抄録
Near threshold fatigue crack growth behavior of high strength steels has been investigated by varying the yield strength (921∼1845MPa) and stress ratio (R=0.06, 0.4). Three kinds of Cr-Mo steels were used in this investigation and the fatigue tests were carried out at room temperature and in laboratory air.
The threshold stress intensity factor range, ΔKth, generally decreased with increasing yield strength and/or stress ratio. Then, the influence of stress ratio decreased as the yield strength became high. Several of the materials used, however, showed different tendencies.
These observations were rationalized in terms of the concept of oxide-induced crack closure. Then, it was found that the intergranular fracture occurring at low fatigue crack growth rates remarkably encouraged oxide-induced crack closure in thee case that the area percentage is more than 50%, and it played the important role to the behavior of ΔKth.
