Lufthärtige

Lufthärtige refers to a specific property of certain materials, particularly steels, that undergo hardening when cooled in air. This is in contrast to materials that require quenching in a liquid medium such as oil or water to achieve their desired hardness. The ability to air harden is primarily determined by the material's composition, specifically the presence and amount of alloying elements like chromium, molybdenum, and vanadium. These elements form carbides during heating, and upon cooling, they can dissolve into the iron matrix to a sufficient degree to allow for martensite formation, which is the hard constituent of steel, even with slower cooling rates like those experienced in air.

The phenomenon of air hardening is advantageous in certain manufacturing processes. It can simplify heat treatment procedures by eliminating the need for specialized quenching baths, reducing the risk of distortion or cracking often associated with rapid liquid quenching, and facilitating easier handling of parts. However, materials that air harden may still require tempering after the initial air cool to reduce brittleness and achieve the optimal balance of hardness and toughness for their intended application. The specific temperature and time for tempering depend on the alloy's composition and the desired mechanical properties.