Role of Slag in Converter Steelmaking Aug01

Role of Slag in Converter Steelmaking...

Role of Slag in Converter Steelmaking The oxygen converter process is the primary steelmaking process for the production of carbon and low-alloy steels. The process is essentially an oxidizing process of refining of the high carbon hot metal (HM) to low carbon liquid steel. The oxidizing process is carried out by blowing oxygen in the converter. This causes liquid iron and the other metallic and non-metallic impurities present in the liquid melt in the converter bath to form oxides that are lighter than the liquid steel and they float to the surface of the bath. The generic name of these oxides is ‘slag’. Some oxides are acidic in nature which can react with the basic refractories of the converter and hence a basic slag using lime and calcined dolomite is usually made for protecting the converter refractories. The oxygen can also react with carbon to create a gas that provides bubbles for foaming the liquid slag and for providing chemical energy needed during steelmaking. In steelmaking process, the slag is predominantly a mixture of oxides with small amounts of sulphides and phosphides. The oxides are either acidic or basic in nature. Slag is formed during refining of hot metal in which Si oxidizes to SiO2, Mn to MnO, Fe to FeO, and P to P2O5 etc., and addition of oxides such as CaO (lime), MgO (calcined dolomite), iron oxide, and others. The addition of oxides is done to obtain desired physico-chemical properties of slag like melting point, basicity, viscosity etc. There are four primary sources for the slag during the steelmaking process in the converter. These are (i) oxidation of metallic elements in the liquid steel (e.g. silicon, manganese, aluminum, titanium, chromium, and vanadium etc.), (ii) due to presence of non-metallics in the liquid...