Iron working was an important step in the development of human society. It was probably invented by the Hittites (northeast of Anatolia) where, according to the ancient Greeks, iron came from. Iron ore was already being smelted in the third millennium BC. It then took a long time before the problem of slag – weak spots in the iron – was solved.
Processing iron ore
Iron was the last metal that was learned to smelt in ancient times. The melting point of iron is at a temperature of 1530 degrees Celsius, which means that it must be melted out as a solid. Iron ore was already being smelted in the third millennium BC. There was a problem with smelted iron: the slag (weak spots in the iron). It took quite some time before this problem could be solved.
In the time before iron working , people were dependent on copper and tin, these metals were very valuable. When iron was discovered, the properties of iron as a metal turned out to be much better than the properties of copper and tin.
It is disputed whether iron was invented by the Hittites (northeast of Anatolia), where the ancient Greeks believed iron came from, or whether the Chinese invented it independently of the Greeks.
Iron and steel
Snails
The slagging process was not under control. As a result, the end result of a meltdown was always a massive lump of iron mixed with remnants of fuel and slag. The lump was further processed by hitting it with a hammer while it was heated, creating wrought iron.
Steel
Around the first millennium BC, an explosive development in the machining process took place. It was discovered how to make steel an alloy of iron with about 0.2 to 0.5% carbon. Iron objects were covered with pulverized coal and heated at high temperatures for hours or days so that some of the carbon mixed with the iron. When this alloy was red hot and then dipped in cold water, it created a much harder and stronger metal, steel.
Steel made from the iron lump had two major disadvantages:
- the iron contained many slags that caused weak spots
- the carbon content was not evenly distributed everywhere
The most obvious solution was to melt the iron-carbon alloy. The problem, however, was that this required a temperature of 1400 degrees Celsius, and such high temperatures could not be achieved. It seems that this problem was first solved at the end of the first millennium BC.
This happened in the area between Northern India and Central Asia. Steel found in the Hellenistic city of Taxila (north of present-day Pakistan) was found to be partially free of slag. In addition, evidence is provided by Zosimos, an alchemist from Alexandria who wrote in the third century AD that the Indians made steel by putting soft iron together with leaves and bark in a smelting furnace, closing it and heating the whole. The end result was crucible steel from which very good swords could be forged. Objects made of crucible steel were always forged and not cast.
The making of crucible steel appears to have been introduced in Europe only in the 18th century. However, it was already widely used in the Middle East, Central Asia and India . In these regions their own iron industry developed very early.
Consequences for society
Steel and iron together formed a great combination that dramatically changed society both directly and indirectly. Communities were no longer dependent on supplies of copper and tin, which often had to be sourced from far away and were expensive. Most communities could now make and process their own iron and the properties of iron and steel were far superior to those of metals previously known.
During the Han Dynasty two thousand years ago, China was far ahead of the world when it came to knowledge of iron. It can safely be said that the world’s first industrial revolution began in China and its surrounding areas.