Heat treatment is a metallurgical process in which a material is subjected to a series of heating and cooling cycles in the solid state, with the objective of achieving a desired organization and set of properties.
Metal heat treatment process can be broadly divided into the overall heat treatment, surface heat treatment and chemical heat treatment of three categories. According to the heating medium, heating temperature and cooling method of different, each category can be distinguished into a number of different heat treatment process. The same metal using different heat treatment processes, can obtain different organizations, thus having different properties. Iron and steel is the most widely used metal in industry, and steel microstructure is also the most complex, so there are a variety of steel heat treatment process. Overall heat treatment is the overall heating of the workpiece, and then cooled at an appropriate rate, to obtain the required metallurgical organization, in order to change its overall mechanical properties of metal heat treatment process. The overall heat treatment of steel roughly annealing, normalizing, quenching and tempering four basic processes.
Heat Treatment
- Annealingis the workpiece is heated to the appropriate temperature, adopt different holding time according to material and the size of workpiece, and then slowly cooled, the purpose is to make the internal organization of the metal to achieve or close to the equilibrium state, to obtain good process performance and using performance, or prepare for further quenching.
- Normalizingis the workpiece is heated to the appropriate temperature, then cool in the air, the effect of normalizing is similar to annealing, but this process can get a finer organization, commonly used to improve the cutting performance of the material, sometimes normalizing is used for some of the less demanding parts as the final heat treatment.
- Quenching is the workpiece after heating and holding, in water, oil or other inorganic salts, organic water solution and other quenching media rapid cooling. After quenching, the steel becomes hard, but at the same time becomes brittle, in order to eliminate brittleness in time, it is generally necessary to temperin time. In order to reduce the brittleness of the steel, the quenched steel is insulated for a long time at an appropriate temperature higher than room temperature and lower than 650 degree centigrade, and then cooled, this process is called tempering.
- Surface Hardened & Partial Quenching
