Ce travail porte sur l'étude expérimentale et numérique de la fissuration et du cloquage induits par l'hydrogène dans des polycristaux de fer déformés plastiquement. Des essais mécaniques de traction et de cisaillement jusqu’à de grandes déformations plastiques ont été effectués sur le fer Armco, suivis de chargement cathodique en hydrogène. Le cloquage et la fissuration induites ont été caractérisés à différentes échelles, à l’aide de la surfométrie et d’analyses MEB-EBSD. Les résultats montrent la réduction du cloquage avec la déformation plastique et l’influence du mode de chargement mécanique avant chargement en hydrogène sur les caractéristiques des cloques et de la fissuration. Les fissures induites par l’hydrogène sont majoritairement transgranulaires et correspondent statistiquement avec les traces de plans de glissement du fer.Des simulations éléments finis de diffusion-piégeage après différents chargements mécaniques on tété effectuées pour mettre en évidence l’effet de la prédéformation sur la distribution d’hydrogène dans le matériau. Une modélisation phénoménologique de la croissance de pores sous pression interne a été proposée pour mettre en évidence de l’effet du mode de sollicitation sur le cloquage, en corrélation avec les tendances expérimentales. / This work deals with the experimental and numerical study of hydrogen-induced cracking and blistering in pre-strained iron polycrystals. Mechanical tensile and shear tests up to large plastic deformations were performed on Armco iron,followed by cathodic hydrogen charging. The induced blistering and cracking were characterized at different scales, using surfometry and MEB-EBSD analyzes. The results show the reduction of blistering with plastic deformation and the influence of the mechanical loading mode before hydrogen loading on the characteristics of the blisters and cracks. The induced hydrogen cracks are mainly transgranular and correspond statistically with the traces of slip planes or iron. Finite element simulations of hydrogen transport after different mechanical loading were carried out to evidence the effect of pre-straining on the hydrogen distribution in the material. A phenomenological modeling of the pore growth under internal pressure has been proposed to show the effect of the loading mode on the blistering, in correlation with the experimental tendencies.

No description available.

L’objectif de cette étude est de caractériser expérimentalement la propagation de fissures de fatigue affectée par l’hydrogène (Hydrogen-Affected Fatigue Crack Growth, HAFCG) dans diverses conditions et de clarifier le mécanisme impliqué en se concentrant sur la plasticité en pointe de fissures. Pour cet objectif, dans une première étape, l’influence de l’hydrogène sur la déformation plastique a été étudiée à l’aide d’essais de traction effectués sur un fer commercialement pur, le fer Armco, sous hydrogène gazeux. Les résultats ont montré que l’effet de l’hydrogène sur la propagation des fissures après apparition de la striction est plus important que celui sur la déformation plastique uniforme. Le HAFCG a ensuite été étudié au moyen d’essais de fissuration pour diverses valeurs de l’amplitude de facteur d’intensité de contrainte ΔK, de pression d’hydrogène (PH2 = 3,5 et 35 MPa) et de fréquence de chargement (f = 0,02 - 20 Hz). Il a été révélé que les vitesses de propagation dans un régime à ΔK élevé étaient fortement augmentées par l'hydrogène, jusqu'à 50 fois plus élevé que celles dans l'air. Le mode de rupture est une rupture intergranulaire fragile dans un régime de propagation à faible ΔK, alors qu’on observe une rupture transgranulaire de type quasi-clivage dans un régime à ΔK élevé. La valeur de ΔKtr (valeur de ΔK déclenchant l'augmentation de la vitesse