Super duplex stainless steel (SDSS) combines corrosion resistance and mechanical properties, interesting to applications in the oil extraction industry. In this process, wear between the tools friction and rocky materials occurs with SDSS pipes. Due to the low tribological properties, plasma nitriding process is applied to provide a surface layer with excellent wear resistance and without significant losses in corrosion resistance. Here, conventional plasma nitriding (CPN) and cathodic cage plasma nitriding (CCPN) techniques were compared to modify SDSS surface. Before and after passing by these two nitriding processes, welded joints (WJ) were subjected to a microstructural and corrosion resistance evaluation. Aiming to characterize the final product obtained, it was used characterization techniques, such as scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results show that using the CPN technique, at 400°C, was responsible for providing greater resistance to corrosion, when analyzing the result of potentiodynamic polarization — jpassivation = 2.60x10-5 A.cm-2 and Epite = 0.83 V than the CCPN technique when applied to the SSDS, and this was attributed to the formed diffusion layer, which is composed of the expanded austenite and ferrite phases.

Resumo: Neste estudo, faz-se uso do método dinâmico e a técnica de ressonância de barras para medir as constantes elásticas da ZF da junta soldada de um aço estrutural ASTM Grau A36. A geometria, massa e frequência de ressonância (na flexão e na torção), de amostras com seção transversal retangular, são usadas para determinar as características elásticas e homogeneidade da junta soldada e do metal base pela norma ASTM E1875-13. As demais propriedades da junta soldada são determinadas pelos ensaios convencionais de tração, impacto (Charpy V), dureza e por microscopia ótica, difração de raios-X e EDS acoplada ao MEV. Os resultados dos ensaios convencionais quantificaram valores dentro dos padrões estabelecidos por norma, demonstraram a formação de fase típica sem a formação de novas fases e a dureza média foi 10% maior na ZF, o comportamento de fratura se mostrou dúctil. O refino de grão na região revelou uma maior quantidade de perlita e maior teor de elementos de liga, as constantes elásticas foram alteradas em relação ao MB de 4,9% a mais para o módulo de Young, 7,65% maior para o cisalhamento e 11,7% menor para a razão de Poisson, mostrando assim que o método é viável tanto para prever no MB e na ZF os valores das constantes elásticas.

Abstract: In this study, the bar resonance technique is used to measure the elastic constants of the welded joint of an ASTM Grade A36 structural steel. The geometry, mass and resonant frequency (flexion and torsion) of samples with rectangular cross section are used to determine the elastic characteristics and homogeneity of the welding and base metal by ASTM E1875-13.The other properties of the weld joint are determined by the conventional tests of traction, impact (Charpy V), hardness and microstructural characterization by optical microscopy, X-ray diffraction and EDS coupled to MEV. The results of the conventional tests quantified values within the norms established by the standard, demonstrated the typical phase formation without the formation of new phases and the average hardness was 10% higher in the ZF, the fracture behavior was ductile. The grain refining in the region revealed a higher amount of perlite and higher alloying content. The elastic constants were changed in relation to the 4.9% higher MB for Young's modulus, 7.65% higher for shear and 11.7% lower for Poisson's ratio, thus showing that the method is feasible to predict both MB and ZF elastic constant values

RESUMO Os aços inoxidáveis superduplex (AISD) apresentam em sua microestrutura as fases ferrita e austenita, de modo a conciliar boas propriedades mecânicas e de resistência à corrosão. Estes materiais possuem grande aplicação na indústria de extração de petróleo e na petroquímica. Quando estão sujeitos a estas aplicações, os dutos de AISD sofrem desgastes. Dentre os tipos, pode-se citar o proveniente do atrito de cabos que levam ferramentas para o interior de poços. Levando em consideração a soldagem dos aços superduplex, a suscetibilidade ao desgaste e à corrosão podem aumentar. Valores de energia de soldagem acima de 1,5 KJ/mm ocasionam o desbalanceamento de fases, prejudicando as propriedades citadas. A ZTA (zona termicamente afetada) da solda destes aços é a região mais suscetível à degradação e fragilização devido ao crescimento do grão ferrítico e possível surgimento de precipitados deletérios. Neste contexto, este trabalho tem como um dos objetivos nitretar a junta soldada do aço SAF 2507 e correlacionar a microestrutura com a dureza superficial. Para alcançar os resultados, amostras de junta soldada foram nitretadas a plasma utilizando as técnicas de nitretação convencional (NC) e em gaiola catódica (NGC) na temperatura de 400 °C. Em decorrência, as amostras nitretadas com o uso da gaiola catódica apresentaram maiores e mais uniformes valores de microdureza.

