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Steel

During the nineteenth century the production of steel fuelled the industrial revolution in Europe and North America bringing steel into almost every aspect of modern life. Around 1.5 billion tonnes of steel are produced across the world each year.

Steel is an alloy of iron and carbon and the majority of steel is referred to as carbon steel and classified according to its carbon content. Low carbon steel contains up to 0.25% carbon, medium 0.25-0.75% and high carbon 0.75 to 1.5%. Higher carbon levels make steel stronger but also more brittle.

Other metals are added to steel to adjust the properties to the requirements of a particular application. These are often called alloy steels. For example, adding manganese makes steel stronger, vanadium makes it less prone to metal fatigue, cobalt improves the ability to withstand extreme temperatures, nickel and chromium make stainless steel.

Most steel is now made in a basic oxygen furnace. This is a refractory lined furnace containing molten iron, scrap steel and a flux material. Pure oxygen is blown into the chamber, raising the temperature. The impurities are oxidised, removing about 90% of the carbon and leaving liquid steel. Electric arc furnaces are also used to make, and remake, steel. They can run on scrap steel alone or with the addition of some direct reduced iron or pig iron. An electric arc of 35 million watts is created between two electrodes in the furnace which raises the temperature and melts the steel for further processing. The advantage of this type of furnace is that it has a lower investment costs and requires less energy than a basic oxygen furnace.
 

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