Popular science on metal heat treatment

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Metal heat treatment is a process in which metal workpieces are heated to an appropriate temperature in a certain medium, held at that temperature for a certain period of time, and then cooled at different rates. Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing methods, heat treatment generally does not change the shape of the workpiece or its overall chemical composition; instead, it enhances or improves the performance of the workpiece by altering its internal microstructure or the chemical composition of its surface. Its feature is improving the internal quality of the workpiece, which is generally not visible to the naked eye. Heat treatment furnaces for large cast steel parts: To endow metal workpieces with the desired mechanical, physical, and chemical properties, in addition to the proper selection of materials and various forming processes, heat treatment processes are often essential. Steel is the most widely used material in the machinery industry. Its microstructure is complex, but it can be controlled through heat treatment; therefore, heat treatment of steel constitutes the main aspect of metal heat treatment. Furthermore, metals such as aluminum, copper, magnesium, titanium, and their alloys can also have their mechanical, physical, and chemical properties altered through heat treatment to achieve different performance characteristics. As society progressed from the Stone Age to the Bronze Age and Iron Age, the role of heat treatment gradually came to be recognized. As early as 770–222 BC, the Chinese had already discovered in their practical manufacturing activities that the properties of copper and iron would change under the influence of temperature and deformation under pressure. The softening treatment of white cast iron is an important process for manufacturing agricultural tools. In the 6th century BC, steel weapons were gradually adopted, and the quenching process developed rapidly in order to increase the hardness of steel. The two swords and one halberd unearthed in Yanxiadu, Yi County, Hebei Province, China, all contained martensite in their microstructure, indicating that they had been quenched. With the development of quenching technology, people have gradually come to realize the impact of quenching agents on the quality of quenching. Pu Yuan from the Shu state during the Three Kingdoms period once forged 3,000 swords for Zhuge Liang in present-day Xiaguo, Shaanxi; it is said that people were sent to Chengdu to fetch water for tempering the swords. This shows that China recognized the cooling capabilities of different water qualities in ancient times, as well as those of oil and urine. The swords found in the tomb of King Jing of Zhongshan from the Western Han Dynasty (206 BC–24 AD) in China have a carbon content of 0.15–0.4% in their core, while the carbon content on the surface exceeds 0.6%, indicating that carburizing techniques were employed. But at that time, as a personal \"skill,\" its secrets were not shared with others, so its development was slow.