de fissuration) diminue en augmentant la pression PH2. En outre, la vitesse augmente en diminuant la fréquence f. Une fois que la fréquence devient inférieure à une valeur critique, la vitesse de fissuration diminue considérablement jusqu'au même niveau que celle sous azote. La plasticité en pointe de fissure a été analysée à plusieurs échelles par microscopie optique, par mesure de déplacement hors plan et par microscopie électronique à balayage par transmission de la structure de dislocation située immédiatement sous la surface de rupture (FIB/STEM). Aucune modification claire de la zone plastique monotone en pointe de fissure sous hydrogène n’a été observée, alors qu’une réduction drastique de la plasticité cyclique associée à l'augmentation de la vitesse a été identifiée. Sur la base des observations expérimentales, des modèles de mécanisme de fissuration intergranulaire induit par l'hydrogène impliquant la coalescence des micro-vides le long de joints de grain et de mécanisme de fissuration transgranulaire induit par l'hydrogène impliquant un clivage cyclique dû à la réduction de la plasticité en pointe de fissure ont été proposés. Trois critères caractéristiques de fissuration assistée par hydrogène (ΔKtr, gradient d'hydrogène (PH2 × f)1/2 et limite supérieure de vitesse de fissuration) ont été établis. Ces critères devraient être utiles pour améliorer la conception en fatigue et la fiabilité des équipements exposés à l'hydrogène gazeux. / The objective of this study is to experimentally characterize Hydrogen-Affected Fatigue Crack Growth (HAFCG) behavior under various conditions and clarify the mechanism by focusing on crack tip plasticity. For this objective, as a first step, the influence of hydrogen on plastic deformation has been investigated by means of tensile tests in a commercially pure iron, Armco iron, under gaseous hydrogen. The results of the tests pointed out that the hydrogen effect on crack propagation is more important than that on uniform plastic deformation. Then, the HAFCG was investigated by means of FCG tests under various conditions of crack tip stress intensity ΔK, hydrogen gas pressure (PH2 = 3.5 and 35 MPa) and loading frequency (f = 0.02 – 20 Hz). It has been revealed that the FCGRs in a high ΔK regime were highly enhanced by hydrogen up to 50 times higher than the one in air. The fracture mode was a brittle intergranular fracture in a low ΔK regime, while it is a brittle transgranular quasi-cleavage one in a high ΔK regime. The value of ΔKtr (value of ΔK triggering the FCGR enhancement) decreases by increasing the pressure PH2. Besides, the FCGR enhancement increases by decreasing the frequency f. Once f becomes lower than a critical value, the HAFCG rate significantly decreases down to the same level as in nitrogen., The crack tip plasticity was analyzed in a multiscale approach by means of optical microscopy, out-of-plane displacement measurement, and scanning transmission electron microscopy of dislocation structure immediately beneath the fracture surface (FIB/STEM). As a result, no clear modification of monotonic crack tip plasticity by hydrogen was observed, while a drastic reduction of cyclic crack tip plasticity associated with the FCGR enhancement was identified. Based on the experimental evidences, models of the hydrogen-induced intergranular FCG mechanism involving microvoid coalescence along grain boundary and the hydrogen-induced transgranular FCG mechanism involving cyclic cleavage due to crack tip plasticity reduction have been proposed. Three characteristic criteria of HAFCG (ΔKtr, hydrogen gradient (PH2 × f)1/2 and upper limit of FCGR) have been established. These criteria are expected to be useful for improving fatigue design and reliability of hydrogen-related equipment.

