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Processes - Ferrous (Iron / Steel): Degassing / Refining

Ladle Refining
A number of processes are often used to refine the molten steel in a ladle after it leaves the BOF or EAF prior to casting (see the diagram on the right). Ladle refining processes include Argon Oxygen Decarburization (AOD), ladle metallurgy, vacuum arc re-melting, and vacuum degassing. Processes selected are based on the desired metallurgy and purity. In ladle metallurgy, alloys are added to the molten steel, which is then reheated to produce the desired metallurgy. In vacuum degassing, molten steel is subjected to a vacuum for de-oxidation, degassing (hydrogen removal), de-carburization, and removal of other impurities from the steel.

Ladle refining is generally performed by electric arc re-heating. The molten metal bath is stirred throughout the process to provide for thermal and chemical homogenization and to accelerate metallurgical reactions. Stirring is provided by inert gas introduced near the bottom of the ladle using porous plugs, tuyeres, or lances. Gas injected from above using water-cooled, refractory-coated metal lances is considered safer than porous plugs or tuyeres; but maintenance is high and heat efficiency reduced.

Because of the high temperatures, erosion from the stirred bath, and high corrosiveness of the metallurgical slag, high-alumina and magnesia-based (slag line) castable refractories are preferred for ladle linings. Still, life remains short (30 to 50 heats). Ladles are continuously repaired or re-lined. After re-lining, drying is performed. Also ladle heating (usually natural gas or oxy-fuel burner) is used to pre-heat ladles prior to filling with molten metal.