By the middle and late Warring States period, the division of iron smelting and cast iron industry had begun, and cast iron sites in the Warring States period had been found in Neicang, Xiping Hotel Village and Dengfeng Gaozhen of Zhenghan Ancient City in Xinzheng.
From recent archaeological excavations, it can be seen that the ironware unearthed during the Spring and Autumn Period and the Warring States Period were all made of "block smelting" or cast iron, and even more, cast iron was softened into malleable cast iron by heating and annealing. ① From smelting cast iron and casting devices to softening cast iron by heating and annealing, there must be a process of experimental improvement. It can be concluded that the invention of cast iron smelting technology in China should be earlier. At least. The smelting technology of this kind of cast iron in Central Plains is relatively mature. We can understand this from the fact that the Jin State cast the Ding in 5 13 BC. We know that it is not a simple matter to cast the torture book on the iron tripod. Even if there are not many words in this punishment book, there should be some rules. If these provisions are cast on the iron tripod, the "mold" will not be big, and there will not be too little cast iron in the flowing state. Otherwise, you can't vote. China invented the technology of smelting cast iron very early in ancient times, because it improved the blast mode of the smelting furnace, raised the temperature of the smelting furnace, turned the smelted iron into liquid, accelerated the smelting process and improved the productivity of iron. This is of decisive significance to the development of iron smelting industry and the popularization and use of iron tools.