilicide phase and graphite, whose properties can be seen in the table below. Because the binder of silicon carbide is easy to decompose in vacuum, and the aluminum disilicide will soften when it exceeds 1300 ℃ in vacuum, these two kinds of electric heating materials are seldom used in vacuum heat treatment furnace.

Graphite has the advantages of small coefficient of thermal expansion, good processability, high humidity resistance, rapid cooling and heating resistance, and low price, but it has strong affinity with oxygen at high temperature, so it should be used in reducing protective atmosphere and vacuum. At present, graphite has been widely used in vacuum heat treatment furnace.