To make a quantitative analysis of the defect size for high strength steels, fatigue properties and fatigue fracture mechanism were examined for 3 different low alloy steels tempered at several temperatures. Fatigue strength was evaluated up to about 108 cycles under rotating bending at room temperature in dry air. Two types of S-N curves were found, the one has fatigue limit for medium strength steels fractured from the specimen surface, the other for higher strength steels has temporal fatigue limit because of the interior fracture in the long life region over about Nf=107. Fatigue strength would be predicted by the liner relation between the threshold stress intensity factor and the hardness of the materials. It is suggested that the defect size to originate the fatigue crack would have important role for high strength steels up to about HV600.
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Masuda et al. (1986) studied this question.