open-hearth process

a process of steelmaking in which the charge is laid in a furnace (open-hearth furnace) on a shallow hearth and heated directly by burning gas as well as radiatively by the furnace walls.

[1885-90]

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or Siemens-Martin process

Steelmaking technique that for most of the 20th century accounted for most steel made in the world.

William Siemens made steel from pig iron in a reverberatory furnace of his design in 1867. The same year the French manufacturer Pierre-Émile Martin (1824–1915) used the idea to produce steel by melting wrought iron with steel scrap. Siemens used the waste heat given off by the furnace: he directed the fumes from the furnace through a brick checkerwork, heating it to a high temperature, and then used the same path to introduce air into the furnace; the preheated air significantly increased the flame temperature. The open-hearth process furnace (which replaced the Bessemer process) has itself been replaced in most industrialized countries by the basic oxygen process and the electric furnace. See also reverberatory furnace.

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▪ metallurgy

also called  Siemens-martin Process,  

 steelmaking technique that for most of the 20th century accounted for the major part of all steel made in the world. William Siemens (Siemens, Sir William), a German living in England in the 1860s, seeking a means of increasing the temperature in a metallurgical furnace, resurrected an old proposal for using the waste heat given off by the furnace; directing the fumes from the furnace through a brick checkerwork, he heated the brick to a high temperature, then used the same pathway for the introduction of air into the furnace; the preheated air materially increased the flame temperature. The first to use the device to produce steel were Pierre and Émile Martin of Sireuil, France, in 1864, charging the furnace with pig iron and some wrought-iron scrap. The ores most readily available in both Great Britain and the United States were especially well suited to the open-hearth process, the product of which proved superior to that from the Bessemer converter.

      Natural gas or atomized heavy oils are used as fuel; both air and fuel are heated before combustion. The furnace is charged with liquid blast-furnace iron and steel scrap together with iron ore, limestone, dolomite, and fluxes. The furnace itself is made of highly refractory materials such as magnesite bricks for the hearths and roofs. Capacities of open-hearth furnaces are as high as 600 tons, and they are usually installed in groups, so that the massive auxiliary equipment needed to charge the furnaces and handle the liquid steel can be efficiently employed.

      Though the open-hearth process has been almost completely replaced in most industrialized countries by the basic oxygen process and the electric arc furnace, it nevertheless accounts for about one-sixth of all steel produced worldwide.

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