Heat treatment is a comprehensive process that gettting the material processed on a certain medium heating, insulation, cooling, by changing the surface or internal structure of the material to control the performance.
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing technologies, heat treatment generally does not change the shape and overall chemical composition of the raw material, but changes the internal microstructure of the workpieces or changes the chemical composition of the surface , Give or improve the performance of the workpiece. Its characteristic is to improve the inherent quality of the workpiece, which is generally not visible to the naked eye.
Metallic materials consist of a microstructure of small crystals called "grains". The nature of the grains (i.e. grain size and composition) is one of the most effective factors that can determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling within the microstructure.
Metal heat treatment process can be broadly divided into overall heat treatment, surface heat treatment and chemical heat treatment three categories. Depending on the heating medium, the heating temperature and the cooling method, each major category can be distinguished as several different heat treatment processes. The same metal using different heat treatment process, access to different organizations, which have different properties.
Heat treatment is one of the important processes in the manufacture of machine parts and tooling. In general, it can guarantee and improve the performance of the workpiece, such as wear-resistant, corrosion-resistant and so on. Can also improve the organization of the rough and stress state, in order to facilitate a variety of cold and hot processing.Eg.malleable iron can be obtained when White cast iron after a long time annealing,the plasticity can be improved as well; the service life of gear with the right heat treatment process can be doubled or dozens of times higher than the gear without heat treatment; In addition, low grade carbon steel by infiltration of a Some alloying elements have some high grade alloy steel performance, which can replace some of the heat-resistant steel, stainless steel; almost all molds need to be heat treated before use.
Case hardening is specified by hardness and case depth. The Case hardening is specified by hardness and case depth. The case depth can be specified in two ways: total case depth or effective case depth. The total case depth is the true depth of the case. The effective case depth is the depth of the case that has a hardness equivalent of HRC50; this is check on a Tukon microhardness tester. This value can be roughly approximated as 65% of the total case depth; however the chemical composition and hardenability can affect this approximation. If neither type of case depth is specified the total case depth is assumed.For case hardened parts the specification should have a tolerance of at least ±0.005 in (0.13 mm). If the part is to be ground after heat treatment, the case depth is assumed to be after grinding.