PRINCIPLE OF STEEL MAKING


PRINCIPLE

Steel making may be defined as the partial and perferencial oxidation of impurities present in steel making. Blast furnace iron oxygen is the main agent which oxidized impurities like Si, C, Mn, P, S. The chemical process of refining is expressed in following reaction.

Fe + O = FeO
C + O = CO
Si + 2O = SiO2
Mn + O = MnO
2P + 5O = P2O5
S + CaO = Cas + O

Removal of impurities in the form of oxides is possible in steel making condition because the affinity of O2 is more with impurities than this bulk Fe.
Affinity of the O in iron oxide 0.0000001 to 0.000000001 strong flux CaO.


ACID PROCESS :

External flux addition is not required.
When melt condition P and S both less than 0.05 and their removal does not required. The process is carried out in acid steel making.

BASIC PROCESS :

In this process capable of removing all impurities
External flux required is allow.
Important flux is CaO for basic slag like CaO, SiO2, FeO, P2O5. which pig iron contain more P is cold Thomas grade.


Difference between acid and basic steel making.

Acid steel making.              Basic steel making

No external flux is              A strong basic flux is
Required.                            add to make basic S/g.

Slag is acidic nature.          Slag is basic nature

PH can't be removed.         All impurities can be removed

Slag composition is.          Slag composition is
FeO, MnO, SiO2, P2O5.   CaO, FeO, K2O, P2O5.

The Sio2 lining of             The lining of
refactory is acidic.              Refractory is basic.


Condition of Removal of Impurities

PHOSPHORUS REACTION :


5(FeO) + 2(P)    = P2O5 + 5Fe.
Cao.     + P2O5  = 3(Cao.P2O5)
------------------------------------------------
2P + 5(FeO) + 3CaO = 3(CaO.P2O5) + 5(Fe)
                                           Tricalcic

Condition :
* Low temperature
* Oxidizing atmosphere
* High basicity
* FeO contain (15 - 20%)
* It is not possible in blast furnace iron making

DEPHOSPHORISING

Dephosphoring
Dephosphoring
* It is the ratio of the phosphorus contain.
* Basic categories like CaO, MgO, FeO, MnO.
* Desulphuring ability Ca, Mg, Fe, Mn = 30000, 10000
   Ex = CaO = 56, MgO = 40
* 1kg of MgO is equal to 20kg of CgO for desulphurisation.

DESULPHURISATION REACTION

3Fe + So2 = FeS + 2FeO
10FeO + So2 = FeS + 3(Fe3O4)
* Sulphur come from other source of fuel
   FeS + CaO = Feo + CaS

Condition :
* High temperature
* Reducing atmosphere provides by activity carbon boil and CaO as flux.
* High basicity by charging more lime
* Higher contain Mn.
* Low Feo
* Iron oxygen activity of O2 0.0000000 - 0.000000001, Air 0o = 0.21 and pure air O2 is 1 or 100%.

SILICON REACTION

Si + 2O = SiO2
It is most stable oxide

K = a(SiO2) / a[si] × a2[o2] = 1/ %[si] × [O2]

Condition:
* Si = 15% contain in steel
* Silicon decide that grade of pig iron

MANGANESE REACTION :

Feo + Mn = MnO + Fe

Steel Making manganese reaction
Manganese reaction
K = a(MnO) × a(Fe) / a(FeO) × a(Mn) = %MnO / %(FeO) × %(Mn)

Condition:
* Mn reaction easy for acid steel making.
* % MnO increase with decrease in basicity.
* At some basicity % MnO increase from bulk process acid 'OH' process.

CARBON REACTION

Theactivity of carbon in liquid-carbon alloys shows -ve deviation. The presence of carbide foaming elements like Nb, V, Cr,Mo, W are decrease, where the presence of anti carbide former like Cu, Ni, Co are increase the coefficient of carbon.

K =  Pco / h[C] . h[O]
Or Fc(%C)Fo(%O) = Pco / K

Condition :
* Carbon contain could be decrease much below the level by treating 1. Under vacuum or 2. Under the inert gas atmosphere.

* It react with pure oxygen and being gas(CO) form, which is always forward direction.





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