Abstract

Refractories used in the side wall of the RH degasser lower vessel have often been attacked by both oxides of Al and Si in the molten steel which is processed by the operation such as an oxygen blowing and a powder blowing for refining to purified high grade products.  Both magnesia-chrome and magnesia-carbon refractories were investigated for application to the above mentioned lower vessel using a molten steel stirring test system.  After stirring in the molten steel incorporated with both oxides, the damages of the refractories samples were observed and analyzed using the optical microscope and scanning electron microscopy (SEM) with the EPMA system.  For the case of molten steel with Al oxide, although the magnesia as a component reacted with the oxide and formed a reaction layer of about 0.5mm thickness at the working surface in the magnesia-chrome refractories, the chromium oxide retained without reacting the oxide.  The magnesia in the refractories also reacted with Si oxide in the molten steel and formed reaction layer of about 0.01mm thickness at the surface with some penetration of the oxide into the inside of the refractories. However, the chromium oxide kept in the structure without reacting the oxide.  In the case of the magnesia-carbon refractories, relatively dense reaction layers of about 0.01mm thickness were formed at the working surface in the refractories by an activated reaction of both metal oxides with Mg vapor generated in the refractories under the circumstance of the elevated temperature with contacting of the molten steel for both cases including Al and Si oxides, respectively.  As a comparison of the refractories for molten steel including the above mentioned metal oxides, the magnesia-chrome was superior in the erosion with remaining chromium oxide phase stably in the refractories.  The damages of the refractories by the attack of the metal oxides in the molten steel for use of the RH degasser were apparently different by the kind of materials used for the refractories.