In the struggle with nature, human beings constantly improve the materials for making tools. At first, tools were made of natural stones and wood, and later, metals were gradually discovered and used. The use of metallic materials in China has a long history. There is a record of "Gold 67" in Flower King Gong Ji more than 2,000 years ago, which is the earliest discussion on the law of composition proportion of bronze alloys. Although humans have known many metals, such as gold, silver, copper, mercury, tin, iron, lead and so on. As early as BC, due to the limitation of mining and smelting technology, many musical instruments were still made of wood or mixed with iron and wood for a long historical period. It was not until 1856 that H. Bessemer, an Englishman, invented converter steelmaking, and 1856 ~ 1864 that K. W. Siemens, an Englishman, and P. Martin, a Frenchman, invented open hearth steelmaking, that a large-scale steelmaking industry appeared, and steel became the most important mechanical engineering material. In 1930s, light metals such as aluminum (see aluminum alloy) and magnesium (see magnesium alloy) were gradually applied. After World War II, scientific and technological progress has promoted the development of new materials, and ductile iron, alloy cast iron, alloy steel, heat-resistant steel, stainless steel, nickel alloy, titanium alloy and cemented carbide have successively formed a series, expanding the application scope. At the same time, with the development of petrochemical industry, the rise of synthetic materials has been promoted, and the proportion of engineering plastics, synthetic rubber and adhesives in mechanical engineering materials has gradually increased. In addition, the application of gemstones, glass and special ceramic materials in mechanical engineering is gradually expanding.