First, it was cast into a blank. Casting is to heat it into molten iron and then condense it to form it. After forging into various instruments, forging is called ironing, plus some fine processing, such as polishing.

Cast iron with carbon in the form of graphite can be roughly divided into three types according to the different graphite States: graphite is flake gray cast iron; Malleable cast iron is flocculent graphite; Spherical graphite is ductile iron. Among them, ductile iron has high strength, high plasticity and toughness, as well as good castability and machinability. China invented ductile iron in the Han Dynasty.

Iron unearthed from Tieshenggou iron smelting site in Gongxian County, Henan Province in the middle and late Western Han Dynasty? 6? 1, metallographic examination shows that there is radial spherical graphite, and the spheroidization rate is equivalent to the first-class level of modern standards. The modern ductile iron was not successfully developed until 1947 abroad. In ancient China, the silicon content of cast iron was low for a long time, that is to say, in the Western Han Dynasty about 2,000 years ago, spherical graphite in iron products in China was obtained by softening and annealing low-silicon pig iron castings. This is a great achievement of China's ancient cast iron technology and a miracle in the world metallurgical history.

Because of its excellent performance, nodular cast iron can sometimes replace expensive cast steel and forged steel, and is widely used in machinery manufacturing. The international metallurgical industry used to think that ductile iron was invented by the British in 1947. Some western scholars even claim that it is unthinkable to invent ductile iron without modern scientific and technological means. 198 1 year, China ductile iron experts studied 5 13 pieces of ancient Han and Wei ironware unearthed by modern scientific means, and drew a conclusion through a lot of data: spherical graphite cast iron appeared in Han Dynasty in China. Related papers were read at the 18 World Congress on the History of Science and Technology, which caused a sensation in the international foundry industry and the history of science and technology. After verifying this point in 1987, international experts in metallurgical history believe that the law of softening cast iron to make nodular cast iron was explored in ancient China, which is of great significance to the re-staging of world metallurgical history.