The document files on open-hearth steelmaking contain information on the following: process descriptions, operating data for U.S. furnaces in 1958-59, operating data for United States Steel Corporation furnaces in 1920-54, U.S. furnace performance and capacity in 1950, tap-to-tap times for stationary open-hearths in 1950-54, furnace design and practice in 1920-46, oxy-fuel burners and oxygen use in open-hearths, KORF submerged open-hearth blowing system, furnace roof data and roof life, open-hearth vs. electric furnace, economics vs. electric furnace for low-carbon steel, chrome and aluminous brick used in basic open-hearths, Carnegie-Illinois/South Works No. 4 open-hearth, Inland Steel No. 3 open-hearth, Siemens Brothers and the open-hearth process, and an obituary of Charles William Siemens. In the book and reference collection see Carnegie-Illinois Steel Corporation’s Steel Melting Furnaces.
Analysis: The open-hearth process , which is used to produce steel from virtually any combination of scrap and/or hot metal, is named for its elongated, saucer-shaped hearth or furnace floor on which the metallic charge rests and steel is made. A slow process that can take some 9-10 hours (less if oxygen is introduced), the open-hearth uses regeneration and reversal to develop and maintain melting temperatures by combusting a variety of fuels, including natural gas, coke-oven gas, fuel oil, or tar. The fuel is combusted with preheated air to pass a flame over the charge, heating both the charge and the refractory-lined furnace roof, which is relatively close to the hearth and radiates added heat into the charge. The hot gases from combustion are directed into one of two regenerative chambers comprised of heat-absorbing brick, arranged in a checker pattern, through which cold air is admitted for preheating to sustain the combustion process. The flame temperature is maintained or increased by periodically reversing the gas flow from one checker chamber to the other.
The open-hearth was first used to make steel in 1867 by process developer Sir Charles William Siemens. Some ten years earlier, the Bessemer converter had ushered in the modern steel age by melting enough steel to displace iron in the manufacture of rails. However, the Bessemer had a number of limitations. It could use a maximum scrap charge of only 10%, was ineffective at refining out phosphorus, and imparted nitrogen to its steel, which became brittle under cold working conditions. By 1910, the open-hearth, without these limitations, had replaced the Bessemer as the principal method for making steel.
Most of the steel produced in the twentieth century was melted in open-hearth furnaces, and as recently as 1960, the process still accounted for 72% of the world’s total steel output. However its share has since declined to less than 4%, and in all but a handful of countries, the BOF and electric furnaces have become the exclusive steelmaking methods. In 2003, the remaining exceptions were countries of the former Soviet Union , where Nikita Khrushchev once had mandated open-hearth investments and where the process still accounted for an output share of some 30%, and India , where its share was about 6%.