Abstract
The fatigue properties of martensitic steels tend to differ significantly from those of low- and medium-strength steels. Even if the hardness is the same, the fatigue strength varies substantially depending on the microstructure. Thus, for using martensitic steel rationally and developing materials with high fatigue strength, it is desirable to establish a fatigue strength evaluation method that can consider the microstructural effects on fatigue properties. For this purpose, 18% Ni bcc martensitic steel was used as a model metal to conduct rotating-bending fatigue tests in this study. The fatigue crack behavior on the smooth specimen surface was examined, and the fracture surface morphology on both sides of the broken specimen and the microplastic strain distribution near the fatigue crack tip were analyzed. The results clarified the mechanism underlying fatigue crack extension (FCE). The analytical results revealed three types of FCE mechanisms dependent on the stress amplitude, stress state (i.e., plane stress or plane strain), and martensitic microstructure. Considering these mechanisms, a unique stress–life curve was predicted, and a particular fatigue crack shape and fractography were confirmed. The material indices were speculated to be the representative properties of martensitic steels.
Published Version
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