Resumo em Português:

Resumo Simulações pelo método dos elementos finitos (MEF) foram realizadas para entender os efeitos das taxas de aquecimento/resfriamento na distribuição de tensões residuais. Dois parâmetros de material dos trilhos foram usados, enquanto as condições de contorno permaneceram constantes: tamanho da zona afetada pelo calor, temperatura máxima e taxa de extração de aquecimento. Para complementar a análise, foi realizada uma solda de topo por centelhamento de um trilho Premium com parâmetros de soldagem ajustado para obter uma baixa extensão de zona afetada pelo calor, sem resfriamento forçado, para examinar a microestrutura formada nas regiões críticas na alma e no extremo do patim. Os resultados mostraram que houve concentração de tensões residuais verticais na região da alma, enquanto a presença de tensão residual de compressão no sentido horizontal foi predominantemente superficial na região do trilho superior. Ao usar dois parâmetros de simulação de materiais semelhantes (trilhos), os resultados foram substancialmente diferentes. Os exames metalográficos mostraram que não havia presença de microconstituintes aciculares (martensita/bainita). Além disso, foi observada ferrita pro-eutetóide na região central, cementita em contorno de grão austenítico prévio na região próxima a AC3 e esferoidização quase completa na região de sítio de esferoidização máxima da alma. Em contrapartida, na região do extremo do patim, apresentou microestrutura completamente perlítica na região central e próxima a AC3 e menor volume de esferoidização na região de máxima esferoidização, provavelmente devido à maior taxa de resfriamento nesta região.

Resumo em Inglês:

Abstract Simulations using the finite element method (FEM) were done to understand the effects of heating/cooling rates on the distribution of residual stresses. Two material parameters from rails were used while the boundary conditions remained constant: heat-affected zone size, maximum temperature and heating extraction rate. To complement the analysis, a flash-butt weld of a Premium rail was done with welding parameters adjusted to obtain a narrow HAZ, without forced cooling, to examine the microstructure formed in the critical regions in the web and the edge of the rail foot. The results showed that there was a concentration of vertical residual stresses in the web region, while the presence of horizontal compression residual stresses was mostly superficial in the rail head region. The main result from the simulation sets was that when using two simulation parameters with similar materials (rails) substantially different results were obtained. Metallographic examinations showed that there was no presence of acicular microconstituents (martensite/bainite). In the rail web, proeutectoid ferrite was observed in the central region, cementite in a previous austenitic grain boundary, in the region that reached temperatures close to AC3, and almost complete spheroidization in the region of maximum spheroidization. In contrast, in the rail foot edge region, there was a completely pearlitic microstructure, in the central region and in the zone that reached temperatures close to AC3, and a lower volume of spheroidization in the region where maximum spheroidization is typically observed, probably due to the higher cooling rate in this region.

Resumo em Português:

Abstract The study of the influence of the nitrogen atmosphere on the behavior of the welding parameters (current and voltage) and on the properties of the deposits of self-protected tubular wires used in the FCAW process for the recharging of pieces and parts subjected to severe abrasion is debated. Three filler materials are evaluated for this type of application: one with high chromium, another with high chromium and alloyed with niobium and the third with lower chromium content and also alloyed with titanium. Deposits are made under the conditions indicated by the manufacturers for the wires (in terms of regime parameters) with and without nitrogen gas protection, using a constant voltage mode welding source. The use of additional gaseous protection (N2) modifies the welding parameters while modifying the microstructure, influencing the mechanical properties of the deposits. The deposits were characterized by optical microscopy, confirming the influence of nitrogen on the operational behavior and on the deposits for the three wires used.

Resumo em Espanhol:

Resumen Se aborda el estudio de la influencia de la atmosfera de nitrógeno sobre el comportamiento de los parámetros de soldadura (corriente y tensión) y en las propiedades de los depósitos de alambres tubulares auto-protegidos utilizados en el proceso FCAW para el recargue de piezas y partes sometidas a abrasión severa. Son evaluados tres materiales de aporte para este tipo de aplicación: Uno de alto cromo, otro de alto cromo y aleado con niobio y el tercero con menores contenidos de cromo y aleado también con titanio. Se realizan depósitos en las condiciones indicadas por los fabricantes para los alambres (en cuanto a parámetros de régimen) con y sin protección de gas nitrógeno, mediante fuente de soldadura en modo de tensión constante. El uso de protección gaseosa adicional (N2) modifica los parámetros de soldadura a la vez que modifica la microestructura, influyendo en las propiedades mecánicas de los depósitos. Los depósitos obtenidos fueron caracterizados por microscopia óptica, confirmando la influencia del nitrógeno sobre el comportamiento operacional y sobre los depósitos para los tres alambres utilizados.

