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.