The present work researches influence of energy focusing effect to the fusion zone defects in the electron beam welding, which include fusion zone shape, welding depth, welding width, rippling and spiking. And to verify the model of welding defects base on theory and experiment. A spike is a sudden increase in penetration beyond what might be called the average penetration line. Many spikes have voids and cold shuts in their lower portions, because molten metal does not fill in completely, producing a condition similar to a cold shut in a casting. Ripples on a workpiece surface are generally associated with segregation, porosity and other microstructure defects. These become the objectives in this project.

The design of high quality electron generators to meet specific requirements is important in the application of these devices to a variety of materials processing systems (including welding, cutting and additive manufacture), X-ray tubes for medical, scientific and industrial applications, microscopy and lithography. Designs can be analysed by field solvers, and electron trajectories plotted to provide an indication of the beam quality. Incremental improvement of designs has normally been executed by trial and error, and this can be a time consuming activity requiring expert intervention for each iteration of the design process. The unique contribution made to knowledge by this work is the application of optimisation techniques to the design of electron guns to produce beams with the required optical properties. This thesis presents a review of the design of electron guns, including a discussion of thermionic cathode material properties and their suitability for use in electron guns for processing materials, the influence of space-charge on gun design and the derivation of salient beam metrics to characterise the beam. Beam quality metrics have been developed that allow quantification of electron beam characteristics, allowing objectives to be set for the optimisation process. Additionally, a method is presented that enables real world measurements to be directly compared with modelled beams. Various optimisation methods are reviewed. A genetic algorithm was selected, which would use gun modelling and beam characterisation calculations as the objective function, as a suitable method for application to this problem. However, it was recognised that selections for the best evolutionary parameters, the population size, number of parents, the mutation rate and mutation scale, were not readily determined from published work. An investigation is presented where a range of evolutionary parameters was tested for a set of geometrical problems, which had some similarity to electron gun design but could be computed sufficiently quickly to enable an extensive survey, and the most efficient combination of parameters was identified. Detail is given of the customisation of a genetic evolutionary optimisation method for the design of electron guns. Examples are presented of electron gun design optimisation processes to meet specified beam requirements within defined geometric and electrical constraints. The results of this work show that optimum evolutionary parameter settings for the geometric problem vary with the complexity of the problem and trends have been identified. Application of these parameters to an electron gun optimisation has been successful. The derived beam parameter metrics have been applied to electron guns as an objective function. Comparisons of modelled predictions of the beam characteristics with the measured real world values have been shown to be reasonable.

Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 109-120). Also available in electronic format on the Internet.

The shaped charges on the market today ranges from about 20 to 200 mm in diameter but there is a need of smaller sizes for example in applications where a small projectile with a high speed is needed or to equip or take out drones with. The objective of this thesis work was to develop a miniaturized shaped charge with dimensions smaller than those available today and preferably with a diameter down to 10 mm. The project was conducted at Karlstad University in collaboration with Saab Dynamics AB. The process used during this project was to start with a feasibility study to obtain information about the limits on dimensions in order to investigate how small dimensions can be used for the casing and liner with respect to manufacturability. The feasibility study was conducted by studying academic literature, contacting companies with expertise within the field of manufacturing. A previously used shaped charge was used as a starting point and the dimensions was scaled in accordance with the objective. The influence of the design parameters was examined using the γSPH module in IMPETUS Afea. The liner material used was restricted to oxygen-free high thermal conductivity copper and different materials for the casing was tested. Two material selections for the casing were made with the aid of Granta Edupack. It has been concluded that it is possible to manufacture a miniaturized shaped charge with dimensions down to about ten mm. Both a design for a jet forming shaped charge and an explosively formed penetrator was developed