Resumo em Português:

Resumo Os processos de Manufatura Aditiva (MA) de Metais permitem criar peças tridimensionais através da adição progressiva de finas camadas de material. Estes processos se enquadram em duas grandes categorias, denominadas Fusão em Leito de Pó e Deposição por Energia Direcionada. A compreensão física dos processos de MA pode fornecer uma visão holística sobre as sensibilidades aos parâmetros de processo. Já a modelagem computacional destes processos não só pode fornecer uma visão importante dos fenômenos físicos que levam às propriedades finais do material e à qualidade do produto, mas também os meios para explorar o espaço de projeto, visando criar produtos funcionais. Esta revisão introdutória foca na MA de materiais metálicos, particularmente nas questões de modelagem física e numérica. São apresentadas considerações sobre os diversos fenômenos físicos atuantes, métodos computacionais mais empregados, técnicas para realizar a modelagem e suas respectivas validações, demonstrando os desafios e limitações atuais, assim como as perspectivas futuras da simulação computacional aplicada aos processos de MA.

Resumo em Inglês:

Abstract Additive Manufacturing (AM) processes of metals allow creating three-dimensional parts through the progressive addition of thin layers of material. These processes fall into two major categories, called Powder Bed Fusion and Directed Energy Deposition. Physical understanding of the AM processes can provide a holistic view of the sensitivity to process parameters. Computational modeling of these processes can not only provide an important view of the physical phenomena that lead to the final properties of the material and quality of the product, but also the means to explore the design space, in order to create functional products. This introductory review focuses on the AM of metallic materials, particularly on issues of physical and numerical modeling. Considerations are presented about the various physical phenomena at work, most used computational methods, techniques to perform the modeling and their respective validations, demonstrating the current challenges and limitations, as well as the future perspectives for computer simulations applied to AM processes.

Resumo em Português:

Resumo: O processo de soldagem é um método de união de materiais metálicos por meio do aquecimento até uma temperatura adequada. Esse processo é crucial na manufatura de diversos componentes, desde a microeletrônica até componentes estruturais de máquinas pesadas. Com o advento da automação industrial, houve o início da utilização de robôs de solda na indústria, visando uma maior produtividade, qualidade e acuracidade do processo. A partir do século XXI, com a chegada da Indústria 4.0, é possível enxergar novas oportunidades de melhoria no processo de solda, tais como a introdução do sistema CPS (Cyber Physical System), a realidade aumentada e a realidade virtual. Tais técnicas permitem não só a automatização da operação de soldagem, mas também um maior controle do processo, cruzando informações do método planejado com a operação real de modo dinâmico e adaptativo. Nesse contexto de diversificado portifólio de tecnologias usadas no processo de soldagem, o presente trabalho se propõe a realizar uma revisão da literatura com o objetivo de mapear as principais evoluções tecnológicas da automação dos processos de soldagem a arco nos últimos anos.

Resumo em Inglês:

Abstract: Welding is a method of joining metallic materials by heating them until an appropriate temperature. This process is crucial for the manufacturing of several components, from microelectronics to structural components of heavy machinery. With the advent of industrial automation, welding robots were developed and implemented in industry, aiming to increase productivity, quality, and accuracy of the process. With the dawning of the 21st century and arrival of Industry 4.0, new opportunities for improvement in the welding process arose, such as the Cyber Physical Systems – CPS, augmented reality, and virtual reality. These techniques go beyond the welding operation automation, by providing greater control of the process control, crossing information of the planned method with the actual operation, in a dynamic and adaptive way. In this context of manifold welding technologies, the present work carries out a literature review with the objective of mapping the main technological developments of arc welding automation over time.

Resumo em Inglês:

Abstract High thermal gradient formed during the fusion welding process results in development of undesirable residual stress in the weldments. This stress is developed due to restraint by the parent metal during weld solidification. The high heat input results in non-uniform heat distribution across the weld region in other words non-uniform microstructural development across the weld region and hence the mechanical properties of the joint are often not uniform. In order to avoid inhomogeneity in the mechanical properties and also to reduce/eliminate undesirable residual stress, the welded samples are given post welding heat treatment. In this research, 500 µm thin SS-316L sheets are welded using micro plasma arc welding process and then the welded specimens are heat treated. The welding experiments are conducted by varying welding speed, welding current and stand-off distance. Weld bead microstructure, micro-hardness, ultimate tensile strength (UTS), yield strength and percentage elongation are determined before and after heat treatment. The effects of welding heat input and process parameters on the measured weld qualities are studied. Analysis of variance is also performed to estimate the influence of factors and their interaction on the weld quality. The post weld heat treatment results in an increase in the grain size of the HAZ and is found in the range of 38.96 µm to 56.22 µm whereas for as-welded samples it is in the range of 29.88 µm to 50.40 µm. The average UTS value of the heat treated samples is increased by 9.9% compared to the as-welded samples. The hardness of the fusion zone varies in the range of 175-215 HV.

