[pt] Tradicionalmente, tanto os metais de solda, quanto os aço da classe Cr-Mo, são considerados susceptíveis ao fenômeno de fragilização ao revenido. O presente trabalho tem como objetivo avaliar metais de solda do tipo 2,25%Cr-1,0%Mo com diferentes teores de Mn (0,4% - 1,1%) obtidos pelo processo de eletrodo revestido submetidos aos tratamentos térmicos de alívio de tensões (TTAT), de step-cooling (TTSC) e TTAT seguido de TTSC. Verificou-se através de ensaios de impacto Charpy-V que o TTAT, promoveu um ganho de tenacidade e resistência para teores de Mn entre 0,9% - 1,1%, enquanto que a aplicação do TTSC não promoveu mudanças significativas na tenacidade para todos os teores estudados. Observou-se que, as variações microestruturais em função dos tratamentos térmicos aplicados para uma estrutura predominantementebainítica, detectáveis por microscopia eletrônica de varredura, foram pequenas para os teores de Mn estudados. A utilização dos índices tradicionais como o fator X , fator PE e fator J de susceptibilidade à fragilização se mostrou incompatível com as respostas obtidas nos ensaios de impacto dos metais de solda avaliados, sugerindo a necessidade de uma revisão dos fatores para a avaliação da tendência para a fragilização ou mesmo considerar que os materiais atualmente produzidos não sejam mais susceptíveis ao fenômeno fragilização ao revenido mesmo após tratamentos térmicos de alívio de tensões. / [en] Traditionally, both Cr-Mo class steels and the weld metals produced in joining such materials have been considered to be susceptible to the phenomenon of temper embrittlement. The current study evaluates 2,25%Cr-1,0%Mo type weld metals with varying Mn levels (0,4%- 1,1%), produced using coated electrodes with an SMAW process. The welded joints were subjected to three types of heat treatment; either stress relief annealing, or step cooling or stress relief annealing and step cooling. Charpy-V impact testing results indicated a gain in toughness and tensile strength for materials with Mn levels in the 0,9% to 1.1% range, and that the step cooling alone did not cause any appreciable changes in toughness for any of the Mn levels studied. Furthermore, scanning electron microscopy revealed that the bainitic microstructure of the materials studied was relatively little affected by the applied heat treatments. The values obtained for the traditional embrittlement indexes, X -Factor, PE-Factor and J-Factor were observed to be inconsistent and incompatible with the actual quantified impact behaviour of the weld metals investigated. This would suggest that a reevaluation of these traditional embrittlement indexes should be considered. The temper embrittlement susceptibility of steels of this type as they are currently manufactured may, in this way, come to be considered much lower than would otherwise be the case, even after post weld heat treatments.

Em projetos de oleodutos e gasodutos utilizam-se aços de alta resistência e baixa liga (ARBL), como o aço API 5L X80. Na soldagem multipasse destas tubulações, a zona afetada pelo calor (ZAC) do passe de raiz é submetida a um novo ciclo térmico pelos passes de soldagem subsequentes. Isto resulta em alterações nos valores das propriedades físicas. Nos aços ARBL, a ZAC de grãos grosseiros reaquecida intercriticamente (IC-ZACGG) pode se tornar uma zona frágil localizada, isto é, uma zona com maior dureza. Consequentemente, falhas estruturais podem ocorrer, ocasionando paradas não desejadas no transporte de fluidos. O objetivo deste trabalho é desenvolver uma metodologia baseada no modelo de fontes de calor distribuídas de Mhyr e Gröng, para avaliar o fluxo de calor na soldagem considerando as propriedades físicas dependentes da temperatura. Estender a aplicação desta ferramenta em soldagens multipasses para identificar sub-regiões da ZAC de um passe anterior sendo afetada pela ZAC de passes subsequentes. As isotermas simuladas foram validadas através de medições realizadas em macrografias de juntas soldadas. Os ciclos térmicos simulados foram validados através das temperaturas máximas atingidas e pelos tempos de resfriamento de 800 a 500 ºC (?t8-5) dos ciclos térmicos experimentais. Ao aplicar a metodologia proposta, foi possível delimitar com acurácia as regiões reaquecidas da ZAC e analisar os efeitos dos passes subsequentes em cada uma das sub-regiões da ZAC do passe de raiz. A IC-ZACGG na região do passe de raiz foi localizada, mas não se comportou como zona frágil devido à boa soldabilidade do aço API 5L X80 comprovada pelos ensaios de dureza e de tenacidade ao impacto Charpy-V. / In pipelines projects, the high strength low alloy (HSLA) steels are used, such as the API 5L X80 steel. During the multipass welding of these pipes, the heat affected