Due to the rising demands of the automotive industry for long products with improved properties, e.g. for manufacturing of springs or gears, research activities to achieve fine grained steels with medium carbon content become more and more important. Therefore, the aim of the diploma thesis was to show how microalloying influences the grain size during rolling and the characteristic heat treatment of case-hardened steels and spring steels. The first part of the work gives an overview of the mechanism of Nb and V in medium carbon steels and their influence on the properties of case-hardened and spring steels. In the second part, on the basis of industry melts from the steels 50CrV4 and 16MnCrB5 laboratory-melts with Nb-microalloying were produced and compared with laboratory-melts free of microalloying elements. Beside the simulation of the rolling processes, which were carried out with a quenching and deformation dilatometer, investigations with respect to the precipitation behaviour and grain coarsening were conducted. In order to investigate the influence of the microalloying on the hardenability and the mechanic properties jominy-tests on both steels, and tensile tests on different heat treated 50CrV4-samples were performed. The investigations revealed that by means of microalloying a higher strength combined with the same tougness can be achieved.