during the project. The resulting projectile for the explosively formed penetrator had a velocity of 2450 m/s, a total length of 7.3 mm and 3.5 mm in diameter, and the jet forming shaped charge had a jet tip velocity of 7060 m/s and was able to penetrate 38-mm into an AISI 4340 steel target according to the models used in IMPETUS Afea. A prototype was planned but due to cost restrictions, it is left as future work. / Riktad sprängverkan (RSV)-laddningarna som finns på marknaden idag sträcker sig från ungefär 20 till 200 mm i diameter. Det finns dock ett behov för storlekar mindre än detta, till exempel i tillämpningar där en liten projektil med hög fart krävs, alternativt att utrusta eller sänka drönare med. Målet med detta examensarbete var att utveckla en miniatyriserad RSV-laddning med dimensioner mindre än vad som finns tillgängligt idag och helst med en diameter neråt tio mm. Projektet utfördes på Karlstads universitet i samarbete med Saab Dynamics AB. Processen som användes under detta projekt gick ut på att börja med en förstudie for att erhålla information om gränserna för mått för att undersöka hur små dimensioner som kan användas för höljet och linern med avseende på tillverkningsbarhet. Förstudien genomfördes genom att studera akademisk litteratur och kontakta företag med expertis inom tillverkningsområdet. En tidigare använd RSV-laddning användes som startpunkt och dimensionerna justerades i enlighet med målet. Påverkan av parametrar på prestanda undersöktes genom att använda γSPH modulen i IMPETUS Afea. Det använda materialet för linern begränsades till OFHC koppar och olika material för höljet testades. Två materialval gjordes för höljet med hjälp av Granta Edupack. Slutsatsen som kan dras utifrån arbetet är att det är möjligt att tillverka miniatyriserade RSV-laddningar med dimensioner neråt tio mm. Både en design för en strålbildande RSV-laddning och en projektilbildande RSV-laddning utvecklades under projektet. Den resulterande projektilen för den projektilbilande RSV-laddningen hade en fart på 2450 m/s, en längd av totalt 7.3 mm och 3.5 mm i diameter och den strålbildande RSV-laddningen hade en spetsfart på 7060 km/s och kunde penetrera 38 mm AISI 4340 stål enligt modellen som användes i IMPETUS Afea. En prototyp planerades men på grund av kostnadsrestriktioner lämnades det som framtida arbete.

Fusion welding of dissimilar metals constitutes a crucial processing stage in a variety of applications, and the use of high energy beams (HEB) like lasers and electron beams for such welding applications has several advantages, such as, precision, narrow heat affected zone, and consequently, low distortion. An understanding of microstructural evolution in the weld is a prerequisite for producing sound joints with desired properties. HEB welding of similar metals have been studied extensively. In contrast, fewer studies have been directed toward understanding the fundamental aspects of solidification of dissimilar welds. This thesis presents an effort in that direction by exploring microstructural evolution in Ti/Ni dissimilar welds. Welding of Ti/Ni serves to illustrate the fundamental differences that distinguish dissimilar welding from the welding of similar metals. These are: (i) Thermophysical properties of the base metals are, in general, different, and this can have important consequences in the heat transfer conditions. (ii) Composition can vary over an wide range, the extreme being for the case of a pure binary couple, and the solid–liquid interface cannot be defined by a single liquidus isotherm. (iii) In addition to the surface energy driven Marangoni convection, a strong solutal convection can arise due to a large difference in the density of the base metals. (iv) Nucleation of phases assumes greater importance, especially in systems with intermediate phases. We have carried out laser and electron beam welding (LW and EBW) experiments in a butt welding geometry to join Ti/Ni dissimilar couples. Weld microstructures were characterised using scanning and transmission electron microscopy (SEM and TEM); composition information was obtained from energy dispersive spectroscopy (EDS) of Xrays in the SEM. In addition to the pure binary couple, we have also studied electron beam welding of Ti/Ni with a thin Ta interlayer. We summarise our findings in each set of experiments in the following sections. Laser welding of Ti/Ni We have studied partial penetration welds obtained within the range of experimental parameters used in our study. These welds show the following interesting features: 1. The welds are asymmetric with respect to the initial joint. Despite its higher melting point, Ti melts more than Ni due to its lower thermal diffusivity, making the average composition of the weld richer in Ti (Ti–40at.%Ni). 2. Composition changes very steeply near the fusion interfaces in both Ti and Ni with associated microstructural changes. The variation is of much lesser magnitude in the rest of the weld, reflecting a well mixed melt pool on a macroscopic scale. 3. Growth of base metal grains into the weld pool at the fusion interfaces is severely restricted at both Ti and Ni ends. 4. The Ti fusion interface is marked by a band consisting of Ti2Ni dendrites which grow toward the Ti base metal. 