# Effect of Heat Treatment on Microstructure and Creep Behavior of Fe-40 Ni-24 Cr Alloy
## 3 Result and Discussion
### Microstructure Evolution during Creeping
However, color contrast was shown in the grain due to the deformation that occurred during the creep test. Grain's average misorientation (GAM) map is as shown in Figure 6d, which shows the average misorientation between the neighboring pair of measurement points within the grains. The misorientation angle was taken from 0\({}^{\circ}\) to 20\({}^{\circ}\). The grains showed a high quantity of misorientation angle between 3\({}^{\circ}\) and 8\({}^{\circ}\). However, recrystallized grain showed a high quantity at a lower misorientation angle, which is from 0\({}^{\circ}\) to 1\({}^{\circ}\). The kernel average misorientation (KAM) map is a set of prescribed size points surrounding the interest scans point. A specific tolerance angle value from 0\({}^{\circ}\) to 3.5\({}^{\circ}\) was selected, and a 0.7\({}^{\circ}\) misorientation angle gave the highest KAM number count. The misorientation developed inhomogeneously due to the deformation. The KAM results also showed that the misorientation tended to be larger near the boundaries and decreased evidently towards the center of the grains, as shown in Figure 6e. Figure 7 shows the TEM micrograph of the selected specimen (heat-treated at 1200 \({}^{\circ}\)C) after undergoing creep at 800 \({}^{\circ}\)C and 100 MPa. The analysis was focused on the rupture area (necking region) to investigate the rupture mode and how it occurred. Since the TEM analysis specimen was very small and about 15 \(\mu\)m \(\times\) 15 \(\mu\)m in size, the result only represented the microstructure of recrystallized grain. The selected area diffraction (SAD) pattern of the grain (matrix) is shown in Figure 7a,b. From the spots indexing, the zone axis was determined as [0 1] (parallel to the electron beam). The stacking faults can be observed in Figure 7c. Stacking fault is a planar defect that characterizes the disordering of crystallographic planes. The stacking fault packets were formed during grain boundary migration, and can generate annealing twins [46; 49]. The result showed no chromium-rich carbide precipitate distribution along the grain boundary (Figure 7d). Figure 7e shows only a few dislocation piles around the NbC precipitates. The identity of carbide precipitates was confirmed using EDX analysis. The TEM morphology of the dynamically recrystallized grain revealed that less dislocation could be observed. This is because the recrystallized grain was a newly reformed grain, which is free from dislocation [53; 54; 55]. Figure 7f,g show dislocation end at the interface of the precipitates and the matrix. Matrix distribution precipitates can retard the dislocation to glide through the grain and form microvo  
Figure 6: EBSD analysis on specimen (heat-treated at 1200 \({}^{\circ}\)C) after creep test at 800 \({}^{\circ}\)C under 100 MPa stresses; (**a**) pattern quality (PQ) map, (**b**) pattern quality grains map, (**c**) inverse pole figure (IPF) map, (**d**) grain average misorientation (GAM) map and (**e**) kernel average misorientation (KAM) map. Figure 8 shows the EBSD results of the selected specimen (heat-treated at 1200 \({}^{\circ}\)C) after undergoing a creep test at 800 \({}^{\circ}\)C and 100 MPa and interrupted at 110.7 h (to understand the high temperature creep mechanism at secondary stage). The analysis focused on the center area of the creep specimen. Figure 8a shows the pattern quality (PQ) image. PQ image generally showed a grayscale map because every point on the map is assigned the brightness based on the pattern quality for every point. Grain boundaries are referred to as low-quality pattern areas, and boundaries are observed as a dark linear feature. They appeared similar to the SEM image. The rainbow-colored map, as shown in Figure 8b was a pattern quality grain map. Each color represents different grains. The results show the grain microstructure with no recrystallization. The grains show less elongation due to the experiment being interrupted at the secondary stage of creep (110.7 h) with 12% elongation.