zone (HAZ) of the root pass is subjected to a new thermal cycle by the subsequent welding passes. This results in changes in the values of the physical properties. In the HSLA steels, the intercritical reheated coarse-grained heat-affected zone (IR-CGHAZ) can become a local brittle zone, that is, a region with greater hardness. Consequently, structural failures could happen, causing undesired shutdowns in fluid transportation. The objective of this work is to develop a methodology based on the distributed heat sources model of Mhyr and Gröng, to evaluate the heat flux in the welding considering the temperature-dependent physical properties. Extend the application of this tool in multipass welds to identify HAZ subregions of a previous pass being affected by the HAZ of subsequent passes. The simulated isotherms were validated through measurements made on macrographs of welded joints. The simulated thermal cycles were validated through the maximum temperatures reached and the cooling times from 800 °C to 500 ºC (?t8-5) of the experimental thermal cycles. By applying the proposed methodology, it was possible to accurately delimit reheated HAZ regions and analyze the effects of subsequent passes in each of the root pass HAZ subregions. The IRCGHAZ in the root pass region was localized, but it did not behave as a brittle zone due to the good weldability of the API 5L X80 steel as proven by the hardness and Charpy-V impact tests.

Os aços inoxidáveis duplex (AIDs) são materiais com um excelente desempenho tanto mecânico como à corrosão. Inúmeras pesquisas tem sido desenvolvidas para aprimorar a soldabilidade destas ligas. Algumas transformações de fase, que são passíveis de ocorrer durante o processo de soldagem, podem prejudicar seriamente o desempenho das juntas. Foram simuladas microestruturas da região da zona afetada pelo calor submetida a temperaturas elevadas (ZACTE), utilizando um modelo proposto de fluxo de calor. Abordaram-se aspectos fundamentais da precipitação de austenita secundária, de nitreto de cromo e as suas interações na ZACTE de soldas multipasse. Finalmente, foram realizados testes de tenacidade e de resistência à corrosão para avaliar o efeito das transformações de fase estudadas no desempenho das juntas soldadas. Os tratamento térmicos e simulações da ZACTE foram realizadas num equipamento GleebleÒ. As microestruturas foram analisadas mediante microscopia ótica e eletrônica de varredura e de transmissão. Junto com a microscopia eletrônica foram realizadas microanálises químicas das fases estudadas. Baseando-se nos resultados obtidos, verificou-se que nem todos os AIDs são susceptíveis de ferritizar. Este fato tem uma grande influência no comportamento metalúrgico e na soldabilidade destes aços. Quanto aos aspectos fundamentais da metalurgia destes aços, observou-se uma estreita interação entre a precipitação da austenita secundária e os nitretos de cromo, chegando-se a propor um mecanismo de nucleação da austenita secundária intragranular a partir dos nitretos. Por último, foi constatado que o efeito deletério da austenita secundária intragranular na resistência à corrosão pode ser evitado mediante a adequada elaboração do procedimento de soldagem. / Duplex stainless steels (DSS) have excellent mechanical and corrosion properties. Many researches have been developed regarding the weldability of these alloys. There are some phase transformations that take place during the welding process, which may impair the welded joint behavior. High temperature heat-affected zone (HTHAZ) microstructures were simulated using a proposed heat flow model. Fundamental aspects of the secondary austenite and chromium nitride precipitation, and its interactions in the HTHAZ of multipass welds, were studied. In addition, toughness and corrosion tests were done to evaluate the influence of the studied phase transformations on the weld behavior. A GleebleÒ system was used to do the heat treatments and HTHAZ simulations. The microstructures were analyzed by means of optic and electron microscopy. Along with the electron microscopy it was done chemical microanalysis of the studied phases. Based on results, it was verified that not all DSSs can be ferritized. This fact has a strong influence on metallurgical behavior and weldability of these alloys. Regarding to the metallurgical fundamental aspects of these steels, it was observed a remarkable interaction between secondary austenite and chromium nitride precipitation. Thus, it was proposed a mechanism of intragranular secondary austenite precipitation from chromium nitrides. It was also verified, how the deleterious effect of intragranular secondary austenite in the corrosion resistance can be avoided by means of appropriate welding procedures.

