This study focused on the effects of different peak (austenitizing) temperatures (Tp) over the martensite start temperature (Ms) and its influence on the final residual stresses after welding simulation. For this purpose, the expansion coefficients obtained through physical (dilatometric) simulations of a high-strength low-alloy steel were considered for three peak temperatures: 1300 °C, 1150 °C, and 920 °C and a cooling rate of 25 °C/s. Aiming at clarifying the physical phenomenon behind GTAW welding, one carried out nonlinear transient thermomechanical finite-element (FE) analyses to reconstitute the welding process and simulate the subsequent formation of residual stresses in the HAZ. Once the heat source simulation was calibrated, four material models were created, one for each Tp, and a fourth model considering a constant expansion coefficient, without considering the martensite transformation for comparison. A Three-bar model was evaluated to isolate the effects of Tp (Ms) in the residual stresses. A composite plate model was also considered, in which the sheet HAZ was subdivided according to the reached peak temperature, and the respective material models were applied. The results show the importance of martensite transformation on the welding-induced residual stress and a clear trend of decreasing tensions with lowering the Tp, especially over HAZ.

This study is focused on the performance evaluation of flash-butt-welded rail joints concerning their mechanical strength and fatigue life. Residual stresses created in the heat-affected zone were measured and the effects of the welding process and notch sensitivity on the fatigue behavior in the weld region were experimentally assessed. Aiming at clarifying the physical phenomenon behind the flash-butt welding, nonlinear transient thermomechanical finite-element analyses were performed to reconstitute the welding process and to simulate the subsequent formation of residual stresses. A new hypothesis for explaining higher temperatures in the rail web than in the rail foot and head was suggested and numerically verified. Experimental fatigue results showed high notch sensitivity and highlighted the effects of microstructure variations on the fatigue life. In general, a good agreement was achieved between numerical and experimental measurements of residual stresses, which was essential for understanding the fatigue phenomenon and the formation of residual stresses in flash-butt-welded rail joints. A relevant outcome is the simulation of the hot burrs from the welding process as prescribed heat inputs on a convenient part of the rail surface. This simulation strategy has shown adequate to explain the non-uniform temperature changes and the corresponding originated residual stresses. flashbuttwelded flash butt welded life heataffected affected assessed flashbutt finiteelement finite element verified general surface nonuniform non uniform

ABSTRACT Duplex stainless steel UNS S31803 exhibits high mechanical strength with high corrosion properties, due to its microstructure composed of ferrite and austenite phases, in equal proportion. When the UNS S31803 steel is submitted to high temperatures, some precipitations can occur, such as nitrites, carbides, and third phases (e.g. sigma phase -σ, and alpha prime - α'). These phases are deleterious in relation to the mechanical properties and corrosion resistance, and their effects are analyzed regarding the properties of the steel. In order to evaluate the precipitation of this deleterious phase, isothermal treatment was done at 500°C for 144 hours (α' phase) and at 850ºC for 80 minutes (σ phase). The results were obtained through the microstructural analysis and tensile tests. The presence of sigma phase was verified in the grain boundary, an increase in the mechanical resistance with a loss of toughness. There was as well as an increase in mechanical resistance with the precipitation of α', with less loss of ductility than that observed in the experiments involving the presence of sigma phase.

Resumo: Trilhos longos soldados por centelhamento elétrico (Flash Butt Welding - FBW) apresentam características desejáveis do ponto de vista do comportamento dinâmico da via, no entanto, as soldas são regiões de descontinuidade estrutural e mecânica onde se originam tensões residuais, e que estão associadas a falhas prematuras por fadiga. Ensaios de dilatometria foram empregados para simular os efeitos do tamanho de grão austenítico sobre a evolução microestrutural pós-soldagem. Simulações numéricas termomecânicas, não-lineares, no domínio do tempo, pelo Método dos Elementos Finitos (MEF), foram empregadas para avaliar os efeitos de modificações de parâmetros do processo de soldagem sobre as tensões residuais. Os resultados apresentados permitem compreender os mecanismos das alterações morfológicas da perlita na Zona Termicamente Afetada (ZTA) em termos de transformações de fases e podem ser utilizados para sistematicamente orientar mudanças nos parâmetros do processo ou controlar a taxa de resfriamento de modo a obter melhores condições metalúrgicas/mecânicas. Ademais, os resultados dos modelos numéricos mostram como a adoção de ZTA estreita influencia nas taxas de resfriamento e no desenvolvimento de tensões residuais em regiões críticas do componente.

