carbonitriding

Carbonitriding results in a very hard case of the component. Specifically, this is useful in the case hardening of gears and similar components which are subject to a great deal of wear in hostile environments. This heat treatment process is especially useful if there is a requirement for a hard, wear resistant surface, overlying a much softer and tougher core. A good example for its application is a gear wheel. The surface of the teeth needs to be extremely hard so that they can withstand constant metal-to-metal contact, without undue wear. The underlying material needs to be tough so that the teeth can tolerate occasional impact loads, without the risk of fracture. 

Carbonitriding is used to give a hard case onto the cheapest steels which are often not capable of being case hardened because of their chemical composition. The carbonitriding process is applied to low carbon and mild steels and results in less distortion than traditional carburizing techniques.