Fracture behaviors at inclusions of very-high-cycle fatigue in newly developed clean bearing steel

Bearing steel is essential for the driving parts of the rotating body, but fisheye crack of inclusions such as TiN, Al2O3 and Cr matrix is formed in the very-high-cycle fatigue (VHCF) regime. Therefore, research on the development of a clean bearing steel that reduces the size of inclusion such as TiN or that does not contain inclusion has been made recently. In this study, the results of long-term attempts by the maker to improve the performance and quality of bearing steel for very long life were quantitatively analyzed from the viewpoint of fracture mechanics. In other words, the phase transformation properties, VHCF characteristics with ultrasonic nanocrystal surface modification (UNSM) treatment and fracture mechanics analysis of this clean bearing are compared quantitatively with those of other common bearing steels from the viewpoint of engineering and industrial applications. The quenching and tempering (QT) specimens of the clean bearing showed fisheye cracks and duplex [Formula: see text]–[Formula: see text] curves in the VHCF regime. The fisheye crack of the clean bearing steel was an internal fatigue crack caused by a small inclusion mainly composed of Al2O3 in the VHCF region. However, fisheye cracking due to TiN and Cr matrix, which was observed in other common bearing steels, did not occur in the clean bearing steel due to the efforts of the developers of new clean bearing.