This study was undertaken with the objective of determining the effect of gap distance on the weld bead geometry and the mechanical properties of the weldments. Low-alloyed and low carbon steel plates were welded under different conditions where each weldment had different gap distance and weld bead grooves. The influences of welding parameters namely, welding speed, current and voltage on the weld bead were examined in terms of weld bead penetration and heat affected zone and weld metal zone hardness variations.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / O objetivo deste trabalho foi avaliar o efeito da tÃcnica de soldagem de aÃos AISI 8630M e ASTM A182 F22 aplicados em componentes estruturais subaquÃticos do setor PetrÃleo e GÃs Natural considerando os parÃmetros operacionais, suas caracterÃsticas metalÃrgicas e suas propriedades mecÃnicas. Foram fabricadas juntas dos aÃos AISI 8630M ou ASTM A182 F22 previamente amanteigados com a liga de nÃquel Inconel 625  ou com uma liga de aÃo baixo carbono comumente utilizada na soldagem do aÃo AISI 8630M. Foram utilizadas diferentes tÃcnicas de amanteigamento com e sem o uso de tratamentos tÃrmicos de alÃvio de tensÃes (TTAT). Para algumas das juntas amanteigadas sem TTAT foram depositadas camadas de amanteigamento de acordo com os parÃmetros sugeridos pelos testes de Higuchi e Higuchi modificado previamente realizados. Foram realizados ensaios de dureza, microdureza e de fratura para caracterizaÃÃo mecÃnica das interfaces de amanteigamento e, alÃm disso, foi realizada uma intensa caracterizaÃÃo microestrutural da mesma utilizando microscopia Ãtica, microscopia eletrÃnica de varredura e anÃlises de EDS e de EBSD. O teste de Higuchi mostrou-se uma boa opÃÃo para escolha dos parÃmetros de amanteigamento dos aÃos AISI 8630M e ASTM A182 F22. As juntas amanteigadas com condiÃÃes indicadas pelo teste de Higuchi apresentaram um intenso refino de grÃo na ZAC dos aÃos baixa liga, enquanto as juntas amanteigadas com condiÃÃes reprovadas apresentaram granulaÃÃo grosseira. A interface dissimilar apresentou composiÃÃo quÃmica intermediÃria entre os aÃos utilizados e a liga de nÃquel, sendo essa interface chamada de zona de alta diluiÃÃo (ZAD). As ZAD apresentaram pontos de microdureza elevada e, mesmo nas amostras submetidas a TTAT, nÃo foi possÃvel revenir essas regiÃes. A zona afetada pelo calor (ZAC) das amostras amanteigadas com parÃmetros indicados pelo teste de Higuchi e sem TTAT apresentou valores de dureza similares aos das amostras soldadas com parÃmetros reprovados no teste de Higuchi e com TTAT. Os ensaios de fratura indicaram que, de uma forma geral, o TTAT nÃo trouxe Ãs ZAC benefÃcios significativos relacionados à tenacidade dessas regiÃes e, alÃm disso, os mesmos podem comprometer a tenacidade da interface dissimilar. A anÃlise do caminho preferencial à propagaÃÃo das trincas indicou que o uso de TTAT tende a fragilizar a interface dissimilar, acredita-se que esse efeito està associado a difusÃo de carbono e possÃvel precipitaÃÃo de carbonetos durante esse tratamento. Acredita-se que essa possÃvel precipitaÃÃo pode ser ainda mais crÃtica quando à considerada uma fonte constante de hidrogÃnio para a junta (como em uma proteÃÃo catÃdica), essa hipÃtese traz à tona um questionamento a respeito da necessidade do uso de TTAT na fabricaÃÃo desse tipo de junta. / The aim of this study was to evaluate the effect of welding technique in the AISI 8630M and ASTM A182 F22 steels applied in offshore structural components for Oil and Natural Gas sectors. Joints of AISI 8630M or ASTM A182 F22 were fabricated and previously buttered with nickel alloy Inconel 625  or an alloy of low carbon steel commonly used in welding of AISI 8630M. Different techniques of buttering were performed with and without post welding heat treatment (PWHT). For some of the joints buttered without PWHT, buttering layers were deposited in accordance with the welding parameters suggested by Higuchi and modified Higuchi tests previously performed. Mechanical tests (hardness, microhardness and fracture) were accomplished for buttering interfaces and an intense microstructural characterization (optical microscopy, scanning electron microscopy, EDS and EBSD) was realized. Higuchi test has been showed as a good option to select parameters for AISI 8630M and ASTM A182 F22 buttering. The joints that were buttered using the conditions indicated by Higuchi test showed an intense grain refinement in the HAZ of low alloy steels, while the ones that was buttered with the conditions disapproved showed a coarse granulation. The dissimilar interface showed off intermediate chemical composition between the steel and nickel alloy, and this interface was