The Average Steel Type
The term steel refers to any of a large number of metallic alloys that contains a mixture of iron and carbon. How malleable, strong or dense a piece of steel depends on the percentage of carbon in the metal. Mild steel, which contains up to .25 percent of carbon, is the most commonly-used type of steel in construction. The history of steel, and its production, dates back to the beginning of the Iron Age.
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Early Forging
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The Bronze Age gave way to the Iron Age when ancient blacksmiths discovered that, through the smelting of iron ore, they could forge a metal stronger and more malleable than bronze. By melting iron ore over a charcoal fire, the iron releases oxygen and forms into an elastic, porous mass referred to as slag. A blacksmith worked this material into wrought iron, a material that contains between .02 and .08 percent of carbon. From this early technique came the process of forging steel.
Steel Production
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Early steel production was done using a difficult and costly process known as the cementation process. Bars of wrought iron were heated in stone boxes after being stacked and packed in powered charcoal. The iron bars absorbed the carbon after a few days under constant heat. To ensure a better distribution of carbon, the iron bars were broken apart, repacked in carbon, and heated again for several days. The mild steel this process yielded was heated and hammered for a more consistent texture. Due to the time and effort required in the cementation process, steel production did not meet the industry's growing demand.
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The Bessemer Process
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In the mid-19th century, British metallurgist Sir Henry Bessemer theorized that the carbon in molten pig iron would immediately bond with any oxygen it came into contact with. By blasting a gust of air through the molten iron, the excess carbon bonded with the oxygen, thus lowering the metal's overall carbon content and transforming the iron into steel. Bessemer's process revolutionized the steel industry by drastically lowering the cost of mild steel, while dramatically increasing production.
Mild Steel Benefits
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Mild steel is used in 85 percent of all steel applications in the United States. Used in everything from cars to construction, mild steel allows engineers to construct durable, longer-lasting structures than if using the more malleable iron. Prior to the widespread use of mild steel, railroad ties made of iron needed to be replaced every few weeks along heavily used lines. The large skyscrapers of the late-18th and early-19th century would not have been possible without the strength and flexibility offered by mild steel.
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References
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