Keywords: heat treatment, history of development, copper-iron, temperature, pressurisation, deformation, white cast iron, softening, hardness, hardening process,

History of heat treatment

　　The role of heat treatment was gradually recognised during the progress from the Stone Age to the Copper and Iron Ages. As early as 770 to 222 B.C., the Chinese had already discovered in their production practice that the properties of copper and iron could be changed by the effects of temperature and deformation under pressure. The softening of white cast iron was an important process in the manufacture of agricultural tools.

　　In the sixth century B.C., steel weapons were gradually adopted, and the quenching process was rapidly developed in order to improve the hardness of steel. Two swords and a halberd unearthed in Yixian Yanxiadu, Hebei Province, China, have martensite in their microstructure, indicating that they were quenched.

　　With the development of quenching technology, people gradually found the quenching agent on the quenching quality. Pu Yuan, a Shu man from the Three Kingdoms, once made 3,000 knives for Zhuge Liang in the present-day Xiangu Valley in Shaanxi Province, and it is rumoured that he sent someone to Chengdu to fetch water for quenching. This shows that China paid attention to the cooling capacity of different water qualities in ancient times, as well as the cooling capacity of oil and urine. China unearthed in the Western Han Dynasty (206 BC ~ AD 24) in the tomb of King Jing of Zhongshan sword, the heart of the carbon content of 0.15 ~ 0.4%, while the surface carbon content is up to 0.6% or more, indicating that the application of carburisation process. But at that time as a personal ‘craft’ secret, refused to spread, so the development is very slow.

 　　In 1863, British metallographers and geologists showed six different metallographic organisations of steel under the microscope, proving that steel in the heating and cooling, the internal organisational changes that will occur in the steel at high temperatures in the phase in the rapid cooling transformed into a harder phase. French Osmond established the theory of iron isotropy, as well as the British Austin's earliest formulation of the iron and carbon phase diagram for the modern heat treatment process initially laid the theoretical foundation. At the same time, people also studied the heating process in the metal heat treatment of metal protection methods to avoid the oxidation and decarburisation of metal in the heating process.

　　1850 ~ 1880, for the application of various gases (such as hydrogen, gas, carbon monoxide, etc.) for the protection of the heating had a series of patents. 1889 ~ 1890 British Leake obtained a variety of metal bright heat treatment patents.

　　Since the twentieth century, the development of metal physics and other new technology transplantation application, so that the metal heat treatment process has been more development. A significant progress is 1901 ~ 1925, in industrial production in the application of rotary furnace gas carburisation; 30 s dew-point potential difference meter, so that the carbon potential of the furnace atmosphere to reach a controllable, and later on the study of carbon dioxide infrared meter, oxygen probe and other further control of the furnace atmosphere of carbon potential method; 60 s, the heat treatment technology using the plasma field, the development of the ion nitriding, carburisation process In the 1960s, the heat treatment technology used the role of plasma field, the development of ion nitriding, carburising process; the application of laser, electron beam technology, and make the metal to obtain a new surface heat treatment and chemical heat treatment methods.

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