Refractories with melting point higher than 1700℃ in intermediate frequency furnace are roughly classified into six categories according to chemical composition: oxides, carbides, nitrides, sulfides, borides and chemical elements. In medium frequency furnace, chemical elements and carbides work in high temperature and oxidizing atmosphere, and are easily oxidized or dissolved in liquid iron. Silicon carbide can be used to repair the iron groove or feed groove of the furnace, but because of its electrical conductivity can not be used as the lining material of induction furnace. Sulfides, borides, etc. can be dissolved in liquid iron or chemical reaction with liquid iron, reduced by iron and carbon, and should not be used as furnace lining materials. Silicon nitride and aluminum nitride in nitride, although they have the advantages of good oxidation resistance and spalling resistance and are not easy to be eroded by metal liquid, but they are expensive and cannot be used in industry.
At present, the refractory materials used in the intermediate frequency furnace lining are mainly oxides, and there are only more than 50 kinds of oxide materials with a melting point higher than 1700℃, some of which have poor chemical stability, and are often reduced by the components in the metal melt. In addition, some oxides are easily hydrated at low temperatures, so they cannot be used as intermediate frequency furnace lining refractories. The oxide resources of some intermediate frequency furnaces are scarce and expensive, such as Y3O4, HFO2, CeO2, etc., which are rarely used as furnace lining materials. Some oxides are radioactive (ThO2), or toxic (BeO), and should not be used as furnace lining materials. Three oxides are widely used in actual production, namely, silicon oxide, alumina and magnesium oxide and a mixture of these three.
