###### Abstract
In contrast, in the HCF regime, the fatigue life is increased, given the nucleation of very fine martensite particles in the area of local plasticity, hindering the dislocation movements [4]. With respect to cyclic softening and/or hardening behavior, it has been shown in [1] that in the LCF regime, for tests conducted at strains in the range of \(\varepsilon_{a,t}=0.6\) to 1.6% only cyclic hardening takes place. On the other hand, it has been shown in [5] after analyzing stress amplitude, mean stress and plastic strain amplitude curves of strain-controlled fatigue tests conducted at different strain amplitudes in the HCF regime (\(\varepsilon_{a,t}=0.165\) to 0.220%), that at the beginning of the test, cyclic softening occurs, followed by cyclic hardening. For both LCF and HCF regimes, there is an incubation period where no \(\alpha\)'-martensite transformation takes place, followed by a continuous increase in the \(\alpha\)'-martensite volume fraction. The duration of the incubation period decreases with higher total strain amplitudes, contrary to the measured \(\alpha\)'-martensite volume fraction at the end of the tests, which increases. Moreover, two austenitic steels of the same type, of which the chemical composition and mechanical properties comply with the standardized limits, but which have differences in chemical composition and grain size, can present substantial differences in the \(\alpha\)'-martensite transformation rate and the \(\alpha\)'-martensite volume fraction achieved at the end of the test, when tested under the same conditions, which can be explained through the different materials' metastability. At an elevated temperature of \(T>200\)\({}^{\circ}\)C, no \(\alpha\)'-martensite formation occurs in the LCF and HCF regimes. Furthermore, the cyclic deformation behavior is characterized by initial cyclic hardening and depending on the applied strain amplitude, a subsequent cyclic softening occurs. The detection of the degradation mechanisms described above relies on the sensitivity of the selected NDT method to those. The motivation of the research is, that mechanical and thermal stresses due to operational conditions together with corrosive influences lead to aging and degradation of a structural material, where the resulting damage can be associated to microstructural changes. The effects of such changes are currently covered rather generally by safety factors in the design of components. Additional qualified information about the microstructural state obtained through monitoring could therefore improve the assessment of an aging condition and better differentiate within the safety margins traditionally set, allowing a component's residual life evaluation to be enhanced without compromising the level of safety. What this paper will also elaborate on is the transfer of materials' data such as generated on unnotched specimens into fatigue life evaluations of notched specimens. Classical approaches such as the one proposed by [PERSON] will be discussed. It will be shown how local assessment in notched specimens can be made. Based on a plasticity model obtained through finite element simulations and application of the Chaboche model, a further correlation can be established between deformation measurements outside of a notch and local stresses and strains within the notch. With this model, the deformation measured through an external extensometer is related to the local strain using a polynomial function. The plasticity model-based notch root strain and the Neuber approach represent two complementary approaches, allowing local stresses and strains in notched specimens to be assessed.