5. Layered structures form at the Ni fusion interface. The sequence of the layers is: solid solution (Ni)→ Ni3Ti→ Ni3Ti+NiTi eutectic → NiTi. We note the absence of the (Ni)+Ni3Ti eutectic in this sequence. 6. NiTi and Ti2Ni are the major phases that appear in the bulk of the weld. Volume fraction and morphology of NiTi vary almost periodically to form microstructural bands. 7. Solid state transformation of NiTi results in the formation of the Rphase and martensite, which reflect the composition heterogeneity in the weld. Sometimes, Ni4Ti3 precipitates are observed also, providing indirect evidence of nonequilibrium solidification. 8. Nitrogen pickup from the atmosphere during welding leads to the formation titanium nitride dendrites in the weld. 9. Solutal convection and buoyancy forces manifest themselves through the segregation of the lighter nitride and Ti2Ni phases toward the top surface of the weld; the heavier liquid forms blocky NiTi in the bottom half of the weld. These observations stand in striking contrast with the microstructures of conventional welds. We have proposed a set of composition and temperature profiles in the weld which reflect the diffusive and advective transport processes; when combined with thermodynamic information from the Ti–Ni phase diagram to yield spatial liquidus temperature profiles, these profiles can adequately explain most of the results. Our observations illustrate the importance of (a) nucleation, and (b) the inhomogeneous nature of the melt in which growth takes place. They also highlight the role of convective currents in bringing about local fluctuations in composition and temperature leading to ‘low velocity bands’. Electron beam welding of Ti/Ni We have carried out full penetration EBW of thin plates of Ti and Ni. The major observations are: (i) Average composition of the weld is in the Ni–rich side of the phase diagram (Ni–40at.%Ti). (ii) Fusion interface microstructures are very similar to that in LW exhibiting restricted base metal growth (although little amount of epitaxy can be seen in the Ni side), growth of Ti2Ni dendrites toward the base metal at the Ti fusion interface and the sequence of layers at the Ni interface: (Ni)→ Ni3Ti→ Ni3Ti+NiTi. Unlike LW, however, Ni3Ti, instead of NiTi, reappeared after the third layer on the Ni side. (iii) General microstructure consists of the Ni3Ti+NiTi eutectic, which appears in several anomalous as well as regular morphologies. (iv) Formation of NiTi is restricted mostly to regions near the Ti fusion interface. (v) Segregation of Ni3Ti was observed in a few places. The most prominent change in the microstructure compared to LW is a shift from the Ti2Ni– NiTi phases in the bulk of the weld to a Ni3Ti+NiTi eutectic structure. This is a direct consequence of the shift in the average composition of the weld to the Ni– rich side. The occurrence of different anomalous and regular eutectic structures bear similarity with bulk undercooling experiments conducted on eutectic systems having a strongly faceting phase as one of its constituents. The asymmetric coupled zone, along with composition and temperature fluctuation due to fluid flow, can be attributed to the origin of these structures. Electron beam welding of Ti/Ni with a Ta interlayer Motivated by the report of superior mechanical properties of Ti/Ni welds with an interlayer of Ta, whose melting point is much higher than those Ni and Ti, we performed EBW experiments using a Ni–Ta– Ti configuration. The key observations are: (i) The process is inherently unsteady in nature, and results in partial and irregular melting of the Ta interlayer. This partial melting essentially divides the weld into Ni–rich and Ti–rich halves. (ii) Microstructure near the fusion interface in Ni and Ti show similarities with that of the pure binary Ti/Ni welds; the phases here, however, contain Ta as a ternary addition. (iii) Microstructure in the Ti–rich half consists of dendrites of the Ni(Ti,Ta) phase with a high Ti:Ta ratio, and an eutectic formed between this phase and a (Ti,Ta)2Ni phase having significant amount of Ta. Two Ni(Ti,Ta) type phases dominate the microstructure in the Ni–rich half: the phase having a higher Ti:Ta ratio forms cells and dendrites, whereas the one of a lower Ti:Ta ratio creates an interdendritic network. (iv) Regions near the unmolten Ta layer in the middle show the formation of a sawtoothlike Ta–rich faceted phase of composition (Ta,Ti)3Ni2. Since very scarce thermodynamic data exist for the Ni–Ta–Ti ternary system, we have taken cues from the binary phase diagrams to understand the microstructural evolution. Such extrapolation, although successful to some extent, fails where phases which have no binary equivalents start to appear. In summary, in this thesis, we explore microstructural evolution in the Ti/Ni dissimilar welds under the different settings of laser and electron beam welding processes. This study reveals a variety of phenomena occurring during dissimilar welding which lead to the formation of an extensive range of microstructural features. Although a few questions do remain, most results can be rationalised by drawing from, and extending the knowledge gained from previous studies by introducing physical and thermodynamic arguments.

