PLACAS DE VÁLVULA GAVETA MAGNESIANAS PARA USO EM PANELAS NO LINGOTAMENTO DE AÇOS DE ALTA PUREZA

The production of cleaner steel has been demand for a growing market in Brazil and worldwide; and for such steels with low level of inclusions, refinement with addition of calcium has been widely used. That addition leaves a remainder of calcium in steel which may form phases of low melting point with silica and alumina present in the refractory during the casting. The slide gate plates, typically aluminous, not resist a single heat at certain levels of calcium and conditions of casting steel. The alternative here is the use of non-aluminous materials such as zirconia insert; however, it is a raw material of high cost, which requires a complex manufacturing process. The big challenge for the magnesia or basic material to be used in ladles, was its low thermal shock resistance, with intense crack formation due to high expansion of MgO. In this paper, it is presented the development and improvement of Magnesia Slide Gate Plates, Basic Plates for ladles, including high capacity ladles, their characteristics and properties. Extensive industrial tests were performed in Brazilian Steel Industry with satisfactory results. Magnesia Plates showed the same performance of plates with zirconia insert, and better cost-benefit.