Calculation of the Fatigue Limit of High-Strength Steel Specimens at Different Loading Conditions Based on Inclusion Sizes

A calculation method for the fatigue limit of components made of high-strength steels that fail at inclusions is described. The method consists of two parts: first, the size of failure-critical inclusions is determined based on metallographic investigations. Then, the fatigue limit is determined based on the expected inclusion sizes using a fracture mechanics model. Influencing factors such as sample size, heat-treatment conditions, and mean stresses are considered. The model parameters are derived from fatigue test data collected over decades within the framework of several research projects. The dominant influencing factors are the inclusion size and the hardness of the steel matrix. Finally, the model is used to predict the fatigue limit of different specimens made of a bearing steel SAE 52 100. The sizes of failure-critical inclusions and fatigue limits calculated with the model are compared and evaluated on the basis of the inclusion sizes found in the samples' fracture surface and the experimentally determined fatigue limits.