Dans le domaine aéronautique la réduction du ratio buy to fly pour les pièces de structure est devenue un enjeu majeur. Il s'agit de développer, à coût matière réduit, des appareils consommant moins de carburant tout en proposant une autonomie et une capacité de transport plus importantes. Ce travail de recherche s'inscrit dans cette problématique industrielle, et accompagne Airbus dans le développement du procédé de soudage par faisceau d'électrons de tôles en alliage TA6V dans le but de concurrencer (en proposant une diminution du ratio buy to fly) les procédés classiques de forgeage/matriçage des pièces de structure. Toutefois, le soudage du TA6V, malgré un traitement thermique de détensionnement, conduit à une hétérogénéité de microstructure caractérisée par l'apparition de très fines lamelles de phase α associées à une diminution de la résistance à la propagation de fissures dans la zone soudée par rapport à celle du matériau de base. Ce gradient de propriétés mécaniques est acceptable pour l'application souhaitée, néanmoins, pour étendre ce procédé d'assemblage à d'autres pièces de structure un Traitement Thermique Post-Soudage (TTPS) est envisagé. On vise ainsi à atteindre, dans l'intégralité de la tôle soudée, un meilleur compromis entre la résistance à la propagation de fissure et les propriétés en statique. Dans ce travail de thèse, des lignes de fusion ont été réalisées par la société Airbus sur des tôles laminées d'épaisseurs 12mm présentant une microstructure biphasée α+β soit équiaxe (dite recuit α-β), soit lamellaire (dite recuit β). La caractérisation de chacune des microstructures et des propriétés mécaniques (via des essais de traction, de résilience et de propagation de fissure en fatigue) de la zone de fusion et du matériau de base a permis d'appréhender les mécanismes d'endommagement de l'alliage soudé. Les résultats macroscopiques des essais mécaniques associés à l'étude des faciès de rupture et des chemins de propagation de fissure ont par ailleurs révélé, pour chacune des microstructures impliquées (recuit α-β et recuit β), une importante anisotropie des propriétés mécaniques et de fortes hétérogénéités de comportement mécanique dans l'épaisseur de la tôle. La caractérisation de la microtexture par analyses EBSD de ces matériaux a mis en exergue la présence de nombreuses macrozones contribuant aux hétérogénéités observées. Le développement d'un Traitement Thermique Post-Soudage (TTPS) à partir de l'état recuit β soudé ne permet pas d'aboutir à des propriétés mécaniques statiques satisfaisantes dans la tôle à cause d'un grossissement excessif des ex-grains β. C'est pourquoi, un TTPS à partir de l'état recuit α-β soudé a été envisagé afin d'homogénéiser la microstructure et d'améliorer la résistance à la propagation de fissure de l'ensemble de la tôle soudée. Finalement, une optimisation du TTPS est proposée en considérant le passage de l'échelle du laboratoire à l'échelle industrielle. Les caractérisations microstructurales et mécaniques après TTPS ont par la suite été confrontées aux résultats obtenus sur le matériau recuit β, ce qui a permis de comprendre les avantages et les limites du TTPS choisi. / In the aeronautic industry, the reduction of the « buy-to-fly » ration for structural parts has become a major issue. The goal is to develop planes, at a reduced material cost, requiring less fuel with an extended range and higher load capacity. This research study has been designed with the Airbus Company in order to contribute to solve this industrial problem. In particular, the development of the electron beam welding process of the β annealed titanium alloy Ti-6Al-4V should concurrence the usual forging/pressing processes of structural parts. However, welding of Ti-6Al-4V, despite a stress relieving heat treatment, lead to a microstructural heterogeneity between the welded zone and the base metal and, as a consequence, to an heterogeneity of the mechanical properties. In comparison to the crack propagation resistance of the base metal, the one measured fusion zone is weaker and is associated to the presence of very thin α platelets. This mechanical properties gradient remains acceptable for the industrial purpose, nevertheless, in order to extend the use of the electron beam welding process to other structural parts, a Post-Welding Heat Treatment (PWHT) is considered. The aim is to achieve, in the entire welded plate, a better compromise between the crack propagation resistance and the static properties. In this PhD work, fusion lines were performed by the Airbus company on two rolled plates of biphasic α+β Ti-6Al-4V presenting either a lamellar microstructure (also called β annealed) or an equiaxe microstructure (also called α-β annealed). Characterizations of the microstructures involved as well as the mechanical properties helped to understand the failure mechanisms of the welded alloy. The analysis of the different test revealed, thanks to the observation of the crack propagation path on the Charpy specimens, that the very thin α platelets in the fusion zone do not act as a strong barrier against the crack propagation. On the contrary, in the case of the β annealed base metal, the α platelets are thick enough (1µm) to be an obstacle and to slow down the crack. In this case, the crack undergoes many deviations at the α/β interfaces, generating a very long and tortuous crack path. In order to improve the mechanical properties of the fusion zone, it seems appropriate to apply a PWHT, which will transform the microstructure and increase the thickness of the α platelets in the fusion zone. This PWHT consists mainly in a treatment in the β field followed by a controlled cooling rate. However, even if the PWHT applied on the β annealed and welded material lead to a thickening of the α platelets and improve the crack propagation resistance in the fusion zone, a strong enlargement of the prior β grain in the base metal is responsible of low tensile properties. That is why, a PWHT applied on the α-β annealed material is considered in order to homogenize simultaneously the microstructure in both fusion zone and base metal and improve the mechanical in the entire welded plate. Results obtained from the Charpy tests underline that the PWHT applied on the α-β annealed and welded material lead to homogeneous fracture energies in the plate, and to an higher fracture energy after PWHT than the one in the fusion zone of the β annealed material, which fulfill the initial industrial goal. An important anisotropy of the mechanical properties as well as important fluctuations of these properties in t he thickness of the plates has also been observed. The EBSD analyses of the crystallographic microtexture revealed the presence of numerous macrozones responsible of the heterogeneities observed for both microstructures.

Neste trabalho estudou-se as propriedades obtidas em juntas soldadas pelo processo de soldagem a laser do tipo estado sólido de onda contínua guiado por fibra, e os resultados foram comparados com juntas soldadas pelo processo feixe de elétrons. O material utilizado foi o aço maraging 350 - ASTM A 538 Grade C. As soldas realizadas com o processo feixe de elétrons possuem um procedimento de soldagem aprovado. A junta selecionada para a elaboração do trabalho foi do tipo sobreposta com material de base de espessuras diferentes, respectivamente iguais a 1,00 e 0,78 mm. As juntas soldadas foram avaliadas por: ensaio de cisalhamento, dureza Vickers e caracterização microestrutural das diversas regiões das juntas soldadas. Foram realizadas análises por microscopia óptica e microscopia eletrônica de varredura usando espectrometria de energia dispersiva (MEV/EDS). Foi realizado o teste de hipótese como técnica para a análise dos dados provenientes dos ensaios experimentais. Nas juntas soldadas com ambos processos não foi verificada a presença de descontinuidades, poros e depressões na superfície do cordão. Os resultados indicam que as condições usadas em ambos os processos de soldagem foram satisfatórias e possibilitaram a soldagem do aço maraging 350 atendendo aos requisitos necessários. / In this work, the welds made by a continuous wave diode pumped solid state laser guided by fiber were studied and the results were compared with welded joints of electron beam welding. The material used was maraging 350 steel ASTM A 538 Grade C. The welding process performed with electron beam welding has a approved welding procedure. The joint chosen for the preparation of the work was the lap joint type with different thicknesses base material respectively equal to 1,00 and 0,78 mm. The welded joints were evaluated by mechanical tests like shear test, Vickers hardness and microstructural characterization of the various regions of the welded joints. Analyzes were performed by optical microscopy and scanning electron microscopy using energy dispersive spectrometry (SEM/EDS). The hypothesis test technique was done for the analysis of data from experimental tests. For both welding process was not detected in the welded joints the presence of discontinuities, pores and depressions on the weld fillet surface. The results indicate that the conditions used for both welding process were satisfactory and allowed the welding of maraging 350 steel meeting necessary requirements.

