cont..

1. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
Vacuum treatment:
• Vacuum treatment of molten steel decreases the partial pressure of
CO, which results in shifting equilibrium of the reaction of carbon
oxidation.
• Bubbles of carbon monoxide form in the liquid steel float up and
then they are removed by the vacuum system.
• In addition to deoxidation vacuum treatment helps to remove
Hydrogen dissolved in liquid steel. Hydrogen diffuses into the CO
bubbles and the gas is then evacuated by the vacuum pump.
• Movement of the molten steel caused by CO bubbles also results in
refining the steel from non-metallic inclusions, which agglomerate,
float up and are absorbed by the slag.
• CO bubbles also favor the process of floating and removal of nitride
inclusions and gaseous Nitrogen.
• Steels refined in vacuum are characterized by homogeneous
structure, low content of non-metallic inclusions and low gas
porosity.
• Vacuum degassing methods are used for manufacturing large steel
ingots, rails, ball bearings and other high quality steels.
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2. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
Vacuum Oxygen Decarburization (VOD):
VOD system is consisting of…
i. Vacuum tank ( with Oxygen lancing Facility)
ii. Ladle furnace (with Stirring facility)
Process flow = EAF  VOD IC or CC
• The ladle has a free board of about 1 to 1.5 meter to contain violent
(vigorous) agitation of the bath during lancing.
• The charge ingredients are similar to the AOD process. The charge
is melted in EAF and transferred to the VOD system.
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3. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
• Oxygen blowing from lid of the vacuum tank and argon bubbling
from the ladle bottom are started when required vacuum is
established.
• Argon stirring is essential otherwise decarburization is delayed due
to lack of mass transport of carbon from bottom portion to the
surface where carbon oxygen reaction is greatly achievable.
• The carbon can be lowered to around 0.02% at around 16-18%Cr.
• At the end of the refining the vacuum is broken and the heat/bath
is deoxidized with Al/Fe-Si – or Fe-Si/Cr-Si(for chromium recovery)
• Then de-sulphurisation is carried out by putting synthetic slag
(Cao,SiO2,Al2O3 or CaF2 = e.g. 40: 40: 20) to the molten steel surface
of about 2-3% by weight of the molten steel and argon Stirring of
the melt through the porous bottom plug results in deep
desulfurization of the steel.
• The total VOD cycle is around 2-2.5Hours.
Benefits of Vacuum Oxygen Decarburization (VOD):
• -Deep carbon removal (ultra low carbon steel can produced
• -Low losses of chromium in treatment of stainless steels;
• -Hydrogen removal (degassing);
• -Sulfur removal (desulfurization);
• -Precise alloying;
• -Reheating; -Non-metallic inclusions (oxides and nitrides) removal;
• -Temperature and chemical homogenizing.
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4. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
• Since many steels are required to be vacuum treated to decrease
the gas content, the vacuum system can be easily done without
extra additional investment.
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5. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
Ladle desulfurization by injection of active agents
• Injection of desulfurizing agents (Ca, Mg, CaSi, CaC2, CaF2+CaO) to
molten steel is the most effective method of sulfur removal.
• Injection methods usually combine supply of a disperse desulfurizing
agent (powder) with stirring by argon blowing.
• A ladle with deoxidized molten steel is transported to the injection
stand where it is placed under a cover, through which the injection
lance may lower and immerse into the melt.
• Steel treated in the stand is covered by a layer of desulfurizing slag
having high solubility of sulfur and capable to absorb sulfides
formed as a result of active agents injection.
• Desulfurization agents are injected in argon stream. Argon bubbles
produce stirring of the molten steel and the slag promoting
desulfurization. Stirring also provides thermal and chemical
homogenization of the melt.
• When the desulfurizing agents are injected into molten steel in form
of a cored wire containing powder of desulfurizing agent stirring by
argon bubbling from the porous plug mounted in the ladle bottom is
used.
• Fumes formed during the operation are extracted through the
cover.
• Injection of desulfurizing agents allows achieving ultra-low
concentrations of sulfur in steel (0.0002%).
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6. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
Benefits of Ladle desulfurization by injection of active agents:
• Deep sulfur removal (desulfurization);
• Temperature and chemical homogenizing;
• Non-metallic inclusions removal.
Page 6 of 9

7. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
Electroslag Remelting
• Electroslag Remelting (ESR) is a process of remelting a consumable
electrode utilizing the heat generated by an electric current passing
through a molten slag between the electrode and the solidifying
ingot.
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8. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
• The consumable electrods are as cast or forged cylindrical
parts made of an alloy to be remelt.
• An electroslag remelting process (ESR) starts when the lower
tip of a consumable electrode is immersed into a pool of
molten slag.
• The premelted slag possessing electrical conductivity is
located on the water-cooled mold base connected to a power
supply.
• The electric current (commonly AC) passing through the the
slag keeps it at high temperature, which is about 360ºF
(200ºC) higher than the melting point of the remelted metal.
• The electrode tip is heated by the hot slag and starts to melt
forming droplets of liquid metal, which disconnect from the
electrode and sink through the slag layer.
• The slag composition is based on calcium fluoride (CaF2), lime
(CaO) and alumina (Al2O3).
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9. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
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10. MY: 301 Steel Making Processes
Lecture No: 20 21, 14 Feb 2011
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