PSI - Issue 23

Ahmed Azeez et al. / Procedia Structural Integrity 23 (2019) 155–160 A. Azeez et al. / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 5. The fraction of low angle grain boundaries (LAGB) in the tested specimen.

4. Conclusions

Specimens made from the steam turbine steel FB2 was tested in isothermal low cycle fatigue. Microstructural investigation (including EBSD mapping) of ruptured specimens revealed that: • Grain boundary voids were detected in specimens tested at 600 ◦ C, indicating significant creep at this tempera ture. • Voids did not only occur for the dwell time test but also for the pure cyclic case, indicating rapid creep rate at this temperature (i.e. 600 ◦ C). • The fraction of low angle grain boundaries (which can be taken as an indication of plastic deformation) was lowest for the specimen with the highest inelastic strain range. The specimen with the lowest inelastic strain range (for which no creep damage could be detected) had the highest amount of low angle grain boundaries. • It is considered likely that a significant amount of the inelastic strain at 600 ◦ C is creep strain, also for the pure cyclic case, which may lead to a di ff erent damage mechanism compared to specimens tested at lower temperatures.

Acknowledgements

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 764545.

References

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