Abstract: Long rails, welded by the Flash-Butt Welding process present desirable characteristics concerning the dynamic behavior of the track, however flash-butt-welded joints are regions of structural and mechanical discontinuity where high residual stresses originate, and, consequently, premature-fatigue failures may take place. This paper employs dilatometric analysis to simulate the austenitic grain size effects on the postweld microstructural evolution. Finite Element Method (FEM) is used to carry out transient, physically non-linear thermo-mechanical analyses to evaluate the effects of the welding parameters on residual stresses. The results allow understanding the mechanisms associated with the morphological changes of the pearlite in the HAZ in terms of phase transformation and can be used to systematically guide changes in the process parameters or to control the cooling rate in order to obtain better metallurgical/mechanical conditions. In addition, from the results of the numerical models, it is demonstrated how the adoption of narrow HAZ influences cooling rates and the development of residual stresses in critical regions of the welded component.

Resumo Trilhos longos, soldados pelo processo Flash Butt Welding (FBW), são a realidade das ferrovias brasileiras de média e alta carga por eixo. Embora apresentem características desejáveis do ponto de vista do comportamento dinâmico da via, as soldas são regiões de descontinuidade estrutural e mecânica onde se originam tensões residuais, e que estão associadas a falhas prematuras por fadiga. Simulações numéricas termomecânicas, fisicamente não-lineares, no domínio do tempo, pelo Método dos Elementos Finitos (MEF), foram empregadas para avaliar o desenvolvimento de tensões residuais originadas durante o processo de soldagem. Uma nova abordagem para a inclusão do aporte de calor envolvido no processo é proposta. Os resultados numéricos são comparados a medidas experimentais de tensões residuais superficiais e aspectos macrográficos das juntas, incluindo largura da Zona Termicamente Afetada (ZTA) e dados de taxas de resfriamento. Os resultados mostram boa correlação entre as análises numéricas e medidas experimentais de tensões residuais. Aspectos fundamentais relacionados ao desenvolvimento de tensões residuais são esclarecidos a partir da correlação entre análises numérica e experimental. Ademais, verifica-se que os modelos computacionais podem ser utilizados na previsão de pontos críticos para nucleação de trincas por fadiga e/ou avaliar efeitos de variáveis de processo sobre o campo de tensões residuais.

Abstract Long rails, welded by the Flash-Butt Welding (FBW) process, are the reality of the Brazilian railroads for medium and high axle loads. Although they present desirable characteristics concerning the dynamic behavior of the track, welded joints are regions of structural and mechanical discontinuity where high residual stresses originate, and, consequently, premature fatigue failures may take place. This paper employs the Finite Element Method (FEM) to carry out transient, physically non-linear thermo-mechanical analyses to evaluate residual stresses evolved in the welding process. A new approach is proposed to take into account the heat input involved in the process. The numerical results are compared to experimentally measured surface residual stresses, and to the macrographic joint aspects, including the HAZ width and cooling rate data. The results show a good correlation between the numerical and experimental measurements of residual stresses. Fundamental aspects related to the development of residual stresses are clarified, correlating numerical and experimental analyses. In addition, it is verified that the computational models can be used to predict critical crack nucleation points by fatigue, and/or to evaluate effects of process parameters on the residual stress field.