Resumo em Inglês:

Abstract The phenomenon of revolution pitch was studied on AA 6061-T6 with a square pin tool for friction stir welding (FSW). The tool rotational speed and traverse speed were varied at four levels and selected in a manner so that the revolution pitch could comprise both lower and higher magnitude of variation when compared among them. An attempt was made to investigate the material flow from the macrostructure of both vertical (transverse to welding direction) and horizontal (parallel to the weld surface) cross-section. The study showed a significant amount of variation in terms of spindle torque, forces, material flow, and tensile properties. The increased material flow was noticed in the top surface of the weld from advancing to the retreating side at increased revolution pitch. Whereas an increased material flow was observed in the downward direction through the retreating side of the nugget. At increased revolution pitch a clear division in the onion ring was noticed towards the retreating side. The variation of torque, force and material flow showed a consistent trend for a higher change in revolution pitch. As the revolution pitch increased finer nugget grains were obtained causing increased tensile properties.

Resumo em Inglês:

Abstract Welded joints for subsea systems are usually buttered with a nickel alloy, heat-treated and then joined together. Although the majority of these joints have been successful throughout their service, some have suffered catastrophic failure, leading to investigations into the possible causes. The use of heat treatment has been considered the primary cause for failure in this type of joint. The main objective of this article is, with background on the methodology used on Double-Layer Controlled Deposition Technique – DL-CDT, along with the LPTS decision diagrams, to determine the relations between the buttering parameters that allow the welding of subaquatic joints, and the low need for heat treatment. MIG single-bead-on-plate welding was executed on samples of AISI 8630M steel. The welded samples were submitted to metallographic analyses of their geometric and microstructural characteristics and the confection of decision diagrams. Among the 200 possible relationships between the buttering parameters, only one presented positive gaps over all criteria. Grain refinements were observed in the HAZ of joints buttered for the parameters approved by the decision diagrams, while for the joints submitted to the Post Welding Heat Treatment (PWHT) peaks of microhardness on the buttering interface were found, which may result in fragilization of that region.

Resumo em Inglês:

Abstract: The present study focuses on the influence of a 5-pass overlapped friction stir lap welding of AA6061-T6 on the mitigation of defects and its simultaneous effect on microstructure and mechanical properties. Tool pin overlapping percentage of 0%, 25%, 50% and 75% was employed, from which it was observed that defects significantly reduced at higher overlapping. Fine equiaxed grains were observed across all the nugget zones in both top, and bottom regions were developed due to simultaneous overlapped passes; the grain size of which varied from 8.5 µm to 3.5 µm. The grains became finer, which increased of overlapping percentage. The microhardness of the processed zone was significantly reduced during overlapping that varied from a range of 43 HV0.1 to 49 HV0.1 as compared to base metal which was interpreted due to changes in grain size and secondary precipitate distribution during overlapping. A maximum ultimate tensile strength of 230 MPa was achieved at 50% overlapping, whereas minimum ultimate tensile strength of 160 MPa was achieved at 0% overlapping. Fractography of fracture surface showed a ductile failure at 50% that showed a number of dimples of varying shapes and sizes.

Resumo em Português:

Resumo: O aço AISI 316L e Inconel 718 são metais de ampla aplicação na indústria. O estudo da soldagem dissimilar entre esses dois materiais é tecnologicamente importante para melhorar o desempenho da junta. Concentramos este estudo na avaliação da soldabilidade dissimilar desses materiais. Três amostras de AISI 316L e Inconel 718 soldadas usando processo multipass GTAW (Gas Tungsten Arc Welding) com diferentes parâmetros foram analisadas. Foram realizadas caracterização microestrutural, medidas da fração volumétrica da ferrita δ e fase Laves, espaçamento entre as dendritas de austenita, além da medição e análise das dimensões do metal de solda e da microdureza. A medição das dimensões do metal de solda e do espaçamento entre as dendritas mostrou que maiores aportes térmicos aumentaram as zonas fundidas e o espaçamento entre as dendritas de austenita. A fração volumétrica de ferrita δ diminuiu com o aumento do aporte térmico, enquanto que a fração da fase Laves aumentou. A microdureza apresentou variação significativa na poça de fusão devido a mudanças nas fases e na composição, conforme evidenciado pela análise de EDS nas juntas dissimilares.

