Hardening and tempering

Hardening and tempering is a Heat treatment process for steels that takes place at temperatures of between 550 and 700°C. This creates a very strong fine-grained Material structure. Hardening and Tempering is used in particular for structural steels that need to be extremely strong and tough. Components made from such steels include screws, splines, pins and shafts.

To enable this process to take place, the material must support hardening and form a stable martensitic structure. Steels with a Carbon content of between 0.2 and 0.6 percent are used in most cases. Steels with a carbon content of 0.35 to 0.6 percent are also referred to as tempering steels. Other steels are more suited to Surface finishing because they are difficult or impossible to harden.

The workpiece that is to be hardened and tempered is heated above the austenitising temperature. The heating rate used eliminates the risk of distortion and cracking. The holding time is selected so as to ensure that the ferrite is fully converted and the carbides are dissolved. During the subsequent quenching process, the medium (water, oil, air) and the cooling rate influence the Microstructure produced.

Tempering after quenching and/or further tempering steps at higher temperatures reduce hardening stresses and result in a further conversion of residual austenite.