In the presence of active nitrogen atoms in the gas, liquid or solid as the medium, under a certain temperature and time treatment on the surface of parts for nitrogen infiltration, this process is called nitriding or nitriding. This chemical heat treatment process was first used on the surface of steel. In the early 20th century, a series of nitriding theories and rules were summarized through comprehensive research.
In industry, nitriding process appeared before 1960s. There are three steps in this process, namely medium decomposition, surface absorption and nitrogen atom diffusion on the surface. After nitriding treatment, the surface hardness of the parts is improved, corrosion resistance and fatigue resistance are improved. Therefore, this process can be applied to all kinds of precision parts, long-term parts in strong corrosive environment and in high demand occasions. Therefore, nitriding treatment is widely used in machinery manufacturing, national defense science and technology, petroleum and other industries.
Nitriding process is usually carried out between 500 ℃ and 600 ℃. Gas, liquid and ion nitriding are three common nitriding methods. Among them, gas nitriding is the most commonly used medium, and the medium used is anhydrous nitrogen. The equipment required by the process is simple and easy to operate, but the disadvantages are obvious, and the time required is dozens of hours, and the efficiency is very low. Liquid nitriding is also salt bath nitriding. The process is widely used, and the operation equipment is simple and easy to understand. The quality of nitriding sample is stable and the nitriding speed is fast. However, the medium used is toxic and has great pollution to the air. With the continuous development of the process, a non-toxic nitriding salt has been developed. In the three nitriding processes, the most energy-saving and environmental protection is ion nitriding. The surface nitriding of the pattern is carried out by the principle of glow discharge point. The nitriding speed is fast and the nitriding quality is high.