オーステンパ球状黒鉛鋳鉄の疲れ特性に及ぼす黒鉛粒径の影響

抄録

  The fatigue strength of ADI is studied in order to clarify the roles of the graphite nodule size from standpoint of the matrix structure. The microstructures of its iron are changed by both of the nodule count and heat treatment of austempering. The fatigue limit of unnotched specimen is improved remarkably with decreasing the graphite nodule size by decreasing the amount of unreacted austenite, i. e. γ pool. It is recognized that the unreacted austenite has a remarkable effect to promote the initiation of fatigue crack, because it is easily transformed to martensite with micro-cracks during fatigue test. But the fatigue crack growth rate for the ADI with small graphite nodules is higher than for ADI with larger nodules. In this case, the unreacted austenite has an effect to repress the crack growth by transformation to martensite at the ahead of crack.