thumb|upright=1.1|Oxygen converter being charged at ThyssenKrupp steel mill in [[Duisburg (Germany)]]

Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter process, is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel. The process is known as basic because fluxes of calcium oxide or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter.

The process was invented in 1948 by Swiss engineer Robert Durrer and commercialized in 1952–1953 by the Austrian steelmaking company VOEST and ÖAMG. The LD converter, named after the Austrian towns Linz and Donawitz (a district of Leoben) is a refined version of the Bessemer converter which replaces blowing air with blowing oxygen. It reduced capital cost of the plants and smelting time, and increased labor productivity. Between 1920 and 2000, labor requirements in the industry decreased by a factor of 1,000, from more than 3 man-hours per metric ton to just 0.003. By 2000 the basic oxygen furnace accounted for 60% of global steel output. and convert it into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace.

History

The basic oxygen process developed outside of the traditional "big steel" environment. It was developed and refined by a single man, Swiss engineer Robert Durrer, and commercialized by two small steel companies in allied-occupied Austria, which had not yet recovered from the destruction of World War II.

In 1856, Henry Bessemer had patented a steelmaking process involving oxygen blowing for decarbonizing molten iron (UK Patent No. 2207). For nearly 100 years commercial quantities of oxygen were not available or were too expensive, and steelmaking used air blowing. During WWII German (Karl Valerian Schwarz), Belgian (John Miles) and Swiss (Robert Durrer and Heinrich Heilbrugge) engineers proposed their versions of oxygen-blown steelmaking, but only Durrer and Heilbrugge brought it to mass-scale production.

By June 1949, VÖEST developed an adaptation of Durrer's process, known as the LD (Linz-Donawitz) process. In December 1949, VÖEST and ÖAMG committed to building their first 30-ton oxygen converters. Thirty-four thousand businesspeople and engineers visited the VÖEST converter by 1963.

Big American steelmakers were late adopters of the new technology. The first oxygen converters in the US were launched at the end of 1954 by McLouth Steel in Trenton, Michigan, which accounted for less than 1% of the national steel market.

  1. Fluxes (calcium oxide or dolomite) are fed into the vessel to form slag, to maintain basicity of the slag – the ratio of calcium oxide to silicon oxide – at a level to minimise refractory wear and absorb impurities during the steelmaking process. During "blowing", churning of metal and fluxes in the vessel forms an emulsion that facilitates the refining process. Near the end of the blowing cycle, which takes about 20 minutes, the temperature is measured and samples are taken. A typical chemistry of the blown metal is 0.3–0.9% C, 0.05–0.1% Mn, 0.001–0.003% Si, 0.01–0.03% S and 0.005–0.03% P.
  2. The BOS vessel is tilted towards the slagging side and the steel is poured through a tap hole into a steel ladle with basic refractory lining. This process is called tapping the steel. The steel is further refined in the ladle furnace, by adding alloying materials to impart special properties required by the customer. Sometimes argon or nitrogen is bubbled into the ladle to make the alloys mix correctly.
  3. After the steel is poured off from the BOS vessel, the slag is poured into the slag pots through the BOS vessel mouth and dumped.

Variants

Earlier converters, with a false bottom that can be detached and repaired, are still in use. Modern converters have a fixed bottom with plugs for argon purging. The energy optimization furnace (EOF) is a BOF variant associated with a scrap preheater where the sensible heat in the off-gas is used for preheating scrap, located above the furnace roof.

The lance used for blowing has undergone changes. Slagless lances, with a long tapering copper tip, have been employed to avoid jamming of the lance during blowing. Post-combustion lance tips burn the CO generated during blowing into carbon dioxide| and provide additional heat. For slag-free tapping, darts, refractory balls, and slag detectors are employed. Modern converters are fully automated with automatic blowing patterns and sophisticated control systems.

See also

  • AJAX furnace, transitional oxygen-based open hearth technology

References

Bibliography

  • McGannon, Harold E. editor (1971). The Making, Shaping and Treating of Steel: Ninth Edition. Pittsburgh, Pennsylvania: United States Steel Corporation.
  • Smil, Vaclav (2006). Transforming the twentieth century: technical innovations and their consequences, Volume 2. Oxford University Press US. .
  • Brock, James W.; Elzinga, Kenneth G. (1991). Antitrust, the market, and the state: the contributions of Walter Adams. M. E. Sharpe. .
  • Tweraser, Kurt (2000). The Marshall Plan and the Reconstruction of the Austrian Steel Industry 1945–1953. in: Bischof, Gunther et al. (2000). The Marshall Plan in Austria. Transaction Publishers. . pp. 290–322.
  • Basic Oxygen Steelmaking module at steeluniversity.org, including a fully interactive simulation (archived)
  • Basic Oxygen Steelmaking cost model showing typical cost structure for liquid steel