Metal heat treatment on the metal workpiece is heated to a certain medium suitable temperature and maintained at this temperature for a certain time after, on a cooling process at different speeds.

1. The metal structure

Metal: an opaque, metallic luster and good thermal conductivity and its electrical conductivity decreases with increasing temperature, full ductility and malleability characteristics of the material. Inside the metal atom has a solid regular arrangement (ie crystal).

Alloy: from two or more metals or metal and non-metal components, with physical metal properties.

Phase: the alloy composition, structure, part of the same performance.

Solid solution: is one (or several) atomic component (compound) was dissolved in the crystal lattice of the other component, while still holding the other component of the crystal lattice type of solid metal, solid solution points interstitial solid solution and substitution solid solution two kinds.

Solid solution strengthening: As solute atoms into the gap or junction point of the solvent lattice, the lattice distortion, so that the solid solution increased hardness and strength, a phenomenon called solid solution hardening phenomenon.

Compound: compounds occurs between alloy component, generating a new solid-state crystal structure having a metal properties.

Mechanical mixture: alloy composition which consists of two crystal structures, although the two sides of the seed crystal, it is a composition, which has an independent mechanical properties.

Ferrite: carbon a-Fe (iron body-centered cubic structure) in the interstitial solid solution.

Austenite: carbon interstitial solid solution (iron face-centered cubic structure) g-Fe in the.

Cementite: carbon and iron to form a stable compound of (Fe3c).

Pearlite: ferrite and cementite mechanical mixture (F + Fe3c carbon content 0.8%)

Ledeburite: mechanical mixture of cementite and austenite (carbon 4.3%)

Metal heat treatment is an important process in the manufacture of machinery, compared to other processing, heat treatment generally does not change the shape and the overall chemical composition of the workpiece, but by changing the internal microstructure of the workpiece, or changing the chemical composition of the surface give or improve the performance of the work. Its characteristics are improved intrinsic quality of the workpiece, which is generally not the naked eye can see.

For the metal workpiece having the desired mechanical properties, physical properties and chemical properties, in addition to the rational use of materials and various forming processes, heat treatment process is often essential. Steel is the most widely used in machinery industry materials, iron and steel complex microstructure can be controlled by heat treatment, so the heat treatment of steel is the main content of metal heat treatment. Further, aluminum, copper, magnesium, titanium and its alloys can also be changed by heat treatment the mechanical, physical and chemical properties, in order to obtain different performance.

In the process of progress from the Stone Age to the Bronze Age and Iron Age, the role of the heat treatment is gradually being recognized. As early as 770 BC, 222 years ago, the Chinese people had discovered in the production practice, Cu and Fe in performance due to deformation of pressure and temperature
Change. Softened white cast iron is an important process of manufacturing tools.

The sixth century BC, iron and steel weapons gradually been adopted, in order to increase the hardness of the steel, the quenching process then developed rapidly. Yan Yi County, Hebei Province, China have unearthed under the two swords and an halberd, which has a martensitic microstructure in the presence of note is hardened.

With the development of hardening technology, people gradually found to affect the quenching agent to quench quality. Three Shu Pu Yuan was in this Shaanxi Xiegu of Zhuge Liang chipped 3000 knife, according to legend was sent to Chengdu water quenching. This shows that in ancient China noticed the cooling capacity of the different water quality, but also pay attention to the cooling capacity of the oil and urine. China unearthed in Western Han Dynasty (206 BC-AD 24) Zhongshan Jing sword in the tomb, the center carbon content of 0.15 to 0.4%, while the surface of the carbon content was more than 0.6%, indicating that it has applied carburizing process. But then as an individual "craft" the secret, refused to rumor, so development is very slow.

In 1863, British scientist and geologist metallurgical steel under a microscope shows six different microstructure proved steel during heating and cooling, internal organizational change will happen, when the high temperature phase transition in steel during quenching as a hard phase. Iron allotrope theory, and the iron-carbon phase diagram Frenchman established British Austin Osmond first developed for modern heat treatment process initially laid the theoretical foundation. At the same time, people also studied during the heating of the metal in the metal heat treatment method of protection, in order to avoid the heating process of metal oxidation and decarbonization and the like.

1850 and 1880, for the application of a variety of gases (such as hydrogen gas, carbon monoxide, etc.) for protection of the heating had a series of patents. 1889 - 1890 British lake access to a variety of metal bright heat treatment of patents.

Since the 20th century, the development of metal physics and other portable applications of new technology, metal heat treatment process to obtain greater development. A significant development is the 1901 ~ 1925, the industrial production application drum furnace gas carburizing
; 30 years appeared dew point potentiometer, the furnace atmosphere carbon potential to achieve controlled, and later developed an infrared device with carbon dioxide, oxygen probes to further control the furnace atmosphere carbon potential of the method; the 1960s, the use of the plasma heat treatment technology the role of the field, the development of ion nitriding, carburizing
; Laser, electron beam technology applications, but also to obtain a new metal surface heat treatment and chemical heat treatment method.