## 3 Results and Discussion
### Results of the Analysis of HiperFer-17 Cr2  
As shown in [12], the HiperFer-17 Cr2 shows significantly more pronounced changes in the microstructure and the mechanical properties. Consequently, stronger changes in micromagnetic properties can be expected than those observed in P91. Accordingly, the evaluation of the 3 MA-X8 measurements performed on the HiperFer-17 Cr2 specimens reveals that several micromagnetic parameters allow for a clear differentiation between the loaded and unloaded states. When analyzing these changes, it must be considered that within the first 10 LCF or 20 HCF cycles, the material shows cyclic hardening only due to an increase in dislocation density, while the changes in the microstructure and cyclic deformation behavior after this initial phase are dominated by the precipitation of the Laves phase [13]. For long-term operation and industrial applications, this initial cyclic hardening and the accompanied microstructural changes are less relevant. To exclude the superposition of this initial change and the precipitation occurring afterwards, the unloaded state, and thus, the changes occurring in the first 10 LCF or 20 HCF cycles, are not considered in the correlation analysis.  
After the initial cyclic hardening, a cyclic saturation phase or a slight cyclic softening can be observed for HiperFer-17 Cr2, which is followed by a second phase of cyclic hardening. Qualitatively, these three phases can be observed in the cyclic deformation curves obtained under both LCF and HCF loading [12; 13]. However, these phases are differently pronounced depending on the load temperature, while the formation of intragranular Laves phases during the second prolonged cyclic hardening phase initiates earlier with increasing temperature. Furthermore, note that an increase in dislocation density up to half of the fatigue life occurs, which also is expected to influence the mechanical and micromagnetic measures.  
When comparing HiperFer-17 Cr2 and P91, HiperFer-17 Cr2 shows a significantly stronger change in mechanical parameters, primarily driven by an enhanced thermo-mechanically induced precipitation and an increased dislocation density. These microstructural changes, caused by the applied loading, introduce numerous new barriers to domain wall motion, leading to significant changes in the micromagnetic properties. In contrast, P91 features a high density of obstacles to domain wall motion in its initial state, owing to its strengthened microstructure with high precipitate and dislocation densities [34]. Due to the relatively short loading time, precipitate coarsening is minimal. Although dislocation density decreases, it remains significantly higher than in HiperFer-17 Cr2 (see [13]), and subgrain coarsening is only weakly developed in the investigated conditions. Consequently, the effect of microstructural obstacles on domain wall motion remains nearly unchanged, reflected by there being no pronounced changes in the micromagnetic parameters.  
In summary, the micromagnetic behavior differs between the materials due to opposing microstructural developments: HiperFer-17 Cr2 forms new obstacles to domain wall motion, while P91 reduces the existing ones. It is also important to note that the martensitic microstructure of P91 exhibits magnetic characteristics that differ from those of conventional ferritic steels, which impacts the results obtained in micromagnetic measurements. Ferrite has a low mechanical hardness and very often also has a low magnetic hardness in terms of coercivity, whereas martensite shows a high mechanical and magnetic hardness and is much more brittle [27; 28; 35].