Fast Furnace

Most U.S. steel is made in massive, slow-acting, open-hearth furnaces. Last week U.S. Steel Corp. announced tests of a new type of furnace which makes the same kinds of steel a great deal faster.

Open-hearth furnaces melt together pig iron, scrap steel, iron ore and limestone. The carbon is oxidized by the oxygen in the iron ore and goes up the stack as carbon dioxide. Other impurities are absorbed by the limestone slag on the surface of the molten iron. U.S. Steel’s new “Turbo-Hearth” furnace blows jets of air across the surface of a pool of molten pig iron. The oxygen in the air combines with the impurities, removes them from the iron, turns the iron to low-carbon steel. This method is not very different from the Bessemer process, which blows air upward through molten iron. But U.S. Steel says the new way is much better, producing superior steel from iron that the Bessemer process cannot handle easily. It works so fast that one 30-ton Turbo-Hearth can make more steel in a day than a 225-ton open-hearth furnace.