| The mechanism of slagline wear which is occurred in flux-metal corrosion line and its adjacent regions of a zirconia graphite submerged nozzles has been investigated. The results can be obtained by the following experimental methods such as the observation of a polarizing microscope, EPMA, X-ray diffractometric techniques and theoretical considerations. Since slag wets and dissolves zirconia in preference to graphite and molten metal wets and dissolves graphite in preference to zirconia, the slag and the metal creeps up and down alternatively to produce local corrosion on the nozzle in contact with slag/metal interface. It was found that the main failure mechanism is that the highly fluid mold flux penetrates into the subgrain boundaries and breaks down the grains into the fine subgrains, which are washed away by the slag. The attack is enhanced by the motion of the slag film induced by the Marangoni effect combined with gas evolution. Another mechanism is that once graphite which holds the ZrO₂ grains together at the hot face is oxidized in contact with slag film, zirconia grains are removed into the slag. The decarburization may be possible by the Na₂O contained in the mold powder and the FeO formed at the slag/metal interface. |
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