Basic oxygen steelmaking (BOS, BOP, BOF, and OSM), also
known as Linz-Donawitz-Verfahren 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 due to the type of refractories—calcium oxide
and magnesium oxide—that line the vessel to withstand the high temperature of
the molten metal.
The process was developed in 1948 by
Robert Durrer and commercialized in 1952–1953 by Austrian 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 where blowing of air is replaced with blowing oxygen. It reduced capital cost of the
plants, time of smelting, and increased labor productivity. Between 1920 and
2000, labor requirements in the industry decreased by a factor of 1,000, from
more than 3 worker-hours per tonne to just 0.003.
The vast majority of steel manufactured in the world is produced using the
basic oxygen furnace; in 2000, it accounted for 60% of global steel output.
Modern furnaces will take a charge of iron of up to 350 tons 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 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
1858, Henry Bessemer patented a steelmaking process involving oxygen blowing for
decarburizing molten iron (UK Patent No. 2207). For nearly a hundred
years commercial quantities of oxygen were not available at all or were too
expensive, and the invention remained unused. During World War II
German (C. V. Schwartz), 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.
In
1943, Durrer, , returned to Switzerland and accepted a seat
on the board of Roll AG,
the country's largest steel mill. In 1947 he purchased
the first small 2.5-ton experimental converter from the U. S., and on April 3,
1948 the new converter produced its first steel. The new process
could conveniently process large amounts of scrap
metal
with only a small proportion of primary metal necessary. In the summer of
1948 Roll AG and two Austrian state-owned companies, VOEST and ÖAMG, agreed to
commercialize the Durrer process.
By
June 1949, VOEST developed an adaptation of Durrer's process, known as the LD
(Linz-Donawitz) process. In December 1949,
VOEST and ÖAMG committed to building their first 30-ton oxygen converters. They were put into
operation in November 1952 (VOEST in Linz) and May 1953 (ÖAMG, Donawitz) and temporarily became the leading edge
of the world's steelmaking, causing a surge in steel-related research.Thirty-four thousand
businesspeople and engineers visited the VOEST converter by 1963. The LD process
reduced processing time and capital costs per ton of steel, contributing to the
competitive advantage of Austrian steel. VOEST eventually
acquired the rights to market the new technology. However, errors made
by the VOEST and the ÖAMG management in licensing their technology made control
over its adoption in Japan
impossible and by the end of the 1950s the Austrians lost their competitive
edge.
The
original LD process consisted in blowing oxygen 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 introduced inert gas blowing for stirring
the molten metal and removing the phosphorus impurities.
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, the Russian physicist Pyotr
Kapitsa
perfected the design of the centrifugal turboexpander. 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 percent of the industrial gas liquefaction and in particular the production
of liquid oxygen for steelmaking.
The
big American steelmakers caught up late with the new technology; the first
oxygen converters in the United States were launched at the end of 1954 by McLouth
Steel
in Trenton, Michigan, which accounted for less than 1 per
cent of the national steel market. U.S. Steel and Bethlehem
Steel
introduced the oxygen process only in 1964. By 1970 half of
world's and 80% of Japan's steel output was produced in oxygen converters. In the last quarter
of the 20th century basic oxygen converters were gradually replaced by the electric arc furnace. 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%.
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