Les travaux effectués au cours de cette thèse ont pour objectif d’étudier et de modéliser une opération de soudage multipasse d’un acier à haute limite d’élasticité utilisé en construction navale. Dans ce cadre il s’agit de prédire les conséquences métallurgiques et mécaniques du procédé et tout particulièrement la répartition et l’intensité des contraintes résiduelles post- soudage nécessaires pour analyser l’intégrité de la structure navale en service. Deux maquettes représentatives d’un joint d’angle en Té ont permis de caractériser l’évolution des cycles thermiques, de la microstructure et des contraintes résiduelles (estimées par les méthodes du contour et du trou profond) après chaque passe de soudage. La suite de l’étude concerne la caractérisation et la modélisation du comportement thermo-métallurgique et thermo- mécanique des différentes phases apparaissant au cours du soudage. La dernière partie porte sur l’implémentation des modèles retenus dans le code de calcul élément finis Abaqus à l’aide de sous-programmes spécifiques. Une étape de transition d’échelle a permis de décrire le comportement thermomécanique multiphasé de cet acier. Des calculs préliminaires ont été conduits pour valider l’implémentation des modèles sur des cas simples. Différents couplages ont été réalisés, soit une analyse thermique puis thermo-métallurgique, pour estimer la dureté après chaque passe et enfin métallurgique-mécanique pour prédire les contraintes résiduelles pour le procédé de soudage multipasse. Les résultats des calculs éléments finis ont été discutés et comparés aux résultats expérimentaux obtenus dans la première partie de cette étude. / This thesis aims at studying and modeling a multipass welding operation of a high strength steel used in shipbuilding. In this framework, work focus on predicting the metallurgical and mechanical consequences of the process and, in particular, the residual stress distribution after welding. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Two welding mock-ups which are representative of a T- joint were used to characterize the evolution of thermal cycles, microstructure and residual stresses (measured by contour method and deep hole drilling) after each welding pass. Metallurgical and mechanical behaviors were thoroughly characterized in order to feed numerical models with reliable constitutive equations. The last part deals with the implementation of the models in the finite element calculation code Abaqus using specific subroutines. A scale transition procedure has been added to describe the thermomechanical multiphase behavior of the steel. Preliminary calculations were carried out for simple cases to validate the implementation of models. Different numerical couplings were made. First a thermal analysis then a thermo-metallurgical analysis, to estimate the hardness after each welding pass. Finally, a metallurgical-mechanical analysis is achieved for the prediction of residual stresses due to multipass welding. The results of the finite element calculations were discussed and compared with the experimental results obtained in the first part of this work.

An experimental investigation has been undertaken to study the depth of cut in multipass abrasive waterjet (AWJ) cutting of an 87% alumina ceramic with controlled nozzle oscillation. The experimental data have been statistically analysed to study the trends of the depth of cut with respect to the process parameters. It has been found that multipass cutting with controlled nozzle oscillation can significantly increase the depth of cut. Within the same cutting time and using the same cutting parameters other than the jet traverse speed, it has been found that multipass cutting with nozzle oscillation can increase the depth of cut by an average of 74.6% as compared to single pass cutting without nozzle oscillation. Furthermore, a multipass cutting with higher nozzle traverse speeds can achieve a larger depth of cut than a single pass cutting at a low traverse speed within the same cutting time. A recommendation has been made for the selection of appropriate process parameters for multipass cutting with nozzle oscillation. In order to estimate the depth of cut on a mathematical basis, predictive models for the depth of cut in multipass cutting with and without nozzle oscillation have been developed using a dimensional analysis technique. The model development starts with the models for single pass cutting which are then extended to multipass cutting where considerations are given to the change of the actual standoff distance after each pass and the variation of kerf width. These predictive models has been numerically studied for their plausibility by assessing their predicted trends with respect to the various process variables, and verified qualitatively and quantitatively based on the experimental data. The model assessment reveals that the developed models correlate very well with the experimental results and can give adequate predictions of this cutting performance measure in process planning.

