What is the purpose of passing nitrogen gas through a vacuum annealing furnace?

The function of nitrogen gas in vacuum annealing furnace is mainly reflected in the following aspects:
1. Prevent oxidation
At high temperatures, most metal materials react with oxygen, leading to oxidation and affecting their properties. Introducing nitrogen gas into the vacuum annealing furnace can create an oxygen free or low oxygen environment, effectively preventing oxidation reactions of materials during the annealing process. This not only maintains the original properties of the material, but also improves its surface quality and service life.
2. Nitriding modification
Nitrogen can react with metal atoms on the surface of materials to form compounds such as nitrides or carbonitrides. The hardness and corrosion resistance of these compounds are usually much better than the raw materials, which can enhance the surface properties of the materials. By nitriding modification, the strength, hardness, and toughness of materials can be improved, enabling them to perform better in extreme environments. For example, in the aerospace field, using nitrogen to treat materials such as aircraft engines and spacecraft components can effectively prevent oxidation corrosion of aluminum alloys and have good corrosion resistance.
3. Cooling medium
In vacuum heat treatment, nitrogen is often used as a cooling medium. By adjusting the flow rate and pressure of nitrogen, the cooling rate of the material can be controlled, thereby optimizing the microstructure and properties of the material. This cooling method helps to obtain a uniform and fine grain structure, improving the overall performance of the material.
4. Protect electric heating elements
In processes such as nitrogen filling and pressure oil quenching, nitrogen can not only protect the electric heating elements of the vacuum furnace from high-temperature oxidation and corrosion damage, but also improve the quenching hardness of steel parts by adjusting the nitrogen pressure. This can not only extend the service life of the equipment, but also improve the processing quality of the product.
5. Improve process efficiency
The use of nitrogen in vacuum annealing furnaces can also improve process efficiency. For example, in heat treatment processes such as carburizing and nitriding, introducing nitrogen gas can accelerate the carburizing rate and improve the quality of the infiltrated layer. At the same time, nitrogen can also be used for furnace blowing, exhaust and other operations to maintain the cleanliness and stability of the furnace environment.
In summary, the role of nitrogen gas in vacuum annealing furnaces is multifaceted, mainly including preventing oxidation, nitriding modification, serving as a cooling medium, protecting electric heating elements, and improving process efficiency. These effects collectively promote the improvement of material properties and the optimization of heat treatment processes.