## 3 Results and Discussion
From a comparison of Figure 13a,b (LPD), limited dislocation activity and/or plastic deformation in sub-grain free areas was evident, which indicates that deformation preferentially occurred due to sub-grain formation. This explained the significantly increased ductility of the specimens that were manufactured when applying HPD. In conventionally produced HiperFer 17 Cr2 sheet material, local sub-grain formation occurred similarly to the LPD HiperFer\({}^{\text{AM}}\) (Figure 13a,e) variant, which explained the matching fracture elongations. Moreover, a stronger tendency toward slip band formation was observed in the conventionally produced HiperFer 17 Cr2 (cf. Figure 13b,d-f). Minimum creep rates of the HiperFer\({}^{\text{AM}}\) variants were determined with respect to the build direction (longitudinal (L) and transversal (T)) at 650 \({}^{\circ}\)C (Figure 14). In the compression creep experiments, the LPD-manufactured HiperFer\({}^{\text{AM}}\) specimens already exhibited unexpectedly high creep rates > 10\({}^{-4}\) h\({}^{-1}\) at a stress of 70 MPa, while much higher stress (130 MPa) was needed for the HPD specimens. The behavior that occurred in the LPD variant is referred to as \"Power Law Breakdown (PLB)\" [57]. At high stresses, higher strain rates occur more often than predicted by the power law relationship. This behavior is known as PLB. The cause for the PLB of LPD-manufactured HiperFer\({}^{\text{AM}}\) at comparatively low stress was a pronounced change in the grain structure: In the as-built state, the microstructure consisted of directionally solidified (Figure 15a) grains, which then changed to a globularly recrystallized microstructure (Figure 15b) during the execution of the  
Figure 13: EBSD- and misorientation mappings taken longitudinally to the fracture surfaces after the tensile tests at 650 \({}^{\circ}\)C on HiperFer\({}^{\text{AM}}\) manufactured with (**a**,**b**) LPD and (**c**,**d**) HPD, as well as on (**e**,**f**) conventional HiperFer 17 Cr2. compression creep experiment. A directionally solidified microstructure obviously cannot effectively be stabilized by Laves phase precipitation and should therefore be avoided. In contrast, the microstructure of the HPD variant remained stable. Only the grain width of the directional grains between the globular ones tended to decrease (cf. Figure 15c,d). The increased creep strength of the HPD manufactured HiperFerAM was based on this stable microstructure. The building direction only had a minor impact on the minimum creep rates measured. Compared with HiperFer 17 Cr2, the minimum creep rate in the first HPD-manufactured HiperFerAM variant (mechanically alloyed) was only about 0.5 to 1 order of magnitude higher (with a tendency of decreasing discrepancy toward higher stress (Figure 14)). This indicates a good potential for high-temperature application of additively processed Hiperfer steel. The white dots in Figure 15a,c were incompletely melted tungsten clusters (cf. Figure 7)  
Figure 14: A 650 \({}^{\circ}\)C Norton plot of HiperFerAM with respect to the area-specific laser power and build direction in comparison to Hiperfer 17 Cr2* Data from [13]. Figure 15: Comparison of as-built and post-compression creep experiment microstructures (specimens taken longitudinally to build direction). LTD: (**a**) as-built and (**b**) after compression creep. HPD: (**c**) as-built and (**d**) after compression creep. Furthermore, the hardness increased after the compression creep testing, independently of the applied area-specific laser power and the building direction (Table 4). This indicates the high strengthening potential of HiperFerAM.