Fatigue Fracture Behavior of High-Strength Steel in Super Long Life Range

抄録

Long term cantilever-type rotational bending fatigue tests of up to 10⁹ cycles were carried out on high carbon chromium bearing steel, SUJ2. The fatigue fracture behavior of SUJ2 in the super long life range was discussed based on scanning electron microscope observations and fracture mechanics. Fatigue failure occurred when the number of cycles exceeded 10⁷. In the super long life range, the fish-eye-type fracture and the subsurface-type fracture were observed. In the fish-eye-type fracture, the stress intensity factor calculated from the area of the facet region was independent of the number of cycles to failure and was almost constant at 5.4MPa• m^1/2. In the subsurface-type fracture, high carbon segregation was observed at the crack initiation area. The stress intensity factor for the carbon segregation area was close to 5.0MPam^1/2. Pure fatigue crack was initiated from the area outside the facet region or the high carbon segregation area.