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Steel is a common metal alloy made of iron and varying amounts of carbon. It has been produced since ancient times, with some of the first steels made in Africa around 1400 BC. Steel is known for its strength, which is given by alloying elements. The modern steel industry uses the basic oxygen furnace to produce steel quickly and with high quality. The Bessemer process was an earlier method that made steel cheap and mass-produced. Different metals can be added to create custom alloys for specific applications.
Steel is the most common metal alloy in the world. In its simplest form, it consists of iron and varying amounts of carbon. Since both iron and carbon have been known since ancient times, the alloy has been produced in one form or another since long before the birth of Christ. Some of the very first steels were produced in the eastern regions of Africa, around 1400 BC
Iron is the main component of steel, with carbon being a distant second, between 0.2% and 2.14%, depending on the grade. Carbon is the cheapest way to alloy iron, but other metals can be used to enhance the element and to give the metal certain properties. The metal known as cast iron is actually a steel that has a very high carbon content, giving it a lower melting point and greater castability. Steel is known for its strength, which is given to it precisely by the alloying elements.
When iron is in the solid metallic state, the atoms form a crystalline lattice structure. While this structure is quite rigid, there can be imperfections that create small weak points in the metal. The atoms of the alloying elements can fill these microscopic weak spots in the lattice, giving the alloy the flexibility and tensile strength for which it is known.
The modern steel industry produces the metal through the use of what is called the basic oxygen furnace. In these furnaces, pure oxygen passes through the molten iron, lowering the levels of impurities. For this same purpose, detergents called fluxes are also added. The main advantage of this process, in addition to a high quality product, is its speed.
Previous processes included the Bessemer process, where air was forced through molten iron to oxidize impurities. Carbon monoxide is a byproduct of this process, with the other impurities forming waste. The invention of the Bessemer process was particularly notable because it made steel a cheap and mass product. The alloy had been produced by various methods in the Middle Ages and before, but none of them were particularly efficient, nor could they be employed on a large scale.
As steelmaking techniques improved, a wider variety of alloys became available. The use of different metals, such as tungsten and chromium, can create custom metals for very specific applications. The range of properties that steel can impart upon the addition of different elements is seen, for example, in the fact that two such different things as samurai swords and automobiles are both made of iron alloyed with other metals.
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