Ferronickel presents a necessary alloying additive for the production of stainless steel. At the industrial manufacturing of this ferroalloy, an oxidic ore, called Laterite, is melted under reducing conditions. Because of the large slag amount, the acid character and the high melting point the refractory material in the furnace is highly stressed. In this thesis experiments with the heating microscope serve for the analyses of the melting behaviour of ferronickel slags on a refractory material. Therefore ten different synthetic slags consisting of the main oxides SiO2, MgO and Fe2O3 were melted in a graphite crucible and afterwards analysed with the heating microscope. The experimental design was created by a statistic software, which includes 20 experiments with different slag compositions and different atmospheres. The evaluation of the experimental results occurred at three different characteristic temperatures of the samples. Additionally the zone, influenced by the slag, was detected and evaluated.