1. MM439 Interaction MEMS Iron and steel making.pptx

Steelmaking

1. Manish M. Pande, Dept. of Meta. Engg . & Mat. Sci., IIT Bombay, Mumbai MM439: Iron and steel making

2. Reduce during steel production and application Ref- worldsteel.org

3. Use and Reuse Remanufacture Cheaper, energy efficient, conservation of raw materials

4. Recycle Melting steel products at the end of their useful life to create new steels. Steel has been recycled ever since it was first made. All available steel scrap is recycled, over and over again to create new steel products in a closed material loop.

5. Some Interesting facts about steel Steel grades: why there are so many steel grades? Correlation between heat treatment, microstructure and mechanical properties For a same composition e.g. for the same carbon content, there can be various grades with varying microstructure and the mechanical properties There are thousands of steel grades that can be classified as plain carbon steels and the alloys steels.

6. Steel making route 6

7. Various forms of Iron/Steel The properties of iron changes to large extent by alloying it with carbon and other elements Carbon wt.% Wrought iron Steel Cast iron Pig iron Hardness Malleability Soft Brittle Weight% C 7

8. Steel { Iron + (less than 2 wt.%) Carbon + desired elements} is easy to work There are undesired elements as well How to get rid of these undesired elements or refine them? Refining of these impurities or undesired elements makes the steel making process the way it is. What is steel? What about the undesired elements? How they enter the steel? 8

9. Typical composition of pig iron Hot metal Composition (%) C 4 – 4.5 Mn 0.2 – 0.7 Si 0.2 – 1.2 P 0.06 – 0.12 S 0.02 O 0.0 Temperature ( O C) 1350 – 1400 Desired Undesired Strength↑ Brittleness ↑ Yield strength ↑ Oxidation resistance ↓ Hot shortness ↓ Strength ↑ Toughness ↓ Formability ↓ Machinability ↑ Impact hardness ↓ Machinability ↑ Hot-shortness ↑ 9

10. Possible routes for removal of impurities from liquid steel Removal to slag phase Removal to gas phase & (d) Formation and dissolution of inclusions in slag phase (e) Reaction with refractory Ref. – Treatise on process metallurgy 2014 Primary (BOF) Secondary (LF) Basic oxygen furnace or Ladle furnace comprises of the steel-slag-refractory-gas-inclusion system 10

11. Schematic showing silicate chain Blue- Bridging oxygen (O O ) Red- Non-bridging oxygen (O - ) Purple- Free oxygen (O 2- ) Green – Cations (M + ) Ref. – Ken Mills, 2011 Silica network The fundamental building unit in solid silica and molten silicates is the silicate tetrahedron SiO4 -4 Each Si atom is tetrahedrally surrounded by four oxygen atoms and each oxygen atom is bonded to two silicon atoms.

12. NBO/T = (number of non-bridging O)/(tetragonally-bonded oxygen) (NBO/T) is a measure of the depolymerisation and a kind of basicity index Q = 4 – (NBO/T) Q is a measure of the polymerisation NBO/T and Q for various CaO-SiO 2 slag compositions Ref. – Ken Mills, 2011

13. Slag Slag is a non-metallic phase on the top of metallic (steel) phase, to which impurities from steel can be transferred under conducive thermodynamic and kinetic conditions It consists of oxides: network formers (e.g. SiO 2 ), network breakers (e.g. CaO) , fluxes to lower the liquidus temperature (e.g. Na 2 O), oxygen source (e.g. FeO ) and the impurities from steel 13

14. End of Lecture 1 14