Steelmaking: Oxygen steelmaking NARRATOR: There are two main methods used to produce steel, basic oxygen steel making and electric arc. Basic oxygen steelmaking, or BOS, is the main bolt production process for refining iron into steel. BOS vessels can take up to 350 tons of molten iron at a time and convert it into steel in less than 30 minutes. To start with, scrap steel is deposited in the vessel. Then the hot metal which may have been pretreated to remove elements such as sulfur is added. A water cooled Lance is lowered into the vessel and high purity oxygen is blown through the lance at about twice the speed of sound, just above the surface of the hot metal. The oxygen combines with impurities and this oxidation produces heat. Temperature is controlled by the quantity of scrap steel and by the addition of iron ore, both of which act as coolants. The oxidized carbon creates carbon monoxide gas, which can be collected, cleaned, and used as a fuel. Lime is added as the oxygen is blown. And this combines with other oxidized impurities to form slag. The quantities of scrap, hot metal ore, lime, and other fluxes are precisely calculated to ensure correct temperature and composition of the steel. Refining can be assisted by injecting argon, nitrogen, or oxygen through the base of the vessel and a sub-lance is used to measure carbon and temperature during the blow. This allows final adjustments to be made. During tapping, the steel composition is adjusted even further by alloy additions. At this stage, the carbon has been reduced from around 4% to about 0.05%. Finally, the vessel is tipped to remove the slag for recycling.