The materials are hardened in an inert gas atmosphere composed of nitrogen, methanol and natural gas. This atmosphere is matched exactly to the carbon content of the respective material. At temperatures that are normally over 780°C the component is first converted into a martensite structure and then quenched or cooled at a controlled rate. This rapid cooling transforms the steel structure and is done by quenching in oil, gas or other quenching media. Then the tempering creates the desired properties of the component, above all the necessary hardness and toughness. In this process, tempering takes place using high temperatures. An optional sub-zero treatment can be carried out after the protective gas hardening. It serves to transform the retained austenite and stabilize the martensite. Because of the high temperatures involved, there will inevitably be some degree of distortion.
It should be noted that Hardening means to fully through harden a material. Hardening and tempering is therefore quite different from surface hardening or precipitation hardening.
Most processes are performed in highly sophisticated furnace equipment, specially designed to give the best results possible.
Atmospheric hardening is the hardening of components in an inert atmosphere. This protects the surface of the component against scaling and oxidation and against carburization and decarburization. By means of a regulated carbon potential in the inert gas atmosphere, decarburization and carburization processes can be reversed.