Hardening steel is a process to increase its mechanical resistance by changing and converting its structure in a targeted manner. This can be done through heat treatment, followed by rapid cooling. Hardening requires first quickly heating up the workpiece above the austenitisation temperature. Heating it up too quickly can result in a significant risk of warping and cracking, and should be avoided.
The steel must have a carbon content of 0.2% - 0.3% for classic hardening. Due to their outstanding suitability, certain machinery steels are also called Q&T steels (generally 0.35 % - 0.6 % carbon).