Le développement du laser a ouvert la voix à l'exploration de nouveaux domaines scientifiques et industriels. Les impulsions laser à haute intensité sont un outil unique pour les études d'interaction lumière/matière et leurs applications. Mais elles sont générées par des systèmes laser reposant sur l'utilisation de milieux à gain en verre pompés par des lampes flashes et sont donc intrinsèquement limitées en termes de cadence et d'efficacité. Le développement, au cours de ces dernières années, des lasers semi-conducteurs a attiré l'attention sur une nouvelle classe de lasers, les « laser solides pompés par diodes » (DPSSL). Ils possèdent une grande efficacité et sont des candidats de choix pour les systèmes compacts à haute puissance moyenne requis pour des applications industrielles, mais aussi en tant que sources de pompe à haute puissance pour des lasers ultra-intenses. Les travaux décrits dans cette thèse s'inscrivent dans le cadre du système laser Lucia (1 kilowatt de puissance moyenne), actuellement en construction au «Laboratoire d'Utilisation des Intenses lasers» (LULI) à l'Ecole Polytechnique, France. La génération d'impulsions laser de durée sub-10 nanosecondes avec des énergies allant jusqu'à 100 joules et des taux de répétition de 10 hertz est principalement limitée par l'émission spontanée amplifiée (ASE) et les effets thermiques. L'étude de ces limitations est le thème central de ce travail. Leur impact est discuté dans le cadre d'un premier jalon énergétique fixé vers 10 joules. Le système laser mis au point est présenté en détails depuis l'oscillateur jusqu'à la fin de la chaine d'amplification. Une discussion complète de l'impact de l'ASE et des effets thermiques est complétée par des vérifications expérimentales. Les modèles de simulation informatique développés sont validés puis utilisés pour prédire les performances du système laser qui, lors d'une première activation, à atteint un niveau d'énergie de 7 joules en régime mono-coup et de 6,6 joules pour un taux de répétition de 2 hertz. Les limitations actuelles sont discutées ainsi que les approches envisagées pour des développements futurs.

An experimental investigation has been undertaken to study the depth of cut in multipass abrasive waterjet (AWJ) cutting of an 87% alumina ceramic with controlled nozzle oscillation. The experimental data have been statistically analysed to study the trends of the depth of cut with respect to the process parameters. It has been found that multipass cutting with controlled nozzle oscillation can significantly increase the depth of cut. Within the same cutting time and using the same cutting parameters other than the jet traverse speed, it has been found that multipass cutting with nozzle oscillation can increase the depth of cut by an average of 74.6% as compared to single pass cutting without nozzle oscillation. Furthermore, a multipass cutting with higher nozzle traverse speeds can achieve a larger depth of cut than a single pass cutting at a low traverse speed within the same cutting time. A recommendation has been made for the selection of appropriate process parameters for multipass cutting with nozzle oscillation. In order to estimate the depth of cut on a mathematical basis, predictive models for the depth of cut in multipass cutting with and without nozzle oscillation have been developed using a dimensional analysis technique. The model development starts with the models for single pass cutting which are then extended to multipass cutting where considerations are given to the change of the actual standoff distance after each pass and the variation of kerf width. These predictive models has been numerically studied for their plausibility by assessing their predicted trends with respect to the various process variables, and verified qualitatively and quantitatively based on the experimental data. The model assessment reveals that the developed models correlate very well with the experimental results and can give adequate predictions of this cutting performance measure in process planning.

