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.

API 5L X80 steels are widely used in welded pipes in the petroleum industry. However, microstructural changes in the heat affected zone are a concern when welding such pipes due to the potential formation of regions with low toughness. Despite all the research concerning mechanical properties of welded joints, the acceptance criteria for the qualification of welding procedures are still limited. Welded joints do not always guarantee the safe operation of industrial equipment, because the current Standards adopted are not able to evaluate the properties at some critical regions of the welded joint. This work studied the characteristics of a girth welded joint and showed evidences of low toughness at 0.5 mm from the fusion line due to the micro-phases necklacing the prior austenite grain boundaries. As this feature is not considered by the current Standards for approval of welding procedures, this work proposes an alternative approach to improve the safety of welded structures.

Abstract Over the last decades, alloy 718 usage has expanded and requirements imposed by its industrial applications became more critical. The knowledge about grain boundary character distribution (GBCD) in alloy 718 and its effect on properties improvement is mostly built based on iterative processing through cold rolling steps interspersed with solution annealing. Alloy 718 is found in the industry in many different forms and geometries, and fabricated by multiple thermomechanical processes such as wire drawing, rolling, forging or extrusion. The present study focused on understanding how wires respond to deformation mode related to drawing in regard to GBCD evolution, crystallographic orientation, precipitation of δ-phase and grain size. Lastly, assessing the resulting mechanical properties. The findings show that microstructural evolution is a consequence of competing mechanisms such as strain induced boundary migration, recrystallization, grain growth and phase precipitation. The deformation gradient along wire cross section plays an important role in affecting microstructural features, such as δ precipitation, GBCD and microtexture.

RESUMO O presente trabalho apresenta os resultados de um programa de pesquisa cujo objetivo principal é o desenvolvimento de consumíveis adequados para a soldagem de componentes de ancoragem fabricados em aços de alta resistência. Após avaliação de diferentes composições químicas, com base no balanço de Mn e Ni é feita uma análise detalhada das propriedades mecânicas e microestruturais da composição química que propiciou os melhores resultados para permitir uma conclusão decisiva. Foram soldadas juntas pelo processo eletrodo revestido utilizando consumíveis de 4,0 mm de diâmetro, com preaquecimento de 200 ºC, corrente contínua, posição plana e energia de soldagem nominal de 1,5 kJ / mm. Após a soldagem, foram realizados ensaios mecânicos (tensão, impacto Charpy-V, dureza) e metalográficos por microscopia ótica, microscopia eletrônica de varredura e EBSD em amostras removidas integralmente do metal de solda, tanto na condição de como soldado quanto após tratamento térmico pós-soldagem (TTPS) realizado a 600 ºC. Os resultados mostram que os metais de solda obtiveram propriedades mecânicas satisfatórias após o TTPS, sendo adequados para aplicação em componentes de ancoragem de acordo com a especificação IACS W22. Além disso, observou-se que a tenacidade ao impacto experimentou uma melhoria com o aumento do tempo de TTPS, o que é crucial para componentes com maiores espessuras.

ABSTRACT The present work show the results of an extensive working program whose the main goal is the development of consumables suitable for welding of mooring components manufactured in high strength steels. After an exhaustive evaluation of different chemical compositions, based on a balance of Mn and Ni, a detailed analysis of the mechanical and microstructural properties is done for the heat which proposed the best results in order to allow a decisive conclusion. Welded joints were produced by using 4,0 mm diameter covered electrodes, with preheat of 200 ºC, direct current, flat position and nominal heat input of 1.5 kJ/mm. After welding, mechanical tests (tension, impact Charpy-V, hardness) and metallographic examination (optical microscopy and scanning electron microscopy, electron back scattering diffraction) were performed in specimens removed integrally from the weld metal both in the as welded condition and post weld heat treatment at 600 º C. The results show that the weld metals obtained satisfactory mechanical properties after PWHT, being adequate for application on high strength steel mooring components with several grades according to the IACS W22 specification. In addition, it was noted that impact Charpy-V results were improved with increasing the time of PWHT, which is crucial for larger components.

Resumo O presente trabalho tem como objetivo estudar o comportamento de juntas soldadas obtidas pelo processo GMAW com eletrodo rotativo (GMAW-RE), de modo a permitir uma análise comparativa de produtividade e propriedades mecânicas com o processo GMAW convencional (GMAW). Foram realizadas soldagens multipasse pelos dois processos GMAW com preaquecimento de 100 °C em chapas de dimensões 500 × 150 × 10 mm em aço ASTM A36, na posição plana e energia de soldagem média de 2,30 kJ/mm. Após a soldagem, foram realizados ensaios de impacto Charpy-V, microdureza e metalográficos em corpos-de-prova removidos transversalmente ao cordão de solda. Adicionalmente, foi realizada uma análise comparativa de produtividade entre os processos. Os resultados mostram que o processo GMAW-RE propicia um aumento de produtividade e redução de custos significativos em relação ao processo GMAW. Adicionalmente, foram observados valores equivalentes de tenacidade ao impacto para o metal de solda, mas uma redução nesta propriedade na zona termicamente afetada. Embora a literatura disponível destaque o elevado potencial deste processo para substituição do processo GMAW convencional em aplicações industriais, verifica-se a necessidade de mais evidências experimentais para um maior suporte a esta indicação.

