Should the heat treatment of the heat exchange tubes be carried out with nitrogen or argon

During the heat treatment of heat exchange tubes, nitrogen or argon can be used depending on the specific situation. Nitrogen can accelerate the surface nitriding hardening, but there is a limit to the thickness of the nitrided layer; argon can better protect the surface quality of the heat exchange tubes, but it is more costly.

1. Why is gas charging required for heat treatment?

During the use of heat exchange tubes, due to long-term high-temperature heating and cooling, they are prone to problems such as reduced hardness, decreased toughness, and decreased corrosion resistance. Therefore, modern processes usually use heat treatment to improve their performance.

During the heat treatment process, by heating and holding at a constant temperature of the heat exchange tubes, they reach a certain temperature and time, and then through cooling to achieve the desired performance indicators. During the heating process, gas needs to be charged into the interior of the heat exchange tubes to play a role of protection and promoting reactions.

2. Application of nitrogen charging in heat treatment

Nitrogen charging is to charge nitrogen into the heat exchange tubes as the protective gas to promote the nitriding hardening reaction on the surface. Nitriding hardening is to form a hard and brittle, high-strength nitride layer on the surface of the interlaced layer structure to improve the surface hardness, wear resistance, and corrosion resistance.

Nitrogen charging has a good effect on improving the surface hardness, wear resistance, and corrosion resistance of the heat exchange tubes. However, there is a certain limit to the thickness of the nitrided layer. If it exceeds the limit, it may cause the nitrided layer to fall off and the substrate to deform. In addition, nitrogen charging may also affect the surface quality of the nitrides, causing pores, cracks, and other defects.

3. Application of argon charging in heat treatment

Argon charging is to charge argon into the heat exchange tubes as the protective gas to protect the surface from oxidation and contamination. Argon gas does not react with the metal during the heat treatment process, thus maintaining the integrity and quality of the heat exchange tube surface.

Argon charging can improve the surface quality of the heat exchange tubes and protect them from contamination and oxidation. However, argon charging is more costly than nitrogen charging. In addition, argon charging does not promote the nitriding hardening reaction, so it cannot play the same role as the nitrided layer hardening.

4. Selection in different situations

When choosing the type of gas to charge, it should be selected based on specific circumstances. If you need to improve surface hardness and wear resistance, you can choose nitrogen charging; if you need to protect the surface quality, you can choose argon charging.

In addition, it is necessary to consider comprehensively based on the material of the heat exchange tube and the temperature and time of the heat treatment process. If it is impossible to determine which gas to choose, it is necessary to conduct experiments to determine the best choice.

【Conclusion】

The selection of gas charging during heat treatment of heat exchange tubes is a complex issue that must be considered from multiple aspects. This article introduces the characteristics and application scenarios of nitrogen and argon charging, hoping to help readers choose the most suitable heat treatment gas.