Atmospheric Hardening

what is hardening?

Hardening is the heating and subsequent cooling of steel at such a speed that there is a considerable increase in hardness, either on the surface or throughout. In most cases hardening takes place in conjunction with subsequent reheating, the tempering. Depending on the material, hardening improves the hardness and wear resistance.

Enhanced properties are high wear resistance, outstanding hardness, fatigue life and increased tensile strength.

the process

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.

fields of application

Practically all technically interesting steel alloys, such as spring steels, cold-worked steels, quenched and tempered steels, anti-friction bearing steels, hot-worked steels and tool steels, as well as a large number of high-alloy stainless steels and cast-iron alloys, can be hardened.

Hardening of metals and steels in general is a very broad subject and there are many different routes which can be used for different materials. If you are in any doubt about the best process for your purpose, we would advise that speak to one of our experienced metallurgists prior to specifying treatments. For details of the best person to speak to within your area refer to your nearest plant site for contact information.