The elements of aluminum, chromium, vanadium and molybdenum in the traditional alloy steel are helpful to nitriding. These elements in the nitriding temperature, contact with the primary nitrogen atoms, the formation of stable nitrogen compounds. In particular, molybdenum is not only used as a nitride element, but also as a brittleness to reduce the nitriding temperature. The elements in other alloy steels, such as nickel, copper, silicon, manganese, etc., do not contribute much to nitriding. Generally speaking, if the steel material contains one or more nitride elements, the nitriding effect is better. Among them, aluminum is a strong nitride element, containing 0.85 ~ 1.5% aluminum nitriding results. In the case of chromium containing chromium steel, if there is enough content, can also get a very good effect. However, there is no alloying carbon steel, because its nitriding layer is very fragile, easy to peel, is not suitable for nitriding steel.