抄録
Nonmetallic inclusions are the cause of a marked reduction and a large scatter of fatigue strength of high-strength steels. The sizes and positions of inclusions influence the fatigue strength. Murakami et al.'s equation has successfully shown the correlation betwween the fatigue strength and the size of the inclusion at the fracture origin, and has enabled us to predict the fatigue strength considering the inclusion size. The maximum size of inclusions contained in a specimen or a machine component must be determined in order to predict the reduction of the fatigue strength. The statistics of the extreme values for the determination of the maximum size have been applied to the experimental microscopic inspection data, though those data give essentially two-dimensional information, because the metallographic inspections were conducted only on a section of a specimen. In order to examine the validity of two-dimensional metallographic inspection data of inclusions, the numerical simulations considering the spatial and size distributions of inclusions are carried out. The prediction errors resulting from conventional metallographic inspections are estimated.
