Tiefkühlen

In the case of high carbon steels (> approx. 0.6%) or steels after case-hardening, the quenching temperature of the medium used is not sufficient to achieve a monophase hardening structure (martensite). This means that the austenite structure present during the hardening process at high temperatures cannot be completely transformed and a certain amount of austenite remains, the so-called retained austenite. This retained austenite is significantly softer than the hardened structure, and also has a smaller atomic lattice volume. This could lead to problems when using the components. For this reason, this retained austenite usually has to be subsequently converted into a hardened structure (martensite). The transformation point, depending on the respective carbon content, is in the temperature minus range (< 0 °C).

Liquid nitrogen is used for deep cryogenic treatment, which is converted into gaseous nitrogen in a chamber. The process involves slow cooling to treatment temperature, a certain holding time and slow heating to room temperature.

Each freezing process must be followed by a new tempering process.