Steel Forging Process
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Introduction
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While iron has been used by humans for around 3,000 years, it has only been in the last 150 years that processing iron into its alloy steel has been commercially viable. Iron is a very common metal and is inexpensive to produce, strong, and relatively easy to form. It is also subject to corrosion, which weakens it. Steel, on the other hand, can more easily be combined with other metals that affect its strength and durability, making it a more versatile building material.
Iron: The Foundation of Steel
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Iron occurs naturally in many different forms and must be purified before it can be used to make steel. Iron ore is smelted in a blast furnace where oxygen and other waste products are removed. The result is brittle pig iron that provides the base material from which steel is made. Pig iron is also made into cast or wrought iron. Wrought iron is the type used by blacksmiths, while the stronger cast iron led to the first construction of skyscrapers. Today, cast iron is most often used for things like cooking pots.
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The Steelmaking Process
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Making steel from pig iron is a chemical process where impurities in the iron are removed and other strengthening materials are added. Pig iron contains about five percent carbon along with trace amounts of other materials. Steel contains less than 1.75 percent carbon. The steel making process was originally called the Bessemer Process after its inventor, Sir Henry Bessemer, but has been improved and updated and is now known as the basic oxygen furnace process.
To make steel, molten pig iron is loaded into a steel furnace lined with calcium carbonate, commonly known as limestone. A blast of oxygen is blown over the molten iron, which creates iron oxide and even more heat. This heat causes the limestone to release calcium oxide that mixes with the impurities in the iron to create slag, a waste product. Oxygen from the iron oxide combines with some of the carbon in the iron, creating carbon monoxide and lowering the carbon content of the iron. The result of these chemical reactions is steel.
Types of Steel
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Depending on the remaining carbon content, the steel can be used for anything from surgical instruments to building girders. The higher the carbon content of the steel, the stronger it is. Stainless steel, used for cutlery, is more resistant to rusting because it contains chromium, nickel, and carbon. Adding tungsten to steel allows the metal to withstand high temperatures, while combining steel and cobalt makes the metal magnetic.
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