Fundamental Research On The Formation Mechanism And Removal Effect Of Alumina Inclusions

Al2O3 inclusions is common deoxidation products in aluminum-killed steel. It is small, hard and brittle inclusions in steel and also difficult to melt. These inclusions have great harm to the quality and fatigue life of steel products, especially for the high-quality steel like tire cord steel and bearing steel. Besides, they can easily deposit inside the submerged nozzle and causes nozzles clogging during the continuous casting process, that will interrupt the casting process and even impact on the production line. Therefore, it has a very important significance to modify and remove the Al2O3 inclusions from molten steel, that will ensure the smooth running of steel production and also improve the quality of steel.At present, the main way to modify alumina inclusions is to feed Ca wire or Ca-Si wire during the refining process, called Ca treatment. However, the yield of calcium during Ca treatment is relatively low, that increase the cost of steel-making,and the modification effect of Al2O3 inclusion is not ideal. On the basis of the these research, this paper study and design the modification agent instead of calcium treatment to modify inclusions in molten steel, and carry out experiments to study the effect of using different types and composition of modification agent to modify and remove Al2O3 inclusion.Combined with literature research, we design and develop Ca O-Al2O3 premelted slag as the modification agent of inclusions instead of Ca wire. The experimental result shows that Ca O-Al2O3 premelted slag has a strong capacity to adsorb Al2O3 inclusions in the liquid steel, and this modification agent has good modification effect on alumina inclusion. When the component of Ca O-Al2O3 premelted slag is Ca O:50%- 60%, Al2O3:40%- 50%, the modification agent of inclusions has good melting performance and strong ability to absorb Al2O3 inclusions, The effect of removing the alumina inclusion is more than 70%, in the meantime the slag has a certain desulfurization capacity.Based on Ca O-Al2O3 premelted agent, we develop Ca O-Al2O3-Ba CO3 ternary modification agent of inclusions. The result of experimental suggests, the Al2O3 in theternary treatment agent plays as the role of a flux to reduce the melting point and accelerates melting. When the content of Al2O3 is about 45%, control the Ba CO3 content in 10%-20%, the modification agent of inclusions has good melting performance and the modification effect of alumina inclusion and sulfide inclusion is the best. After modification treatment, the typical inclusions in aluminum killed steel change into calcium aluminate inclusions, the most shape of inclusions are spherical,and the size become larger, so the inclusions become easier to float and removal.The modification agent of inclusions selected in the experiment research have a good effect on the modification of Al2O3 inclusions in steel. It has great significance to improve the quality of steel, promote the smooth running of continuous casting and reduce the production cost by using different modified agent to replace or partly replace the calcium treatment in the industrial production.