These iron weapons in the picture were all made in the state of Wu during the Three Kingdoms period. It can be seen that iron smelting technology was very mature at that time, iron weapons were widely used, and iron knives, iron halberds, iron spears, iron arrowheads, etc. were also produced in shape and structure. Iron has completely replaced the status of bronze, and human history has entered the Iron Age.
In the Tang Dynasty, the methods of smelting and forging did not change significantly. Through accumulated experience, blacksmiths were able to control the carbon content inside iron products. For example, the carbon content of a representative Tang knife is about 0.5%-0.6%, which already belongs to the category of steel. The carbon content is controlled so that Tang knives have both toughness and hardness, which is one of the reasons why Tang knives are famous overseas. In fact, the most basic part of today’s iron and steel smelting is to control the carbon content, and adjust the carbon content according to different uses to adjust the two main properties of steel toughness and hardness. Of course, in order to make swords tough and hard at the same time, the ancients invented steel-clad, clamped steel and other manufacturing processes, which are beyond the scope of this article.
The first leap in human demand for steel was during the first industrial revolution. The invention of the steam engine freed human beings from heavy manual labor and animal-powered production for the first time, and fuel-driven machines improved human production efficiency by several levels.