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It is a heat treatment to remove the hardness of quenched steels and to give them toughness. The steel is stabilized by keeping it at high temperature. The metal kept at high temperature for a sufficient time is suddenly cooled. The martensite structure formed during hardening is very fragile. High stresses also occur in the part as a result of rapid cooling. In order to obtain a tough structure by removing the hardness of the material and to reduce internal stresses, a heat treatment called tempering is applied.

Normalization is generally a heat treatment to reduce grain size, to obtain a homogeneous microstructure, to improve the processing and mechanical properties of the material, to disperse the carbide network at the grain boundaries of eutectoid steels, to increase the hardness and strength of steels subjected to softening annealing. The steel is heated to a temperature suitable for the alloy and cooled in calm air.

It is a heat treatment to reduce the internal stresses present in the parts to a level that does not cause problems or to completely eliminate them. Internal stresses can occur for a variety of reasons, including rapid cooling due to the temperature difference between the surface and the core, plastic forming such as straightening and bending, welding or after machining thin surface layers. Stress relieving is normally carried out after roughing, before final machining, for example before polishing or grinding. Stress relieving should be applied to parts with dimensionally tight tolerances that will be machined later, e.g. nitrocarburizing. Welded structures can be stress relieved by stress relieving.

Untreated materials show different hardnesses at room temperature, depending on the carbon content. Some materials may not be easily machinable due to their hardness. Especially for plastic deformation processes, the minimum hardness of the materials is desired. For this reason, vacuum softening annealing is performed to soften the materials.

Hydrogen is often a by-product of corrosion and electro-chemical processes with aqueous solutions. Atomic hydrogen is formed on metal surfaces in aqueous, humid environments by the addition of a proton to a hydrogen ion. The combination of this atomic hydrogen penetrating into the metal and the resulting molecular hydrogen retards the strain of the material, causing instantaneous fracture without deformation. This phenomenon is called "hydrogen brittleness". Hydrogen enters the metal in steelmaking, heat treatment, acid cleaning, electrolytic zinc plating, corrosion reactions and cathodic corrosion protection. The risk of brittleness indicates that cracking or fracture will occur when metals are subjected to a certain force or compression. Today, this issue of hydrogen embrittlement is very important; hydrogen embrittlement is required in almost all heat-treated materials.