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...

Oxygen and Steels

Oxygen and Steels  Oxygen (O) (atomic number 8 and atomic weight 15.999) has density of 1.429 gm/litre at standard temperature and pressure. Melting point of oxygen is -218.79 deg C and boiling point is – 182.96 deg C. It is a colourless gas but the colour of liquid oxygen is pale blue. The phase diagram of the Fe-O binary system is at Fig 1. Fig 1 Fe- O binary phase diagram  There is a very strong relationship between oxygen  and steel. Oxygen is first used in the steel making process which is a controlled oxidation process. Excess oxygen going to steel during steel  making process,  if not properly taken care of, is source of many steel defects like porosity, inclusions etc. Oxygen is used in the processes of cutting, lancing, scarfing and welding of steels. Oxygen is also the cause of steel destruction by the processes of rusting, scaling and corrosion. Further transport of oxygen takes place in cylinders, tanks and pipelines made of steel. Oxygen is also used (oxy-fuel process) for heating of the steel. During steel making process, the main sources of oxygen in steel are as follows. Oxygen used for blowing in the steel making process Use of oxidizing slags and oxidizing materials ( ores, sinter etc.) during steel making processes Atmospheric oxygen dissolves in the liquid steel during steel tapping and casting operations Oxidizing refractories used in various vessels for holding liquid steel in the process of steel making Rusted and wet scrap Solubility of oxygen in liquid steel is 0.23 % at the steel making temperatures ( 1600 – 1700 deg C). However it decreases during cooling down and then drops sharply during solidification of steel reaching a level of 0.003 % in solid steel. Solubility of oxygen in steel...

Silicon in Steels

Silicon in Steels  Silicon (Si) (atomic number 14 and atomic weight 28.09) has density of 2.34 gm/cc. Melting point of Si is 1412 deg C and boiling point is 2355 deg C. The phase diagram of the Fe-Si binary system is at Fig 1. Fig 1 Fe-Si phase diagram  Si is present in all the types of steels either as an intentional addition or as a residual from the ore, scrap or deoxidizing agents. Available forms  There are many Si containing addition agents which are used in steel making. Ferrosilicon (Fe-Si) and silico manganese (Si- Mn) are by far the most common addition agents. Fe-Si is a ferroalloy of iron (Fe) and Si. Fe – Si contains 65 % to 90 % of Si and minor amounts of Fe, aluminum (Al) and carbon (C).  Fe – Si is usually produced in four grades. These are standard grade, low Al grade, low C grade, and high purity grade having low content of titanium (Ti). The standard grade of Fe- Si contains Al up to 2 % while the low Al grade has Al content of 0.5 % maximum. It is produced by reduction of quartzite (SiO2) with coke in presence of iron ore.  Fe- Si is made in the submerged arc furnace. Si – Mn is a ferroalloy with high content of Mn and Si. It is produced by heating a mixture of oxides of MnO2, SiO2 and Fe2O3 with C in a furnace. These oxides undergo a thermal decomposition reaction. The standard grade contains Mn in the range of 62 % to 68 %, Si in the range of 12 % to 18 % and C in the range of around 2.0 %.  The low C grade of Si – Mn has a C...

Aluminum in Steels

Aluminum in Steels  Aluminum (Al) is used for deoxidizing and grain refining in steels. It is a strong deoxidizer. It is also used as nitride former and as an alloying agent. Its ability to scavenge nitrogen (N) from steel makes it a useful addition in drawing quality steels, especially for automotive applications. Aluminum (Al) is being used as a deoxidizing element in steels for more than 100 years. Deoxidation of steel with Al is common practice today. Al plays an important role in secondary metallurgy. It forms aluminum oxide or alumina (Al2O3) alumina and decreases the amount of oxygen in the steel during the production of killed steels. Metallic Al is the most common addition agent. It is usually done in the form of notched bars, shots, pigs, small ingots, chopped wire, briquettes and other convenient forms such as coiled machine fed wire. Purity of deoxidation grade of Al is normally over 95 % with the main tramp elements being zinc, tin, copper, magnesium, lead and manganese. Coiled aluminum wire is usually made to 99 % minimum specification. A wire feeding machine is shown in Fig 1. Fig 1 Wire feeding machine Al is also added as ferro-aluminum which is a dense and highly efficient form of aluminum addition. Ferro-aluminum contains 30 % to 40 % Al and normally added in lump form. Al may be added to the steel making furnace, teeming ladle, Ladle furnace, continuous casting tundish or ingot mould. Each type of addition has its specific purpose, and each addition produces its own characteristic results. Al is a very powerful deoxidizer, but has a disadvantage because of its low density. The density of liquid aluminum at steelmaking temperatures (1600 deg C) is about 2.0 tons/cum while the density of steel at...

Deoxidation of Steel Sep03

Deoxidation of Steel

Deoxidation of Steel  Steel making process consists of refining of hot metal to steel which is done under oxidizing atmosphere. During refining process oxygen get dissolve in steel. The following are the main sources of oxygen in steel. Oxygen blowing Use of oxidizing slags and iron ore during the steel making processes Picking of atmospheric oxygen by the liquid steel during the teeming operation Oxidizing refractories of the lining Rusted and wet scrap. Deoxidation is the last stage in steelmaking. During making of steel, the steel bath at the time of tapping contains 400 to 800 ppm activity of oxygen. Deoxidation is carried out during tapping by adding into the teeming ladle appropriate amounts of ferro alloys or other special deoxidizers. If at the end of the blow the carbon content of the steel is below specifications, the liquid steel is also recarburized in the teeming ladle. However, large additions in the teeming ladle have the adverse effect on the temperature of the liquid steel. Solubility of oxygen in steel is negligibly small. During solidification of molten steel, excess oxygen is rejected by the solidifying steel. Solubility of oxygen in liquid steel is 0.23 % at 1700 deg C. It decreases during cooling down process and then drops sharply during the solidification of liquid steel reaching 0.003 % in solid steel. The excess oxygen liberated from the solid solution oxidizes the components of steel such as C, Fe, and alloying elements resulting into blowholes and non metallic inclusions entrapped within the cast steel structure. Both blowholes and inclusions have considerable effect on the mechanical properties and impact adversely the steel quality. In order to prevent oxidizing of steel components during solidification the oxygen content of liquid steel need to be reduced. This is done by deoxidation of steel which...