With the newly developed die life test that simulate actual conditions in cold forging, the effect of the carbide distribution in tool materials is evaluated. Under the short-lived condition of 1x104 cycles or less, the relationship between the maximum carbide size projected to the normal plane to the maximum principal stress in the dangerous volume and fatigue life is revealed. As in high-cycle fatigue, crack initiation from one or a cluster of large carbides, especially multisite cracks, shortens fatigue life. The fracture surface morphology shows no feature of low-cycle plastic fatigue, but shows that of high-cycle fatigue in high-strength steel. The effects of maximum carbide size on fatigue life and fracture surface morphology show the possibility of handling the fracture under the conditions of a high-cycle fatigue fracture. The developed tool life test together with simulation is a potential method of evaluating life of tool materials.
