Basic oxygen steelmaking
Encyclopedia
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 pH
of the refractories
—calcium oxide
and magnesium oxide
—that line the vessel to withstand the high temperature of 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 Austria
n 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
.
.
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 the 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, formerly a professor at the Berlin Institute of Technology, 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, the LD (Linz-Donawitz) process. In December 1949, the VOEST and the 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. 34 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 employed blowing oxygen on top of molten iron through a 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 of phosphorus
impurities.
The big American steelmakers did not catch up to the new technology; the first oxygen converters in the United States were launched in the end of 1954 by McLouth Steel
in Trenton, Michigan
, which had less than 1 per cent of the national steel market. U.S. Steel
and Bethlehem Steel
introduced oxygen process only in 1964. Elsewhere, owing to the Austrian licensing blunder, the technology was adopted quickly. 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 substituted with the electric arc furnace
s. 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%.
Steelmaking
Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...
in which carbon-rich molten pig iron
Pig iron
Pig iron is the intermediate product of smelting iron ore with a high-carbon fuel such as coke, usually with limestone as a flux. Charcoal and anthracite have also been used as fuel...
is made into steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
. Blowing oxygen through molten pig iron lowers the carbon content of the alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
and changes it into low-carbon steel. The process is known as basic due to the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
of the refractories
Refractory
A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...
—calcium oxide
Calcium oxide
Calcium oxide , commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline crystalline solid at room temperature....
and magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
—that line the vessel to withstand the high temperature of molten metal.
The process was developed in 1948 by Robert Durrer
Robert Durrer
Robert Durrer was a Swiss engineer who developed the basic oxygen steelmaking process...
and commercialized in 1952–1953 by Austrian VOEST and ÖAMG
Voestalpine
Voestalpine AG is an international steel company based in Linz, Austria. The company is active in steel, automotive, railway systems, profilform and tool steel industries....
. The LD converter, named after the Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
n towns Linz
Linz
Linz is the third-largest city of Austria and capital of the state of Upper Austria . It is located in the north centre of Austria, approximately south of the Czech border, on both sides of the river Danube. The population of the city is , and that of the Greater Linz conurbation is about...
and Donawitz (a district of Leoben
Leoben
Leoben is a Styrian city in central Austria, located by the Mur river. With a population of about 25,000 it is a local industrial center and hosts the University of Leoben which specialises in mining...
) is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. 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
Open hearth furnace
Open hearth furnaces are one of a number of kinds of furnace where excess carbon and other impurities are burnt out of the pig iron to produce steel. Since steel is difficult to manufacture due to its high melting point, normal fuels and furnaces were insufficient and the open hearth furnace was...
.
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 IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
.
In 1858, Henry Bessemer
Henry Bessemer
Sir Henry Bessemer was an English engineer, inventor, and businessman. Bessemer's name is chiefly known in connection with the Bessemer process for the manufacture of steel.-Anthony 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 the 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, formerly a professor at the Berlin Institute of Technology, returned to Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
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
Scrap Metal
Scrap Metal were a band from Broome, Western Australia who played rock music with elements of country and reggae. The members had Aboriginal, Irish, Filipino, French, Chinese, Scottish, Indonesian and Japanese heritage. The band toured nationally as part of the Bran Nue Dae musical and with...
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, the LD (Linz-Donawitz) process. In December 1949, the VOEST and the 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. 34 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
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
impossible and by the end of the 1950s the Austrians lost their competitive edge.
The original LD process employed blowing oxygen on top of molten iron through a water-cooled nozzle of a vertical lance. In the 1960s steelmakers introduced bottom-blown converters and introduced inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
blowing for stirring the molten metal and removing of phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
impurities.
The big American steelmakers did not catch up to the new technology; the first oxygen converters in the United States were launched in the end of 1954 by McLouth Steel
McLouth Steel
McLouth Steel is a former integrated steel company. The company had three locations. The first plant was in Detroit, Michigan, the second in Trenton, Michigan and the third, a cold mill, in Gibraltar, Michigan. The Detroit plant is currently owned by Jones & Laughlin Steel Company...
in Trenton, Michigan
Trenton, Michigan
Trenton is a small city in Wayne County in the southeast portion of the U.S. state of Michigan. As of the 2010 census, the city population was 18,853...
, which had less than 1 per cent of the national steel market. U.S. Steel
U.S. Steel
The United States Steel Corporation , more commonly known as U.S. Steel, is an integrated steel producer with major production operations in the United States, Canada, and Central Europe. The company is the world's tenth largest steel producer ranked by sales...
and Bethlehem Steel
Bethlehem Steel
The Bethlehem Steel Corporation , based in Bethlehem, Pennsylvania, was once the second-largest steel producer in the United States, after Pittsburgh, Pennsylvania-based U.S. Steel. After a decline in the U.S...
introduced oxygen process only in 1964. Elsewhere, owing to the Austrian licensing blunder, the technology was adopted quickly. 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 substituted with the electric arc furnace
Electric arc furnace
An electric arc furnace is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking...
s. 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%.
