PSI - Issue 68

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Birhan Sefer et al. / Procedia Structural Integrity 68 (2025) 1121–1128 Author name / Structural Integrity Procedia 00 (2025) 000–000

Figure 7. Hydrogen content for hot rolled and AM Hastelloy X measured with TDMS in SSRT specimens tested at room temperature and 800 °C on comparison to hydrogen content measured in as-received state.

4. Discussion In this work the behaviour of a conventionally manufactured, hot-rolled Ni-base alloy (Hastelloy X) was compared with respective AM alloy as relevant candidate for manufacturing components in gas turbines for power generation fuelled on H 2 . In general, it was found that there is no deterioration of the mechanical properties due to H 2 exposure for both AM and hot rolled materials tested at room temperature and 800 °C. Such result, means that neither the hot rolled or the AM Hastelloy materials are sensitive to hydrogen embrittlement for the tested conditions of 200 bar pressure hydrogen gas and for both tested temperatures, room and 800 ° C, respectively. This agrees with previous work reported by Hasegawa et al. (1981). The authors studied the embrittlement of solution-treated Hastelloy X at high temperature and pressure of H 2 and concluded that it is not susceptible to hydrogen embrittlement. However, they also emphasized that the embrittlement susceptibility is depended on whether smooth or notch specimens are tested. For notch specimens where stress is concentrated at the notch embrittlement occurred. For the hollow specimen testing presented in this paper, the inner hole surface can be considered as a smooth drilled surface having an Ra-value of maximum 0.2 µm, but still rougher than a polished surface. In addition, Hasegawa et al. (1981) also concluded that the embrittlement is dependent on whether the Hastelloy X is aged or not. High temperature aging causes precipitation of fine carbides at grain boundaries and act as trapping sites for hydrogen. Recent work by Kim et al. (2024) agrees with the role of carbides precipitation regarding hydrogen embrittlement susceptibility of Hastelloy X, but also highlights materials with larger grain size are more susceptible to embrittlement. The hydrogen content measured in both materials in the as-received state was notably different and being much higher for the conventional hot rolled Hastelloy X than the AM material. The reason for this may be ascribed to the different manufacturing processes used to produce both materials as well as to their microstructural differences. It should be noted, that aim of this work was not to study the microstructural differences between the conventionally and AM produced Hastelloy X materials, but further research regarding this is recommended. On the other hand, no hydrogen uptake was measured for both materials tested at room temperature, but a significant uptake was measured for the specimens tested at 800 ° C. This result was reasonable and expected since at high temperature the hydrogen solubility is notably higher. Gao et al. (1992) studied the hydrogen solubility in conventional Hastelloy X material in high H 2 pressure environment and at high temperatures and concluded that the solubility is function on the microstructure as well as the temperature. The author reported that lower temperatures result in lower solubility due to reduction of dislocation density and favouring the precipitation and coarsening of the carbides at the grain