| Smelting Iron
It is unknown when or where the smelting of iron began. However, archaeological finds suggest that it has been in use for over 5000 years with the earliest surviving iron artefacts, made from hematite and found in Egypt, dating back to 3,500 BC.
Iron smelting is more difficult than tin or copper smelting, since these metals can be cold-worked, melted in simple furnaces and then cast into moulds. However, smelted iron requires hot-working and can be only be melted in specially designed furnaces. Unsurprisingly, humans only mastered the technology of smelting iron after many centuries of bronze metallurgy, and iron artefacts remained a rarity until the 12th century BC.
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98% of mined iron ore is used in the making of steel.
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| Wrought Iron
The use of wrought iron (an alloy of iron with a much lower carbon content than steel) was known in the 1st millennium BC. In Europe, during the medieval period, means were found of producing wrought iron from cast iron, known as pig iron - the product of smelting iron ore, coke and limestone in a blast furnace, using charcoal.
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A modest amount of wrought iron was used as a raw material for the manufacturing of steel.
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| The Development of Steel
The industrial revolution was characterized by an enormous growth in many areas of industry setting up a demand for more raw materials. Although iron was by no means a new material, production was restricted and the amount produced limited. Britain had depleted huge areas of forests - using the timber for making the charcoal needed in smelting iron, to the point where legislation was introduced to ban the harvesting of trees for charcoal production. A new method of smelting iron in large quantities which didn’t require charcoal was needed.
Smelting with coal had long been an objective and in 1755 Abraham Darby opened a new coke-using furnace at Horsehay in Shropshire, supplying coke pig iron to finery forges of the traditional kind for the production of bar iron.
The development of steel from cast iron was achieved by advances in manufacturing methods. The critical step forward was made by Henry Bessemer in 1856. A key discovery was that the amount of carbon present in the iron controlled not only its melting point but also its properties. The result was the Bessemer furnace. By controlling the additions of carbon through coke, a form of iron which could be cast in industrial quantities was made.
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The Bessemer converter was the first inexpensive industrial process for the mass production of steel from molten pig iron.
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