Esta Dissertação abrange a caracterização microestrutural do aço API 5L X65 soldado por feixe de elétrons (EBW) com cinco diferentes aportes térmicos e sem o uso de metal de adição. O aço API 5L X65 pertence à classe de aços ARBL e é empregado na fabricação de oleodutos e gasodutos. As três regiões da solda metal-base (MB), zona termicamente afetada (ZTA) e zona fundida (ZF) foram caracterizadas por microscopia ótica (MO), microscopia eletrônica de varredura (MEV), difração de raios X e medidas de microdureza Vickers. As microestruturas encontradas nestas três regiões são bastante distintas. O MB apresenta grãos ferríticos com bandas perlíticas orientadas paralelamente à direção de laminação. Devido à elevada densidade de potência do processo EBW e às elevadas velocidades de soldagem utilizadas, a ZTA é bastante estreita sendo formada por grãos ferríticos finos e bandas perlíticas degeneradas que a diferem do MB. Na interface ZTA/ZF foi possível observar a presença de grãos com morfologia acicular com a presença dos constituintes M-A (martensita-austenita). A ZF apresentou morfologia similar à encontrada em aços microligados soldados: ferrita alotriomórfica, ferrita acicular, ferrita de Widmanstätten, constituintes M-A, além de regiões bainíticas. Na parte central da chapa foi observada a segregação de manganês. A técnica EBW permite a soldagem de tubos com paredes espessas com apenas um passe. Os resultados desta Dissertação são úteis para avaliar a viabilidade técnica do uso de EBW na fabricação de tubos para o transporte de óleo e gás, especialmente em aços mais resistentes (bainíticos). / This Dissertation aims at the microstructural characterization of electron-beam welded (EBW) API 5L X65 steel using five different processing conditions (heat input) and without filler metal addition. The API 5L X65 steel is a high-strength low-alloy (HSLA) steel employed mainly in the manufacture of pipelines for oil and gas. The three regions of the welds, namely the base metal (BM), heat affected zone (HAZ) and fusion zone (FZ) were characterized by light optical microscopy using different chemical etching agents, scanning electron microscopy, X-ray diffraction and Vickers microhardness testing. The microstructures found in the three regions were quite distinct. The BM consists of elongated ferritic grains with pearlite bands oriented along the rolling direction. Due to the high power density provided by EBW, the HAZ is very narrow and consists of ferritic grains and bands of degenerated pearlite. At the HAZ/FZ interface it is possible to observe the presence of grains with acicular morphology and the presence of M-A (martensite- retained austenite) constituents. The FZ showed a morphology similar to that one found in molten microalloyed steels consisting of allotriomorphic ferrite, acicular ferrite, Widmanstätten-like ferrite, M-A constituents, as well as bainite. In the central part of the plate it was observed the presence of Mn-segregation lines along the BM. The electron beam welding was chosen because it produces a relatively small HAZ and it allows the welding of thick-wall tubes in one single pass. The results of this work are useful to evaluate the possibility of using EBW in the manufacture of pipelines for transport of oil and gas, especially in higher grade steels.