Os aços inoxidáveis duplex (AIDs) são materiais com um excelente desempenho tanto mecânico como à corrosão. Inúmeras pesquisas tem sido desenvolvidas para aprimorar a soldabilidade destas ligas. Algumas transformações de fase, que são passíveis de ocorrer durante o processo de soldagem, podem prejudicar seriamente o desempenho das juntas. Foram simuladas microestruturas da região da zona afetada pelo calor submetida a temperaturas elevadas (ZACTE), utilizando um modelo proposto de fluxo de calor. Abordaram-se aspectos fundamentais da precipitação de austenita secundária, de nitreto de cromo e as suas interações na ZACTE de soldas multipasse. Finalmente, foram realizados testes de tenacidade e de resistência à corrosão para avaliar o efeito das transformações de fase estudadas no desempenho das juntas soldadas. Os tratamento térmicos e simulações da ZACTE foram realizadas num equipamento GleebleÒ. As microestruturas foram analisadas mediante microscopia ótica e eletrônica de varredura e de transmissão. Junto com a microscopia eletrônica foram realizadas microanálises químicas das fases estudadas. Baseando-se nos resultados obtidos, verificou-se que nem todos os AIDs são susceptíveis de ferritizar. Este fato tem uma grande influência no comportamento metalúrgico e na soldabilidade destes aços. Quanto aos aspectos fundamentais da metalurgia destes aços, observou-se uma estreita interação entre a precipitação da austenita secundária e os nitretos de cromo, chegando-se a propor um mecanismo de nucleação da austenita secundária intragranular a partir dos nitretos. Por último, foi constatado que o efeito deletério da austenita secundária intragranular na resistência à corrosão pode ser evitado mediante a adequada elaboração do procedimento de soldagem. / Duplex stainless steels (DSS) have excellent mechanical and corrosion properties. Many researches have been developed regarding the weldability of these alloys. There are some phase transformations that take place during the welding process, which may impair the welded joint behavior. High temperature heat-affected zone (HTHAZ) microstructures were simulated using a proposed heat flow model. Fundamental aspects of the secondary austenite and chromium nitride precipitation, and its interactions in the HTHAZ of multipass welds, were studied. In addition, toughness and corrosion tests were done to evaluate the influence of the studied phase transformations on the weld behavior. A GleebleÒ system was used to do the heat treatments and HTHAZ simulations. The microstructures were analyzed by means of optic and electron microscopy. Along with the electron microscopy it was done chemical microanalysis of the studied phases. Based on results, it was verified that not all DSSs can be ferritized. This fact has a strong influence on metallurgical behavior and weldability of these alloys. Regarding to the metallurgical fundamental aspects of these steels, it was observed a remarkable interaction between secondary austenite and chromium nitride precipitation. Thus, it was proposed a mechanism of intragranular secondary austenite precipitation from chromium nitrides. It was also verified, how the deleterious effect of intragranular secondary austenite in the corrosion resistance can be avoided by means of appropriate welding procedures.

Em projetos de oleodutos e gasodutos utilizam-se aços de alta resistência e baixa liga (ARBL), como o aço API 5L X80. Na soldagem multipasse destas tubulações, a zona afetada pelo calor (ZAC) do passe de raiz é submetida a um novo ciclo térmico pelos passes de soldagem subsequentes. Isto resulta em alterações nos valores das propriedades físicas. Nos aços ARBL, a ZAC de grãos grosseiros reaquecida intercriticamente (IC-ZACGG) pode se tornar uma zona frágil localizada, isto é, uma zona com maior dureza. Consequentemente, falhas estruturais podem ocorrer, ocasionando paradas não desejadas no transporte de fluidos. O objetivo deste trabalho é desenvolver uma metodologia baseada no modelo de fontes de calor distribuídas de Mhyr e Gröng, para avaliar o fluxo de calor na soldagem considerando as propriedades físicas dependentes da temperatura. Estender a aplicação desta ferramenta em soldagens multipasses para identificar sub-regiões da ZAC de um passe anterior sendo afetada pela ZAC de passes subsequentes. As isotermas simuladas foram validadas através de medições realizadas em macrografias de juntas soldadas. Os ciclos térmicos simulados foram validados através das temperaturas máximas atingidas e pelos tempos de resfriamento de 800 a 500 ºC (?t8-5) dos ciclos térmicos experimentais. Ao aplicar a metodologia proposta, foi possível delimitar com acurácia as regiões reaquecidas da ZAC e analisar os efeitos dos passes subsequentes em cada uma das sub-regiões da ZAC do passe de raiz. A IC-ZACGG na região do passe de