Nowadays steel seems to be omnipresent, a vital component in the construction industry as well as being found in a variety of products such as food ware, machinery, weaponry and vehicles. Whilst being integral to our modern world it has a rich history and has been produced and used by mankind for millenia.
In its simplest definition steel is an alloy of iron and carbon with the carbon atoms helping to bind the Iron atoms together. Steel is generally therefore more rust resistant and easier to weld; two properties which lend it to widespread use as a building material and in machinery parts. It can, and usually does, contain combinations of other elements which cause it to display slightly different properties. For example chrome is added to create the stainless steel sheen that you see in much cutlery. Although the introduction of carbon makes steel more brittle, additional elements can increase steel’s ductility and can give it a higher tensile strength than other forms of iron (that is, it is stronger under tension and is more likely to deform and stretch rather than fail). It is this variety and versatility in its production and uses that makes steel such an important material in the modern world but it has been in use for thousands of years.
The history of steel production is tied to the technological developments over the ages in furnaces and the smelting process. The earliest smelting techniques involved a furnace known as a bloomery and the first alloys we know as steel most likely resulted from natural carbon ‘impurities’ finding their way into the resulting blooms (porous lumps of iron) which the smelting process produced.
The earliest found examples of steel come from prehistory and even stretch back beyond what we consider as the bronze and iron ages with discoveries of the material dating back to 4,000BC in Turkey, whilst further evidence of steel production has been found in East Africa going back to the start of the Iron Age in 1,400BC.
High carbon steel has also been produced since the Iron Age in Asia with the earliest examples found in Sri Lanka. The Chinese in particular have a strong history of steelmaking in the centuries before Ad, using a variety of processes including the production of Wootz steel (a tough steel ideal for sharp edged weapons) which had originated in India in 300BC. Wootz steel was a complicated alloy which incorporated a large number of trace elements giving it its unique properties.
Up until the 17th century, Steel was relatively tricky and expensive to produce and so was only used in objects that demanded its distinctive properties, where no other metal would suffice. It was therefore most common in smaller or important artifacts such as swords, knives and other weaponry in earlier periods (even in advanced civilisations like the Romans and Chinese) while becoming more common for intricate metal work such as timepieces in later centuries.
Widespread us of steel in place of other Iron alloys only really started in the 17th century when advances in the methods used for its production in turn made it far more affordable as well as improving the actual quality of the steel itself.
The key development was the larger scale adoption of blast furnaces, in which the smelting of iron was fuelled by the pumping of air into the furnace, during the 17th century, especially across France and Britain. The technology had gradually evolved from the original bloomeries throughout Europe and Mediterranean since the iron age, with influences from China and the East, and in particular progressed significantly during the medieval period.
The 17th century also saw the adoption of the cementation process which created steel by taking wrought iron (bar iron, where the carbon impurities had been removed) and heating it in the presence of a carbon rich substance such as charcoal to increase the level of carbon in the alloy. Much of the wrought iron used in the process at the time was produced in Sweden with furnaces in Britain finding it more affordable to import the higher quality iron.
The next significant step in steel making was integral to the industrial revolution with the introduction of the Bessemer process in 1858. The process focused on reducing the carbon content of pig iron, rather than increasing the carbon content of wrought iron. It smelted the iron in a new Bessemer converter which removed the impurities (including carbon) using a special clay lining and the pumping of air through the molten metal (which also helped to raise the heat of the furnace).
By reverting to (the less refined) pig iron as the source material and using pumped air to fuel the smelt, the Bessemer process made the production of steel far more efficient and economical, therefore allowing production on a truly industrial scale throughout the industrial revolution.
The Bessemer process was still commonly used in various guises up until the 1950s when its successor, Basic Oxygen Steelmaking (BOS) was introduced. The process has one major refinement on the Bessemer process in that it allows pure Oxygen to be pumped into the furnace instead of air, making it far more efficient. As a result around 60% of the world’s ouput now comes from the BOS method.
Despite the invention of more modern materials such as plastic, steel, in all its varieties, is still integral in the fabric of the world we see around us. As a result, Steel Suppliers continue to produce a staggering 1.3 billion tonnes of the metal every year across the world.