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Assignment on steelmaking

MM439: Iron and Steel Making (Summer course)
Assignment on steelmaking
Total weightage/Marks -25
Date – 30th April 2020
1) Explain in brief (qualitatively) your understanding about the overall (primary and
secondary) steelmaking process in terms of oxidation potential, refining of various
impurities and the slag properties required to convert pig iron into a particular steel grade.
The primary steelmaking is carried out through Basic Oxygen Furnace while secondary
steelmaking uses a combination of Ladle Furnace, VD/RH and other treatments.
Assume initial composition in the BOF – C – 4.5%, Si – 0.9%, Mn – 1%, P – 0.06%, S 0.02%
Final desired composition of a steel grade at the end of secondary steelmaking can be
assumed as – C – 0.0030%, Si – 0.03%, Mn – 1.5%, P – 0.015%, N- 0.0040%, S – 0.0030%,
Ti -0.030%.
No calculations are required. You have to mention the process/treatment in brief and
provide an approximate composition at various stages during the steelmaking so that
finally, the steel grade of the above composition can be obtained.
(Max limit
– 1.5 to 2 pages)
2) The liquid steel containing 0.1 wt% Mn and 0.04 wt% oxygen has been tapped into the
ladle from BOF. Now, you would want to deoxidize the molten steel by addition of
ferromanganese (containing 80 wt% Mn) at 1600 OC. The desired final oxygen content
after deoxidation is 0.02 wt%. Calculate the quantity of ferromanganese required to be
added per ton of steel.
Assume that no loss of manganese occurs by oxidation to the atmosphere.
Please understand that the product of Mn deoxidation will not be pure MnO but rather FeOMnO solid solution (This solid solution is ideal).
Data: Below T is temperature in kelvin
(1) Fe(liq) + O(1wt%) = FeO(S)
(2) Mn(1wt%) + O(1wt%) = MnO(S)
ΔGO = -132750 + 59.59T
ΔGO = -293430 + 128.95T
3) A stainless steel scrap of 60 tonnes is melted in EAF. The composition of this 60T melt at
the end of arcing operation is 18.28% Cr, 9% nickel and 2% carbon. A total amount of slag
formed is 300 kg containing negligible amount of solid chromium oxide (Cr3O4).
(a) What are weights of Cr, C, Ni and Fe in this melt.
As you know, such a high amount of carbon is not acceptable in the final stainless steel
melt. So, this melt needs to be further refined in VOD. However, for best VOD operation
the initial carbon content shall be 0.25%. The operator now lances the oxygen in the melt
and brings the carbon to this desired value of 0.25%. The temperature of the melt reaches
to 1973 K.
(b) At the end of lancing, the Cr content of the melt in equilibrium with carbon and Ni will
change. Some Cr will oxidize and join the slag.
Now assume that the slag is saturated with Cr3O4(S) and the saturation content of Cr3O4 is
50%. You may find some excess Cr3O4 in your calculations which will be floated on the
top of slag (verify this). It can be safely assumed that Ni was not oxidised during the oxygen
lancing. Calculate (i) the total weight of the melt (ii) weight of Cr in the melt and in the
slag (saturated and free solid Cr3O4).
You can use the following data for your calculations:
3Cr(1wt%) +4 CO(g) = Cr3O4(S) + 4C(1wt%)
K1973 = 4.329 × 10-8
Use first order interaction coefficients from the thermo data table available on Moodle.
4. Calculate the following:
(a) Molar free energy change, at 1873 K, for change of state of carbon from pure
graphite(S) to a 1 wt% solution in liquid iron, assuming Henry’s law is valid up to this
concentration. The Henry’s Law constant at 1873 K for C in liquid iron γO = 0.57
(b) What is pO2 in equilibrium with pure liquid silicon and pure silica (solid) at 1873 K?
Si(liq.) + O2(g) = SiO2 (liq.)
ΔGO = -952500 + 202.8T J/mol
Please submit the assignment by 20th May. The submission after 20th May
will not be accepted.