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RAW MATERIALS FOR STEEL MAKING
The chief raw materials for steel making are :
- Sources of metalic iron
- Oxidising agents
- Fluxes
- Sources of heat
- Deoxidisers and alloying additions
- Furnace refractories
Primary source of metallic iron is in the form of molten pig iron, often called as hot metal from a blast furnace or solid pigs.
The secondary source of metallic iron is sponge iron and steel scrap from steel plant in the form of spillage, sheared ends, rejected materials etc.
Oxidising agent used for steel making are iron oxide, air and oxygen gas. Iron oxide is used in the form of lumpy heamatile ore and mill scale. Mill scale is the oxide of iron produced during hot fabrication of steel and is readily available in an integrated steel plant. The usual analysis of both of these are as follows :
|
%Fe
|
%S
|
%Volatile
|
Others
|
|
| Iron Ore |
60-69
|
0.03
|
0.5
|
Gangue Oxides (Should
be low in silica)
|
| Mill Scale |
71
|
0.10
|
4.5
|
Minor Impurity oxides
|
Both of these contain nearly 25% of oxygen by weight. The ores are generally low in sulphur and high in gangue oxides, whereas the mill scale is nearly in pure form of oxide but it may contain a high proportion of sulphur. Both are used in practice in suitable proportion. The use of iron oxide as an oxidising agent results in improving the yield of the process but it needs thermal energy to dissciate itself and make oxygen available for refining reactions.
Flux is a substance added during melting and refining to bring down the softening point of the gangue materials in order to reduce the viscosity of slag and to decrease the activity of some component(s) to make it stable in the slag phase.
Typical Analysis of Fluxes Used in Steel Making :
|
%CaO
|
%S
|
*MgO
|
%SiO2
|
|
| Lime |
90-95
|
0.1-0.2
|
2-3
|
1.5
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| Limestone |
50
|
0.01
|
1
|
1
|
| Calcined Dolomite |
55
|
0.1
|
34-38
|
3-4
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| Ganister |
0.5
|
-
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0.1
|
94
|
Sources of Heat
Electrical :
i] Induction Heating
ii] Resistance Heating
iii] Arc Heating
Deoxidisers and Alloying Additions :
Elements like Al, Si, Mn, etc. are added primarily as common deoxidisers. Elements like Zr, B, Ti, etc. are added for deoxidation in special cases and elements like Cr, W, MO, Ni, V, Nb, etc. are added generally as alloying additions. Carbon is added to recarburise steel or as a deoxidiser under vacuum.
Furnace Refractories
Steel making furnace is lined by suitable refractory materials. The lining is eroded during steel making and hence the material of lining is also required as a recurrig consumable raw material. All the basic refractory materials for lining essentially belong to the CaO-MgO system and the % (CaO + MgO) toegther should not be less than 90%.
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Saboo Group of Industries
505-506, Sahyog Building,58-Nehru Place
New Delhi -110019, INDIA
