Characterisation of the surface damage of X38CrMoV5 (AISI H11) tool steel at room temperature and 600 degrees C

International audienceA novel approach is used to characterise the surface damage of AISI H11 hot work tool steel. The fatigue crack growth rate (FCGR) experiments on thin specimens, considered representative of the surface of tool steels, are carried out. Single edge notched tension specimens of 8mm width and different thicknesses are used in the study. Initially, the effect of thickness (scale) on the FCGR is investigated to establish if there exists a difference between bulk and near surface properties of the tool steel. Then, the effect of R value on the thin specimens is investigated. All the experiments are carried out at room temperature and 600 degrees C. These temperatures represent the limits of use of this steel. Paris curves are established. Effect of R ratio on the threshold value of propagation at elevated temperatures is investigated in detail. A special ascending K experiment for establishing the threshold of propagation at elevated temperatures in small specimens is proposed, and the results are presented. The increase in R ratio increases the FCGR at low temperature, while it has no effect at 600 degrees C. A reduction in thickness shows a reduction in the FCGR. Increase in temperature increases the FCGR and dramatically increases the threshold of crack propagation. The sharp increase in threshold value is studied in detail. Scanning electron microscopy of the specimens is performed to explain some of the characteristics observed in the specimen testing