Resumo A soldagem de alto aporte térmico é uma alternativa que tem sido empregada na indústria naval e de petróleo para reduzir o número de passes de soldagem em estruturas espessas por meio do aumento da taxa de deposição. Isso tem levado desenvolvimento de aços e de consumíveis que permitem a obtenção de juntas com aceitável nível de tenacidade na zona termicamente afetada, mesmo com aportes térmicos muito elevados. Contudo, ainda não são muito claras as consequências do ponto de vista metalúrgico que este procedimento pode acarretar na zona fundida. O presente trabalho avalia a influência de aportes térmicos de até 17,1 kJ/mm na microestrutura e características mecânicas da zona fundida obtida na soldagem de um aço naval TMCP EH36 feita em único passe com o processo ao arco submerso multi-eletrodos e com adição de arame frio. A microestrutura foi comparada com a de soldas realizadas com energia menor e mapas de dureza foram produzidos e comparados, avaliando-se também a eficiência dos consumíveis geralmente aplicados para a soldagem e alto aporte. Foi observado que o teor de molibdênio na solda contribui de forma direta para a manutenção das propriedades mecânicas da zona fundida na soldagem de alto aporte térmico.

Abstract High heat input welding is an alternative that has been employed to reduce the number of welding passes in thick structures with increasing deposition rate. This has led to the development of steels and consumables that allow to obtain joints with acceptable level of toughness in the Heat Affected Zone, even with very high heat inputs. However, the metallurgical consequences, which this procedure can cause in the welding zone, are not very clear yet. This research evaluates the heat input effect up to 17.1 kJ/mm on the microstructure and mechanical properties of the welding zone obtained in the welding of a TMCP EH36 shipbuilding steel in single pass with the submerged arc multi-electrodes with addition of cold wire. The microstructure was compared with that of welds performed with lower heat input and hardness maps were produced and compared, also evaluating the efficiency of consumables generally applied for welding and high input. It was observed that the molybdenum content in the weld acts directly to the maintenance of the mechanical properties of the welding zone in the high heat input welding.

This research presents the influence of manufacturing processes and heat treatments on the resulting microstructures and mechanical properties of an API 5L PSL2 seamless steel pipe. Three different conditions are considered - as rolled, normalized and quenched and tempered - to obtain the grades X42R, X42N and X70Q, respectively. Scanning electron microscopy techniques was used to characterize the resultant microstructures. Tensile, hardness, impact, fracture toughness (J integral) and fatigue crack growth tests (da/dN x ΔK) were used to study the materials mechanical behavior. The results show the possibility of achieving API grades for a seamless pipeline steel, through suitable heat treatments. The microstructural modifications and mechanical properties changes observed showed a remarkable structure-properties relationship of the steel, and attempt to a proper selection as required by the structural design. The quenching and tempering process increased tensile mechanical properties and fracture toughness, but combined to a significant decrease in fatigue crack growth resistance.

Resumo Trilhos com perfil TR-57 do tipo intermediário foram soldados por centelhamento em um estaleiro brasileiro e passaram por detalhada caracterização mecânica e metalográfica. Os dados quantitativos da caracterização metalográfica e dos ensaios mecânicos foram submetidos a análises de variância (ANOVA). Na metalografia confirmou-se a presença majoritária de perlita, porém há também ferrita proeutetóide na linha central da solda e globulização parcial da cementita em regiões da Zona Termicamente Afetada (ZTA), sobretudo na zona de transformação parcial. O tamanho das colônias perlíticas e o espaçamento interlamelar foram correlacionados à microdureza Vickers em toda a extensão da junta. Ensaios de tração revelaram que o metal base atendeu às especificações da Norma AREMA, no entanto, as juntas soldadas não atenderam e a fratura dos corpos de prova ocorreu na região de menor dureza da ZTA. Os resultados permitem compreender, em detalhes, as consequências do processo de soldagem sobre a estrutura do aço e as variações de propriedades em diversas regiões da junta, com destaque às alterações morfológicas da perlita. Relações com modos de falha anteriormente relatados na literatura científica também são apresentadas.

