Hydrogen and helium effects on reduced activation Fe-Cr ferrite-martensite and ODS steels

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    Significant amounts of hydrogen and helium are generated in the structural materials of the nuclear reactor systems by the interaction of the alloying elements with both fast and thermal neutrons. Hydrogen can also be effectively absorbed by other environmental processes. Helium and hydrogen stabilize the small vacancy clusters and facilitate the further formation of the voids that causes the swelling of the structural steels. At the same time, hydrogen plays an important role in degradation of the mechanical properties of the structural steels due to the hydrogen embrittlement (HE). In the thesis, the deleterious effects of hydrogen and helium are studied on the reduced activation ferrite-martensite (RAFM) and oxide dispersion strengthened (ODS) RAFM steels, which are promising materials for Gen IV nuclear reactor systems. Hydrogen and helium uptake in RAFM and ODS-RAFM steels are studied by thermal desorption spectroscopy (TDS) evidencing the higher hydrogen and helium concentration in ODS-RAFM steel after hydrogen charging and helium irradiation, respectively, than that observed in the base RAFM steel. Activation analyses for the hydrogen and helium desorption are performed using the obtained TDS curves. Possible role of the dispersoid phase of yttrium oxide nanoparticles in hydrogen and helium trapping is discussed. Mechanical properties of the RAFM and ODS-RAFM steels are studied in terms of their sensitivity to hydrogen embrittlement after electrochemical hydrogen charging at room temperature (RT). The obtained results evidence that there is a critical hydrogen concentration above which the ODS steel suffers from hydrogen embrittlement in form of intergranular fracture. The instrument for hydrogen charging from glow discharge plasma is developed and the suitable conditions of hydrogen charging were obtained experimentally. The mechanical properties of RAFM and ODS-RAFM steels are studied during continuous hydrogen charging using the developed hydrogen charging process instrument at room and elevated temperatures. Sensitivity to HE of the ODS steel is found to be less pronounced at elevated temperatures compared with that at RT, while the susceptibility to hydrogen of the matrix material remains approximately the same at all the testing temperatures. Hydrogen-induced cracking in the studied steels initiates preferably from non-metallic inclusions (NMI) such as chromium and tungsten carbide particles. Possible mechanism of hydrogen interaction with NMIs is discussed.
    Translated title of the contributionVedyn ja heliumin vaikutus matala-aktiivisiin Fe-Cr ferriittis-martensiittisiin ja ODS teräksiin
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Hänninen, Hannu, Supervising Professor
    • Yagodzinskyy, Yuriy, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-6539-7
    Electronic ISBNs978-952-60-6540-3
    Publication statusPublished - 2015
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • hydrogen embrittlement
    • reduced activation ferrite-martensite steels
    • ODS steels
    • thermal desorption spectroscopy
    • fracture
    • non-metallic inclusions

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