Effects of strength level and loading frequency on very-high-cycle fatigue behavior for a bearing steel

Rotating bending (52.5 Hz) and ultrasonic (20 kHz) fatigue tests were performed on the specimens of a bearing steel, which were quenched and tempered at 150 °C, 300 °C, 450 °C and 600 °C, respectively, to investigate the influence of strength level and loading frequency on the fatigue behavior in very-high-cycle regime. Influences on fatigue resistance of materials, characteristics of S–N curves and transition of crack initiation site were discussed. The specimens with higher strength showed interior fracture mode in very-high-cycle regime and with slight frequency effect, otherwise cracks all initiate from the surface and the fatigue strength was much higher under ultrasonic cycling.

► Fatigue strength increases with the increases of strength level of material.
► Fatigue crack tends to initiate from subsurface as tensile strength increases.
► Loading frequency does not alter crack initiation mode.
► Ultrasonic cycling induces higher fatigue strength for low strength materials.
► Frequency effect is substantially diminishing for high strength materials.