Fatigue strength characteristics evaluation of SUH660 considering small fatigue crack propagation behavior and hardness distribution

The fundamental characteristics of SUH660, which a precipitation-strengthened stainless steel, were investigated by tensile, fatigue, and Vickers hardness tests. Owing to the observed crack propagation mechanisms, the S–N diagram had two “fatigue limits”: the fatigue strength at 107 cycles and the safe side of the fatigue limit based on the threshold of PSB crack propagation. There was significant variability between the Vickers hardness distributions of the test zones, which indicated the existence of high and low hardness zones in a single specimen. It was observed that more cracks were initiated and propagated in the low hardness zone than in the high hardness zone. Therefore, the fatigue strength of SUH660 steel is low compared to its high tensile strength.