Thermodynamic features of the modifi cation of non-metallic inclusions by calcium in low-carbon steels deoxidized by aluminum

Low-carbon steels deoxidized by aluminum are the main group of structural steels produced in Russiaand all over the world. These steels work in key sectors of the economy – construction, automotive, mining and transportation of minerals, etc. The deoxidation of steel melt by aluminum leads to the formation of non-metallic inclusions, which can significantly affect quality of rolled products and reduce the manufacturability of production due to overgrowth of submerged

nozzles during continuous casting. So, ceteris paribus, only due to contamination of steel with non-metallic inclusions, the following differences in technical and economic indicators can be observed: sorting by surface defects, reduced yield of cast slabs, increased corrosion wear rate, sorting by ultrasonic inspection defects, etc. Due to the particular shape, size and state of aggregation, non-metallic inclusions based on aluminum deoxidation products are difficult to remove from the steel melt. An effective way to reduce steel pollution by similar inclusions is modifying their composition to a liquid state of aggregation with calcium, which requires careful preparation of the molten slag and metal. The article describes in detail the main thermodynamic features of this process. On the example of IF-steel, we present calculation of the target range of calcium content to ensure the inclusion modification to a liquid state depending on aluminum concentration in the steel melt. The limiting sulfur concentrations in the metal melt are determined depending on aluminum and calcium contents, which ensure prevention of the formation of refractory sulfide shells on oxide non-metallic inclusions.

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