Steelmaking method in which pure oxygen is blown through a long, movable lance into a bath of molten blast-furnace iron and scrap, in a steel furnace with a refractory lining called a converter. The oxygen initiates a series of heat-releasing reactions, including the oxidation of such impurities as silicon, carbon, phosphorus, and manganese; carbon dioxide is released, and the oxidation products of the other impurities form molten slag that floats on the molten steel. The advantages of using pure oxygen instead of air in refining iron into steel were recognized as early as the 1850s (see Bessemer process), but the process could not be commercialized until the late 1940s, when cheap, high-purity oxygen became available. Within 40 years it had replaced the open-hearth process and was producing more than half of all steel worldwide. Commercial advantages include high production rates, less labour, and steel with a low nitrogen content.
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