The influence of austenitizing and tempering temperature on the hardness and fracture toughness of hot-worked H11 tool steel

Linear elastic fracture mechanics was used to optimise the vacuum-heat treatment procedures for conventional hot-work AISI H11 tool steel. The fracture toughness was determined with non-standard, circumferentially notched and fatigue-precracked tensile-test specimens. The fracture-testing method is sensitive to changes caused by variations in the microstructure resulting from the austenitizing and tempering temperatures as well as the homogeneity of the material itself. The combined tempering diagram – Rockwell-C hardness–fracture toughness KIc–tempering temperature – was used for the choice of the vacuum-heat treatment parameters necessary to obtain the best properties for a given application with respect to the investigated steel.