Resumo em Inglês:

Abstract: AISI 316L steel and Inconel 718 are metals of wide application in industries. The study of dissimilar welding between these two materials is technologically important to improve their joint performance. We focused this study on the evaluation of the dissimilar weldability of these materials. Three samples of AISI 316L and Inconel 718 welded using a multipass GTAW (Gas Tungsten Arc Welding) process with different parameters were analyzed. The microstructural characterization, measurements of the volumetric fraction of the δ ferrite and Laves phase, the spacing between austenite dendrites, in addition to measurement and analysis of dimensions of the welding zones and the microhardness were performed. The measurement of the weld metal dimensions and the dendrite spacing showed that higher heat inputs increased the dilution zones and the spacing between austenite dendrites. The volumetric fraction of the δ ferrite decreased with the increase of heat input, while the Laves phase fraction increased. The microhardness presented significant variation in the weld pool due to changes in the phases and composition, as evidenced by EDS analysis in the dissimilar joints.

Resumo em Inglês:

Abstract: The torque and forces in friction stir welding (FSW) are important parameters for the process behavior, weld quality, and mechanical properties of the weld. Torque and forces are mainly influenced by rotational and welding speeds and tool geometry, including the tool pin profile. However, experimental studies to describe the influence of the pin profile on torque and forces have received little attention. In this paper, the influence of the threaded pin on torque and forces in the FSW process of 5052-H34 aluminum alloy is considered. The axial, welding, and transverse forces and the torque are experimentally measured at several combinations of rotational (600, 900, 1200 and 1500 rpm) and welding speeds (100, 200, and 300 mm/min) for two pin profiles: smooth and threaded. Additionally, residual stresses are measured, by X-ray diffraction technique, for some experimental conditions in the stir zone of the weld. The results show that the influence of the pin shape on the torque, forces, and residual stresses depends on the rotational and welding speeds, mainly on the rotational speeds. In general, the threaded pin increases the residual stresses and the maximum values of torque and forces in the axial and transverse directions while reducing the welding force.

Resumo em Português:

Abstract: The effect of the matrix, graphite and ferrochrome-manganese contents in SAW fluxes, obtained with steel slag and rice husk ash, on the composition and hardness of the metal deposited in one layer is addressed. Links were established between the flux composition variables (X1 - Matrix (72.99% slag, 20.44% rice husk ash and 6.57% fluorite), X2- Graphite and X3- Ferrochrome-manganese) and the contents of carbon, chromium, manganese, silicon, the microhardness and the hardness of the deposit and metallographic images were acquired. The best flux deposit was characterized metallographically and was evaluated by a microabrasive wear test with a free rotating sphere, using a commercial reference deposit. It is concluded that the carbon content, the microhardness and the hardness of the deposited metal are ruled by graphite and that the chromium, manganese and silicon contents are governed by ferrochrome-manganese; that the best flux corresponds to 88% matrix, 7% graphite and 5% ferrochrome-manganese, with a deposit hardness of 59 HRc, and with martensite and interdendritic austenite microstructure. This behaves properly to wear, being 6% less resistant than the reference.

Resumo em Espanhol:

Resumen: Se aborda el efecto de los contenidos de matriz, grafito y ferrocromo-manganeso en fundentes SAW, obtenidos con escorias de acería y cenizas de cascarilla del arroz, sobre la composición y dureza del metal depositado en una camada. Fueron establecidos vínculos entre las variables de composición del fundente (X1 – Matriz (72,99% de escoria, 20,44% de cenizas de cascarilla del arroz y 6,57% de fluorita), X2- Grafito y X3- Ferrocromo-manganeso) y los contenidos de carbono, cromo, manganeso, silicio, la microdureza y la dureza del depósito y fueron adquiridas imágenes metalográficas. El depósito del fundente de mejor desempeño fue evaluado mediante ensayo de desgaste microabrasivo, frente a un depósito comercial de referencia. Se concluye, que el contenido de carbono, la microdureza y la dureza del metal depositado son gobernado por el grafito y que los contenidos de cromo, manganeso y silicio son gobernados por el ferrocromo-manganeso; que el fundente de mejor desempeño corresponde a, 88% de matriz, 7% de grafito y 5% de ferrocromo-manganeso, con dureza del depósito de 59 HRc, y con microestructura de martensita y austenita interdendrítica. Este se comporta al desgaste adecuadamente, siendo un 6% menos resistente que el de referencia.

