The increasing strength and quality requirements for hot-rolled flat products result in a continuous improvement of work rolls for hot rolling mills. Rolls with wear resistant surfaces made of high speed steels and produced by spin casting can be applied. The aim of this thesis was to evaluate various possibilities to influence the solidification structure of these high-alloyed materials. Similar to conventional HSS-materials, they contain considerable amounts of C, Cr, W, Mo and V and have a bainitic or martensitic matrix with hard carbides (MC- and M2C-carbides). The theoretical part of the thesis discusses the solidification process of steel, gives an overview of high speed steels for rolls and shows various possibilities for metallurgical treatments of the melt e.g. based on the inoculation effect of heterogeneous nuclei. In the experimental part trials were performed to examine the effect of the cooling rate, nitrogen content and the treatment of the alloy with various elements such as cerium, zirconium and bismuth. The investigation of these melts was carried out by light- and scanning electron microscopy. Based on these images an analysis of the carbide shape and amounts, inclusion types and quantities, macro- and microstructure, the secondary dendrite arm spaces and chemical compositions was conducted. A reduction of the primary grain size visible in the macrostructure and a faster transition from directed to undirected solidification could be observed in all treated melts. A modification of the microstructure and the carbide shape respectively the carbide size occurs only in Zr and Bi treated alloys. Increasing cooling rates lead to a significant size reduction of the secondary dendrite arm spacings and the carbides. The variation of the nitrogen content showed more M2C carbides with increasing N content and an increase of porosities. Such porosities are often found close to M2C-carbides.