基地組織の異なる薄肉球状黒鉛鋳鉄の疲労切欠き感受性に及ぼすレアアースの影響

抄録

  Spheroidal graphite cast iron is widely used for various purposes due to its excellent mechanical properties. The majority of the destruction of machinery and structural members is due to fatigue. The starting point of destruction is parts which change their form such as notches. Fatigue tests in previous researches have suggested that spheroidal graphite cast iron with adjusted RE content does not reduce fatigue strength even if the RE content is reduced to 0.3%. However, the effect of RE content on notches is not clear. Therefore, in this study, spheroidal graphite cast iron was produced using a nodularizer with different RE contents and subjected to plain bending fatigue test, and the influence of RE content on notch sensitivity was investigated.

  In FDI and PDI, the fatigue strength differed by 19 to 20% depending on the presence/absence of RE, and this difference in the fatigue strength was small at 8% maximum in the notched specimens. As a result of observation of the fracture surface, FDI and PDI specimens not containing RE showed reduced fatigue strength due to casting defects. Since the crack propagates from the bottom of the notch, it can be inferred that there was no difference in fatigue strength. It was clarified that the notch sensitivity coefficient becomes high in the vicinity of 10⁷ times. From this, PDI shows higher notch sensitivity than FDI with or without RE.