Resumo em Português:

Resumo: O estudo da fadiga em ambiente subaquático é dificultado pois envolve diversas variáveis, muitas delas estão relacionadas à interação do material com o meio em que está submetido. Em testes de fadiga em ambiente aquoso foi constatado o aparecimento de bolhas que se desprendem da região da ponta da trinca durante o ensaio, porém, até o momento a literatura não havia relatado esse fenômeno. Buscando a repetibilidade, este trabalho apresenta parâmetros de ensaio que promovam o desprendimento de bolhas, facilitando seu estudo e compreensão. Corpos de prova do tipo C(T) fabricados em aço ASTM A36 foram ensaiados em ambiente subaquático sob uma variação de carga constante (ΔP) de 5kN e frequência de 30Hz. Os desprendimentos das bolhas durante os ensaios foram registrados com uma câmera de alta velocidade (captura de 1000fps). Os resultados indicam que as primeiras bolhas desprendidas durante o ensaio são menores e aumentam de volume com o aumento do comprimento da trinca, chegando a um diâmetro médio máximo e após isso ocorre diminuição e supressão do fenômeno ao se aproximar do final do ensaio. A ocorrência foi associada à fragilização por hidrogênio, com existência já comprovada nesse tipo de ensaio

Resumo em Inglês:

Abstract: The study of fatigue in an underwater environment is difficult because it involves several variables, many of them are related to the interaction of the material with the environment in which it is submitted. In fatigue tests in an aqueous environment, the appearance of bubbles that detach from the crack tip region during the test was observed, however, until now the literature had not reported this phenomenon. Seeking repeatability, this work presents test parameters that promote the detachment of bubbles, facilitating their study and understanding. Type C(T) specimens made of ASTM A36 steel were tested in an underwater environment under a constant load variation (ΔP) of 5kN and frequency of 30Hz. The detachments of the bubbles during the tests were recorded with a high-speed camera (capture of 1000fps). The results indicate that the first bubbles released during the test are smaller and increase in volume with increasing crack length, reaching a maximum average diameter and after that, there is a decrease and suppression of the phenomenon when approaching the end of the test. The occurrence was associated with hydrogen embrittlement, with proven existence in this type of test

Resumo em Português:

Resumo A Organização das Nações Unidas (ONU) é formada por 193 países e possui desafios relacionados à melhoria da qualidade de vida. Em 2015, líderes internacionais concordaram em implementar 17 objetivos de desenvolvimento sustentável (ODS), direcionados a países de baixa e média renda. Isto deve garantir, até 2030, que os habitantes vivenciem um maior nível de paz e prosperidade. Cada país da ONU deve medir seu progresso anualmente para monitorar os indicadores de cada ODS. A Universidade Federal de Uberlândia (UFU) e a Associação Brasileira de Soldagem (ABS) recentemente aceitaram o desafio de mostrar como a indústria da soldagem é capaz de contribuir para a melhoria do progresso do Brasil em atingir os 17 ODS. Este documento apresenta como a UFU, a ABS e a indústria de soldagem podem contribuir positivamente para atingir os ODS e melhorar a qualidade de vida do brasileiro. Futuramente, é de interesse da UFU e da ABS traçar estratégias de benefício mútuo e planos de ação com o apoio do governo brasileiro e da indústria com o intuito de atingir um progresso significativo em áreas nas quais seus membros são especialistas.

Resumo em Inglês:

Abstract The United Nations (UN) is made up of 193 countries and has challenges related to improving the quality of life. In 2015, international leaders agreed to implement 17 Sustainable Development Goals (SDGs), targeted at low and middle-income countries. This should ensure, by 2030, that the population experiences a greater level of peace and prosperity. Each UN country must measure its progress annually to monitor the indicators for each SDG. The Uberlandia Federal University (UFU) and the Brazilian Welding Association (ABS) recently accepted the challenge of showing how the welding industry is able to contribute to improving Brazil's progress towards achieving the 17 SDGs. This document presents how UFU, ABS and the welding industry can contribute positively to achieving the SDGs and improving the quality of life for Brazilians. In the future, it is in the interest of UFU and ABS to outline mutually beneficial strategies and action plans with the support of the Brazilian government and industry in order to achieve significant progress in areas in which its members are experts.

Resumo em Português:

Resumo Materiais, quando sob carregamento em ambientes agressivos, como é o caso dos aços de tubulações no setor de petróleo e gás, estão sujeitos à fragilização por hidrogênio devido às condições ambientais. A susceptibilidade do tubo a tal fragilização está diretamente relacionada, entre outros fatores, ao nível de tensões residuais presentes; e impõe ao material severas e danosas reduções de propriedades mecânicas. Nesse contexto, devido à necessidade cada vez mais frequente de evitar falhas catastróficas que conduzem a perdas irreparáveis para os seres humanos e o ambiente, são destinados maciços investimentos para o aprimoramento das propriedades mecânicas e grandes esforços para compreender os mecanismos que levam aos danos causados pelo hidrogênio. A compreensão do efeito das tensões residuais originadas pelos diferentes processos ao qual o aço é submetido ainda é bastante escassa e nem sempre há uma unanimidade entre pesquisadores. Diante desta problemática, o presente trabalho, através de uma revisão bibliográfica, objetiva oferecer uma abordagem de como as tensões residuais podem afetar o nível de fragilização nos aços API 5L, bem como uma melhor compreensão dos mecanismos e dos fatores que facilitam a dissolução do hidrogênio na rede cristalina destes materiais.

