Abstract
Giga-cycle fatigue properties were investigated for spheroidal graphite cast iron of FCD400 with high ductility. Fatigue tests were carried out using ultrasonic fatigue testing at 20 kHz and conventional servo-hydraulic fatigue testing at 30 Hz used specimen with 3mm diameter under stress ratio of R=-1. The effect of frequency and giga-cycle fatigue properties were discussed including a result of FCD800 of the previous report The results of the ultrasonic fatigue testing showed negligible difference from those of the conventional fatigue testing. Accordingly, ultrasonic fatigue testing could be applicable to spheroidal graphite cast iron. Decrease of fatigue strength in the giga-cycle region was in range from 10 to 20%. Namely, fatigue limit was not confirmed even up to 10^<10> cycles. The fatigue strength of FCD800 was lower than that of hot-rolled steels on the fatigue strength versus tensile strength diagram, while that of FCD400 was almost equal to it. This was likely to be caused by difference of the microshrinkage size and the microstructure between FCD400 and FCD800.
