The hardenability of a material is important for tempering, e.g., its ability to form a stable martensite or bainite structure under certain conditions. The steel must have a carbon content of 0.2% - 0.3% for classic tempering. Due to their outstanding suitability, certain machinery steels are also called Q&T steels (generally 0.35 % - 0.6 % carbon).
Glossary