On 2018-08-08 14:48:54
Metal heat treatment are indispensable quenching and tempering
Metal heat treatment, annealing is to heat the workpiece to a proper temperature, adopt different holding time according to the material and workpiece size, and then conduct slow cooling, so as to make the internal structure of the metal reach or close to the equilibrium state, or release the internal stress generated by the previous process, obtain good process performance and use performance, or make organization preparation for further quenching 。 In order to reduce the brittleness of steel parts, the quenched steel parts are kept warm for a long time at a proper temperature higher than room temperature but lower than 650 ℃, and then cooled. This process is called tempering.
Annealing, normalizing, quenching and tempering are the "four fires" in the whole heat treatment, in which quenching and tempering are closely related and often used together. 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 workpiece, but endows or improves the performance of the workpiece by changing the microstructure inside the workpiece or the chemical composition on the surface of the workpiece. Its characteristic is to improve the internal quality of the workpiece, which is generally not visible to the naked eye.
Therefore, it is a special process in mechanical manufacturing and an important part of quality management. Surface heat treatment is a metal heat treatment process that only heats the surface of workpiece to change its mechanical properties. In order to heat only the surface layer of the workpiece without too much heat entering the interior of the workpiece, the heat source used must have a high energy density, that is, to give a large amount of heat energy to the workpiece per unit area, so that the surface layer or part of the workpiece can reach a high temperature in a short time or instantaneously.
The main methods of surface heat treatment are flame quenching and induction heating heat treatment. The common heat sources are flame, induction current, laser and electron beam, etc. White cast iron can obtain malleable cast iron and improve plasticity after long-time annealing treatment; gear with correct heat treatment process can have service life times or dozens of times longer than gear without heat treatment; in addition, low-cost carbon steel can replace some heat-resistant steel and stainless steel by infiltrating some alloy elements to have some valuable alloy steel properties; tools and dies are several It can only be used after heat treatment.
Steel is an alloy mainly composed of iron and carbon. Its carbon content is generally less than 2.11%. Steel is an important metal material in economic construction. According to chemical composition, steel can be divided into carbon steel and alloy steel. Carbon steel is an alloy obtained by smelting pig iron. In addition to iron and carbon as its main components, it also contains a small amount of manganese, silicon, sulfur, phosphorus and other impurities.