Aim of the present thesis was the development, characterisation and optimisation of alternative tool steels for hot-work applications providing multiphase precipitation of secondary hardening carbides and any types of intermetallic precipitates. These alloys are aimed to combine the beneficial effects of conventional secondary hardening steels and maraging steels. Main objective was a comprehensive material characterisation, and the acquisition of scientific knowledge on interactions between multiphase precipitation reactions and their impact on material properties. The combination of high-resolution microstructural analysing methods such as APFIM and SANS provided a powerful tool for characterising these complex multi-component and multiphase materials. Correlations between microstructural data on nanometer scale and mechanical respectively thermo-physical material properties provided valuable information for further alloy optimisation.