PSI - Issue 71

Prasanna Dupare et al. / Procedia Structural Integrity 71 (2025) 118–125

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Fig.1 Geometry of LCF/CFI (M16) specimen a) Schematic b) Actual Specimen

3. Results & Discussion 3.1 Initial microstructure

The optical micrograph of as-received Alloy 617M is presented in Fig. 2. The forged Alloy 617M exhibited a duplex distribution of both larger and smaller austenitic grains, attributed to the Zener pinning mechanism (Shankar et al., 2017a). The average grain size, measured using the linear intercept method, was approximately 216 µm. The optical image in Fig. 2 clearly revealed the presence of chromium and molybdenum-rich carbides (yellow arrow) and twins (red arrow). These carbides, identified as M 23 C 6 , were located along the grain boundaries and within the grains, with sizes ranging from approximately 2 to 5 μm, as confirmed by energy dispersive spectroscopy, shown in Fig. 3

Fig. 2 Microstructure of as-received sample