During the continuous casting of low-carbon steels, the free carbon contained in the casting powder repeatedly leads to carburization of the steel, which is associated with a change in the product properties. To prevent this, it is necessary to control the melting behavior of the casting powder by substituting the free carbon with a proper raw material. In the first part of the work, different amounts of free carbon in the form of graphite were added to a casting powder that is used for casting ultra-low carbon (ULC) steels to investigate its effect on controlling the melting in dependence on the carbon amount. A high-temperature treatment was carried out in a preheated furnace between 700 and 1300°C. The subsequent mineralogical investigation of the annealed samples was conducted by way of X-ray diffraction, reflected light microscopy and scanning electron microscopy including energy dispersive X-ray spectroscopy. In the second part of the work, a model powder was prepared based on the chemical composition of the ULC casting powder. For this sample the carbon was completely replaced by silicon carbide (SiC). The aim was to determine whether similar melting behavior as the carbon containing mould powder can be achieved by adding SiC. The model powder was annealed under the same conditions as the samples of the first part of the work and was examined mineralogically. Subsequently, the melting behaviors of the annealed casting powder samples were compared based on their mineralogical composition as a function of temperature. From the investigations carried out, it was found that annealing the samples in a preheated furnace followed by mineralogical characterization is a suitable method for investigating the melting behavior of a casting powder as a function of the carbon content. It was found that the reactions between the raw material components could be reduced by increasing the carbon content, which significantly decelerates the melting behavior of the casting powder. The comparison of the casting powder samples after carbon addition or the replacement of carbon by SiC showed that SiC exhibits similar behavior to carbon. Solid diffusion and thus the formation of new phases (e.g. cuspidine) are suppressed similarly in the presence of free carbon. This is especially true at temperatures below 1000°C, where the effect is even more pronounced. It follows that free carbon in the casting powder can be replaced by SiC to control the melting behavior of the casting powder.