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Vacuum hardening is the hardening of components under a controlled partial pressure, during which temperatures of up to 1,300°C can be reached. The aim of this process variant is to provide a protective atmosphere free from oxidation and decarburization and the creation of bright metallic workpiece surfaces which render further mechanical processing unnecessary.
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 the case of vacuum hardening, this process is done in vacuum furnaces in which temperatures of up to 1,300°C can be reached. The quenching methods will differ with regards to the material treated but gas quenching using nitrogen is most common.
In most cases hardening takes place in conjunction with subsequent tempering. In some cases, a cryogenic treatment follows the hardening process before tempering which greatly improves the properties of the steels involved.
Vacuum hardening is a specialized form of heat treating that utilizes vacuum technology to create an environment with no oxygen or other gases during the heating phase. This eliminates oxidation from occurring on the surface of the metal being treated, resulting in higher purity and surface fineness than what can be achieved through traditional processes such as normal hardening. Additionally, vacuum technologies can provide better control over temperature uniformity, leading to a more consistent result when compared to traditional heat-treating processes. Finally, this hardening also helps reduce energy consumption since vacuum furnace systems require less energy than traditional furnaces due to their improved insulation capabilities.
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 in a vacuum.
Vacuum hardening however, is mostly used for high-alloy tool steels and steels that require a bright metallic workpiece surface finish.
