High hardness steels (HHS) are vulnerable to hydrogen embrittlement, which can lead to rapid degradation of mechanical properties. Improved resistance to hydrogen embrittlement would be beneficial to many industries including construction, automotive, and military. A comparison study was performed to assess the hydrogen susceptibility of select commercially available and in-house designed HHS alloys. Slow strain rate tensile tests, performed with specimens charged with various levels of hydrogen, provided a macroscopic view of the onset of hydrogen embrittlement. Hydrogen permeation and thermal desorption spectroscopy tests determined the uptake and diffusivity of hydrogen through the material. The evaluation of hydrogen susceptibility for various HHS alloys provided a baseline for the design of an HHS alloy containing hydrogen embrittlement mitigation strategies. By incorporating strong hydrogen traps, titanium carbide and epsilon carbide, a HHS was produced that demonstrated a lower sensitivity to hydrogen embrittlement

M. S.

No description available.

Dual-phase (DP) advanced high-strength steels (AHSSs) are widely used in the automotive industry due to their excellent combination of strength, ductility, and work hardening properties. However, defects occurring during processing make these ferrous alloys expensive. Toward this ends, high-temperature tensile tests using a Gleeble thermomechanical simulator have been conducted to determine the stress/strain behaviour at temperatures between 1250 to 1480 C in order to quantify the tensile strength and ductility. The results of both as-cast and transfer-bar material will be presented as well as three different sample geometries in order to better understand the effects of starting microstructure, thermal gradient, and tress/strain distribution on the reproducibility of high temperature properties. Optical and scanning electron microscopy are then performed to further elucidate the structure/property relationships. The results show that the presence of preexisted prorosities in the as-cast structure decreases the high-temperature strength of the material, while the transfer-bar samples show lower ductility at ultra-high temperatures, (T 1450 C), due to their severe susceptibility to melting. In terms of the two mentioned thermomechanical characteristics, voids nucleation, growth, and coalescence initiated with porosity clustering are the main mechanisms behind the lower strength of the as-cast samples, whilst tearing apart of the melt plays an important role to drastically drop the ductility of transfer-bars at mentioned temperature interval. Moreover, the long-gauge-length (LGL) geometry proposes better reproducibility of data compared with the other geometries. This is attributed to a suitable combination between low stress localization and high thermal gradient during the Gleeble testing that provides a condition in which the samples experience sharp localized necking right on the hot-spot zone. The obtained data can be used as part of multi-physics process and microstructure continuous casting models. / Thesis / Master of Applied Science (MASc)

Acoustic emission activity resulting from plastic deformation of mild steel disks that were clamped and then pressurized from one side with either hydrogen or nitrogen was recorded and analyzed. It was found that during monotonic pressurization of disks in nitrogen gas, more cumulative counts were recorded than for similar disks pressurized in hydrogen gas. Possible signatures of the "births" of cracks were observed during hydrogen pressurization of disks that typically failed by leaking. The records of the nitrogen tests show very high energy and high count events occurring early in the deformation process. These events are believed to be the result of the breaking away of near-surface dislocations that had been pinned by nitrogen. The disks tested in nitrogen typically failed by bursting (ductile failure) while those tested in hydrogen typically failed by leaking ("brittle" failure). / M.S.

Electrolytic charging of hydrogen, at room temperature and in the absence of externally applied stress, induced surface cracking in 316 stainless steel and cobalt based ZIMALOY. Hot Isostatic Pressed (H.I.P.) ZIMALOY showed less susceptibility to surface cracking than 316 stainless steel samples. The susceptibility of 316 stainless steel to surface cracking was determined with samples in the High Energy Rate Forged (HERF), the sensitized, the annealed, and the annealed and sensitized conditions. Investigations showed that surface cracking typically occurred at specific microstructural features. Hence, the relative susceptibilities of twin boundaries, slip bands, grain boundaries, and heavily sensitized regions was established. It was observed that twin boundaries crack most readily in non-sensitized samples, and that both grain boundaries and twin boundaries crack easily in sensitized structures. These observations, coupled with the similarity between hydrogen embrittlement and failure of orthopedic implants, suggest that orthopedic applications should use H.I.P. ZIMALOY in preference to 316 stainless steel whenever possible, and that when the use of 316 stainless steel is unavoidable, HERFed parts should be used. Further investigations are recommended to better assess the hydrogen compatibility of sensitized 316 stainless steel, and to determine the influence of sensitization on the suitability of 316 stainless steel for orthopedic application. / Master of Science

M.S.

