PSI - Issue 13

M. Seleznev et al. / Procedia Structural Integrity 13 (2018) 2071–2076 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

2076

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4. Conclusions

• Surface hardening of a quenched steel gives significant increase of fatigue limit, which is believed to correlate with the change in internal stress distribution according to Matsumoto [3, p. 108]. • Under fatigue load plate-like NMIs concentrate stress not with their cross-section area perpendicular to the loading direction, but with their entire disk-area, even being tilted to the cross section plane. • For the given total NMI number and volume, form-factor of NMI can influence the fatigue behavior of steel and should be taken into account for fatigue life prediction. • Influence on the fatigue limit from maximum size of plate-like NMIs can be detected by metallographic section imaging by counting the relation of maximum to minimum Feret diameter for each particle. • Equivalent crack area of plate-like NMI can be estimated as the area projected by NMI on the plane perpendicular to loading direction. This general rule is found to work for small tilt angles (α<30°), whereas for large ones further investigations are needed.

Acknowledgements

The authors gratefully acknowledge the German Research Foundation (DFG) for supporting the Collaborative Research Center CRC 920, subproject C04. In addition, the authors would like to thank colleagues from TU Bergakademie Freiberg for providing the casts, specimen preparation and metallography inspection and colleagues from Togliatti State University (Russia) for allowance of laser confocal microscope usage.

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