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Ladle Metallurgy

• satyendra
• April 23, 2014
• 2 Comments
• AOD, CAAS-OB, Ladle metallurgy, refining

Ladle Metallurgy

After tapping of steel from a primary steelmaking furnace such as BOF, EAF or EOF, molten steel for high quality or specialty applications is subjected to further refining in a number of alternative processes collectively known as ladle metallurgy. Ladle metallurgy is sometimes also called ladle refining or secondary steelmaking. Ladle metallurgy processes are commonly performed in ladles. Tight control of ladle metallurgy is associated with producing high grades of steel in which the tolerances in chemistry and consistency are narrow. The objectives of ladle metallurgy are the following.

• Homogenization – Homogenization of chemical composition and temperature of liquid steel in the ladle
• Deoxidization or killing – Removal of oxygen
• Superheat adjustment – Heating of the liquid steel to a temperature suitable for continuous casting
• Ferro alloys and carbon additions – Making adjustments in the chemistry of liquid steel.
• Vacuum degassing – Removal of hydrogen and nitrogen
• Decarburization – Removal of carbon for meeting the requirement of certain grades of steel.
• Desulfurization – Reduction of sulfur concentrations as low as 0.002%
• Micro cleanliness – Removal of undesirable nonmetallic elements
• Inclusion morphology – Changing the composition of remaining impurities to improve the microstructure of the steel
• Mechanical properties – Improvement in toughness, ductility, and transverse properties

Argon oxygen decarburization process

Argon oxygen decarburization (AOD) is a process primarily used in stainless steel making and other high grade alloys with oxidizable elements such as chromium and aluminum. After initial melting, the metal is then transferred to an AOD vessel where it will be subjected to three steps of refining namely (i) decarburization, (ii) reduction, and (iii) desulphurization. AOD was invented in 1954 by the Lindé division of The Union Carbide Corporation, which became known as Praxair in 1992.

The liquid steel is decarburized and refined in the AOD vessel to less than 0.05% carbon. The key feature in the AOD vessel is that oxygen for decarburization is mixed with argon or nitrogen inert gases and injected through submerged tuyeres. This argon dilution minimizes unwanted oxidation of precious elements contained in specialty steels, such as chromium.

AOD is widely used for the production of stainless steels and specialty alloys such as silicon steels, tool steels, nickel-base alloys and cobalt-base alloys. The process is popular because it combines higher metallic yields with lower material costs. Other benefits include accuracy in chemistry control down to 0.01 % carbon and lower, rapid desulfurization to less than 0.001 %, and lead removal to less than 0.001 %. The end result is cleaner steel coupled with increased productivity.