On the overaging behaviour of tool steel X38 CrMoV 5-3

In this study, a combination of small-angle neutron scattering, energy-filtered and conventional transmission electron microscopy and X-ray diffraction has been used to characterize the overaging behaviour of the hot-work tool steel X38 CrMoV 5-3. Hot-work tool steels are mainly used for hot-forging dies, casting dies and extruding tools where high strength is required at high service temperatures. As a consequence, thermal fatigue and softening play the most important role with regard to tool life, and they are strongly influenced by coarsening of the nanometer-sized secondary hardening carbides. The microstructural response to three different overaging treatments in the temperature range of 650-680 °C has been analyzed regarding precipitate types, particle size distributions and corresponding volume fractions. The combination of the different methods used in this study enables a very precise determination of these parameters. This allows for a profound discussion on the evolution of particles occurring in the analyzed samples.