Process
The basic oxygen steel-making process is as follows:- Molten pig iron (sometimes referred to as "hot metal") from a blast furnaceBlast furnaceA blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...
is poured into a large refractory-lined container called a ladleLadle (metallurgy)In a foundry, a ladle is a vessel used to transport and pour out molten metals. Ladles range in size from small hand carried vessels that resemble a kitchen ladle and hold or to large steelmill ladles that hold up to...
; - The metal in the ladle is sent directly for basic oxygen steelmaking or to a pretreatment stage. Pretreatment of the blast furnace metal is used to reduce the refining load of sulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, siliconSiliconSilicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, and phosphorus. In desulfurising pretreatment, a lance is lowered into the molten ironIronIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
in the ladle and several hundred kilograms of powdered magnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
are added. Sulfur impurities are reduced to magnesium sulfideMagnesium sulfideMagnesium sulfide is an inorganic compound with the formula MgS. It is a white crystalline material but often is encountered in an impure form that is brown and non-crystalline powder. It is generated industrially in the production of metallic iron....
in a violent exothermicExothermicIn thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
reaction. The sulfide is then raked off. Similar pretreatment is possible for desiliconisation and dephosphorisation using mill scaleMill scaleMill scale, often shortened to just scale, is the flaky surface of hot rolled steel, iron oxides consisting of Iron oxide, hematite, and magnetite....
(iron oxide) and lime as reagents. The decision to pretreat depends on the quality of the blast furnace metal and the required final quality of the BOS steel. - Filling the furnaceFurnaceA furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...
with the ingredients is called charging. The BOS process is autogenous: the required thermal energy is produced during the process. Maintaining the proper charge balance, the ratio of hotmetal to scrap, is therefore very important. The BOS vessel is one-fifth filled with steel scrap. Molten iron from the ladle is added as required by the charge balance. A typical chemistry of hotmetal charged into the BOS vessel is: 4% C, 0.2–0.8% Si, 0.08%–0.18% P, and 0.01–0.04% S. - The vessel is then set upright and a water-cooled lance is lowered down into it. The lance blows 99% pure oxygen onto the steel and iron, igniting the carbon dissolved in the steel and burning it to form carbon monoxideCarbon monoxideCarbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
and carbon dioxideCarbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, causing the temperature to rise to about 1700°C. This melts the scrap, lowers the carbonCarbonCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
content of the molten iron and helps remove unwanted chemical elementChemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s. It is this use of oxygen instead of air that improves upon the Bessemer processBessemer processThe Bessemer process was the first inexpensive industrial process for the mass-production of steel from molten pig iron. The process is named after its inventor, Henry Bessemer, who took out a patent on the process in 1855. The process was independently discovered in 1851 by William Kelly...
, for the nitrogen (and other gases) in air do not react with the charge as oxygen does. High purity oxygen is blown into the furnace or BOS vessel through a vertically oriented water-cooled lance with velocities faster than Mach 1. - FluxesFlux (metallurgy)In metallurgy, a flux , is a chemical cleaning agent, flowing agent, or purifying agent. Fluxes may have more than one function at a time...
(burnt limeLime (mineral)Lime is a general term for calcium-containing inorganic materials, in which carbonates, oxides and hydroxides predominate. Strictly speaking, lime is calcium oxide or calcium hydroxide. It is also the name for a single mineral of the CaO composition, occurring very rarely...
or dolomiteDolomiteDolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
) are fed into the vessel to form slagSlagSlag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...
, which absorbs impurities of the steelmaking process. During blowing the metal in the vessel forms an emulsion with the slag, facilitating the refining process. Near the end of the blowing cycle, which takes about 20 minutes, the temperature is measured and samples are taken. The samples are tested and a computer analysis of the steel given within six minutes. A typical chemistry of the blown metal is 0.3–0.6% C, 0.05–0.1% Mn, 0.01–0.03% Si, 0.01–0.03% S and P. - The BOS vessel is tilted again and the steel is poured into a giant ladle. This process is called tapping the steel. The steel is further refined in the ladle furnace, by adding alloying materials to give the steel special properties required by the customer. Sometimes argonArgonArgon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
or nitrogenNitrogenNitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
gas is bubbled into the ladle to make sure the alloys mix correctly. The steel now contains 0.1–1% carbon. The more carbon in the steel, the harder it is, but it is also more brittle and less flexible. - After the steel is removed from the BOS vessel, the slag, filled with impurities, is poured off and cooled.
External links
- Basic Oxygen Steelmaking module at steeluniversity.org, including a fully interactive simulation
- Basic Oxygen Steelmaking cost model showing typical cost structure for liquid steel