called high dilution zone (HDZ). The HDZ revealed points of high hardness and, even in samples subjected to PWHT was not possible to anneal these regions. The heat affected zone (HAZ) of the samples buttered using the parameters indicated by Higuchi (without PWHT) showed hardness values similar to those of the samples welded with parameters that failed in the Higuchi test and with PWHT. In general, fracture tests showed that the PWHT not bring significant toughnessâs benefits to the HAZ, furthermore, may impair the toughness of dissimilar interface. The analysis of the preferred path for cracks propagation showed that the use of PWHT tends to weak the dissimilar interface, possibly this effect is related to carbon diffusion and possible carbide precipitation during this treatment. It is believed that this precipitation can be even more critical when considering a constant supply of hydrogen to the board (as in a cathodic protection), this reinforces the use of buttering techniques without subsequent heat treatment in the manufacture of this type of joints.

La première partie de ce travail présente une nouvelle méthode qui permet de détermination rapidement de la température et de la concentration en fer d'un plasma d'arc MAG utilisé dans la technologie de soudage par plasma. Le plasma est un mélange [Ar-CO2] en présence de fer, avec un rapport molaire entre Ar et CO2 constant de 82%-18%. La seconde partie s'intéresse au rayonnement d'un plasma d'argon utilisé dans la technologie soudage GTAW et pouvant conduire à des dangers photobiologique. Dans le chapitre 1, le contexte et la motivation de ce travail sont présentés. Les travaux déjà effectués et publiés dans ces deux axes scientifiques sont passés en revue. Dans le chapitre 2, les compositions à l'équilibre sont calculées par la méthode de la minimisation de l'énergie libre de Gibbs. Les densités et fonctions de partitions obtenues pour chaque espèces présente dans le plasma sont ensuite utilisées pour déterminer les pertes radiatives des plasmas [Ar-CO2]-Fe via la méthode du coefficient d'émission net (CEN). Cette estimation des pertes ne peut se faire sans le calcul préalable du coefficient d'absorption spectral que nous avons réalisé finement par la méthode " raie par raie ". Tous les mécanismes radiatifs prédominants dans le plasma ont été pris en compte: continua atomique et moléculaire, raies atomiques et moléculaires. Cette partie constitue la base de cette étude sur laquelle se fonde notre nouvelle méthode de diagnostic destinée à déterminer à la fois la température et la concentration en fer d'un plasma d'arc de soudage. Le chapitre 3 est dédié à l'étude expérimentale d'un plasma d'arc MAG constituée d'une analyse spectroscopique permettant de remonter au profil de température et tester l'hypothèse de l'Équilibre Thermodynamique Local. La température d'excitation est obtenue par la méthode de Boltzmann tandis que la mesure d'élargissement de Stark pour les raies de fer et d'argon permet de remonter à la température et la densité des électrons. / This PhD thesis introduces a method that allows the fast determination of temperature and iron concentration for MAG-P Arc. The MAG-P Arc is in fact [Ar-CO2]-Fe mixtures, with a constant molar ratio between Ar and CO2 [82%Ar-18%CO2]. In a second time, this thesis presents a study of the optical radiation associated to photobiological hazards for argon GTAW Arc. In chapter 1, the background and motivation of this work is introduced. The previous works published in this field are reviewed. In chapter 2, the equilibrium compositions are calculated firstly using the minimization of Gibbs free energy. Then the radiative properties of [Ar-CO2]-Fe plasmas are obtained in the frame of the net emission coefficient (NEC) approach, using the accurate "line by line" method. All significant radiative contribution mechanisms are taken into account in the calculation. This study will constitute a groundwork to build the diagnostic method that allows determination of temperature and iron concentration profiles in welding arc. In chapter 3, spectroscopic investigation of the LTE hypothesis across the MAG-P Arc is made. Excitation temperature is obtained with Boltzmann plot method while iron and argon lines Stark broadening measurements are used to get electron temperature and electron density. LTE hypothesis validity across the arc is discussed considering the agreement between the two temperatures, the electron density and iron content. Results show supporting evidence for the main part of the plasma, along radial and axial directions. Discrepancies occur only at the fringe of the arc, where the two temperatures differ by more than 2000 K. In chapter 