Influence of the Cooling Rate on the Mechanical Properties of a Hot-work Tool SteelEinfluss der Abkühlgeschwindigkeit auf die mechanischen Eigenschaften eines Warmarbeitsstahls

Hot-work tool steels have to possess excellent mechanical and thermophysical properties in order to fulfil the requirements for their application fields which are mainly light-alloy processing and die-casting moulds. The aim of the present study was to gain a deeper understanding of the relationship between mechanical properties and various microstructures obtained by different cooling rates. All investigations were performed on the steel grade X38CrMoV5–1 (DIN 1.2343) from the same charge, thus keeping the chemical composition constant. Detailed mechanical tests were applied to obtain strength data, deformation behaviour, impact toughness, and plane strain fracture toughness of the heat-treated material. Furthermore, scanning electron microscopic examinations were used to study the microstructural features relevant for the material properties. The results provide information on the effect of bainite in an otherwise martensitic microstructure which leads to degradation in toughness and strength even if the volume fraction of the bainitic phase is low. From the results it is obvious that a complete martensitic microstructure is most suitable for the performance of hot-work tool steels.