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The US iron and steel industry has paralleled the industry in other countries in technological developments. In the 1800s, the US switched from charcoal to coke in ore smelting, adopted the Bessemer process, and saw the rise of very large integrated steel mills. In the 20th century, the US industry successively adopted the open hearth process, then the basic oxygen furnace. Since the American industry peaked in the 1940s and 1950s, the US industry has shifted to small mini-mills and specialty mills, using iron and steel scrap as feedstock, rather than iron ore. ==Colonial== Iron manufacture before the 19th century required charcoal, and Britain’s once-vast forests could no longer supply enough charcoal for the nation’s increasing need for iron. By 1700, Britain was becoming increasingly dependent on iron imported from its sometimes-adversary Sweden. Britain looked to the seemingly limitless forests of its American colonies to supply Britain with iron. British investors started an iron furnace near Perryville, Maryland, which in 1718 started exporting iron back to Britain. That success prompted formation of more companies, which built numerous iron furnaces around Chesapeake Bay, supplied by bog iron ore, which was widespread. By 1751, Virginia and Maryland were exporting 2,950 tons of pig iron to Britain each year; at the time, British iron production was about 20,000 tons per year.〔Norman J. G. Pounds and William N Parker, Coal and Steel in Western Europe (Bloomington: Indiana Univ. Press, 1957) 22.〕 While the Chesapeake Bay furnaces were established for export, iron furnaces were established in the 1700s throughout the American colonies for domestic consumption. Iron furnaces were located along rivers to supply water power. Also required were forests for charcoal, iron ore, and limestone for flux. In addition, the furnace needed to be close to a major market or close to water transport. British business interests were split on colonial iron: manufacturers appreciated the lower prices due to colonial imports, but the British iron and steel industry objected to the competition. Parliament compromised in the Iron Act of 1750, which eliminated the import duty on colonial pig iron, but barred the manufacture of steel or of iron plate in the colonies. The law was widely ignored by colonial governments. By 1776, up to 80 iron furnaces throughout the American colonies were producing about as much iron as Britain itself. If one estimate of 30,000 tons of iron each year is accurate, then the newly formed United States was the world’s third-largest iron producer, after Sweden and Russia. Notable pre-19th-century iron furnaces in the US 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of the iron and steel industry in the United States」の詳細全文を読む スポンサード リンク
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