5. Heat treatment after carburizing or carbonitriding

After carbon or carbon and nitrogen have been introduced to the surface, the case-hardened or carbonitrided part undergoes a heat treatment designed to give it its working properties. This generally involves hardening by quenching, followed by stress-relieving tempering at temperatures usually between 150 and 200°C, to maintain the layer's high hardness. Sometimes, these treatments are preceded by annealing to enable machining before hardening. Finally, cryogenic or sub-zero treatments are sometimes carried out after quenching to reduce residual austenite content and improve certain working characteristics.