Abstract TR-57 intermediate steel rails were welded in a Brazilian flash butt welding plant and the joints were subjected to a detailed mechanical and structural characterization. Quantitative data were subjected to ANOVA analysis. The metallography has confirmed the majority presence of pearlite, but pro-eutectoid ferrite was also verified in the weld centerline. Globulized cementite appeared in some regions of the Heat Affected Zone (HAZ), particularly in the partial transformation zone. The pearlite colony size and pearlite interlamellar spacing were related to Vickers microhardness over the full joint length. The base metal met the minimum specified tensile properties in the AREMA standard. However, the weld joints did not meet the minimum tensile strength and all samples fractured in the partial transformation zone, which has lower hardness. The results help to deep understand the structure-properties relationships over the full joint, highlighting the relations between the welding process and the resultant pearlite morphology. Considerations about the component failure modes previously related in scientific literature are also presented.

Threaded and coupled connections generally present a non-uniform stress distribution, which is related to the higher stiffness of the box when compared to the pin. The non-uniform stress distribution can contribute to fatigue cracks and other failure modes in high pressure oil wells. An API 5CT P110 steel obtained from a seamless pipe was mechanically characterized. FEA models were carried out to investigate and compare two API casing connections under make-up torque and tensile efforts. A parametric study was performed using numerical models to determine the influence of some geometric features on the behavior of the API Buttress threaded connection. The API Buttress connection supported higher tensile loads than the API Short Round, however both standard connections showed high stress concentration in the last engaged thread and a non-uniform stress distribution. The manufacturing of grooves at the first and the last engaged threads proved to be an efficient way to reduce the stress concentration of Buttress casing connection and could be an alternative to the development of new products.

Abstract This paper presents a study about the fracture mechanism of a ferritic stainless steel (UNS S44400 type) during a tensile test. The applied materials for the experimental procedures were 25 specimens of the steel, machined in the rolling direction. Each specimen was submitted to standard polishing procedures. One of the samples, in the original state, was structurally characterized by reflected light optical microscopy. The other samples were submitted to tensile tests with a constant displacement rate. Three samples were tested until failure (complete tests) and the others just until specific strain values, when the tests were interrupted and the samples were characterized by using optical and scanning electron microscopy. The main objective of these characterizations was to evaluate the structural damage evolution and to identify the fracture mechanism for the tested conditions. A methodology to quantify the damage evolution by surface roughness, identified by optical microscopy, was proposed. A new index - Damage by Diffuse Reflection Index (DRI) - was proposed to quantify the damage evolution in function of the specimen deformation. It was possible to confirm the ductile behavior of the studied steel and that the main fracture mechanism was the traditional dimpled rupture.

Extended sheets are produced by a pressure cutting process to transform common sheets in expanded metal. These sheets are usually made of carbon steel, but due to their corrosion susceptible, studies have been developed with the aim to evaluate the viability of replacing these common steels by stainless steels. This study proposed an experimental method to characterize structural and mechanically samples of stainless steel extended sheets (410D, 444A, 439 and 304A) and a 1010 carbon steel sheet thicker than the others. This study has a practical importance because nowadays there are not standardized procedures to do this kind of evaluation. The obtained results showed that the methodology was effective for the proposed objective and that the expanded sheets made of stainless steels have a better performance in terms of mechanical strength compared to the 1010 steel sheet.

Resumo Neste trabalho, investigaram-se efeitos do fenômeno de envelhecimento por deformação em juntas obtidas por soldagem a arco elétrico com proteção gasosa (GMAW), de tubos sem costura de aço API5L X65Q. Corpos de prova (CPs) obtidos a partir das juntas soldadas foram submetidos à uma deformação plástica a frio de 3% e posteriormente envelhecidas por 1h a 250°C, de forma a se induzir envelhecimento estático. Buscando avaliar o envelhecimento dinâmico, os CPs foram deformados até 3% e o carregamento foi mantido durante 1h a 250°C. Os CPs envelhecidos foram submetidos a ensaios de tração e amostras representativas foram analisadas ao microscópio óptico e microscópio eletrônico de varredura. Observou-se que o fenômeno modificou a fração volumétrica de constituintes secundários no metal de solda e na ZTA, com aumento na proporção de agregados ferrita-carbonetos. Com relação às propriedades mecânicas, constatou-se que o fenômeno reduziu a razão elástica das juntas soldadas devido a um aumento no limite de resistência, além de aumentar o alongamento total, não prejudicando, portanto, as propriedades mecânicas em tração das juntas soldadas. Ao se comparar o envelhecimento estático com o envelhecimento dinâmico, observou-se que o aumento na capacidade de deformação plástica das juntas soldadas foi maior após envelhecimento estático por deformação.

