Forging Iron
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Forging Iron Iron and steel are perhaps the most useful materials in the history of industrialized society. They are responsible for tools, factories, machines, and many other fundamental components of civilization. Indeed, the widespread use of iron, and later steel (an alloy of iron and small amounts of carbon), made the Industrial Revolution possible. Together, iron and steel account for 95% of the world's current metal production. Iron is the second most abundant element on Earth (next to aluminum). Most of our planet's core is metallic iron, but on the surface the iron reacts readily with oxygen to form rust, or iron oxide. Hence, very little pure iron is found in rocks, except in meteorites. The ancient Aztecs made implements of meteoritic iron long before Europeans brought the process of smelting to the New World; the Aztecs prized their meteoritic tools above gold. Iron smelted from rock was probably first discovered in Asia between 4000 and 3000 B.C. in the ashes of fires built on outcroppings of red iron ore. Noting the presence of that reddish metallic substrance, people built bonfires against banks of ore exposed to prevailing winds. These fires were surrounded by boulders and fanned by bellows to increase the heat of the flame; later the people collected the lump iron puddled on the ground. From the metal thus extracted from the rock, they could make new weapons and tools. Iron artifacts do not last a long time, thanks to extreme oxidation over the centuries, but small items have been found in Egypt's Great Pyramid of Giza (2900 B.C.). Around 1300 B.C., the Hittites, one of the dominant peoples of the ancient Middle East, worked with iron in an area of what is now Turkey. They discovered a "recarburization" process that forced carbon into the outer layers of iron, forming a crude steel. The Hittites' iron was superior to bronze for weapons use, and less expensive than stone for agricultural implements. The iron dagger found in Tutankhamen's tomb was made by Hittites, and later Rameses II asked the King of the Hittites to supply Egypt with iron. Also around this time, the Chinese independently created a blast furnace to remove metallic iron from iron ore. The Greeks developed iron-making into a sophisticated art. Homer writes that Achilles received a ball of iron as a
prize in an athletic conquest. The Greeks passed their knowledge to the Romans, who later carried the techniques throughout Europe. Old examples of Roman cast iron have been found in France, Great Britain, and parts of Eastern Europe. In early iron-working, iron oxides are reduced when the ore is heated in a furnace. Chemical by-products, called slag, separate from the metal—but iron itself, with its relatively high melting temperature, solidifies around the pockets of slag into a hard spongy-looking mass. The smelter must reheat and hammer this mass several times to force out the inclusions of slag and mold the separated globules of iron into a single lump. The resulting metal is called wrought iron, which is relatively pure (less than 2
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