4, a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase is introduced. This method consists in measuring the plasma spectral radiation of the arc with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570-590 nm and 606-627 nm respectively; calculating theoretically the dependence of the absolute emissivity e570-590 nm and relative emissivity e570-590 nm/e607-627 nm versus the plasma temperature and the iron concentration. This method has also been validated for a layer of plasma by adopting other existing diagnostics such as Stark broadening, which demonstrates the effectiveness of this new method. In chapter 5, a theoretical investigation of the UV (180-400 nm), UVA (315-400 nm) and blue light (300-700 nm) radiation associated with the photobiological hazards to workers for argon GTAW arcs is presented. The radiative properties of argon plasma are calculated for the three spectral regions, and a two-dimensional model of a GTAW arc is then developed to determine the local emissions in the arc, the total radiation escaping from the arc and corresponding effective irradiances. This study clearly supports the importance of undertaking an effective protection strategy for workers, particularly for skin and eyes, in the welding environment. Finally, a general conculsion is given in chapter 6.

<p>This master thesis deals with problems in the arc length control in Pulsed MIG/MAG Welding. The main problem is that it is not possible to measure the arc length. In the present solution the voltage over both the electrode and the arc represents the arc length. </p><p>To improve the arc length control a model of the electrode melting has been built. One output from the model is the voltage over the electrode and with this voltage together with the measured voltage it is possible to calculate the voltage over just the arc. Then, having the arc voltage as a value of arc length the arc length control can be improved, which is showed in the end by simulations. Simulations with the present control system are compared with the new one, when the controller is able to control the arc voltage instead of the sum of both the electrode voltage and the arc voltage.</p>

This master thesis deals with problems in the arc length control in Pulsed MIG/MAG Welding. The main problem is that it is not possible to measure the arc length. In the present solution the voltage over both the electrode and the arc represents the arc length. To improve the arc length control a model of the electrode melting has been built. One output from the model is the voltage over the electrode and with this voltage together with the measured voltage it is possible to calculate the voltage over just the arc. Then, having the arc voltage as a value of arc length the arc length control can be improved, which is showed in the end by simulations. Simulations with the present control system are compared with the new one, when the controller is able to control the arc voltage instead of the sum of both the electrode voltage and the arc voltage.

This study focuses on joining pearlitic ductile cast iron with low carbon steel by welding and investigation of this joint in microstructural and mechanical viewpoints. For this purpose E355 steel and GJS600-3 cast iron were joined using metal active gas (MAG) welding process by G3Si1 filler wire. The joining process is shaped mainly by the problems related to the low weldability of cast. Preheating was applied to prevent formation of cooling cracks and effects of post weld heat treatments (PWHT) were surveyed. Micro examination and micro hardness tests were applied to characterize the general microstructure. Grain size measurements were done for E355. Hardness profiles, tension and impact toughness properties were designated via mechanical tests. Fatigue behavior was surveyed and general fracture characteristics were determined via scanning electron microscopy (SEM) examinations. According to study it was concluded that successful weld joint could be formed between the materials by suitable preheating. Formation of ledeburitic white cast iron and martensite in heat affected zone of cast piece was witnessed. It was possible to lower high hardness values of these phases gradually by increasing post weld heat treatment temperatures. The weld joint behaved superior to the base metals under tension and fatigue tests. In tension tests failure occurred at E355 base metal whereas fatigue loading resulted failure at GJS600-3. A great impact toughness variation was determined between two pieces. It is seen that heat treatments had minor effect on mechanical test results except hardness. The study was concluded that a useful fusion weld joint between these materials can be built.