Abstract In this work was investigated the influence of the strain ageing on joints obtained by gas-metal arc welding (GMAW) of API 5L X65Q seamless pipes. Specimens were machined from the welded joints, plastically strained to 3% and aged at 250°C for 1h posteriorly, in order to characterize effects of static strain ageing. For the dynamic strain ageing characterization, the specimens were simultaneously strained and aged. Then, the aged specimens were submitted to tensile tests and representative samples were analyzed at a light optical microscope and a scanning electron microscope (SEM). From the results, it was observed that the strain ageing phenomenon changed the volumetric fraction of secondary constituents in the weld metal and in the heat-affected zone, increasing the proportion of ferrite-carbide aggregates. Regarding the mechanical properties, it was noticed that the phenomenon led to higher tensile mechanical properties such as ultimate tensile strength and total elongation and lower elastic ratio, and, therefore, not impaired the mechanical properties under tensile of the welded joints. Comparing the static strain ageing with dynamic strain ageing it was observed that the effect on the plastic straining ability of welds was higher after static strain ageing.

This research compares the mechanical behavior of two API steels (X60 and X70) used in the longest pipeline in the world for the conveyance of iron ore. Tensile tests, Charpy impact tests, CTOD tests and fatigue crack growth tests are performed at ambient temperature. Metallographic examination showed a banded microstructure consisting of polygonal ferrite and pearlite in both steels, with smaller grain size and the presence of a small quantity of bainite in the X70 steel. All the mechanical tests revealed a ductile behavior for the two steels. The X70 steel is preferable for the pipeline project, due its better mechanical resistance, with no significant loss of fracture toughness and fatigue resistance. Its performance could be even better, if an appropriate combination of thermomechanical processing parameters were able to produce a microstructure with minor amount of pearlite, where acicular ferrite/bainite are present.

A arte da Cantaria usando o quartzito foi utilizada na construção dos monumentos históricos de Ouro Preto/MG. Após mais de 300 anos de existência, parte de algum desses monumentos encontra-se em avançado estágio de deterioração. Na restauração desses monumentos, alguns restauradores empregam a resina poliéster ortoftálica. Nesse trabalho, o quartzito itacolomi não colado e colado com diversas resinas foi submetido a ensaio de resistência em flexão e constatou-se que a resina suportou carga maior que o quartzito. Todos os corpos-de-prova romperam fora da região da aplicação da resina, confirmando a eficácia das resinas para colar a rocha.

The art of carving stone using itacolomi quartzite was employed in the monuments of Ouro Preto city in Minas Gerais. More than 350 years after being built, some of these monuments are in an advanced stage of deterioration. In the restoration of these buildings, some restaurateurs employ orthophthalic polyester resin. In the present study, both non-glued and glued (using different types of resins) itacolomi quartzite were submitted to a flexion strength test. After some trials, it was verified that the resins supported greater loads than the quartzite. All specimens broke outside the resin's application area, thus confirming the effectiveness of resin adherence to rock.

Aluminum-lithium alloys are candidate materials for many aerospace applications because of their high specific strength and elastic modulus. These alloys have several unique characteristics such as excellent fatigue crack growth resistance when compared with that of the conventional 2000 and 7000 series alloys. In this study, fatigue crack propagation behavior has been examined in a commercial thin plate of Al-Li-Cu-Mg alloy (8090), with specific emphasis at the fatigue threshold. The results are compared with those of the traditional Al-Cu-Mg alloy (2024). Fatigue crack closure is used to explain the different behavior of the compared alloys.