| Heat treatment is defined as one or more controlled heating and cooling processes that are applied one or more, one after the other, according to the location, in order to give the desired properties to the solid metal or alloys. All basic heat treatments applied to steel are related to the transformation of the austenite phase in the iron-cementite equilibrium diagram. In other words, the physical and mechanical properties of a steel depend on the type, quantity and metallographic structure of the transformation products it contains. | ||||||||||||||||||||||||
| Heat treatment of steel starts with austenitization. For the austenitization process, the material is heated to a temperature above the lower critical temperature line (Ac1). In order to prevent distortions, materials subjected to cold deformation, that is, materials with excessive internal stress, should be heated more slowly than materials that do not contain tension. In addition, the differences between the heating or temperature increase rates in thin and thick sections should be taken into account during the heating of the parts with cross section changes. Thin parts of the piece should be heated slower than the thick parts in order to avoid any distortion due to the temperature effect. Steel parts are generally heated slowly to reduce the risk of damage during heat treatment. | ||||||||||||||||||||||||
| Some Annealing Operations; | ||||||||||||||||||||||||
| 1. | Soft Annealing ( +A ) | |||||||||||||||||||||||
| 2. | Spheroidized Annealing ( +AC ) | |||||||||||||||||||||||
| 3. | Normalizing ( +N ) | |||||||||||||||||||||||
| 4. | Stress Relieving ( +SR ) | |||||||||||||||||||||||
| 5. | Quenching ( +Q ) | |||||||||||||||||||||||
| 6. | Tempering ( +T ) | |||||||||||||||||||||||
| Some Hardening Operations; | ||||||||||||||||||||||||
| 1. | Quenching and Tempering ( +QT ) | |||||||||||||||||||||||
| Some Surface Hardening Operations; | ||||||||||||||||||||||||
| 1. | Case Hardening | |||||||||||||||||||||||
| 2. | Nitration Hardening | |||||||||||||||||||||||
| 3. | Induction Surface Hardening | |||||||||||||||||||||||
| 4. | Flame Surface Hardening | |||||||||||||||||||||||
| We can collect the steels to be heat treated in two groups according to the carbon content they | ||||||||||||||||||||||||
| contain in their structures. | ||||||||||||||||||||||||
| 1. | Sub-eutectoid steels ( %C < 0,8 ) | |||||||||||||||||||||||
| 2. | Supereutectoid steels ( %C > 0,8 ) | |||||||||||||||||||||||
