Deoxidation is the process of removing residual oxygen from refined steel to prevent defects. Sources of oxygen in steel include rust, oxygen blowing during manufacturing, slag, and atmospheric oxygen during teeming. The kinetics of deoxidation involve the dissolution of deoxidizers like aluminum, their reaction with oxygen, and the nucleation and growth of deoxidation products. Effective deoxidizers are then removed from the steel through flotation and absorption into slag. Common deoxidizers include aluminum, silicon, and manganese. Calcium injection can be used to modify inclusions and produce cleaner steels.

1. Deoxidation
Madhava . J,
R161529,
B.Tech IInd
year,
Metallurgical and Materials Engineering

2. Introduction to deoxidation
At first, refining of hot metal to steel is done under oxidizing atmosphere.
During refining oxygen dissolves in steel and solubility of oxygen in steel in
negligibly small.
At the end of refining, a considerable amount of oxygen (0.05-0.10%) is
left in liquid steel.
If a steel with 0.05% oxygen is cast, the residual oxygen is evolved in the
form of gases will leads to blow holes and non metallic inclusion.
The removal of residual oxygen content of refined steel is known as
deoxidation or killing of steel.
This defects of considerable effect on mechanical properties of steel.

3. Sources of oxygen in steel
❖ Rust on steel, it is one of the oxide form of iron and forms when oxygen
reacts with iron or steel.
❖ Oxygen blowing, it is to remove the unwanted elements like Si, Mn, C, P
which appears in various states of manufacturing process.
❖ Steel making slag, such that this unwanted elements in the form oxides
in the slag may result in excess oxygen.
❖ Atmospheric oxygen dissolved in during teeming.
❖ Oxidizing refractories

4. Kinetics of deoxidation
Kinetics of deoxidation before elimination :
➔ It consists of dissolution of deoxidisers into molten steel, chemical reaction
between dissolved oxygen and the deoxidizing element, nucleation and intial
growth of the deoxidation product.
In detail :
● Mechanism of dissolution depends on melting point. In this case the aluminium is
expecte dmelt faster than iron or steel
● Nucleation of solid becomes easier if interface is present. Here the deoxidation
of Al produces solid Al2O3 and this interface is useful nucleation

5. ● Deoxidation with single elements like Al, Si etc., produce solid deoxidation
product at the steelmaking temperature.
● As we know that a liquid product can easily coalesce when compared to the
solid product
● Deoxidation with ferro silicon + ferro manganese produces liquid
deoxidation product.
● Boron, titanium, zirconium are also quite effective deoxidizers but expensive.
Kinetics of elimination of deoxidising products :
❏ It consists of further growth of deoxidation products by agglomeration
and their elimination from liquid steel.
❏ This is a slow process and it is important to removal deoxidation
product it is achieved by floatation and absorption into a slag.

6. ❏ The following steps are important for removal of deoxidation products from
steel.
1. Growth of deoxidation product.
2. Movement through molten steel to surface.
3. Absorption of inclusion by a suitable designed synthetic slag
❏ For the removal, flotation of deoxidation product depends on physical properties
of steel(laminar flow) it can be described at steady state by stoke’s law
Vt
= terminal velocity(m/s) of the inclusion
ᑭᑭ = difference in the density of steel and deoxidation
product and ŋ is the viscocity of steel (kg./m.s)
❏ Degree of stirring in the melt is important, stirring may help floating of
deoxidation product.

7. Deoxidisers
Aluminum :
➔ It is effective deoxidiser which is
used in most steel making
operations.
➔ It is used in the form of rods,
pellets, powders etc.,
➔ Usually the aluminium deoxidation
is carried out in the ladle.
➔ It is an alloying addition in the heat
resistant steels.

8. Silicon :
➢ It is used as primary deoxidising agent in a furnace where a reducing
slag is to be made.
➢ It is used in the form of ferro-silicon.
➢ Silicon is used as alloying element for better strength, hardenability
and electrical properties.
Manganese :
● It is a weaker deoxidiser than silicon.
● As an alloying element it gives strength and toughness.
● It is used in the form ferro-manganese of various grades

9. ❖ Aluminum is very effective since Al2O3 is far more stable oxide than
SiO2, MnO, etc.
❖ But Al2O3 is solid even at steel making temperatures and hence cannot
be used alone to deoxdise steel completely.
❖ It is generally used along Mn and Si when aluminium has a chance to
join the liquid slag product of deoxidation.
❖ B, Ti, Zr are also effective deoxidisers. They aren’t used primarily.

10. Inclusion control
➔ We can’t avoid the inclusion formation in steels. The only thing is to
modify or minimise them such that they won’t act as stress raisers
during rolling.
Calcium injection :
❏ Much cleaner steels can get from the Ca injection.
❏ It is either pure Ca metal ar as Ca-Fe-Al alloy with 32% Ca and 40% Al in
powder form.
❏ Ca must injected deep so it can improve it’s efficiency.
❏ After that it reacts with sulphides and silicate inclusions to form complex
sulphide-oxide.
❏ The inclusions are modified step by step and by assimilation of CaO in
Al2O3 particles.

11. ❏ It converts some of the solid alumina into liquid alumina particles(liquid phase
inclusions) and others will be semi-solid state and other oxides also.
❏ This inclusions surround solid alumina to form inclusions with solid core and
liquid periphery.
❏ The size of alumina inclusion increases slightly when it gets enveloped by the
liquid phase.
❏ Thus it changes the morphology of sulphide and alumina inclusions and rises
them to join the slag at the surface for the cleaner steels.

12. Thank you