Neste trabalho estudou-se as propriedades obtidas em juntas soldadas pelo processo de soldagem a laser do tipo estado sólido de onda contínua guiado por fibra, e os resultados foram comparados com juntas soldadas pelo processo feixe de elétrons. O material utilizado foi o aço maraging 350 - ASTM A 538 Grade C. As soldas realizadas com o processo feixe de elétrons possuem um procedimento de soldagem aprovado. A junta selecionada para a elaboração do trabalho foi do tipo sobreposta com material de base de espessuras diferentes, respectivamente iguais a 1,00 e 0,78 mm. As juntas soldadas foram avaliadas por: ensaio de cisalhamento, dureza Vickers e caracterização microestrutural das diversas regiões das juntas soldadas. Foram realizadas análises por microscopia óptica e microscopia eletrônica de varredura usando espectrometria de energia dispersiva (MEV/EDS). Foi realizado o teste de hipótese como técnica para a análise dos dados provenientes dos ensaios experimentais. Nas juntas soldadas com ambos processos não foi verificada a presença de descontinuidades, poros e depressões na superfície do cordão. Os resultados indicam que as condições usadas em ambos os processos de soldagem foram satisfatórias e possibilitaram a soldagem do aço maraging 350 atendendo aos requisitos necessários. / In this work, the welds made by a continuous wave diode pumped solid state laser guided by fiber were studied and the results were compared with welded joints of electron beam welding. The material used was maraging 350 steel ASTM A 538 Grade C. The welding process performed with electron beam welding has a approved welding procedure. The joint chosen for the preparation of the work was the lap joint type with different thicknesses base material respectively equal to 1,00 and 0,78 mm. The welded joints were evaluated by mechanical tests like shear test, Vickers hardness and microstructural characterization of the various regions of the welded joints. Analyzes were performed by optical microscopy and scanning electron microscopy using energy dispersive spectrometry (SEM/EDS). The hypothesis test technique was done for the analysis of data from experimental tests. For both welding process was not detected in the welded joints the presence of discontinuities, pores and depressions on the weld fillet surface. The results indicate that the conditions used for both welding process were satisfactory and allowed the welding of maraging 350 steel meeting necessary requirements.

Esta Dissertação abrange a caracterização microestrutural do aço API 5L X65 soldado por feixe de elétrons (EBW) com cinco diferentes aportes térmicos e sem o uso de metal de adição. O aço API 5L X65 pertence à classe de aços ARBL e é empregado na fabricação de oleodutos e gasodutos. As três regiões da solda metal-base (MB), zona termicamente afetada (ZTA) e zona fundida (ZF) foram caracterizadas por microscopia ótica (MO), microscopia eletrônica de varredura (MEV), difração de raios X e medidas de microdureza Vickers. As microestruturas encontradas nestas três regiões são bastante distintas. O MB apresenta grãos ferríticos com bandas perlíticas orientadas paralelamente à direção de laminação. Devido à elevada densidade de potência do processo EBW e às elevadas velocidades de soldagem utilizadas, a ZTA é bastante estreita sendo formada por grãos ferríticos finos e bandas perlíticas degeneradas que a diferem do MB. Na interface ZTA/ZF foi possível observar a presença de grãos com morfologia acicular com a presença dos constituintes M-A (martensita-austenita). A ZF apresentou morfologia similar à encontrada em aços microligados soldados: ferrita alotriomórfica, ferrita acicular, ferrita de Widmanstätten, constituintes M-A, além de regiões bainíticas. Na parte central da chapa foi observada a segregação de manganês. A técnica EBW permite a soldagem de tubos com paredes espessas com apenas um passe. Os resultados desta Dissertação são úteis para avaliar a viabilidade técnica do uso de EBW na fabricação de tubos para o transporte de óleo e gás, especialmente em aços mais resistentes (bainíticos). / This Dissertation aims at the microstructural characterization of electron-beam welded (EBW) API 5L X65 steel using five different processing conditions (heat input) and without filler metal addition. The API 5L X65 steel is a high-strength low-alloy (HSLA) steel employed mainly in the manufacture of pipelines for oil and gas. The three regions of the welds, namely the base metal (BM), heat affected zone (HAZ) and fusion zone (FZ) were characterized by light optical microscopy using different chemical etching agents, scanning electron microscopy, X-ray diffraction and Vickers microhardness testing. The microstructures found in the three regions were quite distinct. The BM consists of elongated ferritic grains with pearlite bands oriented along the rolling direction. Due to the high power density provided by EBW, the HAZ is very narrow and consists of ferritic grains and bands of degenerated pearlite. At the HAZ/FZ interface it is possible to observe the presence of grains with acicular morphology and the presence of M-A (martensite- retained austenite) constituents. The FZ showed a morphology similar to that one found in molten microalloyed steels consisting of allotriomorphic ferrite, acicular ferrite, Widmanstätten-like ferrite, M-A constituents, as well as bainite. In the central part of the plate it was observed the presence of Mn-segregation lines along the BM. The electron beam welding was chosen because it produces a relatively small HAZ and it allows the welding of thick-wall tubes in one single pass. The results of this work are useful to evaluate the possibility of using EBW in the manufacture of pipelines for transport of oil and gas, especially in higher grade steels.