Martensitic steels with an ultimate tensile strength beyond 2000 MPa exhibit an excellent fatigue strength in the high cycle fatigue regime. The fatigue resistance can be enhanced by compressive residual stresses which are introduced by shot peening. However, the influence of residual stresses on the emergence and growth of cracks in martensitic steels has not been sufficiently investigated yet. For this reason, further research work is required concerning the extent of the typical stage I and stage II crack propagation in martensitic steels under the influence of residual stresses.
This study targets to reveal the fracture behavior in shot peened martensitic steels. Special attention is given to the extent of stage I and stage II crack propagation. For this purpose axial and torsional fatigue tests in the high cycle fatigue regime are carried out and the fractured surface is charcterized by means of electron scanning microscopy. Subsequently, electron backscatter diffraction is used to link the local crystallographic orientation of the crack initiation site with microstructural features. In order to determine the effect of residual stresses, samples are tested with and without prior shot peening treatments. The residual stresses are measured by means of x-ray diffraction analysis.
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