The Study On High Temperature Service Performance And Harmlessness Of Al₂O₃-SiC-C Castable For Iron Runner

Al₂O₃-SiC-C castables have been widely used in blast furnace iron runners of iron and steel plants because of their excellent properties.However,with the development trend of large-scale and high-pressure blast furnaces,the temperature,volume and velocity of liquid iron from blast furnaces increase.And at the same time the iron tapping is more frequent than before with a longer single tapping time.Therefore,the damage of hot metal and slag to castable for iron runner become more serious,that is,the service environment of iron runner is worse.And there are higher requirements for the performance of the castable.In industrial applications,in order to ensure the necessary fluidity of the castable and enhance the strength,mirco-silica powder is usually added.But the commonly used mirco-silica powder is not pure enough and contains high contents of impurities.Therefore,there are more liquid phases generated in the service process,which will deteriorate the high temperature performance.In order to further improve the high temperature performance of the castable,the high purity silicon nitride was introduced into the material,and good results were achieved.But the high cost limits the large-scale industrial application.Moreover,in order to ensure the necessary construction performance of the castable,ball pitch is generally used as carbon source.However,asphalt will decompose and produce a large number of carcinogenic gases at high temperature.This not only pollutes the environment and threatens the health of the surrounding people,but also degrades strength and the performance related to carbon content of the material due to this process.In order to solve the above problems,Al₂O₃-SiC-C castable for iron runner was prepared with brown corundum,white corundum,tabular corundum,silicon carbide,silicon,activated alumina,mirco-silica powder,calcium aluminate cement and ball pitch.The formation of low melting phase was controlled by mirco-silica powders,and the formation of favorable phase was promoted by silicon nitride containing powders.Finally,the modified coke was used instead of ball pitch to reduce the environmental pollution of the castable.The following conclusions are drawn:（1）Improving the purity of mirco-silica powder is helpful to enhance the slag resistance of castable for iron runner,while decreasing the particle size of it is helpful to increase the initial fluidity of castables.But the ultra-fine mirco-silica powder will make the fluidity decay rapidly.（2）Compared with the commonly used purity mirco-silica powder,the addition of more high purity mirco-silica powder（3wt%）in the castable will not cause a significant decline in material properties.Within a certain content range（no more than 3wt%）of high purity mirco-silica powder,with the increase of the content,the HMOR and slag resistance of the material increase.（3）The introduction of silicon nitride containing powders can reduce the fluidity of castables,while increase the density and HMOR,and improve the oxidation resistance of the material at the same time.（4）Among the three silicon nitride containing powders used in this work,the improvement of silicon nitride-silicon oxynitride composite powder on the HMOR and slag resistance is remarkable,and is roughly equivalent to that of high purity silicon nitride powder.While ferrosilicon nitride powder can significantly improve the density and oxidation resistance of the castable for iron runner,this powder seriously deteriorate the slag corrosion resistance of the castable and make the HMOR unstable at the same time.When silicon nitride-silicon oxynitride composite powder and ferrosilicon nitride powder are added together,the construction performance is better than that of the castable containing only the composite powder,and the deterioration of the HMOR and slag resistance of ferrosilicon nitride is restrained.The comprehensive performance is even better,which is only slightly worse than that of high-purity silicon nitride powder.（5）Compared with the one only containing ball pitch,the construction performance,oxidation resistance,HMOR and density of the castable containing only modified coke are better.However,its slag resistance,especially its permeability resistance,is worse.When ball pitch and modified coke are used together as composite carbon source,the pollution of the material is reduced by reducing the use of asphalt,and the comprehensive performance is also better.