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UBC Theses and Dissertations

Removal of calcium containing inclusions during vacuum arc remelting Samuelsson, Eva


The mechanism of removal of calcium containing inclusions in steel during Vacuum Arc Remelting has been investigated. Laboratory Electron Beam and industrial Vacuum Arc remelting electrodes and ingots were examined. Properties of the steels were determined with the aid of chemical and metallographic methods. It is proposed that the major mechanism of removal is rejection of calcium aluminates to a free surface. One third of the calcium sulphide is rejected with the calcium aluminates. The remainder reacts with aluminium oxide in the aluminates according to the following reaction: CaS + 1/3Al₂O₃= CaO + 2/3[Al] + [S]. Subsequently, the calcium oxide is also rejected and the dissolved sulphur reacts with sulphide forming elements during solidification. The final calcium content of the remelted steels, 5-10 ppm, was independent of the calcium content of the electrode. The results of this study are not in agreement with previous work, which attempts to establish the composition of the calcium aluminates as a function of the steel content of sulphur, aluminium and calcium. Specifically it is found that the influence of oxygen content has not previously been sufficiently taken into account.

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