Desulphurization of Liquid Steel Jul30

Desulphurization of Liquid Steel...

Desulphurization of Liquid Steel Solubility of sulphur (S) in liquid iron (Fe) is quite high. But the solubility of S in solid iron is limited. It is 0.002 % in ferrite at room temperature and 0.013 % in austenite at around 1000 deg C. Hence, when liquid steel cools down, sulphur is liberated from the solution in the form of iron sulphide (FeS) which forms a eutectic with the surrounding iron. The eutectic is segregated at the iron grain boundaries. The eutectic temperature is comparatively low at around 988 deg C. Fe-FeS eutectic weakens the bonding between the grains and causes sharp drop in the properties of steel at the temperatures of hot deformation. During the continuous casting of liquid steel, sulphur present in liquid steel (i) causes the formation of undesirable sulphides which promotes granular weaknesses and cracks in steel during solidification, (ii) lowers the melting point and inter-granular strength, (iii) contributes to the brittleness of steel and thus acts as stress raiser in steel, and (iv) results in the hot shortness. Sulphur, present in solid steel as FeS inclusions, has several detrimental effects on steel processing. During deformation, FeS inclusions act as crack initiation sites and zones of weakness. Such inclusions from sulphur adversely affect the toughness, ductility, formability, weldability, and corrosion resistance of steel. An increase in manganese (Mn) content (not less than 0.2 %) however, helps prevent formation of FeS. Sulphur is thus an undesirable element in steel. Manganese actively reacts with iron sulphides during solidification of steel transforming FeS to MnS according to the following reaction. FeS (slag) + Mn (steel) = MnS (slag) + Fe The melting temperature of manganese sulphide (MnS) is comparatively high (around 1610 deg C). Hence steel containing manganese can be deformed in hot state. However...

Materials needed for Steel Production in Basic Oxygen Furnace Oct16

Materials needed for Steel Production in Basic Oxygen Furnace...

Materials needed for Steel Production in Basic Oxygen Furnace The following types of materials are needed for the production of liquid steel in the basic oxygen furnace (BOF) steelmaking process (Fig 1). Basic raw materials such as hot metal, scrap, and lime etc. Secondary raw materials such as deoxidizers and carburizers. Utility gases such as oxygen, nitrogen, and argon etc. Refractories and Refractory materials such as lining material, gunning material and patching materials etc. Consumable probes such as temperature probes and sampling probes etc. Cooling water for cooling of oxygen blowing lance and exhaust gases. Fig 1 Materials needed for the production of steel in basic oxygen furnace Basic raw Materials The basic raw materials needed for making steel in the BOF converter include (i) hot metal from the blast furnace, (ii) steel scrap and/or any other metallic iron source, (iii) iron ore, and (iv) fluxes.  Scrap, charged from a scrap box, is the first material to be charged into the BOF. The hot metal is then poured into the converter from a hot metal charging ladle, after which the blowing with oxygen gas is started. The fluxes, usually in lump form, are charged into the BOF through a bin system after the start of the oxygen blow. The fluxes can also be injected into the furnace in powder form through bottom tuyeres. The composition and amounts of basic raw materials used in the BOF converter vary from one steel melting shop to another, depending on their availability and the economics of the process. The hot metal or liquid iron is the primary source of iron units and energy. Hot metal is received from the blast furnaces in either open top or torpedo cars. In case of open top ladles, hot metal is poured...

Quality of Lime for Steelmaking in Converter Sep08

Quality of Lime for Steelmaking in Converter...

Quality of Lime for Steelmaking in Converter Lime is a white crystalline solid with a melting point of 2572 deg C. It is a basic oxide and is used to react with the acidic oxides (e.g. silica). It is calcium oxide (CaO) produced on heating (calcination) of limestone (CaCO3) to a temperature of 900 deg C and above (usually 1100 deg C). CaCO3(s) + heat = CaO(s) + CO2 (g) This reaction is reversible. Calcium oxide reacts with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing of carbon dioxide from the mixture as it is released. Hydrated lime Ca(OH)2 is formed by reaction of lime with water (slaking). Hydrated lime is also known as slaked lime. CaO + H2O = Ca(OH)2 + heat Lime as a basic flux in steel production and it plays an important role in the sequence of metallurgical reactions taking place in a converter. Steel is produced from hot metal by oxidizing sulphur (S), phosphorus (P), carbon (C), silicon (Si), manganese (Mn), and other impurities so that they can enter the slag or gas phases, thus separating from the metal phase. Lime in steelmaking is mainly used to produce slag for the removal of these harmful elements in liquid bath and optimize the quality of liquid steel. The basic oxygen process oxidizes impurities in an oxygen converter also known as basic oxygen furnace (BOF) where the hot metal comes in contact with oxygen. Oxidized impurities of the hot metal are absorbed in a slag, which is formed with the help of calcined lime. Metallurgical lime in the fifties consisted of a mixture of particles of all sizes from very coarse to very fine, with additional components such as silicon dioxide and sulphur concentrated...

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...

Lime and Calcined Dolomite for Use in Steel Plant...

Lime and Calcined Dolomite for Use in Steel Plant Lime is a versatile compound.  Various forms of lime are used in environmental, metallurgical, construction, and chemical/industrial applications etc.  The largest single use of lime is in steel manufacturing, where it serves as a  flux for removing impurities (silica, phosphorus, and sulphur) during refining of steel. The fastest growing use of lime is in environmental applications, where lime is used for treatment of flue gases, wastewater, solid waste, and drinking water. Lime is a white crystalline solid with a melting point of 2572 deg C. It is a basic oxide and is used to react with the acidic oxides (e.g. silica) in various smelting operations. With water it makes milk of lime used for neutralizing acidic waste water. It is also being known as quick lime, lime flux, unslaked lime, and fluxing lime. Lime having some percentage of MgO (usually 2 % to 4 %) is also known as dolomitic lime. Lime is a hygroscopic material and absorbs moisture from the air. With the absorption of moisture it loses its reactivity and gets hydrated. Lime is calcium oxide (CaO) produced on heating (calcination) of limestone (CaCO3) to a temperature of 900 deg C and above (usually 1100 deg C). CaCO3(s) + heat = CaO(s)  +CO2(g) This reaction is reversible. Calcium oxide reacts with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing of carbon dioxide from the mixture as it is released. Hydrated lime [Ca(OH)2] is formed by reaction of lime with water (slaking). CaO + H2O = Ca(OH)2 + heat Hydrated lime is also known as slaked lime. It is in the form of a dry white powder. Hydrated lime is an alkali and used for neutralizing acidic solutions. In...