PSI - Issue 68

Birhan Sefer et al. / Procedia Structural Integrity 68 (2025) 1129–1139 Author name / Structural Integrity Procedia 00 (2025) 000–000

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values (Rel. A h (RT) = 41 % and Rel. A h (800 °C) = 39 %) strongly suggest that hydrogen have deteriorated to similar extent the mechanical properties of SiMo51 regardless of the testing temperature. The CGI material was also affected by hydrogen, but in contrast to the SiMo51, the relative A h reduction was more pronounced at room than at high temperature (Rel. A h (RT) = 52 % and Rel. A h (300 °C) = 91 %). This indicated that CGI material exhibited better performance at high than room temperature. At last, for the NCF3015 material only a small impact on the elongation to leakage caused by the hydrogen was observed. This is valid for both testing temperatures. 3.2 Fractographic analysis Figures 3 to 5 shows SEM-micrographs with representative fracture surfaces of specimens tested in Ar (left) and H 2 (right) at room (a) and high (b) temperature. The SEM-micrographs on the top are showing an overview with the hole in the centre. These SEM-micrographs contain areas indicated with white rectangular box marked with number. Higher magnification SEM-micrographs taken in these white marked areas are given below the respective overview SEM-micrograph. From Figure 3a it can be seen that the specimens tested in Ar and H 2 at room temperature have no apparent differences in fracture mode. Both present brittle failure with quasi-cleavage decohesion type of fracture mode. In addition, no internal damage and macroscopic deformation with little to not necking present was observed. The fractographic analysis in this work is in good agreement with others Sahiluoma et al. (2017).

Figure 3. Representative fracture surfaces taken from SSRT specimens tested in argon (left) and hydrogen (right) at a) room and b) high temperature for SiMo51 material. Higher magnification micrographs taken in the area marked with numbers in the white boxes are given below the overview micrographs.