Basic oxygen steelmaking
Basic oxygen steelmaking ("BOS, BOF, Linz-Donawitz-Verfahren, LD-converter") is a method of
steelmakingin which carbon-rich molten iron is made into steel. The process is an improvement over the historically important Bessemer process. The LD-converter is named after the Austrian placenames Linzand Donawitz(a district of Leoben).
oxygenthrough molten pig iron, the carbon content of the alloyis lowered and changes the material into low-carbon steel.
A typical BOS vessel holds about 280
tonnes of steel. The vessel is lined with heat-resistant refractory bricks that can withstand the high temperatureof molten metal.
The basic oxygen steel-making process is as follows:
#Molten iron from a
blast furnaceis poured into a large refractory-lined container called a ladle;
#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
sulfur, silicon, and phosphorus. In desulfurising pre treatment, a lance is lowered into the molten ironin the ladle and several hundred kilograms of powdered magnesiumare added. Sulfur impurities are reduced to magnesium sulfidein a violent exothermicreaction. The sulfide is then raked off. Similar pretreatment is possible for desiliconisation and dephosphorisation using mill scale(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.
furnacewith 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 ironfrom 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
oxygenonto the steel and iron, igniting the carbon dissolved in the steel and burning it to form carbon monoxideand carbon dioxide, causing the temperature to rise to about 1700 °C. This melts the scrap, lowers the carboncontent of the molten iron and helps remove unwanted chemical elements. It is this use of oxygen instead of air that improves upon on the Bessemer process, for the nitrogen (and other gases) in air do not react with the charge as oxygen does.
#Fluxes (burnt lime or
dolomite) are fed into the vessel to form slagwhich 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, .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 argonor nitrogengas 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.
The first basic oxygen steelmaking process was the LD process developed in
1952by voestalpine AGin Linz, Austria. Some major steelmaking companies in the US did not convert to this process for decades, with the last Bessemer converter still operating commercially until 1968.
The LD process replaced both the previously common
Siemens-Martin process, also known as the open-hearth process, and the Bessemer process.
* [http://www.steeluniversity.org/content/html/eng/default.asp?catid=24&pageid=2081272110 Basic Oxygen Steelmaking module at steeluniversity.org] , including a fully interactive simulation
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Look at other dictionaries:
basic oxygen steelmaking — Смотри конвертерное производство … Энциклопедический словарь по металлургии
basic-oxygen process — basic( oxygen) process noun A steelmaking process in which oxygen is blown at high pressure through molten pig iron • • • Main Entry: ↑basic … Useful english dictionary
basic(-oxygen) process — noun A steelmaking process in which oxygen is blown at high pressure through molten pig iron ● basic … Useful english dictionary
basic oxygen process — a high speed method of steelmaking in which oxygen of high purity is blown through an oxygen lance at high velocity onto the surface of a bath containing steel scrap and molten pig iron within a vessel with a basic lining (basic oxygen furnace).… … Universalium
basic oxygen process — a high speed method of steelmaking in which oxygen of high purity is blown through an oxygen lance at high velocity onto the surface of a bath containing steel scrap and molten pig iron within a vessel with a basic lining (basic oxygen furnace) … Useful english dictionary
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… … Wikipedia
basic process — noun : a process (as in steelmaking) carried on in a furnace lined with basic material (as magnesite, dolomite, lime, or iron oxide) and under a slag that is dominantly basic opposed to acid process; compare bessemer process * * * basic( oxygen)… … Useful english dictionary
basic — /bay sik/, adj. 1. of, pertaining to, or forming a base; fundamental: a basic principle; the basic ingredient. 2. Chem. a. pertaining to, of the nature of, or containing a base. b. not having all of the hydroxyls of the base replaced by the acid… … Universalium
oxygen — oxygenic /ok si jen ik/, oxygenous /ok sij euh neuhs/, adj. oxygenicity /ok si jeuh nis i tee/, n. /ok si jeuhn/, n. Chem. a colorless, odorless, gaseous element constituting about one fifth of the volume of the atmosphere and present in a… … Universalium
basic — /ˈbeɪsɪk/ (say baysik), Chiefly US /ˈbæsɪk/ (say basik) adjective 1. of, relating to, or forming a base; fundamental: a basic principle; a basic ingredient. 2. (of manufactured commodities) equipped with essential components, without optional… … Australian English dictionary