The aim of diploma work was to compare one slag and double slag practice in AOD convertor during the industrial 1.4307 stainless steel production. Focus was to achieve low sulphur content in the molten steel, while monitoring the composition of and the cleanliness of steel. Eight heats were produced using one slag practice and 5 heats using double slag practice. The main chemical elements were compared, active oxygen content of the melt and the temperature after transferring the melt to the ladle furnace were measured, the composition and also the basicity of the AOD and VOD slags were monitored. Steel samples were taken in the form of lollypops after reduction, double slag practice, transfer to ladle furnace, before transfer to casting machine, and the last sample from tundish.
Using scanning electron microscope (FE-SEM) automatic analyses of non-metallic inclusions were performed and results were presented in three ternary systems (CaO-Al2O3-MgO, SiO2-Al2O3-CaO, (Mn,Ca)S).
After the reduction process in AOD convertor the highest number of non-metallic inclusions was analysed, belonging to ternary system SiO2-Al2O3-CaO. After the application of double slag process, we notice decrease of inclusion in the system SiO2-Al2O3-CaO, presence of non-metallic inclusions in CaO-Al2O3-MgO ternary system was increased. In the last sample taken from tundish, we found a higher total number of inclusions in the case of secondary slag process. Most of non-metallic inclusions were classified in the CaO-Al2O3-MgO ternary system. We found a large increase of spinel Al2O3·MgO inclusions. In the one slag process, most non-metallic inclusions in the steel sample were seen in the SiO2-Al2O3-CaO ternary system.
For two representative heats (one from one slag process and one from secondary slag process), we also measured the total oxygen content. For those two heats also point EDS analyses of characteristic inclusions were made and compared.
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