Basic oxygen steelmaking (BOS, BOP, BOF, and OSM), also known as Linz-Donawitz- steelmaking or the oxygen converter process[1] 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 because fluxes of burnt lime or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter.[2]
https://en.wikipedia.org/wiki/Basic_oxygen_steelmaking

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Note added at 13 мин (2016-03-13 16:58:08 GMT)
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There exist several variations on the BOS process: top blowing, bottom blowing, and a combination of the two. This study will focus only on the top blowing variation.
http://www.steel.org/making-steel/how-its-made/processes/pro...