Abstract
The combined effects of hardness and non-metallic inclusions on fatigue strength of high strength steels were investigated and the reasons for the relatively low fatigue strength of high static strength steel and the large scatter of fatigue strength values were examined. From the viewpoint of fracture mechanics non-metallic inclusions are equivalent to small defects or cracks. Inclusion parameters, such as size, shape and location, influence fatigue strength and these become the cause of the large scatter of fatigue limit values. However, it is possible to predict the upper and the lower limits of fatigue strength from the Vickers hardness of a matrix and the maximum size of inclusions defined by the square root of the projected area of an inclusion. The expected value of inclusion size in a definite numbers of specimens or machine components can be estimated using the statistics of extreme values. Several examples of the measurements of distribution of inclusion size are presented. The agreements of the predicted values with the experimental results are shown for quenched and tempered SAE 10L45, 0.35% C steels and 0.55% C steels.
Published Version
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