PSI - Issue 68

Vahid Javaheri et al. / Procedia Structural Integrity 68 (2025) 1098–1104 V. Javaheri et. al, Structural Integrity Procedia 00 (2025) 000–000

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4. Conclusions This study highlights the dual role of retained austenite (RA) in influencing the mechanical behavior of medium manganese steel, particularly in the context of hydrogen embrittlement. In hydrogen-free conditions, the presence of around 40% retained austenite significantly enhances ductility and toughness through the transformation-induced plasticity (TRIP) effect, where the gradual transformation of RA into martensite during deformation contributes to energy absorption and improved mechanical performance. However, when hydrogen is introduced, the material's response changes drastically. The hydrogen-induced transformation of retained austenite to fresh martensite (α′), coupled with the high hydrogen diffusivity in the newly formed α′, leads to stress concentration at phase boundaries and hydrogen-enhanced decohesion (HEDE). This promotes the nucleation of hydrogen-induced cracks (HIC), leading to a severe reduction in ductility and premature fracture. The experimental results show an 80 MPa loss in ultimate tensile strength (UTS) and a significant drop in elongation from 17% to 2% under hydrogen-charged conditions, demonstrating the material's susceptibility to hydrogen embrittlement. The fractography analysis further revealed the embrittling effect of hydrogen, with multiple microcracks and embrittled zones propagating into the material, in contrast to the ductile fracture observed in hydrogen-free samples. This study underscores the critical interplay between retained austenite stability and hydrogen embrittlement, indicating that the stability of retained austenite is key to enhancing the steel's resistance to hydrogen-induced failure. To mitigate hydrogen embrittlement, future work should focus on optimizing heat treatment processes to stabilize retained austenite, reduce hydrogen diffusion, and improve the steel's overall mechanical resilience in hydrogen-rich environments. Tailored microstructural design strategies, particularly in controlling the transformation behavior of RA, are essential to balance ductility and resistance to hydrogen-induced damage in advanced high-strength steels. Acknowledgements Authors would like to thank Jane and Aatos Erkko (J&AE) Foundation and Tiina and Antti Herlin (TAH) Foundation for their financial supports on Advanced Steels for Green Planet project (AS4G) as well as the University of Oulu & The Research Council of Finland Profi 352788 for their funding of the H2Future project. SSRT tests were conducted within the ALL4HYDRO II Project # 2022 01582 (Alloy development for hydrogen related applications; Part II), due to which the Swedish strategic innovation program “Metalliska Material”, Vinnova, and industrial partners within the project are acknowledged for their support. References Chen, Y.-S., Huang, C., Liu, P.-Y., Yen, H.-W., Niu, R., Burr, P., Moore, K. L., Martínez-Pañeda, E., Atrens, A., & Cairney, J. M. (2024). Hydrogen trapping and embrittlement in metals – A review. International Journal of Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2024.04.076 Jacob, R., Raman Sankaranarayanan, S., & Kumaresh Babu, S. P. (2020). Recent advancements in manganese steels – A review. Materials Today: Proceedings, 27, 2852–2858. https://doi.org/10.1016/j.matpr.2020.01.296 Kumar, D., Sen, I., & Bandyopadhyay, T. K. (2024). A Systematic Review of Medium‐Mn Steels with an Assessment of Fatigue Behavior. Steel Research International, 95(2). https://doi.org/10.1002/srin.202300375 Lee, Y.-K., & Han, J. (2015). Current opinion in medium manganese steel. Materials Science and Technology, 31(7), 843–856. https://doi.org/10.1179/1743284714Y.0000000722 Liu, Y., Cao, Z., Huang, C., Hu, C., & Huang, M. (2023). Enhancing hydrogen embrittlement resistance of TRIP-rich medium Mn steel by morphology optimization. Science China Materials, 66(11), 4258–4266. https://doi.org/10.1007/s40843-023-2658-6 Oriani, R. A. (1978). Hydrogen Embrittlement of Steels. Annual Review of Materials Science, 8(1), 327–357. https://doi.org/10.1146/annurev.ms.08.080178.001551 Sadeghpour, S., Javaheri, V., Somani, M., Kömi, J., & Karjalainen, P. (2022). Heterogeneous Multiphase Microstructure Formation through Partial Recrystallization of a Warm-Deformed Medium Mn Steel during High-Temperature Partitioning. Materials, 15(20), 7322. https://doi.org/10.3390/ma15207322 Zhang, Y., Ye, Q., & Yan, Y. (2024). Processing, microstructure, mechanical properties, and hydrogen embrittlement of medium-Mn steels: A review. Journal of Materials Science & Technology, 201, 44–57. https://doi.org/10.1016/j.jmst.2024.03.014 Zou, Y., Xu, Y. B., Hu, Z. P., Gu, X. L., Peng, F., Tan, X. D., Chen, S. Q., Han, D. T., Misra, R. D. K., & Wang, G. D. (2016). Austenite stability and its effect on the toughness of a high strength ultra-low carbon medium manganese steel plate. Materials Science and Engineering A, 675, 153–163. https://doi.org/10.1016/j.msea.2016.07.104