PSI - Issue 68

Reza Khadem Hosseini et al. / Procedia Structural Integrity 68 (2025) 409–414 R. K. Hosseini / Structural Integrity Procedia 00 (2025) 000–000

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2.4. Scanning Electron Microscope Analysis To closely examine the microstructure of the damaged area of tube sample B, a TESCAN MIRA3 field emission gun scanning electron microscope (FEG-SEM) was employed. Different parts of the deep hole created at the inner surface of sample B were studied by SEM, as shown in Fig. 5a. According to the images presented in Fig. 5c-d, three distinct microstructures were observed in these zones. While the microstructure of zone “A” predominantly exhibited a bainitic structure, zone “F” displayed a ferritic-pearlitic microstructure. Conversely, zone "E" demonstrated a unique microstructure characterized by areas of a ferrite matrix interspersed with a dense network of carbides. Additionally, the elemental composition of these regions, analyzed using EDAX, indicated variations in the concentrations of key alloying elements, including Cr and Mo, compared to the chemical composition of the tube material, as shown in Table 2.

Fig. 5. The SEM micrographs of different parts of failed tube sample B adjacent to the hole as shown in Fig. 2a; (a) inner surface of the hole, (b) tube's outer wall, (c) tube's inner wall.