IRON PROCESSING

use of a smelting process to turn the ore into a form from which products can be fashioned. Included in this article also is a discussion of the mining of iron and of its preparation for smelting. Iron ore is one of the most abundant elements on Earth, and one of its primary uses is in the Iron (Fe) is a relatively dense metal with a silvery white appearance and distinctive magnetic properties. It constitutes 5 percent by weight of the Earth's crust, and it is the fourth most abundant element after oxygen, silicon, and aluminum. It melts at a temperature of 1,538 C (2,800 F). Iron is allotropicthat is, it exists in different forms. Its crystal structure is either body-centred cubic (bcc) or face-centred cubic (fcc), depending on the temperature. In both crystallographic modifications, the basic configuration is a cube with iron atoms located at the corners. There is an extra atom in the centre of each cube in the bcc modification and in the centre of each face in the fcc. At room temperature, pure iron has a bcc structure referred to as alpha-ferrite; this persists until the temperature is raised to 912 C (1,674 F), when it transforms into an fcc arrangement known as austenite. With further heating, austenite remains until the temperature reaches 1,394 C (2,541 F), at which point the bcc structure reappears. This form of iron, called delta-ferrite, remains until the melting point is reached. The pure metal is malleable and can be easily shaped by hammering, but apart from specialized electrical applications it is rarely used without adding other elements to improve its properties. Mostly it appears in iron-carbon alloys such as steels, which contain between 0.003 and about 2 percent carbon (the majority lying in the range of 0.01 to 1.2 percent), and cast irons with 2 to 4 percent carbon. At the carbon contents typical of steels, iron carbide (Fe3C), also known as cementite, is formed; this leads to the formation of pearlite, which in a microscope can be seen to consist of alternate laths of alpha-ferrite and cementite. Cementite is harder and stronger than ferrite but is much less malleable, so that vastly differing mechanical properties are obtained by varying the amount of carbon. At the higher carbon contents typical of cast irons, carbon may separate out as either cementite or graphite, depending on the manufacturing conditions. Again, a wide range of properties is obtained. This versatility of iron-carbon alloys leads to their widespread use in engineering and explains why iron is by far the most important of all the industrial metals. Additional reading Comprehensive and up-to-date information on many aspects of metallurgy, individual metals, and alloys can be found in convenient reference-form arrangement in the following works: Metals Handbook, 9th ed., 17 vol. (197889), a massive and detailed source prepared under the direction of the American Society for Metals, with a 10th edition that began publication in 1990; Herman F. Mark et al. (eds.), Encyclopedia of Chemical Technology, 3rd ed., 31 vol. (197884), formerly known as Kirk-Othmer Encyclopedia of Chemical Technology, with a 4th edition begun in 1991; and its European counterpart, the first English-language edition of a monumental German work, Ullmann's Encyclopedia of Industrial Chemistry, 5th, completely rev. ed., edited by Wolfgang Gerhartz et al. (1985 ). The Editors of the Encyclopdia Britannica Richard Serjeantson, Raymond Cordero, and Henry Cooke (eds.), Iron and Steel Works of the World, 10th ed. (1991), is a directory containing details on equipment used by most iron and steel companies. Useful data on both steels and cast irons appear in E.C. Rollason, Metallurgy for Engineers, 4th ed. (1973). R.D. Walker, Modern Ironmaking Methods (1986), is an introductory text for students of iron making that has chapters on raw materials, blast furnace design, and blast furnace operation. More advanced treatments are available in J.G. Peacey and W.G. Davenport, The Iron Blast Furnace: Theory and Practice (1979); and Anil K. Biswas, Principles of Blast Furnace Ironmaking: Theory and Practice (1981).A wide range of statistical data on production is presented in World Steel in Figures (annual). Current technology is explored in specialized articles of such periodicals as Iron & Steelmaker (monthly); Ironmaking & Steelmaking (bimonthly); Iron & Steel Engineer (monthly); Journal of the Iron and Steel Institute of Japan (monthly); and many others published similarly by learned institutes in the field. Robert Donald Walker