Damage mechanisms in materials for cold forging dies under loading conditions typical for dies

PM-tool steels are the most widely used materials for cold forging dies. The lifetime of such dies is mainly controlled by fatigue damage, which consists of the fatigue crack initiation and fatigue crack growth. A special technique was developed in order to characterise the fatigue crack initiation under stress ratios which are typical in cold forging dies. The fatigue cracks are simultaneously generated by the cracking of carbides, debonding of carbide/metallic matrix interfaces or by crack initiation in the matrix. Fatigue crack growth of these high-strength tool steels is plasticity-controlled and comparable to that of ductile materials.