| Modification in morpbology of the oxide and sulfide inclusions effected by calcium treatment of the Al-killed steel has been studied. Samples were taken from a 40 ton VAD vessel and examined under an optical microscope and the electron optics. Activities of oxygen measured by oxygen sensors and aluminum contents were utilized in thermodynamic calculations, which lead, in association with plant data, to the following In steels containing more than 0.01% Al, calcium is not so effective deoxidizer as an inclusion modifier. To maximize desulfurization and the conversion of alumina into calcium aluminates, sulfur and aluminum should be below certain threshold levels. It may be added that the total calcium retention is not a good measure of the effectiveness of inclusion modification. |
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