What are the causes of damage to refractory materials used in secondary refining?

Thread Content

There are currently many methods of off-ferment refining, with various devices and different refractory materials being used. However, in general, the main reasons for their damage can be summarized as follows: (1) Melting loss and chemical reactions. During the refining process, the slag comes into prolonged contact with the surface of the bricks; CaO, SiO2, and other substances with low melting points present in the slag react with MgO, Al2O3, and similar compounds in the bricks, resulting in the formation of low-melting-point silicate compounds such as orthoclase. This causes the bricks to gradually erode and get dispersed within these silicate compounds. 　 (2) Volatilization and reduction under high temperature and vacuum Magnesium-chromium bricks, which are relatively stable in air, become prone to the volatilization of their main oxides, MgO and Cr2O3, once placed under high temperature and vacuum conditions; the amount of volatilization depends on temperature and time. After volatilization, the chemical and mineral composition of the refractory material changes, and its high-temperature properties, such as slag resistance and high-temperature mechanical strength, decrease. 　 The oxides in refractory materials are easily reduced by carbon in molten steel under vacuum. This reaction accelerates the erosion of refractory materials. 　 (3) Effect of slag basicity on erosion Refractory materials based on MgO-CaO systems are severely eroded in low-basicity, i.e., acidic slags, due to the formation of the low-melting-point compound 3CaO·MgO·2SiO2. In alkaline slag, it exhibits better erosion resistance, mainly due to the formation of the high-melting-point 2CaO·SiO2. 　 MgO-Cr2O3 series refractory materials exhibit good resistance to slag erosion in acidic slags, due to the formation of the high-melting-point 2MgO·SiO2. In alkaline slag, its erosion resistance decreases due to the formation of 3CaO·MgO·2SiO2 and the decomposition of spinel to form 12CaO·7Al2O3 and CaO·Al2O3. 　 (4)) Thermal shock and mechanical erosion: When in use, the lining of off-furnace refining units is often exposed to high temperatures of around 1700°C; after the processing is complete, the temperature drops. By the time of the next processing cycle, it is again under high-temperature conditions; this process repeats itself, and the refractory materials get damaged due to expansion and contraction. 　 During vacuum treatment, the reduction in pressure causes the molten steel to erupt and boil, resulting in mechanical erosion of the brick structure and its damage.