L’objectif de ces travaux de thèse est d’étudier l’influence du rapport entre taille de défaut et longueur caractéristique de la microstructure, sur la limite de fatigue pour une durée de vie fixée d’un matériaux métallique,dans le cadre de la fatigue à grand nombre de cycle (FGNC). Le fer pur Armco est choisi comme matériau d’étude, car sa microstructure simple présente une seule longueur caractéristique à l’échelle mésoscopique (échelle des grains) : la taille de grain. Le but de l’étude revient ainsi à étudier la compétition entre un effet de structure (défaut surfacique)et un effet matériau (taille de grain) dans le cadre de sollicitations mécaniques en FGNC.Afin d’obtenir une taille de défaut comparable mais aussi inférieure à la taille de grain du matériau, un protocole thermomécanique a été élaboré pour augmenter la taille de grain. Des essais de FGNC, utilisant des éprouvettes issues des deux tailles de microstructures (matériau initial et celui écroui traité) dans lesquelles sont introduits des défauts hémisphériques de tailles différentes, ont été effectués pour estimer les limites de fatigue pour différents rapports taille de défaut / taille de grain. Lorsque les diagrammes de Kitagawa sont présentés en valeurs relatives(limite de fatigue / celle du matériau sans défaut en fonction de la taille de défaut / taille de grain), il existe une seule courbe qui combine les deux microstructures. Ce diagramme de Kitagawa sans dimension permet ainsi d’analyser la réduction de la limite de fatigue causée par un défaut. L’utilisation de la taille relative du défaut par rapport à la dimension microstructurale caractéristique apparaît comme plus pertinente que l’emploi de la taille physique réelle du défaut.Ces résultats expérimentaux sont utilisés pour reproduire les essais en FGNC avec des simulations Éléments Finis sur des microstructures 3D représentatives du fer Armco. La compétition existant entre la concentration de contrainte induite par le défaut géométrique et les régions fortement sollicitées de la microstructure engendrées parl’anisotropie du comportement mécanique des grains est étudiée. Un critère mésoscopique (à partir des grandeurs mécaniques moyennées par grain) basé sur une approche statistique permet de retrouver l’allure du diagramme de Kitagawa adimensionné, c’est-à-dire la taille relative du défaut critique à partir de laquelle ce dernier prend le passur l’hétérogénéité de la réponse de la microstructure et conditionne ainsi la tenue en fatigue du polycristal. La modification du critère mésoscopique par la prise en compte des hétérogénéités intragranulaires (via l’écart-type par grain des grandeurs mécaniques) est discutée. / The objective of this thesis is to study the influence of the ratio between the defect size and themicrostructure characteristic length on the fatigue limit (for a fixed fatigue life) of a metallic material, under highcycle fatigue (HCF). Pure Armco iron is chosen because its simple microstructure has a single characteristic lengthat the mesoscopic scale (grain scale) : the grain size. The aim of the study is thus to study the competition betweena structural effect (surface defect) and a material effect (grain size) in the context of mechanical stresses in HCF.In order to obtain a comparable different grain size, a thermomechanical protocol has been developed. HCF tests,using specimens from both microstructure sizes (initial material and processed hardened material) in which hemisphericaldefects of different sizes were introduced, were performed to estimate the fatigue limits for different defectsize / grain size ratios. When Kitagawa diagrams are presented in relative values (fatigue limit / fatigue limit ofdefect free material versus defect size / grain size), there is a single curve that combines the two microstructures.This dimensionless Kitagawa diagram thus makes it possible to analyze the reduction of the fatigue limit inducedby a defect. The use of the relative size of the defect with respect to the characteristic microstructural dimensionappears to be more relevant than the use of the physical size of the defect.These experimental results are used to reproduce the HCF tests with Finite Element simulations on 3D microstructuresrepresentative of Armco iron. The competition existing between the stress concentration induced by thegeometrical defect and the highly stressed regions of the microstructure generated by the anisotropy of the mechanicalbehavior of the grains is studied. A mesoscopic criterion (involving mechanical quantities averaged by grain)based on a statistical approach allows to find the evolution of the dimensionless Kitagawa diagram, ie the relativesize of the critical defect from which it predominates over the response heterogeneity of the microstructure and thusgoverns the fatigue behavior of the polycrystal. The modification of the mesoscopic criterion by taking into accountintragranular heterogeneities (with the standard deviation per grain of mechanical quantities) is discussed.

