AbstractIn the present work, fatigue test results in the very high cycle fatigue (VHCF) regime are discussed. Experiments were performed with smooth specimens in which crack initiation mostly originated at non-metallic inclusions. Additionally, the influence of small artificial defect, i.e. circumferential notches, drilled holes and corrosion pits, was investigated. Fatigue tests in the VHCF regime were conducted using ultrasonic fatigue testing technique. Further experiments in the high cycle fatigue regime were performed using rotating bending and servo-hydraulic testing machines.For smooth specimens, fatigue fracture was observed even at more than 1010 number of cycles. In contrast, no fatigue failure occurred above approximately 107 cycles in the presence of artificial defects, i.e., a pronounced fatigue limit was determined. Furthermore, it was found that the fatigue limit is not only depending on the defect size but also on the notch root radius of a defect. Consequently, different approaches were used to predict the fatigue limit in the presence of different defects.