球状黒鉛鋳鉄の高温疲労強度に及ぼす繰返しひずみ時効の影響

概要

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Rotating bending fatigue tests of a spheroidal graphite cast iron with a ferrite matrix were performed at temperatures between room temperature and 450℃. The behaviors of both the nucleation and the propagation of small surface cracks were observed. Because of the strengthening effect due to cyclic strain aging, the maximum fatigue limit could be seen at about 350℃. The peaking phenomenon of fatigue limit, however, was not so striking as that seen in carbon steels. The contribution of cyclic strain aging to the increase in fatigue life was not made so much that the peaking phenomenon could not be readily identified, differing from the remarkable peaking phenomenon in carbon steels. It is concluded that the existence of graphites in a ferrite matrix promotes not only the nucleation of small surface cracks but the coalescence of them and cancels the strengthening effect of ferrite matrix due to cyclic strain aging.
1986-08-25