Resumo em Inglês:

Abstract Materials, when loaded in aggressive environments, as high strength low alloy pipeline steels used in Oil and Gas industry, are subjected to hydrogen embrittlement due to the environment conditions. The pipeline susceptibility is related to, among others factors, residual stresses; and causes several losses of mechanical properties. In this context, due to the increasingly frequent need to avoid catastrophic failures leading to irreparable losses to humans and the surrounding environment, massive investments are made to improve mechanical properties and to understand the mechanisms that lead to damages caused by hydrogen. The actual bibliography about the residual stresses influence is very scarce and there is not always an unanimity between researchers. This study, aims to offer an approach about how the residual stress can affect the embrittlement level, as well as better understanding about the mechanism and factors that facilitate the dissolution of hydrogen on crystalline lattice.

Resumo em Inglês:

Abstract Welding operations are one of the most important operations during pipeline construction and most are still carried out manually with SMAW. The challenges associated with the automation of orbital welding are related to several variables, including the weld pool behavior in vertical and overhead positions, monitoring of parameters and metal transfer, bevel preparation and orbital welding head control. In order to achieve a 360º orbital root pass with GTAW process, this study was focused on evaluating the influence of the arc voltage control (AVC) system for pulsed current process, the bevel geometry and filler wire insertion technique on the welding process and weld bead. Experiments were carried out using 16” ASTM A36 pipes with ½” wall thickness and an automated orbital welding head. The results show that the AVC control must be appropriate for the current mode applied (pulsed or constant) in order to avoid arc length oscillation. Also, the counterboring operation during the bevel preparation increases the amount of material of the groove land and promotes less penetration. Regarding the metal transfer, the continuous bridge transfer mode is recommended for automated orbital GTAW welding and this is achieved with an appropriate AVC control method and filler wire positioning.

Resumo em Português:

Resumo O desgaste por cavitação representa um dos principais problemas encontrados em turbinas hidráulicas, sendo as áreas danificadas recuperadas com a deposição de revestimentos resistentes a cavitação pelo processo MIG/MAG. Este trabalho buscou caracterizar amostras obtidas após deposição de um revestimento inoxidável austenítico a base de cobalto sobre substrato de ASTM A-743 CA6NM, realizada por meio do processo MIG mecanizado, avaliando as microestruturas obtidas com auxílio das técnicas de microscopia ótica, MEV/EDS, EBSD, DRX e Microdureza. Pode-se identificar a presença de microestrutura austenítica na superfície depositada, com tamanho de grão médio de 11,27 μm e traços de ferrita delta próximos a linha de fusão, com substrato majoritariamente martensítico. Acima da ZF a morfologia da microestrutura se deu em forma colunar na direção da extração de calor. O aporte térmico não afetou a superfície do revestimento, mantendo suas características químicas e de dureza, sem que houvesse uma diluição elevada do metal base no revestimento, se apresentando como uma excelente alternativa para utilização na recuperação de componentes cavitados, devido a sua baixa EFE e microestrutura que favorecem a absorção da energia proveniente do processo de cavitação.

Resumo em Inglês:

Abstract Cavitation wear represents one of the main problems encountered in turbines, being one of the areas of protection of hydraulic solutions recovered with a cavitation resistant protection by the GMAW process. This work aimed to characterize samples obtained after deposition of a cobalt-based austenitic stainless coating on ASTM A-743 CA6NM substrate, performed through the mechanized MIG process, evaluating the microstructures obtained with the aid of optical microscopy, MEV/EDS, EBSD, DRX and Microhardness techniques. It can be identified the presence of austenitic microstructure on the surface, with an average grain size of 11.27 μm and traces of ferrite from the next surface line with mostly martensitic substrate. Above the ZF, the morphology of the microstructure was in a dendritic form with a direction towards heat. The size provided did not adjust the thermal components, maintaining their characteristics and durability, without having superior protection of the thermal coating, without adequate protection of the supervised components, its use can maintain an excellent alternative for its use and durability. microstructure that favors the absorption of energy from the cavitation process.

