PSI - Issue 59

Hryhoriy Nykyforchyn et al. / Procedia Structural Integrity 59 (2024) 82–89 H. Nykyforchyn et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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diffusion of which the presence of energetically favourable paths for the implementation of such mobility (grain boundaries and between phase boundaries) is important, as shown by Luu and Wu (1996), Stopher et al (2016), Galindo- Navaa et al. (2017), Hüter et al. (2018), Liu et al (2019), Díaz et al. (2020), Chen et al. (2020), Mogilny et al. (2020) and others. On the other hand, molecular (recombined) hydrogen, which is usually localized in high energy trap defects, creates high pressure in them and, accordingly, a high level of internal tensile stresses in the metal near these defects (Zvirko et al. (2024)). Thus, it is important to operate not only by the total concentration of hydrogen in the metal but also by its components, as it was shown for example by Dmytrakh et al. (2021). In addition, it cannot be excluded from the consideration that hydrogen can enhance the strain aging of steel due to its ability to intensify diffusion processes and microplastic deformation. This means that the mechanical and physical factors of hydrogen exposure should be comprehensively taken into account. 4. Conclusions We demonstrated the feasibility of implementing strain aging at a micro scale using the pipe steel as an example, without the need for any prior plastic deformation created by an applied load. This was possible due to residual internal stress generated by hydrogenation. The feature of such type of strain aging is that metal becomes brittle locally (only in local areas of dominant hydrogen diffusion paths), but not in whole volume. As a result, it was revealed that the mechanical characteristics at a macro-scale, such as plasticity and impact toughness, are not sensitive to hydrogen-induced strain aging. Furthermore, fracture toughness, which is characteristic of a meso-scale, determined by J-integral method, is more sensitive to hydrogenation. However, the most efficient method among all the methods used was resistance to SCC, which is considered a micro-scale characteristic. The microfractographic analysis revealed a correlation between the steel's sensitivity to strain aging, as determined by fracture toughness and SCC resistance indices, and the signs of brittle fractures. In the case of tests of steel for fracture toughness, such signs were generally shallower dimples of ductile relief with less deformation of the bridges of the adjacent voids. For SCC testing, the signs of embrittlement consisted in the appearance of areas of intergranular or transgranular fracture with the decoration of intergranular facets by the secondary cracks. These features correspond to the well known regularity of the dominance of the intergranular pathways for hydrogen transport in carbon and low-alloy steels. Since the studied deformation aging process involves both diffusively mobile atomic hydrogen and hydrogen that has recombined in traps to a molecular state, it is important to consider not only its overall concentration in the metal but also the ratio of its components when analysing the effect of hydrogen. References ASTM E 813. Standard test method for J-integral characterization of fracture toughness. Belotteau, J., Berdin, C., Forest, S., Parrot, A., Prioul, C., 2006. Mechanical behavior modeling in the presence of strain aging. In: Gdoutos, E.E. (eds) Fracture of Nano and Engineering Materials and Structures. Springer, Dordrecht. Chen, Y. S., Lu, H., Liang, J., Rosenthal, A., Liu, H., Sneddon, G., McCarroll, I., Zhao, Z., Li, W., Guo, A., Cairney, J. M., 2020. Observation of hydrogen trapping at dislocations, grain boundaries, and precipitates. Science 367(6474), 171-175. De, A. K., De Cooman, B. C., Vandeputte, S., 2001. Kinetics of strain aging in bake hardening ultra low carbon steel — a comparison with low carbon steel. Journal of materials engineering and performance 10, 567-575. Díaz, A., Cuesta, I. I., Martinez - Pañeda, E., Alegre, J. M. , 2020. Analysis of hydrogen permeation tests considering two different modelling approaches for grain boundary trapping in iron. International Journal of Fracture 223, 17-35. Dmytrakh, I.M., Syrotyuk, A.M., Leshchak, R.L., 2021. Effect of preliminary hydrogenation – dehydrogenation of low-alloy steel on its ability to absorb electrochemical hydrogen. Materials Science 57(3), 387 – 396. DSTU 9166:2021, 2021. Metal materials determination for ability to mechanical ageing by impact bend testing. Galindo-Navaa, E.I., Bashaa, B.I.Y., Rivera- Díaz -del-Castillo, P.E.J., 2017. Hydrogen transport in metals: Integration of permeation, thermal desorption and degassing. Journal of Materials Science & Technology 33(12), 1433-1447. Gredil, M. I., 2008. Operating degradation of gas-main pipeline steels. Metallofizika i Noveishie Tekhnologii 30(SPEC. ISS.), 397 – 406. Hredil, M.I., 2011. Role of disseminated damages in operational degradation of steels of the main gas conduits. Metallofizika i Noveishie Tekhnologii 33, 419-426. Hüter, C., Shanthraj, P., McEniry, E., Spatschek, R., Hickel, T., Tehranchi, A., Guo, X., Roters, F., 2018. Multiscale modelling of hydrogen transport and segregation in polycrystalline steels. Metals 8(6), 430. Kharchenko, L. E., Kunta, O. E., Zvirko, O. I., Savula, R. S., Duryahina, Z. A., 2016. Diagnostics of hydrogen macrodelamination in the wall of a bent pipe in the system of gas mains. Materials Science 51(4), 530 – 537.