LAUSR

Abstract The isothermal softening behaviour of the hot work tool steel Bohler W400 VMR (AISI H11) was investigated as a function of both temperature and time. Two mechanism-based tempering kinetic models were used to describe thermal softening and the suitability of each model was evaluated. Scanning electron microscopy analysis was carried out to represent the evolution of the microstructure during the isothermal softening resistance tests. A new model for hardness change prediction during anisothermal loading of steels was proposed and validated. The analysed material showed thermal softening behaviour, which appeared as time and temperature dependent loss of hardness. Differences in suitability of each tempering kinetic model used for the description of thermal softening were observed. Microstructure evolution during the isothermal softening resistance tests of the analysed material confirms that secondary carbides coarsening is the main cause for thermal softening. A good agreement between experimental and prediction results was obtained with use of the new proposed model for hardness change predictions during anisothermal loading.