Le bruit magnétomécanique correspond à la réorganisation de la microstructure magnétique d'un matériau ferromagnétique sous l'effet d'une contrainte. Ce phénomène est dû à la mobilité des parois de Bloch à 90°.<br />Différents états métallurgiques d'un fer à 0,1% C (recuit, trempe, revenus) ont été caractérisés, les résultats ont été comparés à ceux des méthodes Barkhausen et PTE.<br />Un dispositif d'essai en fatigue en flexion rotative avec mesure in situ du bruit magnétomécanique a été réalisé. Le fer Armco a été étudié sous différentes charges, les résultats interprétés en termes d'interaction microstructure cristalline, microstructure magnétique et phénomène de traînage magnétique. L'identification du début de l'endommagement s'inscrit dans l'évaluation «du potentiel restant ». <br />Une modélisation à une dimension traduisant l'équilibre énergétique d'une paroi de Bloch à 90° soumise à une contrainte est proposée.<br />Cette étude préliminaire se situe à l'interface entre le micromagnétisme, le contrôle non destructif et le frottement intérieur.

Foi avaliada a influência de microrganismos na corrosão e na reação de absorção ou liberação de hidrogênio em amostras de ferro Armco e do aço SAE 4140. Utilizou-se um consórcio microbiano, no qual estava presente a bactéria redutora de sulfato (BRS) Desulfovíbrio desulfuricans que, por meio de reações metabólicas, produz gás sulfídrico (H2S), conhecido por catalisar a reação de hidrogênio. Através de ensaios de permeação de hidrogênio em amostras de ferro Armco determinou-se a corrente de permeação e a concentração superficial de hidrogênio desenvolvida, utilizando-se uma célula de Devanathan-Stachurski. Primeiramente determinou-se a corrente em meio bacteriológico Postgate C abiótico, substituindo-o então pelo meio bacteriológico inoculado com o consórcio de microrganismos. Os conseqüentes transientes de corrente foram determinados em diferentes valores de potenciais catódicos, entre –1500 mV(ENH) e o potencial de corrosão do ferro. Observou-se um aumento na corrente de permeação após a colocação dos meios inoculados o que significa um maior fluxo de hidrogênio se difundindo através da amostra. Porém, após um determinado período de tempo (em torno de 30 horas) a corrente de permeação tende a se estabilizar em decorrência de alguns fatores como os depósitos biológicos formados na superfície metálica (biofilme), a formação de filmes de precipitação de sais em função da polarização catódica aplicada e também devido ao filme de sulfeto de ferro, dificultando desta forma a passagem do hidrogênio. Ensaios de tração de baixa taxa de deformação (BTD) com corpos de prova de aço SAE 4140, foram utilizados nos mesmos meios citados, ao potencial de corrosão e com aplicação de potencial catódico de –750 e –1000 mV(ENH), para avaliar a morfologia da fratura. Em meios com H2S produzido metabolicamente, observou-se fratura frágil, associada à fragilização pelo hidrogênio, ao contrário dos resultados obtidos em meios sem o H2S, que promoveram fratura dúctil. Ensaios potenciostáticos com as amostras de ferro Armco e o aço SAE 4140 foram realizados em condições semelhantes aos ensaios de permeação e de baixa taxa de deformação. Os corpos de prova foram analisados por microscopia eletrônica de varredura para observar o biofilme, bem como a morfologia da corrosão. Nos ensaios de potencial a circuito aberto intensa colonização da superfície por bactérias foi observada após duas horas, porém com aplicação de potenciais catódicos (–1000 mV(ENH)), observou-se um número menor de células bacterianas aderidas à superfície metálica. Os produtos metabólicos, principalmente o H2S, provenientes do metabolismo das bactérias redutoras de sulfato (BRS), aceleram o processo de corrosão, principalmente quando o meio em questão propicia zonas de anaerobiose como a formação de biofilme e a formação de sulfeto de ferro (FeS) sobre a superfície metálica. / The