Fatigue behavior and mechanism of KMN in a very high cycle regime

Abstract The fatigue behavior of KMN with different heat treatments (marked as S and I) used in compressor blades was investigated in a very high cycle fatigue regime. It was found that the S-N curve of KMN-I had a slow decline after 10 6 cycles, while the fatigue limit was observed in KMN-S. In order to explain the difference between the two steels, mechanical property tests, metallographic observation, and SEM analysis were carried out. The results showed that surface fractures were mostly observed in KMN-I, while interior cracks initiated from nonmetallic inclusions which were identified as MnS by SEM. In addition, the surface defects were simplified as cracks using fracture mechanics and the fatigue strength model with surface defects was modified, which proved to be more in agreement with the experimental results than the Murakami model.