ABSTRACT Superduplex stainless steels (SDSS) present in their microstructure the ferrite and austenite phases, in order to reconcile good mechanical properties and resistance to corrosion. These materials are widely used in the petroleum extraction and petrochemical industries. When subjected to these applications, the SDSS ducts are worn. Among the types, we can mention the coming from the friction of cables that take tools into the wells. Taking into account the welding of superduplex steels, the susceptibility to wear and corrosion may increase. Solder energy values above 1.5 KJ / mm cause phase imbalance, damaging the mentioned properties. The HAZ (heat affected zone) of welding of these steels is the region most susceptible to degradation and embrittlement due to the growth of the ferritic grain and possible emergence of deleterious precipitates. In this context, this work has as one of the objectives to nitrate the brazed joint of the SAF 2507 steel and to correlate the microstructure with the surface hardness. To achieve the results, samples of welded joint were nitrided to plasma using conventional (CN) and cathodic cage (CCN) techniques at a temperature of 400 °C. As a result, the nitrided samples with the cathodic cage showed larger and more uniform values of microhardness.

This study investigated the softening mechanisms of the AISI 410 martensitic stainless steel during torsion simulation under isothermal continuous in the temperature range of 900 to 1150 °C and strain rates of 0.1 to 5.0s-1. In the first part of the curves, before the peak, the results show that the critical (εc) and peak (εp) strains are elevated for higher strain rate and lower temperatures contributing for higher strain hardening rate (h). Moreover, this indicated that dynamic recrystallization (DRX) and dynamic recovery (DRV) are not effective in this region. After the peak, the reductions in stresses are associated to the different DRX/DRV competitions. For lower temperatures and higher strain rates there is a delay in the DRX while the DRV is acting predominantly (with low Avrami exponent (n) and high t0.5). The steady state was reached after large strains showing DRX grains, formation of retained austenite and the presence of chromium carbide (Cr23C6) and ferrite δ at the martensitic grain boundaries. These contribute for impairing the toughness and ductility on the material. The constitutive equations at the peak strain indicated changes in the deformation mechanism, with variable strain rate sensitivity (m), which affected the final microstructure.

The aim of this work is evaluate the influence of welding conditions on abrasive wear resistance in coating of Fe-Cr-C. The metal base used in this investigation was the steel SAE 1020 and as welded metal the selfshilded tubular wires of Fe-Cr-C with 1.6 mm of diameter. The welding parameter such as amperage, voltage, welding speed, wire feed speed and the distance between the point and samples were kept constant by varying the electrode inclination and the number of layers deposited. These resulted in four different weld conditions: pulling and pushing the weld pool and hardfacing formed with 1 end 2 layers. Their influences on dilution, microhardness and microstructure were evaluated and correlated with the abrasive wear according to the standard tests methods for abrasion measurements through the usage of dry sand/rubber wheel apparatus, ASTM G-65-04. The results showed that the wear resistance of the four different conditions was affected by dilution, microstructure morphology and carbide volume fraction. The best conditions for hardfacing deposition were for pushing the torch and two layers added.

Resumo: Vários estudos têm demonstrado a influência dos parâmetros e proteção gasosa sobre a estabilidade de transferência metálica ou sobre a geração de fumos em soldagem MIG/MAG, mas pouco ou nada tem sido discutido sobre a emissão de gases tóxicos e asfixiantes, particularmente no que tange a parametrização do processo. O objetivo deste estudo foi analisar e avaliar o efeito de aspectos operacionais dos processos de soldagem (estabilidade da transferência metálica e composição do gás de proteção) sobre os níveis de emissão gasosa de durante a soldagem MIG/MAG (aspectos ambientais e de saúde ocupacional). Utilizando-se misturas de argônio com CO2 e O2 e mantendo-se a mesma corrente média e o mesmo volume de cordão de solda, soldagens com transferência por curto-circuito foram realizadas com arame de aço carbono em ambientes aberto (zona de respiração do soldador) e confinados. A tensão de soldagem foi ajustada gradualmente para modificar a estabilidade da transferência. Verificou-se que quanto mais rica a composição do gás em CO2, mais CO2 e O2 são emitidos pelo arco. No entanto, ao contrário de emissão de fumos, tensão e estabilidade da transferência metálica não têm efeito sobre a geração de gases. Verificou-se também que, apesar da grande quantidade de CO e CO2 emitida pelo arco, especialmente quando se utiliza gás de proteção CO2 puro, não se forma concentração residual de alto nível de CO e CO2 perto de zona de respiração do trabalhador, mesmo em células de trabalho confinadas.

Abstract: Several studies have demonstrated the influence of parameters and shielding gas on metal transfer stability or on the generation of fumes in MIG/MAG welding, but little or nothing has been discussed regarding the emission of toxic and asphyxiating gases, particularly as it pertains to parameterization of the process. The purpose of this study was to analyze and evaluate the effect of manufacturing aspects of welding processes (short-circuit metal transfer stability and shielding gas composition) on the gas emission levels during MIG/MAG welding (occupational health and environmental aspects). Using mixtures of Argon with CO2 and O2 and maintaining the same average current and the same weld bead volume, short-circuit welding was performed with carbon steel welding wire in open (welder’s breathing zone) and confined environments. The welding voltage was adjusted to gradually vary the transfer stability. It was found that the richer the composition of the shielding gas is in CO2, the more CO and CO2 are generated by the arc. However, unlike fume emission, voltage and transfer stability had no effect on the generation of these gases. It was also found that despite the large quantity of CO and CO2 emitted by the arc, especially when using pure CO2 shielding gas, there was no high level residual concentration of CO and CO2 in or near the worker’s breathing zone, even in confined work cells.