On the one hand, nitrogen infiltrated into steel forms iron nitride with different nitrogen content with iron from outside to inside, and on the other hand, it combines with alloying elements in steel to form various alloy nitrides, especially aluminum nitride and chromium nitride. These nitrides have high hardness, thermal stability and high dispersibility, so that the nitrided steel parts have high surface hardness, wear resistance, fatigue strength, bite resistance, atmospheric and superheated steam corrosion resistance, tempering softening resistance and reduced notch sensitivity. Compared with carburizing process, nitriding temperature is lower, so the distortion is smaller. However, due to the low hardness of the center and shallow carburized layer, it can only meet the requirements of wear resistance and fatigue resistance under light and medium loads, or mechanical parts with certain requirements on heat resistance and corrosion resistance, as well as various tools, cold working and hot working molds. There are many nitriding methods, among which gas nitriding and ion nitriding are commonly used.

The research of steel nitriding began in the early 20th century, and it was applied in industry after the 20th century. The initial gas nitriding was limited to steels containing chromium and aluminum, and later it was extended to other steels. Since 1970s, nitriding has developed rapidly in theory and technology, and the applicable materials and workpieces have been expanding, becoming one of the important chemical heat treatment processes.