The transformation of iron manufacturing affected the nation almost as much as railroad development. Output rose from
920,000 tons in 1860 to 10.3 million tons in 1900, but the big change came in the development of ways to mass-produce steel. In its pure form (wrought iron) the metal is tough but relatively pliable: It bends under great stresses. Ordinary cast iron, which contains large amounts of carbon and other impurities, is hard but brittle. Steel, which contains 1 or 2 percent carbon, combines the hardness of cast iron with the toughness of wrought iron. For nearly every purpose—structural girders for bridges and buildings, railroad track, machine tools, boiler plate, barbed wire— steel is immensely superior to other kinds of iron.
But steel was so expensive that it could not be used for bulky products until the invention in the 1850s of the Bessemer process, perfected independently by Henry Bessemer, an Englishman, and William Kelly of Kentucky. Bessemer and Kelly discovered that a stream of air directed into a mass of molten iron caused the carbon and other impurities to combine with oxygen and burn off. When measured amounts of carbon, silicon, and manganese were then added, the brew became steel. What had been a rare metal could now be produced by the hundreds and thousands of tons. The Bessemer process and the open-hearth method, a slower but more precise technique that enabled producers to sample the molten mass and thus control quality closely, were introduced
This 1900 photograph of steel factories at night in Duquesne, near Pittsburgh, was tinted by hand. Source: North Wind Picture Archives.
World History