raiz foi localizada, mas não se comportou como zona frágil devido à boa soldabilidade do aço API 5L X80 comprovada pelos ensaios de dureza e de tenacidade ao impacto Charpy-V. / In pipelines projects, the high strength low alloy (HSLA) steels are used, such as the API 5L X80 steel. During the multipass welding of these pipes, the heat affected zone (HAZ) of the root pass is subjected to a new thermal cycle by the subsequent welding passes. This results in changes in the values of the physical properties. In the HSLA steels, the intercritical reheated coarse-grained heat-affected zone (IR-CGHAZ) can become a local brittle zone, that is, a region with greater hardness. Consequently, structural failures could happen, causing undesired shutdowns in fluid transportation. The objective of this work is to develop a methodology based on the distributed heat sources model of Mhyr and Gröng, to evaluate the heat flux in the welding considering the temperature-dependent physical properties. Extend the application of this tool in multipass welds to identify HAZ subregions of a previous pass being affected by the HAZ of subsequent passes. The simulated isotherms were validated through measurements made on macrographs of welded joints. The simulated thermal cycles were validated through the maximum temperatures reached and the cooling times from 800 °C to 500 ºC (?t8-5) of the experimental thermal cycles. By applying the proposed methodology, it was possible to accurately delimit reheated HAZ regions and analyze the effects of subsequent passes in each of the root pass HAZ subregions. The IRCGHAZ in the root pass region was localized, but it did not behave as a brittle zone due to the good weldability of the API 5L X80 steel as proven by the hardness and Charpy-V impact tests.

La diffusion Compton inverse est l’interaction entre un photon et un électron de haute énergie. Il en résulte l’émission d’un nouveau photon d’énergie supérieure à celle du photon incident suivant la trajectoire de l’électron. Ces propriétés rendent possible la création d’une source de rayonnement X hautement directive, monochromatique accordable dans une large gamme spectrale. Il suffit d’accélérer les électrons sur quelques mètres pour leur faire gagner l’énergie minimale requise. Les photons proviennent d’une chaîne laser fortement amplifiée. Une telle source est donc relativement compacte, peu couteuse à mettre en oeuvre et facilement accessible aux utilisateurs. Elle est particulièrement adaptée aux besoins des musées ou des hôpitaux pour des applications comme l’analyse d’oeuvres historiques ou la radiothérapie. L’objectif de cette thèse est de mettre en oeuvre une source de rayonnement X par diffusion Compton inverse en bout de ligne de l’accélérateur ELSA (Electrons et Laser, Sources X et applications). L’installation ELSA comprend un accélérateur linéaire d’électrons appartenant à la Direction des Applications Militaires du Commissariat à l’Energie Atomique à Bruyères-le-Châtel (CEA DAM). Le but est de produire des impulsions de rayonnement X ultra-courtes dans une gamme énergétique allant de 10 à 100 keV. Elle servira notamment à la caractérisation de détecteurs à réponse ultra-rapide développés à la DAM. Un système optique destiné à augmenter le flux de rayonnement X produit a été développé. Il consiste à replier la trajectoire du laser pour empiler les impulsions au point d’interaction. Dans le même but, une mise à niveau de l’installation à été réalisée afin d’augmenter l’énergie des électrons de 18 à 30 MeV. Les résultats expérimentaux ont enfin été comparés aux résultats obtenus à l’aide de simulations PIC 3D. / X-ray sources based on inverse Compton scattering process produce tunable near-monochromatic and highly directive X-rays. Recent advances in laser and accelerator technologies make the development of such very compact hard X-ray sources possible. These sources are particularly attractive in several applications such as medical imaging, cancer therapy or culture-heritage study, currently performed in size-limited infrastructures. The main objective of this thesis is the development of an inverse Compton scattering source on the ELSA linac of CEA at Bruyères-le-Châtel as a calibration tool for ultra-fast detectors.A non-resonant cavity was designed to multiply the number of emitted X-ray photons. The laser optical path is folded to pile-up laser pulses at the interaction point, thus increasing the interaction probability. Another way of optimizing the X-ray yield consists in increasing the electron bunch density at the interaction point, which is strongly dependent on the electron energy. A facility up-grade was performed to increase the electron energy up to 30 MeV. The X-ray output gain obtained thanks to this system was measured and compared with calculated expectations and 3D PIC simulations.