Vacuum ladle treatment

The toughness of steel was also increased by improved ladle and process metallurgy. Most accompanying elements - sulfur and oxygen - can be removed by vacuum ladle treatment (VOD/AOD) and calcium injection into the liquid melting bath and so the number of non-metallic inclusions, e.g. sulfides and oxides, in the alloy is considerably reduced. Today a sulfur content below 20 ppm and an oxygen content below 30 ppm can be reached. 

Vacuum Processes. More complete control over ladle treatment is achieved by the abiHty to seal a vessel weU enough so that a good vacuum can exist over the steel. Although the expense can be justified for steels with the most difficult property requirements, for many purposes less elaborate treatments are adequate. Many possible configurations exist (21). 

Ladle metallurgy, the treatment of Hquid steel in the ladle, is a field in which several new processes, or new combinations of old processes, continue to be developed (19,20). The objectives often include one or more of the following on a given heat more efficient methods for alloy additions and control of final chemistry improved temperature and composition homogenisation inclusion flotation desulfurization and dephosphorization sulfide and oxide shape control and vacuum degassing, especially for hydrogen and carbon monoxide to make interstitial-free (IF) steels. Electric arcs are normally used to raise the temperature of the Hquid metal (ladle arc furnace). 

Secondary Steelmaking. The treatment of steel in the ladle (e.g. by vacuum degassing) to improve cleaness, composition control and steelplant productivity. See Appendix B.l. 

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