Resumo em Inglês:

Abstract Weld bead geometry is a critical factor for determining the quality of welded joints, for this the welding process input parameters play a key role. In this study, the relationships between welding process variables and the size of the weld bead produced by pulsed GMAW process were investigated by a neural network trained with Bayesian-Regulation Back Propagation algorithm and a second degree regression models. A series of experiments were carried out by applying a Box-Behnken design of experiment. The results showed that both models can predict well the bead geometry. However, the neural network model had a slightly better performance than the second-order regression model. Both models can be used for further analyses and using them may surmount or reduce the need of experimental procedures especially in thermal analysis validations of welding finite element modelling.

Resumo em Português:

Resumo A Aspersão Térmica (ASP) é um processo para fabricação de revestimentos metálicos de baixo custo e alta produtividade. Esses revestimentos são usados em tubos de trocadores de calor para promover boa resistência a corrosão e ao desgaste. Este trabalho avaliou um revestimento metálico Fe-Cr-Nb-Ni-B depositado por ASP, nas condições sem selante e com selante à base de resina de silicone e alumínio, na proteção de tubos de aço quanto à corrosão e desgaste por atrito de partículas no ambiente de uma caldeira para geração de vapor d`água. Selantes ou esquemas de pintura, são soluções comumente usadas para melhorar a resistência à corrosão. As situações testadas expuseram o revestimento e substrato de amostras com e sem selante, em uma caldeira durante sete e doze meses. Utilizou-se técnicas de metalografia, microscopia eletrônica de varredura, análise química por espectroscopia de energia dispersiva e análise e processamento digital de imagens. Os resultados mostraram que embora o selante tenha sido removido do revestimento pelo atrito do fluxo de partículas presentes na água em operação na caldeira, o revestimento metálico manteve-se integro em relação à sua aderência ao substrato e camada de espessura depositada, sendo considerado uma solução promissora para a proteção de tubulações de caldeiras.

Resumo em Inglês:

Abstract The Arc Spray Process (ASP) is a low-cost and high-productivity process for making metallic coatings. These coatings are used in heat exchanger pipes to promote good corrosion and wear resistance. This work evaluated a metallic coating of Fe-Cr-Nb-Ni-B alloy deposited by ASP to protect carbon steel pipes boiler to generate steam. Were considered the coating performance about corrosion resistance and the wear due to particles' friction. Two conditions were tested, coating with sealant based on silicone resin with aluminum and without sealant. Sealants or paint layers are commonly used to improve coatings corrosion resistance. Two samples for each condition tested remained in the boiler environment for seven and twelve months. Metallographic preparation techniques, Scanning Electron Microscopy, chemical analysis by Energy Dispersive Spectroscopy, and Digital Image Analysis and Processing were used. The results showed that sealant was removed from the coating by the friction of the flow of particles present in the boiler's water operation. Nevertheless, the metallic coating remained intact in its adhesion to the substrate and layer of deposited thickness. The proposed solution was considered a promising solution for protecting steel pipes of boilers.

Resumo em Inglês:

Abstract: Friction stir processing (FSP) is a novel method of metal surface modification during the process by the addition of strengthening particles. FSP produced refined microstructures with the development of added ceramic particles on surface metal. In this FSP, mechanical characteristics were enhanced by FSP parameters, tool spinning speed, traverse speed and the axial force of high carbon high chromium die steel (non-consumable tool). In this research, FSP technique was employed on the surface of the base metal AA6082 aluminium alloy to modify composites of metal surface utilizing Cr3C2 particles. Mechanical properties like tensile strength, processed surface hardness and microstructure were studied. This research mainly focused on the parametric optimization of FSP on AA6082 with multiple responses (tensile strength and processed surface hardness) based on Taguchi L9 orthogonal array and grey relational analysis (GRA). The significant FSP parameters were obtained by grey relational grade (GRG) with an analysis of variance tool. Axial force and traverse speed were the most significant FSP parameters, which the most influence of performance characteristic of friction stir processed specimens. The predicted values were validated by confirmation test at setting of optimum level exhibits better conformity with investigational values. Field Emission Scanning Electron Microscope (FESEM) was carried out to determine the presence of strengthening particles in the processed Aluminium alloy.

Resumo em Inglês:

Abstract The thermal current pulsation is a technique widely used mainly in the GTAW process. The advantages of this technique range from operational gains in the process to metallurgical weld improvements. However, despite the advantages already reported in several studies that employ the GTAW and GMAW processes, there is no reference in the literature to the use of this technique in the submerged arc process. From this perspective, an investigation was carried out regarding the use of the current pulsation technique at low frequencies. Bead-on-plate tests were performed, varying the pulsation times from 0.5 to 2.0 s for two different welding speed (18 and 36 cm/min). The results showed that, besides being viable, the application of the thermal pulsation technique in SAW welding resulted in greater process efficiency. This result was obtained without causing instabilities or problems related to the inclusion of slag. However, unlike what is reported in the literature for the GTAW process, thermal pulsation did not show significant metallurgical improvements for any of the operating conditions used.

