With the progress of smelting technology and new requirements for refractory materials, traditional magnesia-carbon bricks have found the following problems in the long-term application and practice process:
①Due to the increase of heat loss due to the high thermal conductivity, the tapping temperature is increased, resulting in an increase in energy consumption, and at the same time, a series of problems such as increased erosion of refractory materials;
②As the lining material of a special refining furnace, such as smelting high-quality clean steel and ultra-low carbon steel in a VOD refining ladle, it will cause carbon increase problems;
③ Consume a lot of precious graphite resources.
In view of the above situation, in recent years, the development of low-carbon magnesia-carbon bricks with low carbon content and excellent performance for refining ladle has received attention from domestic and foreign industries.
The main problems caused by the reduction of carbon content in magnesia-carbon bricks are the decrease in thermal shock stability and resistance to slag penetration. As we all know, after the carbon content in magnesia-carbon bricks decreases, the thermal conductivity of the bricks decreases and the elastic modulus increases, so that the thermal shock resistance of the bricks deteriorates. After the carbon content is reduced, the wettability of slag and molten steel and the material is enhanced, and the permeability of the material to slag and molten steel is deteriorated.
The understanding of solving these problems mainly includes the following three aspects:
①Improve the thermal shock stability of magnesia-carbon bricks by improving the carbon structure of the combined carbon:
The binder of traditional magnesia-carbon bricks is mostly phenolic resin. The carbon structure after carbonization of this binder is in an isotropic glass state, so the magnesia-carbon brick is brittle and has a high elastic modulus, which is not good for the thermal stability of the product. And the high temperature strength of the product is also low. After introducing graphitizable carbon precursor into phenolic resin, this composite binder can be carbonized into secondary carbon with flow-like or mosaic-like structure under the use environment of magnesia-carbon brick, or form carbon nanofibers in situ. The improvement of carbon structure and the reinforcing effect of nano-carbon fiber formation can improve the thermal shock stability and high temperature strength of low carbon magnesia carbon bricks;
②Optimize the matrix structure of magnesia-carbon bricks:
The thermal shock stability and slag penetration resistance of magnesia-carbon bricks mainly depend on the composition and structure of the matrix. When the carbon content is greatly reduced, how to increase the contact frequency between aggregate particles and carbon particles? That is, reducing the size of the carbon particles and ensuring that they are highly dispersed. It is one of the important measures to improve the thermal shock stability and slag penetration resistance of low-carbon magnesia-carbon bricks. Controlling the size, shape and distribution of pores by adjusting the particle size composition of the matrix ingredients will also have a significant impact on the thermal conductivity of the material;
③Using high-efficiency antioxidants:
With the reduction of carbon content in magnesia-carbon bricks, the oxidation protection of carbon is particularly important, so it is also necessary to use suitable high-efficiency antioxidants.