The effect of inclusions on the fatigue behavior of fine-grained high strength 42CrMoVNb steel

The fatigue properties of high strength 42CrMoVNb steel with three fine grain sizes produced by different heat treatment procedures are studied in this paper. The experimental results illustrate that there is no horizontal asymptote in fatigue S–N curves for smooth specimens at 106–107 cycles regime, hence the conventional fatigue limit eliminates. The fatigue crack initiation sites in smooth specimens were related closely to fatigue life, and most of the fracture origins initiated at the inclusions. The diameters and locations of these inclusions were measured, and their morphology was observed in SEM. The critical size of inclusion and the appropriate grain size of prior austenite, which should be controlled in practical production, are obtained by analyzing the experimental data.