Gigacycle fatigue behavior of a high chromium alloyed cold work tool steel

The influence of carbides and the effect of surface residual stresses (RS), resulting from heat treatment or from the grinding/polishing process, on the fatigue behavior in the gigacycle regime of ingot metallurgy produced D2 type tool steel was examined. RS were found to be responsible for the occurrence of two failure modes: Internal cracks initiating at large primary carbides (clusters) were observed in the cycle number range of 105–106, while in the gigacycle regime near-surface cracks originating at primary carbides caused failure, which was related to degradation of the RS by cyclic loading. Simple models were employed estimating the RS degradation process and the local fatigue strength along the specimen cross section as a function of active RS. In absence of considerable RS predominantly near-surface crack initiation was obtained.