Modern Steelmaking - Steel Making - Lecture Notes, Study notes of Metallurgy

Download Modern Steelmaking - Steel Making - Lecture Notes and more Study notes Metallurgy in PDF only on Docsity! L 2 Modern steelmaking Contents: Concept Primary steelmaking Secondary steelmaking Continuous casting and thin strip casting Final finishing operations Key words: Primary steelmaking, ladle metallurgy, ingot casting, continuous casting Concept The concept of modern steelmaking is to make use of the steelmaking vessels like converter, ladle and tundish of a continuous caster. In all these vessels molten steel is handled for one or the other purpose. For examples ladles are used to transfer the molten steel either to ingot casting or continuous casting. Tundish of a continuous caster is used to transfer molten steel to the continuous casting mould. In all these vessels the residence time of molten steel is sufficiently long so as to carry out some refining operations like composition adjustment, removal of gases, control of S, removal of inclusions etc. in ladle and tundish. This has led into the development of ladles, tundishes for some refining operations like deoxidation, inclusion modification, desulphurization etc. and other operations like composition adjustment, inclusion removal etc. The basic idea of employing ladles and tundishes for either refining or composition adjustment or for producing clean steels is to use the steelmaking units like converter and electric furnace for producing steels without much bothering for final chemistry. Modern steelmaking comprises of hot metal / scrap to finished products through the following a) Primary steelmaking b) Secondary steelmaking c) Continuous casting d) Finishing operations Primary steelmaking Primary steelmaking consists of refining of hot metal or scrap +hot metal to steel in a) converter and b) Electric furnace. The objective is to refine hot metal to the nearly desired chemistry. a) Types of converter steelmaking • In converter steelmaking pure oxygen is blown from top through a water cooled lance fitted with multi-hole nozzles. This technology of refining of hot metal is called top blown steelmaking. • In another version of converter steelmaking oxygen is blown from top and bath is gas stirred through the bottom. These are called combined top blowing and bottom stirred processes. • In some converters, 𝑂𝑂2 is blown from top and bottom and these processes are called top and bottom blowing, Duplex blowing or hybrid blowing. • In some converters oxygen is blown through the bottom and the process is bottom blown converter. This variant is not popular amongst steelmakers Docsity.com Fig. 2.1 Types of converter steelmaking (a)Top blown steelmaking (b) Combined top and bottom blowing, and (c) Bottom blowing It is important to note that in all different types of converter steelmaking practices, a pear shaped vessel is used and blast furnace hot metal is refined to plain carbon steel. Some amount of scrap is also used. Principle chemical reactions Hot metal contains C ~ 3.5 to 4%, Si ~ 0.6 to 1%, Mn~ 0.6 to 0.8% and P ~ 0.1 to 0.2%. Oxygen is blown from top and the following reactions occur: [Fe] + [O] = (FeO) 1 [C] + [O] = {CO} 2 [Si] + 2[O] = (SiO2) 3 [Mn] + [O] = (MnO) 4 2[P] + 5[O] = (P2O5) 5 [C] + (FeO) = {CO} + [Fe] 6 (Fe) + (MnO) = (FeO) + [Mn] 7 Note the following: • No heat is supplied from outside. The heat produced due to chemical reactions is sufficient enough to raise the temperature of hot metal from around 1250℃ to 1300℃ to molten steel tapping temperature of 1600℃ to1650℃ . • Except carbon which is removed as a gaseous phase rest all other elements form slag. Slag formation of desired chemistry and physico-chemical properties is vital for the successful operation of converter steelmaking technology. Docsity.com