present investigation was undertaken to evaluate the influence of microorganisms on the corrosion and on the hydrogen absortion and evolution reaction of Armco iron and SAE 4140 steel samples. A mixed group of microbes was used, in which was present the Sulfate-Reducing Bacteria (SRB) Desulfovibrio desulfuricans that, through metabolic reactions, produces hydrogen sulfide gas (H2S), recognized for catalyzing the hydrogen reaction. The permeation current of hydrogen and its concentration on the surface were determined on Armco iron samples, using a Devanathan-Stachurski cell. The experiments were carried out in an abiotic Postgate C bacterial growth medium and after the current stabilization, which lasted 24 hours, this medium was replaced by on environment inoculated with microorganisms. The consequent current transients were determined for different cathodic potentials, from –1500 mV(ENH) to the iron corrosion potential. An increase in the permeation current was observed after the addition of the inoculated environment, which means a higher flux of hydrogen diffusing through the sample. However, after a certain period of time (around 30 hours), the permeation current tended stabilize, due to the biologic deposits formed on the metallic surface and to the films precipitated due to the cathodic polarization, which reduce hydrogen ion migration. Low-strain rate tests with SAE 4140 steel samples were used in the same environments, at the corrosion potential and with the application of cathodic potentials of –750 and –1000 mV(ENH) to evaluate the fracture morphology. In environments with metabolically produced H2S, a fragile fracture was observed, associated with hydrogen embrittlement, while in H2S-free environments a ductile fracture was produced. Potentiostatic tests with Armco iron and SAE 4140 steel samples were performed in similar conditions to permeation and low-strain rate tests. The samples were analyzed by Scanning Electron Microscopy (SEM) in order to observe the biofilm, as well as the corrosion morphology. In the samples without applied potential, a heavy surface colonization by bacteria was observed after 2 hours, while in the samples under cathodic potential (–1000 mV(ENH)) only few bacterial cells adhered to the metallic surface. It was observed that Sulfate-Reducing Bacteria (SRB) accelerate the corrosion process, mainly when the environment is able to provide anaerobeose zones such as the biofilm and the iron sulfide (FeS) on the metallic surface.

Foi avaliada a influência de microrganismos na corrosão e na reação de absorção ou liberação de hidrogênio em amostras de ferro Armco e do aço SAE 4140. Utilizou-se um consórcio microbiano, no qual estava presente a bactéria redutora de sulfato (BRS) Desulfovíbrio desulfuricans que, por meio de reações metabólicas, produz gás sulfídrico (H2S), conhecido por catalisar a reação de hidrogênio. Através de ensaios de permeação de hidrogênio em amostras de ferro Armco determinou-se a corrente de permeação e a concentração superficial de hidrogênio desenvolvida, utilizando-se uma célula de Devanathan-Stachurski. Primeiramente determinou-se a corrente em meio bacteriológico Postgate C abiótico, substituindo-o então pelo meio bacteriológico inoculado com o consórcio de microrganismos. Os conseqüentes transientes de corrente foram determinados em diferentes valores de potenciais catódicos, entre –1500 mV(ENH) e o potencial de corrosão do ferro. Observou-se um aumento na corrente de permeação após a colocação dos meios inoculados o que significa um maior fluxo de hidrogênio se difundindo através da amostra. Porém, após um determinado período de tempo (em torno de 30 horas) a corrente de permeação tende a se estabilizar em decorrência de alguns fatores como os depósitos biológicos formados na superfície metálica (biofilme), a formação de filmes de precipitação de sais em função da polarização catódica aplicada e também devido