Hardening is a heat treatment process involving heating of steel to a temperature slightly above critical, maintaining the same temperature until its structural transformation is fully complete, and then cooling it at a rate necessary to obtain the martensitic structure, which makes steel so hard.
Hardened steel is characterized by high hardness, but also considerable brittleness and substantial internal stress. In order to reduce the stress, the steel parts must be reheated and cooled after quenching.
Reheating and fast cooling may be regarded as an integral part of quenching, because it reduces internal stress and increases toughness without affecting the hardness.
Reheating and moderate cooling is applied in cases in which high strength and elasticity, as well as sufficient toughness are required.
PPT-TMO S.A. uses modern equipment for hardening steel in the classic chamber furnaces (Cer Čačak) and Degussa shaft furnaces, in which there is a possibility of tempering in a protective atmosphere. The furnace reaches temperatures up to 1080°C with an accuracy of ±15°C. Workspace dimensions of these furnaces are 900 x 2000 mm and maximum batch weight up to 1000 kg.