Abstract
The low-cycle fatigue (LCF) properties of a number of different grades of austempered ductile irons (ADIs) were investigated. Four different base-irons were prepared with varying nodularity, nodule count, and alloy elements. Each base-iron was austenitized at 900°C and then austempered at 300 and ∼ 360°C, respectively. Uniaxial LCF tests were conducted under strain-control at several strain amplitudes in tension-compression cyclic loading. No simple rule existed between LCF strength and monotonic tensile strength or toughness for the given ADIs as it depended on the nodule count of spheroidal graphite. The effects of austempering temperatures, nodularity, nodule count, and morphology of retained austenite in the matrix of ADI on the LCF behavior are discussed. Fractography with scanning electron microscopy was used to determine the LCF failure mechanisms and fatigue crack propagation modes.
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