Basic oxygen steelmaking

1. Molten iron from a refractory-lined container called a ladle;
2. 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 exothermic reaction. 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.
3. Filling the 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.
4. The vessel is then set upright and a water-cooled lance is lowered down into it. The lance blows 99% pure 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.
5. dolomite) are fed into the vessel to form slag 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, .01-0.03%Si, 0.01-0.03%S and P.
6. The BOS vessel is tilted again and the steel is poured into a giant nitrogen 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.
7. 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 1952 by voestalpine AG in 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 Bessemer process.