Orientadores: Célia Marina de Alvarenga Freire, Itamar Ferreira / Dissertação (mestrado - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T02:38:33Z (GMT). No. of bitstreams: 1 Carvalho_IcaroZanettide_M.pdf: 13083038 bytes, checksum: c152edb400a89f8aecfa16c8073e6488 (MD5) Previous issue date: 2012 / Resumo: O fenômeno da fragilização por hidrogênio no aço AISI 4340 foi investigado devido ao fato do mesmo ser um aço baixa liga de alta resistência bastante suscetível a este fenômeno. A análise foi feita por meio do ensaio de tenacidade à fratura por flexão baseado na norma ASTM E 399 - 09. A matéria prima utilizada foi fabricada segundo dois diferentes processos, sendo o primeiro pelo método convencional de fundição e o segundo pelo processo VAR (vacuum arc refining) de maneira a se obter uma liga com menores quantidades de impurezas. Corpos-de-prova foram retirados da posição L-C das ligas, temperados a 845 oC e revenidos a 3 diferentes temperaturas (350 oC, 400 oC e 500 oC). O carregamento de hidrogênio foi feito por meio de uma célula eletroquímica, onde os corpos-de-prova foram imersos numa solução de H2SO4 0,01 M com aplicação de uma densidade de corrente de 10 mA/cm2 e dois diferentes tempos de hidrogenação, de maneira a se obter dois níveis de contaminação. Após os ensaios, foram feitas fractografias dos corpos-de-prova ensaiados para cada condição de revenimento e contaminação por hidrogênio, sendo observadas as alterações nos micromecanismos de fratura para as diferentes condições. Os resultados obtidos no ensaio de tenacidade à fratura por flexão foram correlacionados ao micromecanismo de fratura em função da dureza e contaminação por hidrogênio. O aço AISI 4340 convencional nas condições de revenimento de 400 oC e 350 oC mostrou-se bastante susceptível à fragilização por hidrogênio, apresentando reduções da ordem de 10% e 20%, respectivamente, nos valores de tenacidade à fratura de corpos-de-prova contaminados. O mesmo não foi observado no aço AISI 4340 convencional temperado e revenido a 500 oC, que não sofreu fragilização devido à sua baixa dureza. O aço AISI 4340 VAR em todas as condições de revenimento apresentou-se muito menos susceptível ao fenômeno, não sendo evidenciadas variações expressivas nas tenacidades à fratura dos corpos-de-prova contaminados e nas superfícies de fratura resultantes / Abstract: The phenomenon of hydrogen embrittlement in AISI 4340 steel was investigated due to the fact that it is a high strength low alloy steel quite susceptible to this phenomenon. The analysis was done through the fracture toughness test by bending based on ASTM E 399-09. The material used was manufactured according two different processes, the first by conventional casting process and the second by VAR (vacuum arc refining) process in order to obtain an alloy with minor amounts of impurities. Specimens were removed from the position L-C of the alloy, quenched at 845 oC and tempered at 3 different temperatures (350 oC, 400 oC and 500 oC). The hydrogen loading was made by means of an electrochemical cell where the specimens were immersed in a solution of 0.01 M H2SO4 by applying a current density of 10 mA/cm2 and two different hydrogenation times, in order to obtain two levels of contamination. After the tests were performed fractographies of specimens tested for each condition of temper and contamination by hydrogen, with observed changes in the micromechanisms of fracture for the different conditions. The test results of fracture toughness by bending were correlated with the micromechanisms of fracture, the microstructure and hydrogen contamination. The conventional AISI 4340 steel under conditions of tempering of 400 °C and 350 °C proved to be very susceptible to hydrogen embrittlement, with reductions of 10% and 20%, respectively, on the values of fracture toughness of contaminated specimens. The same was not observed in conventional AISI 4340 quenched and tempered at 500 °C, which did not presented embrittlement due to its low hardness. The AISI 4340 VAR steel in all conditions of temper proved to be much less susceptible to the phenomenon, not showing significant variations in fracture toughness of the contaminated specimens and the resulting fracture surfaces / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

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