ao filme de sulfeto de ferro, dificultando desta forma a passagem do hidrogênio. Ensaios de tração de baixa taxa de deformação (BTD) com corpos de prova de aço SAE 4140, foram utilizados nos mesmos meios citados, ao potencial de corrosão e com aplicação de potencial catódico de –750 e –1000 mV(ENH), para avaliar a morfologia da fratura. Em meios com H2S produzido metabolicamente, observou-se fratura frágil, associada à fragilização pelo hidrogênio, ao contrário dos resultados obtidos em meios sem o H2S, que promoveram fratura dúctil. Ensaios potenciostáticos com as amostras de ferro Armco e o aço SAE 4140 foram realizados em condições semelhantes aos ensaios de permeação e de baixa taxa de deformação. Os corpos de prova foram analisados por microscopia eletrônica de varredura para observar o biofilme, bem como a morfologia da corrosão. Nos ensaios de potencial a circuito aberto intensa colonização da superfície por bactérias foi observada após duas horas, porém com aplicação de potenciais catódicos (–1000 mV(ENH)), observou-se um número menor de células bacterianas aderidas à superfície metálica. Os produtos metabólicos, principalmente o H2S, provenientes do metabolismo das bactérias redutoras de sulfato (BRS), aceleram o processo de corrosão, principalmente quando o meio em questão propicia zonas de anaerobiose como a formação de biofilme e a formação de sulfeto de ferro (FeS) sobre a superfície metálica. / The present investigation was undertaken to evaluate the influence of microorganisms on the corrosion and on the hydrogen absortion and evolution reaction of Armco iron and SAE 4140 steel samples. A mixed group of microbes was used, in which was present the Sulfate-Reducing Bacteria (SRB) Desulfovibrio desulfuricans that, through metabolic reactions, produces hydrogen sulfide gas (H2S), recognized for catalyzing the hydrogen reaction. The permeation current of hydrogen and its concentration on the surface were determined on Armco iron samples, using a Devanathan-Stachurski cell. The experiments were carried out in an abiotic Postgate C bacterial growth medium and after the current stabilization, which lasted 24 hours, this medium was replaced by on environment inoculated with microorganisms. The consequent current transients were determined for different cathodic potentials, from –1500 mV(ENH) to the iron corrosion potential. An increase in the permeation current was observed after the addition of the inoculated environment, which means a higher flux of hydrogen diffusing through the sample. However, after a certain period of time (around 30 hours), the permeation current tended stabilize, due to the biologic deposits formed on the metallic surface and to the films precipitated due to the cathodic polarization, which reduce hydrogen ion migration. Low-strain rate tests with SAE 4140 steel samples were used in the same environments, at the corrosion potential and with the application of cathodic potentials of –750 and –1000 mV(ENH) to evaluate the fracture morphology. In environments with metabolically produced H2S, a fragile fracture was observed, associated with hydrogen embrittlement, while in H2S-free environments a ductile fracture was produced. Potentiostatic tests with Armco iron and SAE 4140 steel samples were performed in similar conditions to permeation and low-strain rate tests. The samples were analyzed by Scanning Electron Microscopy (SEM) in order to observe the biofilm, as well as the corrosion morphology. In the samples without applied potential, a heavy surface colonization by bacteria was observed after 2 hours, while in the samples under cathodic potential (–1000 mV(ENH)) only few bacterial cells adhered to the metallic surface. It was observed that Sulfate-Reducing Bacteria (SRB) accelerate the corrosion process, mainly when the environment is able to provide anaerobeose zones such as the biofilm and the iron sulfide (FeS) on the metallic surface.

