Editing Basic oxygen steelmaking (section)

==Process==
[[File:Schéma LD métallurgie.svg|lang=en|thumb|Principle of a LD (Linz Donawitz) converter]]
[[File:LDkonverter01.jpg|thumb|upright|Cross-section of a basic oxygen furnace]]
[[File:BOS Plant (Scunthorpe Steelworks).jpg|thumb|The outside of a basic oxygen steelmaking plant at the [[Scunthorpe]] steel works (England)]]

Basic oxygen steelmaking is a primary steelmaking process for converting molten [[pig iron]] into [[steel]] by blowing [[oxygen]] through a lance over the molten pig iron inside the converter. [[Exothermic process|Exothermic]] heat is generated by the [[Redox|oxidation]] reactions during blowing.

The basic oxygen steel-making process is as follows:

# Molten [[pig iron]] (sometimes referred to as "hot metal") from a [[blast furnace]] is poured into a large refractory-lined container called a [[ladle (metallurgy)|ladle]].
# The metal in the ladle is sent directly for basic oxygen steelmaking or to a pretreatment stage where [[sulfur]], [[silicon]], and [[phosphorus]] are removed before charging the hot metal into the converter. In external desulfurizing pretreatment, a lance is lowered into the molten [[iron]] in the ladle and several hundred kilograms of powdered [[magnesium]] are added to reduce sulfur impurities to [[magnesium sulfide]] in a violent [[exothermic]] reaction. The [[sulfide]] is then raked off. Similar pretreatments are possible for external desiliconisation and external dephosphorisation using [[mill scale]] ([[iron oxide]]) and [[Lime (material)|lime]] as [[Flux (metallurgy)|fluxes]]. The decision to pretreat depends on the quality of the hot metal and the required final quality of the steel.
# Filling the [[Metallurgical furnace|furnace]] with the ingredients is called ''charging''. The BOS process is autogenous, i.e. the required thermal energy is produced during the oxidation process. Maintaining the proper ''charge balance'', the ratio of hot metal from melt to cold scrap is important. The BOS vessel can be tilted up to 360° and is tilted towards the deslagging side for charging scrap and hot metal. The BOS vessel is charged with steel or iron scrap (25–30%), if required. Molten iron from the ladle is added as required for 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, all of which can be oxidised by the supplied oxygen except sulfur (which requires reducing conditions).
# The vessel is then set upright and a water-cooled, copper tipped lance with 3–7 nozzles is lowered into it to within a few feet of the surface of the bath and high-purity oxygen at a pressure of {{convert|700|-|1000|kPa|psi}} is introduced at [[supersonic speed]]. The lance "blows" 99% pure oxygen over the hot metal, igniting the carbon dissolved in the steel, raising the temperature to about 1700&nbsp;°C as [[carbon monoxide]] and [[carbon dioxide]] are formed. This melts the scrap, lowers the [[carbon]] content of the molten iron and helps remove unwanted [[chemical element]]s. It is this use of pure oxygen (instead of air) that improves upon the [[Bessemer process]], as the nitrogen (an undesirable element) and other gases in air do not react with the charge or decrease the efficiency of the furnace.<ref>McGannon, p 486</ref>
# [[Flux (metallurgy)|Fluxes]] ([[calcium oxide]] or [[dolomite (rock)|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.
# 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.
# 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.