O objetivo deste trabalho é estudar a influência dos parâmetros do processo de soldagem MAG com transferência do metal do tipo Curto-circuito Controlado (CCC) sobre a geometria do cordão de solda. Foi utilizado um dispositivo de soldagem automatizado para realização dos testes de simples deposição sobre um tubo de aço API 5L X65 diâmetro interno 204 mm e espessura 8 mm. Os parâmetros do processo analisados foram a corrente de pico de arco (Ia1), o tempo de atuação desta corrente (ta1), o tempo de atuação da corrente Ia2 (ta2), a velocidade de alimentação do arame (W) e a velocidade de soldagem (v). Tais parâmetros foram ajustados na interface homem-máquina (IHM) de uma fonte de potência microprocessada e do dispositivo de soldagem automatizado. As características geométricas do cordão de solda analisadas foram a largura, a altura do reforço e a penetração. Foi utilizado um Projeto de Experimento Composto de Segunda Ordem para obter a relação entre os parâmetros do processo e as características geométricas do cordão. Os modelos matemáticos obtidos foram considerados adequados, sendo possível determinar estatisticamente o nível de significância de cada um dos parâmetros controláveis – e de suas interações – sobre as respostas analisadas. Foram encontradas sobreposição e falta de fusão lateral em 60% dos corpos de prova avaliados, sendo levantada a hipótese de que a combinação de altos valores da corrente de pico de arco Ia1 com baixos valores do tempo de atuação deste parâmetro – ta1, aliada à utilização de gases de proteção com alta porcentagem de Ar, pode comprometer a eficiência de fusão nas laterais do cordão de solda. Os cordões de solda foram produzidos com quantidade reduzida de salpicos, representando um avanço do processo CCC quando comparado ao processo com transferência do metal por curto-circuito convencional. Os parâmetros controláveis Ia1 e ta1 produziram efeitos muito similares nas respostas de largura e penetração, quando considerados de forma isolada e também quando da interação destes com os demais parâmetros controláveis. A análise dos efeitos das interações principais revelou que Ia1 e ta1 são os parâmetros de maior influência nas respostas da geometria do cordão de solda, porém, com elevada dependência de um ajuste adequado da velocidade de alimentação do arame W para a obtenção de estabilidade do processo. / This work aims to study the influence of MAG welding process parameters with controlled short-circuit (CSC) metal transfer mode on weld bead geometry. The simple deposition weld tests were performed using a micro controlled power supply and an automatized device which enabled achievement of weld beads with standard conditions on API 5L X65 steel pipe whose inner diameter is 204 mm and thickness is 8 mm. The welding process parameters analyzed were the peak arcing current (Ia1), times (ta1) and (ta2), wire feed speed (W) and welding speed (v). Such parameters were set on Human-Machine Interface (HMI) of the micro controlled power supply and automatized welding device. The weld bead geometric features evaluated were width, reinforcement height and penetration depth. A Central Composite Face- Centred Design of Experiment was performed to obtain the relationship between the process parameters and the weld bead geometric features. Statistical analysis allowed development of mathematical models and they were found appropriate to determine the significance level of the process parameters – and their interactions – on output responses analyzed. Overlap and lack of fusion was detected on weld beads side in 60% of all specimens evaluated. The hypothesis formulated states that the origin of these discontinuities is from specific combination of parameters – high values of Ia1 and low values of ta1 together with usage of a shielding gas with high percentage of Ar – which would lead to lower fusion efficiency on weld bead side. The weld beads were produced with low spatter rates so it can be considered an improvement of the CSC process if compared with conventional short-circuit metal transfer mode. The peak arcing current Ia1 and time ta1 yielded similar effects on width and penetration depth, and it was valid when that parameters were taken both isolated and on interactions with other welding process parameters. The present study also revealed that Ia1 and ta1 are the most important parameters on influencing weld bead geometry, however, there is also strong dependence on a proper adjustment of wire feed speed W to obtain process stability.

