The development origin of cast iron

Cast iron is the product of the development of block ironmaking and liquid ironmaking. Block ironmaking first appeared in southwest Asia, from 1200 BC to 1000 BC, and its use has reached a certain scale. In 8O0 BC, smelting method spread to Europe; It spread to England in 500 BC. Block ironmaking is the most primitive ironmaking method. Its ironmaking furnace is made of stone or clay, and its furnace body is very short, with a small hole on its side, which is inserted into a conduit made of clay and supplied with gas by a leather bag; Use abundant iron ore and use charcoal or firewood as fuel. Solid reduction is carried out at about 1000℃, and the refined iron sinks to the bottom of the furnace and is taken out after the furnace is cooled. Every furnace has to be reheated, and the furnace temperature can't go up. This kind of iron has loose structure, many oxide inclusions and almost no elements such as carbon, silicon and manganese. Therefore, iron blocks are soft and can be forged at a certain temperature to remove inclusions, which is called dart iron, forged iron or sponge iron.

In the 6th century BC, China carried out liquid ironmaking, about 1000 years earlier than the west. Block ironmaking furnace has low temperature, slow chemical reaction, low output and many inclusions. Inspired by the big fan of copper shaft furnace, liquid ironmaking was created. When the furnace is raised, the contact time between the airflow in the furnace and the ore is long, the preheating effect of the ore is improved, the blast is enhanced, and the combustion is vigorous. The furnace can maintain a high temperature state for a long time (>: 1200℃), and the carburizing effect of charcoal is correspondingly enhanced, thus obtaining liquid cast iron. Casting Zhu China is one of the earliest countries in the world to produce iron castings. According to Zuo Zhuan, in the 29th year of Zhao Gong (565438 BC+03 BC), the State of Jin cast a cast iron tripod with a weight of 270kg, on which the full text of the criminal law was cast, which is the earliest record of China casting large pieces. After Sui and Tang Dynasties, there were more and more large castings. In 953 A.D., that is, on Wednesday of the Five Dynasties of China, the Cangzhou Iron Lion was cast.

Distribution map of ironware unearthed during the Warring States period

China's iron smelting industry developed rapidly in the late Spring and Autumn Period and the early Warring States Period, when the production of cast iron farm tools was particularly prominent. For example, 1955 cast iron farm tools unearthed from Zhao site in Shijiazhuang, Hebei Province account for almost 65% of all farm tools (including bone and stone materials), and a large number of iron molds (metal molds) unearthed in Xinglong, Hebei Province are used to cast farm tools, accounting for about 60%. This shows that China entered the Iron Age in the middle of the Warring States Period. According to the research after liberation, centering on the Central Plains in the north and south of the Yellow River, Liaoning in the north, Guangdong and Guangxi in the south, Sichuan in the west, Shandong in the east and Gansu in the northwest, it is an important area for iron smelting and iron making in ancient China (Figure 3). China's ancient metallurgy was more advanced than that of Europe, especially its casting technology was more than 1000 years earlier than that of Europe. The management of iron in the Han Dynasty has been put on the agenda, as evidenced by The Theory of Salt and Iron. A.D. 1637 Song Yingxing's Tiangong Kaiwu in the late Ming Dynasty recorded in detail the metallurgy and casting technology in China at that time. Although cast iron has a long history, its development is slow. Since the Qing Dynasty, casting technology has been stagnant for a long time, and it didn't develop gradually until after 1949. Education, scientific research and production systems have been formed throughout the country.