Resumo em Português:

Resumo: No Brasil mais de 60% da energia elétrica vem da geração hidrelétrica. Neste tipo de geração, alguns componentes são frequentemente expostos a fenômenos de desgaste, sendo um dos principais a erosão por partículas sólidas. A utilização de revestimentos é uma interessante alternativa para a redução de desgaste, sendo que a aspersão térmica se destaca como uma solução de baixo impacto ao material base do componente. Neste trabalho, uma liga comercial para aplicações anti-desgaste foi aplicada por aspersão térmica a arco elétrico (ASP) em substrato de aço carbono e submetida a tratamentos superficiais de lixamento, polimento e jateamento com esferas de aço (shot peening). Os revestimentos com e sem tratamentos superficiais foram avaliados quanto à morfologia e dureza e então submetidos a ensaios de erosão por jato de lama (slurry jet). Foi verificado que o revestimento tende a apresentar os mesmos mecanismos de erosão de materiais brutos. Além disso, observou-se que o lixamento e polimento reduzem a erosão nos primeiros minutos de ensaio, porém o ganho não compensa a massa perdida na execução dos próprios tratamentos. O shot peening reduziu a resistência à erosão do revestimento.

Resumo em Inglês:

Abstract: Currently in Brazil, more than 60% of electric energy comes from hydro generation. In hydroelectric generation, some mechanical components are often exposed to wear phenomena, and solid particle erosion is one of the most usual. The use of coatings is an interesting alternative to reduce the wear and thermal spray technology appears as a relevant solution with minimum impact to the component substrate. In this work, a commercial wear resistant alloy was applied on carbon steel substrate by Arc Spray Process (ASP) and subjected to surface finishing of single-step sanding, full polishing and shot peening. Coatings with and without surface treatments were evaluated for morphology and hardness and then subjected to slurry jet erosion tests. The results indicated that the coating tends to present the same erosion mechanisms expected for bulk materials. The surface sanding and polishing reduced the initial wear rates however, it did not compensate the mass loss caused by the finishing processes themselves. The shot peening reduced the erosion resistance of the coating.

Resumo em Inglês:

Abstract Mineral coal is a fuel that can be used by thermoelectric plants to generate electricity, however, the solid residues of its combustion, so-called ash, cause erosion and corrosion in the internal components of boilers that operate at high temperatures, causing failures in the system. This study proposes a metallic coating based on Fe-Cr-Si, obtained using the electric arc thermal spray technique as an alternative for protecting the most affected parts of boiler tubes by the ash impact. Optical microscopy (OM), scanning electron microscopy (SEM), semi-quantitative chemical analysis by Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), roughness measurements, pull-off adhesion tests were used. Thermal diffusivity measurements and mathematical modelling were elaborated to evaluate the thermal exchange efficiency impact of the coating in thermoelectric plant boiler tubes. The results showed that the chemical components of the sprayed wire were well incorporated into a coating with a hardness of 730.54 ± 164.28 HV, approximately three times greater than the hardness of boiler pipes and only 11% less than the hardness of ash. XRD identified the presence of crystalline phases in the coating and adhesion tests showed that the failures were cohesive without substrate exposure. The presence of the coating reduced heat exchange of approximately 0.64% / tube length. These results showed that the proposed coating, which has a lower cost compared to others, be a promising solution to avoid unscheduled shutdowns in thermoelectric boilers.

Resumo em Inglês:

Abstract This work investigates the performance of high strength cast steel welded joints to confirm their feasibility for application in mooring components. Three welded joints, with ultimate tensile strength in the range of 700 to 900 MPa, were obtained by the shielded metal arc welding process, the most applied in repair operation. After welding, a post welding heat treatment was performed to relieve the residual stresses. The results obtained in tension, impact Charpy-V, and hardness tests, at different positions of the heat affected zone were compared with equivalent welded joints performed with rolled steels currently applied in mooring chain links. These results showed that cast steels can obtain results equivalent to the rolled steels. Furthermore, the composition of cast steels for more stringent requirements (UTS > 860 MPa) is adjusted with higher nickel contents, while rolled and forged steels show increased C, Cr, and Mo contents. As a consequence, a refined microstructure with excellent impact toughness was obtained. Thus, these steels present a high potential to be used in this application contributing to reduce manufacturing costs.