Foi avaliada a influência de microrganismos na corrosão e na reação de absorção ou liberação de hidrogênio em amostras de ferro Armco e do aço SAE 4140. Utilizou-se um consórcio microbiano, no qual estava presente a bactéria redutora de sulfato (BRS) Desulfovíbrio desulfuricans que, por meio de reações metabólicas, produz gás sulfídrico (H2S), conhecido por catalisar a reação de hidrogênio. Através de ensaios de permeação de hidrogênio em amostras de ferro Armco determinou-se a corrente de permeação e a concentração superficial de hidrogênio desenvolvida, utilizando-se uma célula de Devanathan-Stachurski. Primeiramente determinou-se a corrente em meio bacteriológico Postgate C abiótico, substituindo-o então pelo meio bacteriológico inoculado com o consórcio de microrganismos. Os conseqüentes transientes de corrente foram determinados em diferentes valores de potenciais catódicos, entre –1500 mV(ENH) e o potencial de corrosão do ferro. Observou-se um aumento na corrente de permeação após a colocação dos meios inoculados o que significa um maior fluxo de hidrogênio se difundindo através da amostra. Porém, após um determinado período de tempo (em torno de 30 horas) a corrente de permeação tende a se estabilizar em decorrência de alguns fatores como os depósitos biológicos formados na superfície metálica (biofilme), a formação de filmes de precipitação de sais em função da polarização catódica aplicada e também devido ao filme de sulfeto de ferro, dificultando desta forma a passagem do hidrogênio. Ensaios de tração de baixa taxa de deformação (BTD) com corpos de prova de aço SAE 4140, foram utilizados nos mesmos meios citados, ao potencial de corrosão e com aplicação de potencial catódico de –750 e –1000 mV(ENH), para avaliar a morfologia da fratura. Em meios com H2S produzido metabolicamente, observou-se fratura frágil, associada à fragilização pelo hidrogênio, ao contrário dos resultados obtidos em meios sem o H2S, que promoveram fratura dúctil. Ensaios potenciostáticos com as amostras de ferro Armco e o aço SAE 4140 foram realizados em condições semelhantes aos ensaios de permeação e de baixa taxa de deformação. Os corpos de prova foram analisados por microscopia eletrônica de varredura para observar o biofilme, bem como a morfologia da corrosão. Nos ensaios de potencial a circuito aberto intensa colonização da superfície por bactérias foi observada após duas horas, porém com aplicação de potenciais catódicos (–1000 mV(ENH)), observou-se um número menor de células bacterianas aderidas à superfície metálica. Os produtos metabólicos, principalmente o H2S, provenientes do metabolismo das bactérias redutoras de sulfato (BRS), aceleram o processo de corrosão, principalmente quando o meio em questão propicia zonas de anaerobiose como a formação de biofilme e a formação de sulfeto de ferro (FeS) sobre a superfície metálica. / The present investigation was undertaken to evaluate the influence of microorganisms on the corrosion and on the hydrogen absortion and evolution reaction of Armco iron and SAE 4140 steel samples. A mixed group of microbes was used, in which was present the Sulfate-Reducing Bacteria (SRB) Desulfovibrio desulfuricans that, through metabolic reactions, produces hydrogen sulfide gas (H2S), recognized for catalyzing the hydrogen reaction. The permeation current of hydrogen and its concentration on the surface were determined on Armco iron samples, using a Devanathan-Stachurski cell. The experiments were carried out in an abiotic Postgate C bacterial growth medium and after the current stabilization, which lasted 24 hours, this medium was replaced by on environment inoculated with microorganisms. The consequent current transients were determined for different cathodic potentials, from –1500 mV(ENH) to the iron corrosion potential. An increase in the permeation current was observed after the addition of the inoculated environment, which means a higher flux of hydrogen diffusing through the sample. However, after a certain period of time (around 30 hours), the permeation current tended stabilize, due to the biologic deposits formed on the metallic surface and to the films precipitated due to the cathodic polarization, which reduce hydrogen ion migration. Low-strain rate tests with SAE 4140 steel samples were used in the same environments, at the corrosion potential and with the application of cathodic potentials of –750 and –1000 mV(ENH) to evaluate the fracture morphology. In environments with metabolically produced H2S, a fragile fracture was observed, associated with hydrogen embrittlement, while in H2S-free environments a ductile fracture was produced. Potentiostatic tests with Armco iron and SAE 4140 steel samples were performed in similar conditions to permeation and low-strain rate tests. The samples were analyzed by Scanning Electron Microscopy (SEM) in order to observe the biofilm, as well as the corrosion morphology. In the samples without applied potential, a heavy surface colonization by bacteria was observed after 2 hours, while in the samples under cathodic potential (–1000 mV(ENH)) only few bacterial cells adhered to the metallic surface. It was observed that Sulfate-Reducing Bacteria (SRB) accelerate the corrosion process, mainly when the environment is able to provide anaerobeose zones such as the biofilm and the iron sulfide (FeS) on the metallic surface.