In continuous casting, steel liquid and refractory materials play a very important role. Refractory materials are essential to continuous casting, and the quality of their performance directly affects the quality of continuous cast billets and the normal production of the plant.
The role of refractory materials in continuous casting includes: providing local heat insulation, avoiding direct contact between molten steel and molten steel; forming liquid bridge between molten steel and molten steel, preventing molten steel from being poured and causing overflow; providing necessary lubrication for steel liquid, reducing friction between liquid steel and mold wall; minimizing or avoiding the oxidation of molten steel; mechanically fixing the wall of the mold; and absorbing the heat of solidification of steel liquid.
Steel liquid has a certain surface tension and viscosity. Its viscosity increases with the decrease of temperature and the increase of chemical composition factors, such as aluminum and manganese. Especially when the aluminum content exceeds 0.06%, its slag viscosity rapidly increases and the fluidity of steel becomes worse, which affects the quality and production of continuous casting. In addition, some chemical elements, such as sulfur, phosphorus and other elements, can react with molten steel at high temperature and change its chemical properties, which influence the shape, composition and properties of steel liquid. In continuous casting process, the cooling process of steel liquid, concentration of sulfur and phosphorus, distribution of miscellaneous, heat preservation, free flow characteristics all need to reflect the excellent performance of refractory materials.
The agglomeration and erosion of refractory materials are the main causes of deflection and defections of the continuous cast billets.The strength and stability of the refractory materials play an important role in keeping the surface of the billet smooth and ensuring the normal production of continuous casting.
High temperature erosion, thermal shock, chemical attack and thermal expansion are the main factors that lead to the refractory materials’ damage and accelerated aging phenomenon during the continuous casting process. There are many kinds of refractory materials used in different parts of continuous casting, such as chill wall, riser bottom powder, dry riser lengthwise powder and riser refractory material.Therefore, it is very important to select the refractory materials according to their properties and choose the appropriate materials.
In the continuous casting process, the maximum temperature of steel liquid is close to 1400 - 1500℃, so the refractory materials used should have high thermal strength, high bonding strength and strong erosion resistance. In addition, because of the large volume of steel liquid, the thermal loss due to heat conduction of refractory materials is also great. Therefore, the refractory materials used should have good heat insulation performance, low thermal conductivity and small thermal expansion coefficient.
In addition, some special steel smelting processes have special requirements on the properties of refractory materials. For example, the requirements for flux application refractory materials are different from those for traditional refractory materials. In addition, the volume of molten steel is required to be large and uniform in continuous casting, so some special additives, such as sulfur and phosphorus, must be added to the steel liquid. The refractory materials used must be conducive to the dissolution of these elements, so the refractory materials should also be considered when selecting the refractory materials.
In summary, choosing suitable refractory materials and improving the performance of refractory materials is very important for the normal production of continuous casting. The choice of refractory materials should pay attention to their performance and applicability, and take into account the specific conditions of steel furnace and continuous casting process. It is also necessary to strengthen the maintenance and repair of refractory materials to ensure their normal use and improve the production efficiency.
