The fatigue properties of inserted steel tubes in a large iron casting was investigated under two types of stress cycles. The fatigue limit of the inserted steel tube was about double of that in high-phosphorus cast iron while decarburization and grain coarsening occurred at the inner surface of the tube. Under the intermittent stress cycles simulating actual stress state of an engine part fatigue limit depends markedly on surface flaws, while it has no significant effect under constant sinusoidal stress cycles. The reason was inferred that the microflaws act as crack origins only under the intermittent stress cycles.
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