DEOXIDISER IN STEEL MAKING AND ALLOYING ELEMENTS

DEOXIDIZED ELEMENTS

Oxidizing Agents :  

The oxidizing agents used for steelmaking are iron oxide, air and oxygen. Iron oxide is used as a lumpy hematite and mill scale. Mill scale is the oxide of the iron produce during hot fabrication of steel which is avilavail in the integrated steel plant. Both iron ore and mill scale containing 25% of oxygen by weight. The ore are high in gangue and low sulphur content where mill scale is nearly pure form of oxides but high sulphur contains. The use of iron oxide improve the yield of the process but it need to thermal energy to dissociate itself and make oxygen required for refining.


FLUXS : 

 It is a substance which added during smelting and refining to
● bring down the softening point of the gangue materials
● reduce the viscosity of slag
● decrease the activity of some component to make it stable in the slag phase.

Lime and limestone is used during steelmaking to make the slag basic and to retain phosphorus and sulphur in slag.

Lime = CaO : 90 to 95, S : 0.1 to 0.2, MgO : 2 to 3, SiO2 : 1.5% respectively.
Limestone = CaO : 50, S : 0.01, MgO : 1, SiO2 : 1% respectively
Calcined dolomite = CaO : 55, S : 0.1, MgO : 34 to 38, SiO2 : 3 to 4% respectively


Alloying Addition and deoxidation : 


Primary or common deoxidizer -  Al, Si and Mn.
Special or micro alloys deoxidizer - Zr, B, Ti, Cr, W, Mo, Ni, V, Nb etc.
Carbon is added to recarburise steel or as a deoxidizer under vacuum. Excess addition of Al, Si, Mn, Ti etc are consumed for deoxidation as well as alloying addition. Generally ferrophysical silicon, ferro manganese and silicon Manganese are used as a alloying addition in steel shops.

Silicon :  It is used as a primary deoxidising agents in a furnace where reducing slag is to be made. It is used as a common deoxidizer in furnace or ladle when killed or semi killed steel. It is used in the from of ferro silicon which gives better strength, hardenability and electrical properties in steel.
aluminium bar
aluminium ingots

fesimn
silicon manganese
carbon for steel making
calcined petroleum coke 
Manganese :  It is a weaker deoxidizer according to the silicon. It is used as alloying elements for making hadfield and structural steels. This element gives the toughness and strength for steel. Generally silicon and manganese added together and makes silico manganese or individual ferro manganese which is used in steelmaking processes.

Aluminum :  It is very effective and good deoxidizer and used in the from of pellets, wires and starts. Sometimes it used as ferro aluminum or aluminum silicon compound.

Nickel :  It is added as a alloying addition in stainless steels but not used as a deoxidizer. It can be added any time during the process. Carbonyl nickel is preferred to electrode nickel for its low adsorbed.

Chromium :  It is used an alloying element for stainless and heat resistance steel. It is available in the form of ferro-crome of several grades. It increase the hardness, strength, yield point and elasticity. It's so costly therefore it used in some special grade as deoxidizer.

Titanium :   It is a strong deoxidizer and neutralises the effect of nitrogen on steel by bonding it into stable insoluble nitraide compound. These steel are useful for aircraft industry for its lightness with strength. It contains 23 to 25 percentage Ti, 0.15% C and Si and aluminum in certain proportion to the Titanium content.

Vanadium :  It is strong deoxidizer and increases the strength, plasticity and resistance to attrition and impact. It usally added in structural, tool and spring steel. It is used in form of ferro vanadium in which V is 35% minimum, 0.75 to 1.00% C, 2 to 3.5% Si and 1 to 2% Al.

Tungsten :   It also a strong deoxidizer used for increasing hardness, strength and elasticity of steel which is used for tools, high speed and cemented carbide alloys of steel. It is added as ferro tungsten where W is 70%.

Molybdenum :   It is only the alloying addition to improve the mechaniability property. Its presence ensure uniform microcrystalline structure, augment hardenability and eliminates post temper brittleness. It is used for shaft, gears, rolls etc. It is added at any time during refining. Here Mo content is 55%.

Zirconium :   It is used as a deoxidizer which decrease the deleterious effect of nitrogen and sulphur in steel. It is added in the form of zirconium ferro silicon having 40% Zr. It has a ratio of Si/Zr not exceed to 0.55 and Al/Zr to 0.20.

Boron :  This alloying element enhanced the mechanical property and hardenability of steel. It is added to steel in almost negligible 0.0025 to 0.0030% in the form of ferro boron and ferroboral which contains minimum to 5%B, maximum 3%Si, 5%Al and 0.55%C.

Niobium :   The addition of niobium to stainless steel and heat resisting steels enhanced their plasticity and corrosion resistance. It improves welding property of structural steels and stabilising influence on stainless steel. It added as ferro niobium tantalum with minimum 50% Nb+Ta, 0.1 to 0.2%C, 11 to 12% Si, 7%Al and 7% Ti.

Cobalt :  It is used as an alloying addition for magnetic steel and like Ni or Mo, it can be added at any time of refining.

Carbon :  Coke, graphite and anthracite are used as recarburiser. Coke is used to prepare reducing slag in an electric arc furnace. Mainly calcined petroleum coke is used during refining if carbon is required in steel, which contains 95 to 98% of carbon.



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