# Effect of Heat Treatment on Microstructure and Creep Behavior of Fe-40 Ni-24 Cr Alloy
## 4 Conclusions  
In this study, the effect of heat treatment's on the microstructure evolution and creep characteristic of Fe-40 Ni-24 Cr alloy was studied. Concerning Fe-40 Ni-24 Cr alloy, after heat treatment, 62 \(\upmu\)m and 158 \(\upmu\)m grain sizes are taken as fine-grain, whereas 183 \(\upmu\)m and 312 \(\upmu\)m grain size are coarse grain. The creep property for Fe-40 Ni-24 Cr alloy is improved by 51% with increasing temperature from 800 \({}^{\circ}\)C to 900 \({}^{\circ}\)C. Creep test at a temperature of 800 \({}^{\circ}\)C shows better creep properties compared to the test performed at temperature 900 \({}^{\circ}\)C. The minimum steady-state creep strain rate results for Fe-40 Ni-24 Cr at temperature 800 \({}^{\circ}\)C and 900 \({}^{\circ}\)C show 5% and 1% increase, respectively, with increased grain size. The microstructural evolution results also revealed that the grain boundaries acted simultaneously as dislocation sources and barriers for dislocation mobility. For small grain size alloy of 62 \(\upmu\)m to 183 \(\upmu\)m, the minimum creep rate increased with a decrease in grain size due to grain boundary sliding. The rupture morphology Fe-40 Ni-24 Cr alloys after creep test at 800 \({}^{\circ}\)C presented dimple ductile mode for fine grain alloys and mixed mode of intergranular and dimple rupture for coarse grains alloys. The rupture surface for Fe-40 Ni-24 Cr alloy undergoing creep at 900 \({}^{\circ}\)C presented dimple ductile mode. Creep test at high temperature caused chromium-rich carbides (Cr\({}_{23}\)C\({}_{6}\)) to precipitate along the grain boundaries in Fe-40 Ni-24 Cr alloy. The carbides can hinder grain boundary sliding and migration during high temperature creep service. Dynamic recrystallized grains are free from Cr\({}_{23}\)C\({}_{6}\) carbides, and the rupture surface at the necking area showed intergranular rupture along the recrystallized grains' boundaries. The TEM examination also exhibited the alloy's dislocation substructure after mechanical assessment at high temperature and verified that dislocation climb over precipitates is the primary creep strain mechanism. This result indicates that the creep characteristic of Fe-40 Ni-24 Cr alloy is significantly dependent on microstructural change affected by the heat treatment regime.  
The following are available online at [[https://www.mdpi.com/article/10.3390/app11177951/s1](https://www.mdpi.com/article/10.3390/app11177951/s1)]([https://www.mdpi.com/article/10.3390/app11177951/s1](https://www.mdpi.com/article/10.3390/app11177951/s1)), Figure S1 to Figure S11: Effect of Heat Treatment on Microstructure and Creep Behavior of Fe-40 Ni-24 Cr Alloy. Table S1: Effect of Heat Treatment on Microstructure and Creep Behavior of Fe-40 Ni-24 Cr Alloy.  
Writing--original draft preparation, methodology, formal analysis, M.M.; Conceptualization, supervision, formal analysis, writing--review and editing, E.H.; Conceptualization, validation  
ization, writing--review and editing, H.R.B.-R.; Conceptualization, writing--review and editing, funding acquisition, F.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
All data provided in the present manuscript are available to whom it may concern.  
The authors would like to acknowledge the Universiti Teknologi Malaysia and Bruker Singapore Pte Ltd. for providing the EBSD facilities support.  
The authors declare that they have no competing/financial conflict of interests in this paper.