In recent years, there has been a growing concern over the adverse effects of traditional fossil fuels on the environment and health. Therefore, there is an increased interest in hydrogen as a fossil-free fuel source, making the need for hydrogen solutions apparent. This supports the purpose and research questions of this study, which aim to determine the suitable materials for handling hydrogen and the necessary design for structural integrity to withstand pressure. This will be achieved through additive manufacturing using polymers. The study also considers the potential of additive manufacturing for large-scale production. After conducting literature studies, polymers are of special interest due to their different structural build compared to metals. Metals do not handle hydrogen well because of the phenomenon known as hydrogen embrittlement. The preferred material properties in polymers are a crystalline structure, high density, and strong mechanical properties. The design and production are conducted using SolidWorks, with simulations of pressure and topology optimization, making it possible to create a part ready for 3-D printing after slicing. The results provide insights into the effects of parameter adjustments on the structure of the parts and the feasibility of large-scale production through additive manufacturing. By analysing the slicer program, conclusions can be made that additive manufacturing is a viable option for large-scale production, given the availability of multiple printers. However, the conclusion regarding the optimal design for handling pressurized hydrogen could not be made due to a lack of time for testing.

This work deals with the damage due to the simultaneous presence of hydrogen in atomic form and stress – straining.<p>The aim of this work is twofold: to better understand the hydrogen embrittlement mechanisms and to translate the acquired knowledge into a more appropriate qualification test. <p>The phenomena of hydrogen entry and transport inside the metals, together with the different types of damages due to the presence of hydrogen, are presented.<p>The analysis of the most important models proposed up to now for hydrogen embrittlement (HE) indicated that the slow dynamic plastic straining is a key factor for the embritteling process. There is a synergistic effect of hydrogen – dislocations interactions: on one hand hydrogen facilitates the dislocations movement (according to the HELP mechanism) and on the other hand dislocations transport hydrogen during their movement when their velocity is lower than a critical value. <p>This work is focused on supermartensitic stainless steels, base and welded materials. The interest on these materials is due to their broad use in offshore oil production. <p>First, the material’s characterisation with regards to hydrogen content and localisation was performed. This was conducted in charging conditions that are representative of industrial applications.<p>Because of previous industrial experience it was necessary to find a more appropriate qualification test method to asses the risk of HE. <p>In this work we proposed the stepwise repeated slow strain rate test (SW R – SSRT) as a qualification test method for supermartensitic stainless steels. <p>This test method combines hydrogen charging, test duration, plastic, dynamic and slow strains. Thus, this test method is coherent with both the model HELP proposed for hydrogen embrittlement and the observations of industrial failures. <p>The stepwise repeated slow strain rate test (SW RSSRT) is interesting not only as a qualification test of martensitic stainless steels, but also as a qualification test of conditions for using these materials (type of straining, range of strain and stress, strain rate, hydrogen charging conditions, etc.).<p><p><p><p>Ce travail se rapporte à l’endommagement provoqué par la présence simultanée de l’hydrogène sous forme atomique et une contrainte (appliquée où résiduelle). <p>Ce travail a comme but une meilleure compréhension du mécanisme de la fragilisation par l’hydrogène (FPH) et la recherche d’un essai de qualification qui soit cohérent avec ce mécanisme. <p>Les phénomènes liés à l’entrée et au transport de l’hydrogène au sein des métaux, ensemble avec les différents types d’endommagements dus à la présence de l’hydrogène, sont présentés.<p>L’analyse des modèles proposés jusqu’au présent pour la fragilisation par l’hydrogène (FPH) suggère que la déformation lente plastique dynamique est le facteur clé pour le processus de la fragilisation. Il y a un effet synergétique des interactions entre l’hydrogène et les dislocations: d’un coté l’hydrogène facilite le mouvement des dislocations (d’après le modèle HELP) et d’un autre coté les dislocations transportent l’hydrogène pendant leur mouvement, pourvu que leur vitesse soit en dessous d’une valeur critique. <p>Le travail a été conduit sur des aciers supermartensitiques, matériau de base et soudé. L’intérêt pour ces matériaux réside de leur large utilisation dans la production du pétrole en offshore. <p>D’abord, le matériau a été caractérisé du point de vu de la teneur et de la localisation de l’hydrogène. Les essais ont été conduits dans des conditions représentatives pour les cas industriels. <p>L’expérience industrielle d’auparavant indique qu’il est nécessaire de trouver un test de qualification plus approprié pour estimer la susceptibilité à la fragilisation par l’hydrogène. <p>Dans ce travail on propose un essai de traction lente incrémentée (SW R – SSRT) comme méthode de qualification pour les aciers supermartensitiques. <p>L’essai combine le chargement en hydrogène, la durée d’essai, la déformation lente, plastique et dynamique. Donc, cette méthode d’essai est cohérente avec le modèle HELP proposé pour FPH et les observations des accidents industriels. <p>Cet essai est intéressant pas seulement comme essai de qualification pour les aciers supermartensitiques, mais aussi comme essai de qualification pour les conditions d’utilisation des ces matériaux (type de déformation, niveau de déformation et contrainte, vitesse de déformation, conditions de chargement en hydrogène, etc.).<p> <p><p><p><p><p><p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Understanding the effects of the process parameters on the distribution behaviour of antimony between metal and slag in the iron blast furnace is critical to develop a universal method of controlling temper embrittlement in commercially pure low alloy steels.