Induction furnaces present one of the most challenging environments for the application of refractory materials. The successful assembly of large-scale induction steelmaking units urgently requires improvements in the performance of refractory materials, which in turn promotes the continuous enhancement of refractory materials for induction steelmaking.

The selection of refractory materials for induction furnaces depends on factors such as furnace type, furnace structure, types of steel to be melted, smelting processes, and operating conditions. It is also essential to consider the phase changes and physical properties of refractory materials from room temperature to operating temperature, as well as application conditions.

1. When melting cast iron and non-ferrous metals in coreless induction furnaces, refractory materials composed of SiO2, ZrO2•SiO2, and their composite phases are generally selected. The uniform distribution of ZrO2 and SiO2 in the material provides high-temperature plasticity and corrosion resistance, indicating that ZrO2 can extend the service life of SiO2-based refractory materials.

2. Both acidic and basic steelmaking methods can be employed in coreless induction furnaces. Acidic steelmaking uses acidic refractory materials similar to those used for melting cast iron, while basic steelmaking utilizes neutral or alkaline refractory materials.

3. Magnesia-based refractory materials are commonly used for lining in small coreless induction furnaces for steelmaking. However, these materials exhibit poor thermal shock resistance and are susceptible to penetration by molten slag, leading to structural spalling and premature failure, making them unsuitable for environments with large capacities and intermittent operations.

4. Medium-sized coreless induction furnaces operating under normal conditions use refractory materials made from MgO-Al2O3 or MgO-Spinel mixtures, both of which belong to MgO-spinel refractory materials.

5. Medium-sized coreless induction furnaces, which utilize various scrap steels as raw materials, use Al2O3-MgO (approximately 10% MgO) refractory materials to achieve extended service life.

6. Medium-sized induction furnaces using direct reduced iron balls as additives should use MgO-Al2O3-Cr2O3 (with added chromite) refractory materials. The formation of composite spinel at high temperatures enhances refractory performance and corrosion resistance, improving adaptability to high-iron/manganese slag erosion and extending service life.

7. Large coreless induction furnaces use spinel refractory materials made from pre-synthesized spinel aggregates or mixtures composed of coarse and fine particles of MgO, spinel, and Al2O3 microparticles carefully balanced to achieve suitable operation conditions.

8. Core induction furnaces, used for melting gray iron and cast iron, operate at temperatures ranging from 1450 to 1550°C, which are not excessively high. Although temperatures at the induction coil and water-cooled areas can reach 1600 to 1700°C, refractory material selection is not overly challenging due to implemented water cooling.

9. Coreless induction furnaces primarily use ramming method for lining, while core induction furnaces mainly use casting method. Rammed lining refractory materials form a sintered layer during firing. To achieve high adaptability, the extension of the sintered layer and the increase in strength should proceed slowly. Therefore, the formulation design and raw material selection of refractory materials should ensure that the working surface in contact with the high-temperature melt forms a sintered layer with certain strength, while the non-working layer maintains a dispersed structure before sintering. This structure helps prevent the migration of cracks in the working layer and absorbs crack propagation, laying a solid foundation for extending the service life of the lining.