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The influence of selected slag properties and process variables on the formation of the slag skin during electroslag remelting (ESR) is currently under investigation at IME, RWTH Aachen University. It is common knowledge that the slag skin affects the heat transfer to the water-cooled copper mould and therefore the solidification structure of the final ingot. Especially for segregation prone alloys, a rapid heat extraction from the melt is desired to minimize the local solidification time and hence the extent of segregation effects in the final ingot. As part of the current investigation, twelve 110 mm electrodes of alloy 718 were remelted in the 400 kW lab scale ESR furnace at IME to investigate the influence of selected process variables on the formation of the slag skin. Beside parameters like the melt rate or the height of the bulk slag, the chemical composition of the utilized slag systems has been varied in particular. Regarding the choice of the slag composition, the focus lay on the methodical variation of properties that - according to literature - are supposed to have an influence on the formation of the slag skin. Therefore, eight different mixtures within the system CaF2-CaO-Al2O3 were blended in such a way, that significant differences in viscosity, the liquidus temperature or the solidification path were existent with only the smallest possible variation of other properties at the same time. To investigate the influence of the afore mentioned parameters on the solidification of the slag and the metal, different characterization techniques were applied. The slag skin was analysed via SEM-EDX for selected trials and its thickness was measured as a function of the process variables. Furthermore, the secondary dendrite arm spacing of the produced ingots was determined under an optical microscope to enable the calculation of the local solidification time. Additionally, the chemical composition and in particular the niobium content of the interdendritic phases were determined via SEM-EDX and compared to the results of the micro-optical analysis. Finally the obtained pool depth and shape were compared to melt rate as well as to the secondary dendrite arm spacing.