Fatigue crack initiation and propagation behavior of forging die steels

In this paper, fatigue crack initiation and propagation behavior of forging die steels are reviewed mainly on the basis of the author’s experimental results. First of all, low cycle fatigue strength, fatigue crack propagation behavior and thermal fatigue properties of the representative hot forging die steel SKD62 are summarized with respect to testing temperature, steel hardness, stress concentration factor of the specimen and surface treatments effect. Then, the emphasis is focused upon the recently obtained experimental results on low cycle, high cycle and giga cycle fatigue behavior of cold forging die steels. Fatigue crack initiation and propagation behavior of cold forging die steels is discussed with respect to steel hardness, surface roughness and stress concentration factor of specimen. Characteristics of fatigue fracture surface morphology is summarized and related to fatigue crack initiation and propagation mechanism of hot and cold forging die steels. Finally, recommended studies on fatigue of forging die steels are touched on briefly.