Iron is one of the most abundant elements on Earth, but it does not occur in nature in a useful metallic form. Although ancient people may have recovered some iron from meteorites, it wasn’t until smelting was invented that iron metal could be derived from iron oxides. After the beginning of the Iron Age in about 1200 B.C., knowledge of iron- and steelmaking spread from the ancient Middle East through Greece to the Roman Empire, then to Europe and, in the early 17th century, to North America. The first successful furnace in North America began operating in 1646 in what is now Saugus, Mass. Introduction of the Bessemer converter in the mid-19th century made the modern steel age possible.
Pig iron is a high-carbon alloy made by smelting iron ore in a blast furnace with carbonaceous material, typically coke, as a reducing agent. Limestone is added to the iron ore-coke charge as a fluxing agent to remove impurities. Steel is produced from pig iron by removing some of the carbon in a basic oxygen converter and adding several alloying elements, such as manganese, chromium, copper, nickel, titanium, molybdenum, tungsten and vanadium. Steel is also made by recycling ferrous scrap in an electric arc furnace.
There are many grades of steel, but the three major types of steel are carbon, alloy and stainless. About 93 percent of the steel made in the United States is carbon steel, which contains a maximum 2 percent carbon. Applications are found in appliances, construction, shipbuilding, containers and packaging, as well as in the automotive, machinery and equipment industries. Alloy steel, about 5 percent of annual production, contains as much as 4 percent alloying elements. Special applications for alloy steel include use in machined parts and tool fabrication. Stainless steel, which accounts for about 2 percent of annual steel production, is formed by adding chromium and usually nickel to steel to make it highly corrosion-resistant.
Since 2008, steelmaking capacity has greatly exceeded apparent steel consumption, primarily as a result of China’s rapid economic expansion and rapidly increasing capacity. This has resulted in an influx of steel products into the United States and other steelmaking countries that already have excess capacity. Demand by China’s steelmakers has also driven unprecedented increases in the prices of iron ore and metallurgical coal. In the short term, steelmaking capacity, globally and especially in China, is expected to continue to exceed steel consumption, with steel prices and production costs remaining stable.
|Mineral resource of the month: Iron and steel
|American Geological Institute
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