Basic oxygen steelmaking (BOS,BOP,BOF, orOSM), also known asLinz-Donawitz steelmaking or theoxygen converter process,[1] is a method of primarysteelmaking in which carbon-rich moltenpig iron is made intosteel. Blowingoxygen through molten pig iron lowers the carbon content of thealloy and changes it intolow-carbon steel. The process is known asbasic becausefluxes ofcalcium oxide ordolomite, which are chemicalbases, are added to promote the removal of impurities and protect the lining of the converter.[2]
The process was invented in 1948 by Swiss engineerRobert Durrer and commercialized in 1952–1953 by the Austrian steelmaking companyVOEST and ÖAMG. The LD converter, named after theAustrian townsLinz and Donawitz (a district ofLeoben) is a refined version of theBessemer converter where blowing of air is replaced 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.[3] By 2000 the basic oxygen furnace accounted for 60% of global steel output.[3]
Modern furnaces will take a charge of iron of up to 400 tons[4] and convert it into steel in less than 40 minutes, compared to 10–12 hours in anopen hearth furnace.
The basic oxygen process developed outside of the traditional "big steel" environment. It was developed and refined by a single man, Swiss engineerRobert Durrer, and commercialized by two small steel companies inallied-occupied Austria, which had not yet recovered from the destruction ofWorld War II.[5]
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 (Durrer and Heinrich Heilbrugge) engineers proposed their versions of oxygen-blown steelmaking, but only Durrer and Heilbrugge brought it to mass-scale production.[5]
In 1943, Durrer, formerly a professor at theTechnische Hochschule in Charlottenburg (nowTechnische Universität Berlin), returned toSwitzerland and accepted a seat on the board ofRoll AG, the country's largest steel mill. In 1947 he purchased the first small 2.5-ton experimental converter from the US, and on April 3, 1948 the new converter produced its first steel.[5] The new process could conveniently process large amounts ofscrap metal with only a small proportion of primary metal necessary.[6] In the summer of 1948, Roll AG and two Austrian state-owned companies, VÖEST and ÖAMG, agreed to commercialize the Durrer process.[6]
By June 1949, VÖEST developed an adaptation of Durrer's process, known as the LD (Linz-Donawitz) process.[7][8] In December 1949, VÖEST and ÖAMG committed to building their first 30-ton oxygen converters.[8] They were put into operation in November 1952 (VÖEST in Linz) and May 1953 (ÖAMG, Donawitz)[8] and temporarily became the leading edge of the world's steelmaking, causing a surge in steel-related research.[9] Thirty-four thousand businesspeople and engineers visited the VÖEST converter by 1963.[9] The LD process reduced processing time and capital costs per ton of steel, contributing to thecompetitive advantage of Austrian steel.[7] VÖEST eventually acquired the rights to market the new technology.[8] Errors by the VÖEST and the ÖAMG management in licensing their technology made control over its adoption inJapan impossible. By the end of the 1950s, the Austrians lost their competitive edge.[7]
In the original LD process, oxygen was blown over the top of the molten iron through the water-cooled nozzle of a vertical lance. In the 1960s, steelmakers introduced bottom-blown converters and developedinert gas blowing for stirring the molten metal and removingphosphorus impurities.[3]
In the Soviet Union, some experimental production of steel using the process was done in 1934, but industrial use was hampered by lack of efficient technology to produce liquid oxygen. In 1939, theRussian physicistPyotr Kapitsa perfected the design of the centrifugalturboexpander. The process was put to use in 1942–1944. Most turboexpanders in industrial use since then have been based on Kapitsa's design and centrifugal turboexpanders have taken over almost 100% of industrial gas liquefaction, and in particular the production of liquid oxygen for steelmaking.[10]
Big American steelmakers were late adopters of the new technology. The first oxygen converters in the US were launched at the end of 1954 byMcLouth Steel inTrenton, Michigan, which accounted for less than 1% of the national steel market.[3]U.S. Steel andBethlehem Steel introduced the oxygen process in 1964.[3] By 1970, half of the world's and 80% of Japan's steel output was produced in oxygen converters.[3]
In the last quarter of the 20th century, use of basic oxygen converters for steel production was gradually, partially replaced by theelectric arc furnace using scrap steel and iron. In Japan the share of LD process decreased from 80% in 1970 to 70% in 2000; worldwide share of the basic oxygen process stabilized at 60%.[3]
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Basic oxygen steelmaking is a primary steelmaking process for converting moltenpig iron intosteel by blowingoxygen through a lance over the molten pig iron inside the converter.Exothermic heat is generated by theoxidation reactions during blowing.
The basic oxygen steel-making process is as follows:
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. Theenergy 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 theCO generated during blowing intoCO2 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.[citation needed]
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