Component specific influences on the fracture behaviour of high speed steels under static loading

This paper presents the first results of a series of investigations into the fracture behaviour of high speed steels with regard to component specific influences. The aim of the investigations was the analysis of the interaction of internal and external notches during the fracture process. Hardened and tempered high speed steel S 6‐5‐2 of various degrees of hot forming, which was produced by electroslag remelting, as well as powder‐metallurgically produced high speed steel ASP 23 were tested to investigate the influence of different carbide sizes and distribution. In‐situ bend tests showed the role of the carbides as fracture initiating defects, which form subcritical cracks as a result of the higher stiffness and lower failure stress at loads smaller than the global failure load of the specimen. The observed fracture process was simulated by FEM using the observations and results of the in‐situ bend tests. The interaction of internal flaws and external notches was proven using notched and coated specimens as well as specimens of various surface roughness. The fracture initiating defect is the largest defect in the loaded volume regardless of whether it is an internal flaw (carbide) or an external notch (surface roughness, surface layer). Information can be derived from the investigations allowing the optimisation of the manufacture of high speed steel tools with regard to their fracture behaviour.