O objetivo deste trabalho é estudar a influência dos parâmetros do processo de soldagem MAG com transferência do metal do tipo Curto-circuito Controlado (CCC) sobre a geometria do cordão de solda. Foi utilizado um dispositivo de soldagem automatizado para realização dos testes de simples deposição sobre um tubo de aço API 5L X65 diâmetro interno 204 mm e espessura 8 mm. Os parâmetros do processo analisados foram a corrente de pico de arco (Ia1), o tempo de atuação desta corrente (ta1), o tempo de atuação da corrente Ia2 (ta2), a velocidade de alimentação do arame (W) e a velocidade de soldagem (v). Tais parâmetros foram ajustados na interface homem-máquina (IHM) de uma fonte de potência microprocessada e do dispositivo de soldagem automatizado. As características geométricas do cordão de solda analisadas foram a largura, a altura do reforço e a penetração. Foi utilizado um Projeto de Experimento Composto de Segunda Ordem para obter a relação entre os parâmetros do processo e as características geométricas do cordão. Os modelos matemáticos obtidos foram considerados adequados, sendo possível determinar estatisticamente o nível de significância de cada um dos parâmetros controláveis – e de suas interações – sobre as respostas analisadas. Foram encontradas sobreposição e falta de fusão lateral em 60% dos corpos de prova avaliados, sendo levantada a hipótese de que a combinação de altos valores da corrente de pico de arco Ia1 com baixos valores do tempo de atuação deste parâmetro – ta1, aliada à utilização de gases de proteção com alta porcentagem de Ar, pode comprometer a eficiência de fusão nas laterais do cordão de solda. Os cordões de solda foram produzidos com quantidade reduzida de salpicos, representando um avanço do processo CCC quando comparado ao processo com transferência do metal por curto-circuito convencional. Os parâmetros controláveis Ia1 e ta1 produziram efeitos muito similares nas respostas de largura e penetração, quando considerados de forma isolada e também quando da interação destes com os demais parâmetros controláveis. A análise dos efeitos das interações principais revelou que Ia1 e ta1 são os parâmetros de maior influência nas respostas da geometria do cordão de solda, porém, com elevada dependência de um ajuste adequado da velocidade de alimentação do arame W para a obtenção de estabilidade do processo. / This work aims to study the influence of MAG welding process parameters with controlled short-circuit (CSC) metal transfer mode on weld bead geometry. The simple deposition weld tests were performed using a micro controlled power supply and an automatized device which enabled achievement of weld beads with standard conditions on API 5L X65 steel pipe whose inner diameter is 204 mm and thickness is 8 mm. The welding process parameters analyzed were the peak arcing current (Ia1), times (ta1) and (ta2), wire feed speed (W) and welding speed (v). Such parameters were set on Human-Machine Interface (HMI) of the micro controlled power supply and automatized welding device. The weld bead geometric features evaluated were width, reinforcement height and penetration depth. A Central Composite Face- Centred Design of Experiment was performed to obtain the relationship between the process parameters and the weld bead geometric features. Statistical analysis allowed development of mathematical models and they were found appropriate to determine the significance level of the process parameters – and their interactions – on output responses analyzed. Overlap and lack of fusion was detected on weld beads side in 60% of all specimens evaluated. The hypothesis formulated states that the origin of these discontinuities is from specific combination of parameters – high values of Ia1 and low values of ta1 together with usage of a shielding gas with high percentage of Ar – which would lead to lower fusion efficiency on weld bead side. The weld beads were produced with low spatter rates so it can be considered an improvement of the CSC process if compared with conventional short-circuit metal transfer mode. The peak arcing current Ia1 and time ta1 yielded similar effects on width and penetration depth, and it was valid when that parameters were taken both isolated and on interactions with other welding process parameters. The present study also revealed that Ia1 and ta1 are the most important parameters on influencing weld bead geometry, however, there is also strong dependence on a proper adjustment of wire feed speed W to obtain process stability.

