heat treatment
close In the process from the Stone Age to the Bronze Age and the Iron Age, the role of heat treatment [1] has gradually been recognized. As early as 770-222 BC, the Chinese had found in production practice that the properties of copper and iron would change due to the influence of temperature and pressure deformation. The softening treatment of white cast iron is an important process for manufacturing farm tools. In the sixth century BC, steel weapons were gradually adopted. In order to improve the hardness of steel, quenching technology was developed rapidly. Two swords and one halberd unearthed in Yanxiadu, Yixian County, Hebei Province, China, have martensite in their microstructures, indicating that they have been quenched. With the development of quenching technology, people gradually find the influence of quenching agent on quenching quality. Pu Yuan, a man from Shu in the Three Kingdoms, once made 3000 knives for Zhuge Liang in today's Shaanxi Valley. It is said that he sent people to Chengdu to fetch water for quenching. This shows that China has noticed the cooling capacity of different water quality in ancient times, as well as the cooling capacity of oil and urine. The sword unearthed in China from the Western Han Dynasty (206 B.C. to 24 A.D.) in the tomb of King Jing of Zhongshan has a carbon content of 0.15~0.4% in the heart and more than 0.6% in the surface, which indicates that the carburizing process has been applied. However, as the secret of personal "craftsmanship" at that time, it refused to be spread, so it developed slowly. In 1863, British metallographists and geologists showed six different metallographic structures of steel under the microscope, proving that when steel is heated and cooled, the internal structure will change, and the phase at high temperature in steel will change into a harder phase during rapid cooling. The allotropy theory of iron established by French Osmond and the iron carbon phase diagram first formulated by British Austin laid a preliminary theoretical foundation for modern heat treatment process. At the same time, people also studied the methods of protecting metals during the heating process of metal heat treatment to avoid oxidation and decarburization of metals during the heating process. From 1850 to 1880, there were a series of patents for the application of various gases (such as hydrogen, gas, carbon monoxide, etc.) for protective heating. From 1889 to 1890, the Englishman Lake obtained a patent for bright heat treatment of various metals. Since the 20th century, the development of metal physics and the transplantation and application of other new technologies have made greater progress in metal heat treatment technology. One notable development was that from 1901 to 1925, the rotary hearth furnace was used for gas carburization in industrial production; In the 1930s, dew point potential difference meter appeared, which made the carbon potential of furnace atmosphere controllable. Later, methods to further control the carbon potential of furnace atmosphere with carbon dioxide infrared instrument, oxygen probe, etc. were developed; In the 1960s, heat treatment technology used the role of plasma field to develop ion nitriding and carburizing processes; With the application of laser and electron beam technology, new surface heat treatment and chemical heat treatment methods have been obtained for metals.