Chapter 9 Section 2 The Boom of Pig Iron Smelting and Casting Technology

According to archaeological excavations, meteorite iron was used in my country during the Yin and Shang dynasties, and iron smelting by block smelting appeared in the late Western Zhou Dynasty, and pig iron smelting began in the late Spring and Autumn Period in the 6th century BC. Block smelting is a method of smelting iron at relatively low temperatures.It uses red-hot charcoal to directly reduce iron ore into iron from solid state, and the refined iron is loose, so it is called sponge iron.Sponge iron contains many inclusions, and it must be repeatedly heated and forged to be made into ironware.Pig iron is made at a furnace temperature of 1100°C-1200°C, so that the reduced solid iron accelerates the absorption of carbon due to the high temperature, thereby lowering the melting point, and it is in a molten state, which can be directly cast into a mold.It eliminates the labor-intensive and time-consuming defects of block ironmaking processing, improves production efficiency, reduces costs, and makes large-scale and high-efficiency production of ironware possible.Although some European countries produced lump iron smelting 3,000 years ago, hundreds of years earlier than China, they stayed in the stage of lump iron smelting for a long time. The Romans occasionally smelted pig iron around AD, but it was discarded as waste.It was not until the 14th century that Europeans realized the significance of pig iron and began to produce pig iron.China has mastered the pig iron smelting and casting technology very early, and has come from behind. It has long been in the leading position in the world's steel production and has become an exporter of steel.Historically, China's steel was not only exported to neighboring countries, but also exported to ancient Rome and Southwest Asia.

The biggest feature of pig iron is its castability, so it is also called cast iron.However, pig iron has a high carbon content, generally more than 2%, and often contains impurities such as sulfur and phosphorus, so it is brittle and has low toughness. The directly cast agricultural tools, tools and weapons are easy to break when used.In order to make up for this defect, our ancestors invented cast iron softening in the Warring States Period. Cast iron softening is a technology that decarburizes and softens cast iron through heat treatment.After softening, the pig iron has enhanced strength and toughness, and becomes ductile cast iron, which can be used to cast high-quality production tools and weapons in large quantities.This is an epoch-making achievement in the history of metallurgy. It has greatly accelerated the historical process of iron ware replacing copper ware, effectively promoted the development of social productivity, and brought Chinese society into a new period of development.