It has been indicated that subsurface fracture occurred at stress levels below the conventional fatigue limit in long life region more than 10
cycles, particularly in high strength steels (Dahlberg [
]). A notable feature of subsurface fracture is the presence of a fish-eye with an inclusion near its centre, and the formation mechanism of fish-eye has not been fully understood. High strength steels usually possess very high sensitivity to notch and surface defect. Therefore, it is very important to understand the effects of notch and surface roughness on crack initiation and associated
characteristics. In the present study, rotary bending fatigue tests have been conducted in laboratory air at ambient temperature using notched specimens with different stress concentration factors and specimens with roughened surfaces in high strength steel. The effects of notch and surface roughness on step-wise
characteristics, particularly on the transition stress, were discussed.