Stainless steel is a corrosion-resistant steel that contains at least 10% chromium. The chromium forms a thin, protective oxide film on the steel's surface. There are several types of stainless steel classified by their chromium and other elemental contents. Producing stainless steel from an electric arc furnace alone is difficult because it requires very high temperatures to remove carbon without excessively oxidizing chromium from the melt. Solutions include increasing temperature to favor carbon removal over chromium oxidation and adding ferroalloys to recover oxidized chromium and adjust alloy content.

1. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
What is Stainless Steel?
• Stainless steel is the name given to a group of corrosion resistant
and high temperature steels.
• The corrosion resistant property is due to a thin, adherent stable
chromium oxide or nickel oxide film that effectively protects the
surface from many corroding media.
• When ordinary carbon steel is exposed to rain water, it corrodes,
forming a brown iron oxide, commonly called rust, on the surface.
• This is not protective and eventually the entire piece of steel will
corrode and be converted to rust.
• But when enough chromium (more than about 10%) is added to
ordinary steel, the oxide on the surface is transformed - it is very thin,
virtually invisible and protective in a wide range of corrosive media.
This is what we call stainless steel.
• There are several different types, and many different grades.
1. Ferrite stainless steels.(14 – 27 %Cr)
2. Martensitic stainless steels. (11.5 – 18 % Cr)
3. Austenitic stainless steels. (Cr - Ni or Cr – Ni - Mn)
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2. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
4. Duplex stainless steels.
5. Precipitation hardening stainless steels.(16.5-17%Cr)
Stainless Steel Production from the Arc Furnace alone:
Steps
1. Charging (Scrap not more than 4 % Cr)
2. Melting
3. Sampling (If “C”,“P” and “S” does not with in the limit than)
Oxidizing Condition
4. Decarborization and Dephosphorization (Pure Oxygen
Blowing/Lancing + CaO)
5. Deslagging of Salg (Oxidizing slag)
Reducing Condition
6. Desulphurization (CaO + FeMn)
7. Deslagging (Reducing Slag)
Oxidizing Condition
8. Oxygen Blowing (Lancing) for more decarburization.
9. Addition of FeSi (to Recover the choromium which has been
oxidized
(Cr2O3) + 2/3[Si]  2[Cr] + 3/2(SiO2)
10. Chemical Adjustment
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3. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
11. Temperature Adjustment
12. Tapping to ladle
Problem:
• “Most of the stainless steel contains equal or less than 0.03%C.It
is difficult to obtain low carbon with out excessive oxidation of
chromium”.
• During Oxygen Blow
3/4 <Cr> + {O2}  2/3 <Cr2O3> Reaction #1
2<C> + {O2}  2{CO} Reaction #2
Solution:
• From thermodynamics, the activity of the “C” is increased by
raising the temperature or by reducing the pressure (Vacuum
Creation).
• The possible way in EAF is only rising the temperature.
• At high temperature the reaction # 2 takes place efficiently in
comparison to reaction # 1. (As Shown in Figure).
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4. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
• In figure, curves clearly shows that carbon is removed from the bath,
the equilibrium Cr content is also lowered and any Cr in excess of
equilibrium is very rapidly oxidised out.
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5. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
For- example,
At 0.05%C and 17000
C (Point A in Figure)
• The equilibrium Cr content is approximately 2%.
At 0.05%C and 18000
C (Point B in Figure)
• The equilibrium Cr content is approximately 7.5%.
• Most Stainless steel production requires carbon at or below 0.03%C at
which the equilibrium Cr level even at 18000
C is only 4%Cr
• Since C is present/contained in small amount in all Ferro alloys
• For a specification of 0.03%C, it would be necessary to finish at
0.02%C, than low carbon FrCr is added to maintain Cr % up to the
required level
Production of 188 steel (18% Cr , 8% Ni and 0.04%C-Steel)
• It is only possible to use a charge mix with 4 % Cr in it; the molten
charge would be blown down with pure oxygen to about 0.02%C
giving a temperature to about 18000
C.
• During the blow about 2% Cr of the charge would be oxidised into
the slag.
• About 1%Cr would be reduced back into the metal by using FeSi.
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6. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
(The Ni content is largely unaffected by the decarburisation reaction)
• By using only EAF for the production of stainless steel the following
difficulties were arise.
1. Needs very high temperatures (about 18000
C or above) for
decarburization (require high cost refractories).
2. It was only possible low charge chromium… this meant that only
small amount of stainless steel scrap were used.
3. Low carbon FeCr was used for alloying… (requiring high cost)
4. One or more treatment (double slag practice)… (Time consuming)
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7. MY: 301 Steel Making Processes
Lecture No: 18, 10 Feb 2011
(The Ni content is largely unaffected by the decarburisation reaction)
• By using only EAF for the production of stainless steel the following
difficulties were arise.
1. Needs very high temperatures (about 18000
C or above) for
decarburization (require high cost refractories).
2. It was only possible low charge chromium… this meant that only
small amount of stainless steel scrap were used.
3. Low carbon FeCr was used for alloying… (requiring high cost)
4. One or more treatment (double slag practice)… (Time consuming)
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