Basic oxygen steelmaking

Basic Oxygen Steelmaking

The (BOS) vessel holds about 280 tonnes of steel. It is lined with special bricks called refractories that tolerate very hot temperatures. 1. The BOS vessel is one-fifth filled with steel scrap. Molten iron is added until the vessel is full. Filling the furnace with the ingredients is called charging.

	2. The vessel is then stood upright and a lance is lowered down into it. The lance blows 99 percent pure oxygen onto the steel and iron, causing the temperature to rise to about 1700°C. This melts the scrap, lowers the carbon content of the molten iron and helps remove unwanted elements.  

3. Fluxes (burnt lime or dolomite) are fed into the vessel to form slag which absorbs impurities of the steelmaking process. Near the end of the blowing cycle, which takes about 20 minutes, a temperature reading and samples are taken. The samples are tested and a computer analysis of the steel given within six minutes.

	4. The BOS vessel is tilted again and the steel is poured into a giant ladle. This process is called tapping the steel. In the ladle furnace, the steel is further refined by adding alloying materials which give the steel special properties required by the customer. Sometimes argon or nitrogen gas is bubbled into the ladle to make sure the alloys mix correctly. The steel now contains 0.1-1 percent carbon. The more carbon in the steel, the harder it is, but it is also more brittle and less flexible. 

5. After the steel is removed from the BOS vessel, the slag, filled with impurities, is poured off and cooled.