L. Bartosiewicz et al., INFLUENCE OF MICROSTRUCTURE ON HIGH-CYCLE FATIGUE BEHAVIOR OF AUSTEMPERED DUCTILE CAST-IRON, Materials characterization, 30(4), 1993, pp. 221-234
An investigation was carried out to examine the influence of austemper
ing heat treatments and the resultant microstructure of austempered du
ctile cast iron, on the fatigue crack growth rate, fatigue threshold,
and high-cycle fatigue strength of the material. Two different approac
hes were used to study the fatigue behavior of this relatively new mat
erial, that is, a traditional S-N curve approach for determination of
fatigue strength and a fracture mechanics-based approach for determina
tion of the fatigue threshold. Compact tension and cylindrical specime
ns prepared from alloyed nodular ductile cast iron were given three di
fferent austempering heat treatments to produce three different micros
tructures. The fatigue threshold and high-cycle fatigue behavior of th
ese specimens were studied in room temperature ambient atmosphere. The
results of the present investigation demonstrate that the fatigue thr
eshold of the material increases with increase in volume fraction of c
arbon-saturated austenite. The fatigue strength of the material, on th
e other hand, was found to increase with decrease in austenitic grain
size. The crack growth process in the material was a combination of du
ctile striations and microvoid coalescence, and crack propagation by c
onnecting the graphite nodules along its path.