Analysis of rotary bending gigacycle fatigue properties of bearing steel GCr15

Gigacycle fatigue properties of bearing steel GCr15, were investigated under cantilever-type rotary bending fatigue tests in an open environment at room temperature. S-N data obtained from fatigue test showed continuous gradual decline and large dispersion. These data could not be described by a step wise S-N curve. From the results of fractography, fatigue fracture mainly occurred at surface flaws or an inclusion in the region of high stress amplitude level, whereas it mainly occurred at a subsurface inclusion in the region of low stress amplitude level. Fish-eye marks were always observed around the subsurface inclusions on the fracture surface, and for most subsurface inclusions, a granular bright facet (GBF) area was observed in the vicinity around them. The experimental results were analyzed and showed that a larger scatter of inclusion size and clusters of smaller inclusion particles are key factors influencing the scatter of fatigue life. Influence of inclusion size on the dispersion of fatigue life can be quantitatively analyzed by using the estimated GBF growth rate from the S-N data.