The effect of microstructure, by varying cooling rate, and the independent influence of ferrite grain size, by varying annealing temperature, on intermediate temperature embrittlement of ferritic spheroidal graphite cast irons have been investigated. The intermediate temperature embrittlement of ferritic spheroidal graphite cast irons depends on the triaxial stress field around the graphite nodules and also depends on ferrite grain size. When the carbon content of ferritic spheroidal graphite cast irons is constant, the hydrostatic tensile stress does not change by varying microstructure. Therefore, intergranular fracture will exist when the ratio of the hydrostatic tensile stress to equivalent stress is larger than one (σ m /σ eq 1). It can still be eliminated by decreasing the ferrite grain size.
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