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NOV 01 2012

Heat treatment of metals


Heat treatment of metals is one of the important processes in mechanical manufacturing, comparing with other technologies, heat treatment generally does not change the shape of the workpiece and the overall chemical composition, but by changing the workpiece internal microstructure, or change the surface chemical composition, give or improve product performance. Its characteristic is to improve the inherent quality of work pieces, but this is generally not visible to the naked eye can see, therefore, it is the machinery of special process, is also the important links of quality management.

In order to make the metal workpiece with desired mechanical properties, physical properties and chemical properties, in addition to the reasonable selection of materials and various forming process, heat treatment process is often essential. Iron and steel machinery industry is the most widely used material, microstructure of iron and steel complex, can be controlled by heat treatment, so the steel heat treatment is the main content of metal heat treatment. In addition, aluminum, copper, magnesium, titanium and its alloy by heat treatment can also change its mechanical, physical and chemical properties, in order to obtain different performance.

Process development

In from the stone age to the bronze age and the iron age in the process of heat treatment, the effect of gradually known by people. In the early Shang Dynasty, there were already after the recrystallization annealing gold ornaments. BC 770 ~ 222 years ago, Chinese in the production practice have been found, copper and iron performance due to the temperature and pressure the influence of deformation and change. White cast iron farm tools to create softening treatment is the important technology.

Sixth Century BC, the steel weapon gradually adopted, in order to improve the hardness of steel, quenching process has obtained the rapid development. Chinese Hebei province Yixian County Xiadu unearthed two swords and a halberd, the microstructure are martensite, that is after quenching.

As the quenching technology development, people gradually found quenching agent on quenching quality influence. The Three Kingdoms of Pu Yuan Shu people have in this Shaanxi diagonal Valley as Zhu Geliang made 3000 knives, which is sent to the Chengdu Water quenching. This shows China in ancient times came to the attention of different water cooling capacity, but also pay attention to oil and urine cooling capacity. China unearthed in Han Dynasty (206 BC – ad 24 ) Jing Zhongshan the sword in the heart of the tomb, carbon content is 0.15 ~ 0.4%, and the surface of the carbon content is more than 0.6%, that has been applied in carburizing technology. But it was as a personal ” craft ” secret, not unauthorized biography, and development is very slow.

In 1863, British metallographer and geologist shows steel under a microscope in six different microstructure, proved that steel during heating and cooling, occur within tissue changes in steel, high temperature phase in quenched into a hard phase. The Frenchman Osmond established the allotropic iron theory, as well as the British Austen first developed by iron carbon phase diagram, for modern heat treatment process initially laid the theoretical foundation. At the same time, it is also studied in metal heat treatment heating process on the metal protection method, in order to avoid the heating of the metal in the process of oxidation and decarburization.

From 1850 to 1880, the application of various gas ( such as hydrogen, carbon monoxide gas, etc.) to protect heating was a series of patent. From 1889 to 1890, the British Lake access to a variety of metal heat treatment of patent.

Since twentieth Century, the metal physical development and other new technology application, the heat treatment of metals technology gets greater progress. A significant progress is 1901 ~ in 1925, in the industrial production of a rotary drum furnace for gas carburizing; 30 time appear dew point potential difference meter, so that the furnace carbon potential control to, later studies using carbon dioxide infrared instrument, such as oxygen probe further control of carbon potential of the atmosphere in the furnace method; 60 time heat treatment technology, using a plasma field function, development of ion nitriding, carburizing technology; laser, electron beam technology, and makes the metal gained a new surface heat treating and chemical treating method.