O objetivo deste trabalho é estudar a influência dos parâmetros do processo de soldagem MAG com transferência do metal do tipo Curto-circuito Controlado (CCC) sobre a geometria do cordão de solda. Foi utilizado um dispositivo de soldagem automatizado para realização dos testes de simples deposição sobre um tubo de aço API 5L X65 diâmetro interno 204 mm e espessura 8 mm. Os parâmetros do processo analisados foram a corrente de pico de arco (Ia1), o tempo de atuação desta corrente (ta1), o tempo de atuação da corrente Ia2 (ta2), a velocidade de alimentação do arame (W) e a velocidade de soldagem (v). Tais parâmetros foram ajustados na interface homem-máquina (IHM) de uma fonte de potência microprocessada e do dispositivo de soldagem automatizado. As características geométricas do cordão de solda analisadas foram a largura, a altura do reforço e a penetração. Foi utilizado um Projeto de Experimento Composto de Segunda Ordem para obter a relação entre os parâmetros do processo e as características geométricas do cordão. Os modelos matemáticos obtidos foram considerados adequados, sendo possível determinar estatisticamente o nível de significância de cada um dos parâmetros controláveis – e de suas interações – sobre as respostas analisadas. Foram encontradas sobreposição e falta de fusão lateral em 60% dos corpos de prova avaliados, sendo levantada a hipótese de que a combinação de altos valores da corrente de pico de arco Ia1 com baixos valores do tempo de atuação deste parâmetro – ta1, aliada à utilização de gases de proteção com alta porcentagem de Ar, pode comprometer a eficiência de fusão nas laterais do cordão de solda. Os cordões de solda foram produzidos com quantidade reduzida de salpicos, representando um avanço do processo CCC quando comparado ao processo com transferência do metal por curto-circuito convencional. Os parâmetros controláveis Ia1 e ta1 produziram efeitos muito similares nas respostas de largura e penetração, quando considerados de forma isolada e também quando da interação destes com os demais parâmetros controláveis. A análise dos efeitos das interações principais revelou que Ia1 e ta1 são os parâmetros de maior influência nas respostas da geometria do cordão de solda, porém, com elevada dependência de um ajuste adequado da velocidade de alimentação do arame W para a obtenção de estabilidade do processo. / This work aims to study the influence of MAG welding process parameters with controlled short-circuit (CSC) metal transfer mode on weld bead geometry. The simple deposition weld tests were performed using a micro controlled power supply and an automatized device which enabled achievement of weld beads with standard conditions on API 5L X65 steel pipe whose inner diameter is 204 mm and thickness is 8 mm. The welding process parameters analyzed were the peak arcing current (Ia1), times (ta1) and (ta2), wire feed speed (W) and welding speed (v). Such parameters were set on Human-Machine Interface (HMI) of the micro controlled power supply and automatized welding device. The weld bead geometric features evaluated were width, reinforcement height and penetration depth. A Central Composite Face- Centred Design of Experiment was performed to obtain the relationship between the process parameters and the weld bead geometric features. Statistical analysis allowed development of mathematical models and they were found appropriate to determine the significance level of the process parameters – and their interactions – on output responses analyzed. Overlap and lack of fusion was detected on weld beads side in 60% of all specimens evaluated. The hypothesis formulated states that the origin of these discontinuities is from specific combination of parameters – high values of Ia1 and low values of ta1 together with usage of a shielding gas with high percentage of Ar – which would lead to lower fusion efficiency on weld bead side. The weld beads were produced with low spatter rates so it can be considered an improvement of the CSC process if compared with conventional short-circuit metal transfer mode. The peak arcing current Ia1 and time ta1 yielded similar effects on width and penetration depth, and it was valid when that parameters were taken both isolated and on interactions with other welding process parameters. The present study also revealed that Ia1 and ta1 are the most important parameters on influencing weld bead geometry, however, there is also strong dependence on a proper adjustment of wire feed speed W to obtain process stability.

The project elaborated in frame of Master's studies branch 2303T002 presents a study of welded joints for hot-dip galvanizing. On the basis of literature study it is assumed that zinc influences the properties of welded joints. Samples were made of high strength steels DOMEX and wear-resistant steels HARDOX which were welded using MAG. Subsequently, half of the samples treated with zinc. The evaluation is used tear test and test Vickers hardness. Finally, the project is the comparison of the measured values of galvanized steel and steel without zinc.