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Firstly, nitriding is a chemical heat treatment process that involves the infiltration of nitrogen atoms into the surface of a metal. As the name suggests, the nitriding medium used is gas, usually ammonia. Because ammonia is easy to be thermally cracked on the metal surface to generate hydrogen and nitrogen, a small amount of active nitrogen atoms will be generated during this cracking process. These active nitrogen atoms are captured by metal atoms to produce nitrides or diffuse into the interior of the metal, and this process is called nitriding. The nitriding process makes the metal surface produce Solid solution strengthening of nitrogen atoms and dispersion strengthening of nitrides, thus obtaining high hardness and wear resistance. A dense nitride layer also occurs on the metal surface, with higher hardness and high resistance to acid and alkali corrosion. It also maintains a white bright color under metallographic corrosion, hence it is also known as the "white bright layer".

Gas nitriding can also be further subdivided into "hard nitriding" and "soft nitriding". Hard nitriding "refers to a nitriding process that only uses ammonia gas as the nitriding medium and only nitrogen atoms are infiltrated. Soft nitriding "refers to a nitriding process that uses multiple nitriding media, with both nitrogen and carbon atoms infiltrating. Of course, this term lacks rigor, and the true scientific name of "soft nitriding" should be "Nitro carburizing", which refers to the process of carburizing while nitriding. It is only one word different from another important chemical heat treatment process - carbon nitrocarburizing, and attention should be paid to distinguishing it. Nitrocarburizing is mainly achieved by nitriding, supplemented by carburizing, so its working temperature is lower than the eutectoid temperature of Fe-N binary alloy by 590 ℃, usually between 530 ℃ and 570 ℃, slightly higher than the traditional gas nitriding temperature. Carbonitriding is mainly carburizing, supplemented by nitriding, and its working temperature is 727 ℃ higher than the eutectoid temperature of Fe-C binary alloy, usually between 830 ℃ and 880 ℃, slightly lower than the traditional gas carburizing temperature.

According to the different nitriding media, "soft nitriding" can be divided into solid, liquid soft nitriding, and gas soft nitriding. Among them, the earliest liquid soft nitriding process emerged, which is a nitrogen carbon co nitriding process carried out in a highly toxic cyanide salt bath. Due to the large amount of cyanide that pollutes the environment, this method is gradually prohibited from use. Instead, it is the most widely used gas nitrocarburization process, which uses NH3 and its decomposition products as the nitriding medium and CO2 or organic compounds such as methanol and propane as the carburizing medium.