Abstract The main goal of the present work is to evaluate the behavior of welded joints obtained by the GMAW with rotating electrode process (GMAW-RE) in comparison to the Conventional GMAW process (GMAW). Multipass welding by both processes were performed in ASTM A36 steel plates with dimensions of 500 × 150 × 10 mm, preheating of 100 °C in the flat position and average welding energy of 2.30kJ/mm. After welding, Charpy-V notch and microhardness tests and metallographic examination were performed in samples removed transversally to the weld bead. Additionally, a comparative analysis of productivity and costs between processes were done. The results show that the GMAW-RE promotes higher productivity and reduction of costs in comparison to GMAW. Additionally, similar impact toughness results were observed in weld metals and a reduction on this property at the HAZ. Although the literature states the high potential of the GMAW-RE for replacement of the conventional GMAW in industrial applications, it was concluded that other experimental results are still necessary before the final conclusion.

ABSTRACT Nickel-based weld overlays (cladding) are commonly used in oil & gas industry to extend the life of equipment under corrosive environment, as it improves the corrosion resistance without a significant increase in the manufacturing cost, when compared to a full nickel-based alloy equipment. Although there are extensive literature involving overlays applied by SMAW, GMAW or GTAW processes, works about the use of FCAW process are limited. Consequently, an investigation of the performance of the overlays deposited by this process, which provides a higher productivity in comparison to the processes usually used, can be an interesting option for this application. The present work evaluates the mechanical and microstructural properties of the nickel-based superalloy 625 weld overlay deposited on a ASTM A516 Grade 70 carbon steel plate by the flux cored arc welding process (FCAW), both in as welded and heat treated conditions. Bending and microhardness tests were performed in order to verify possible effects of welding thermal cycles on the mechanical properties. The microstructure was evaluated through both optical (OM) and scanning electron microscopy (SEM), with the use of electron backscatter diffraction (EBSD) technique. Corrosion tests were conducted on samples removed from the top layer of the weld overlay according to ASTM G 48 Method A. All results obtained with this welding process, in both as welded and heat treated samples, were considered satisfactory.

Resumo Os torpedos de ancoragem são estruturas tubulares de aço carbono soldadas, e que tem sua ligação com as linhas de ancoragem que impedem o movimento das plataformas através de olhais de carregamento que são soldados nos tubos de construção. Como estes olhais apresentam geometria complexa, é importante a utilização de peças fundidas para a fabricação destes componentes, de forma a possibilitar o atendimento da demanda do mercado. Como a literatura técnica sobre este tipo de união soldada é ainda limitada, o presente trabalho estuda o comportamento de juntas soldadas de um aço fundido de alta resistência para utilização em olhais de torpedos de ancoragem de plataformas offshore. Para tanto, foram produzidas juntas soldadas com chanfro em K utilizando um aço de classificação ASTM A 148 Gr. 105-85 com resistência mecânica da ordem de 700 MPa, pelo processo eletrodo revestido, na posição plana, com preaquecimento de 200 °C e energia de soldagem média de 1,5 kJ/mm. Após a soldagem, foi realizado tratamento térmico pós-soldagem (TTPS) consistindo de aquecimento a 620 °C por 1 hora com resfriamento ao ar. As propriedades foram avaliadas por ensaios de tração, dureza, impacto Charpy-V e metalográficos por microscopia óptica e eletrônica de varredura com utilização da técnica de EBSD (eléctron backscatering difraction), tanto na condição de como soldado quanto após TTPS. Os resultados revelaram que, embora as propriedades mecânicas obtidas na junta soldada atendam os requisitos para a aplicação em todas as condições de análise, recomenda-se a execução do TTPS para alívio das tensões residuais e promover um revenimento da martensita de alta dureza do último passe de soldagem. Adicionalmente, verificou-se ser possível obter propriedades similares as de juntas soldadas de aços laminados usualmente utilizados em componentes de ancoragem.

Abstract Torpedo anchor piles are tubular carbon steel welded structures that are connected to the mooring lines, which prevent the oil platform from moving, through padeyes welded to the structural pipes. Due to the complex geometry of these padeyes, cast pieces are an important option in the manufacturing of these items, in order to meet market demand. Considering the limited availability of information about such type of welded junction in the technical literature, the present work studies the behavior of welded joints of a high strength cast steel used on offshore platforms torpedo anchor padeyes. Thus, K-type joints were used for the welding of an ASTM A 148 Gr. 105-85 steel with an ultimate tensile strength of about 700 MPa, by using shielded metal arc welding process, in flat position, with a preheating of 200 °C and an average welding energy of 1.5 kJ/mm. After welding, a post weld heat treatment (PWHT) was applied, at 620 °C for 1 hour, followed by air cooling. The properties were evaluated through tensile, hardness and Charpy-V impact tests, as well as metallographic examination by optical and scanning electron microscopy with the use of EBSD (electron backscatter diffraction) technique, in both as welded and after PWHT conditions. The results shown that, although the mechanical properties obtained for the welded joint achieved the requirements for the application in all analyzed conditions, the execution of PWHT is recommended for the relief of residual stresses and promotion of a tempering of the high hardness martensite of the last welding pass. Additionally, it was verified that it is possible to obtain properties that are similar to those of welded joints of rolled steels, which are usually used on mooring components.

Resumo A aplicação de revestimentos de ligas de níquel é comumente realizada na indústria de petróleo e gás para aumento da vida de equipamentos em ambientes agressivos, dado que este procedimento melhora a resistência à corrosão, sem um aumento significativo do custo de produção quando comparado com equipamentos maciços fabricados com outras ligas. Normalmente, as juntas são soldadas pelos processos de eletrodos revestidos, MIG/MAG ou TIG. Neste aspecto, o processo eletroescória realiza deposições com elevada energia de soldagem e baixa diluição, podendo ser uma opção interessante, uma vez que proporciona uma elevada produtividade, permitindo a soldagem com aplicação de apenas uma camada. O presente trabalho avalia propriedades mecânicas, microestruturais e de corrosão de revestimentos de liga de níquel 625 depositada em aço carbono ASTM A516 Grau 70 pelo processo eletroescória, tanto na condição como soldado quanto tratado termicamente. A deposição foi realizada com uma e duas camadas sobre chapas de dimensão 50x400x400 mm, na posição plana e energia de soldagem média de 11,7 kJ/mm. Após a soldagem realizou-se tratamento térmico a 620°C por 10 horas, sendo esta condição comparada ao estado de como soldado. Os ensaios de dobramento não indicaram evidências de defeitos. A avaliação microestrutural realizada por microscopia ótica (MO), eletrônica de varredura (MEV) e eletrônica de transmissão (MET) mostrou uma microestrutura austenítica para o depósito com pequena fração volumétrica de fases secundárias e o tratamento térmico de alívio de tensões não promoveu mudanças significativas nas propriedades. Na região de grãos grosseiros da zona termicamente afetada (RGGZTA) foi observada a ocorrência de ferrita pró-eutetóide, perlita e bainita para o depósito com 1 camada e basicamente ferrita e perlita refinadas para o deposito com 2 passes devido às baixas taxas de resfriamento. Adicionalmente, não foi verificada evidência de zona parcialmente diluída (ZPD). Os ensaios de corrosão realizados de acordo com a norma ASTM G-48 em amostras retiradas a partir da camada superior do depósito foram considerados satisfatórios, uma vez que não mostraram evidências de pites e a perda de massa foi pequena.

Abstract Nickel base alloy weld overlays are commonly used in oil & gas industry to extend the life of equipments under aggressive corrosion environments, since the overlays improve the corrosion resistance without a significant increase the cost of manufacture when compared to massive equipment. Usually, the joints are welded by SMAW, GMAW or GTAW processes. In this respect, the electro slag welding process (ESW), which promotes high heat inputs and low dilution welds, can be an interesting option for this application as it provides a high productivity, once only one layer is necessary. The present work evaluates mechanical, microstructural and corrosion properties of an Alloy 625 weld overlay deposited on ASTM A516 Grade 70 carbon steel by ESW process. The deposition was done with 1 and 2 layers in plates of dimension 50x400x400 mm, in the flat position and an average energy welding 11.7 kJ/mm. After welding, a post weld heat treatment at 620°C for 10 hours was performed, this condition being compared with the as welded condition. Bending tests showed no evidences of cracks. Microstructural evaluation performed using both optical (OM), scanning (SEM) and transmission electron microscopy (TEM) techniques showed an austenitic microstructure of the weld deposit with low proportion of secondary phases for all conditions and the post welding heat treatment did not promote significant changes on the mechanical properties. At the coarse grain heat affected zone (CGHAZ) the occurrence of proeutectoid ferrite, pearlite and bainite were found for 1 layer deposit and refined pearlite and ferrite for 2 layer deposits were the microstructural constituents observed due to the low cooling rate. In addition, no evidences of partially diluted zones (PDZ) were verified. Corrosion tests conducted on samples removed from top layer of weld overlay cladding deposit according to ASTM G 48 Method A Standard were considered satisfactory once no evidences of pittings were verified and the loss of mass was very reduced.