Resumo Os aços inoxidáveis duplex (AID) vêm

Resumo Os aços inoxidáveis duplex (AID) vêm IntroduçãoOs aços inoxidáveis duplex são utilizados industrialmente devido à sua resistência à corrosão em ambientes encontrados nas operações onshore e offshore e à sua alta resistência mecânica [1]. Aplicações típicas para esses tipos de aço são tubos coletores submarinos, flowlines ou tubos condutores, redes de tubos submarinas e sistemas de processamento topside. Os aços duplex têm sido também amplamente utilizados em muitas áreas além da petroquímica, como na indústria de papel e celulose.No entanto, devido ao teor de níquel (5% -7%) e molibdênio (cerca de 3%) requerido em sua composição, o aço inoxidável duplex tem um alto custo de produção e por apresentar uma solidificação iniciada como ferrita, a soldabilidade dos aços duplex é inferior à dos aços austeníticos, sendo necessário um controle rigoroso de composição química e ciclo térmico de soldagem.

Duplex stainless steel (DSS) has been considered as an excellent material of construction for applications where high corrosion resistance and high mechanical strength are required. The use of this material can minimize costs related to corrosion in different industries, for example, in the biodiesel industry. The objective of this study is to evaluate the electrochemical and electronic properties of passive films of thick welded joints of UNS S32304 lean duplex stainless steel (LDSS) fabricated by different welding processes, in acidified glycerin, a byproduct of the biodiesel industry. The electrochemical and electronic behavior of the passive films formed on UNS S32304 LDSS was evaluated using electrochemical impedance spectroscopy and Mott–Schottky measurements. The capacitance study shows that the passive films formed on welded DSS behave as n‐ and p‐type semiconductors above and below the flat band potential, respectively. Furthermore, the samples welded by the gas metal arc welding process exhibited better corrosion resistance than other welding process using the same filler metal.

Thick welded joints of UNS S32304 lean duplex stainless steel (LDSS) has been studied in acidified glycerin, a byproduct of biodiesel plants, using cyclic polarization technique. LDSS S32304 thick plates were welded by different processes commonly employed in the fabrication process: shielded metal arc welding, gas metal arc welding and flux cored arc welding. The electrochemical behavior of different weldment zones was characterized. Transmission electron microscopy and scanning electron microscopy (SEM) were used for sample characterization. SEM images showed that the heat affected zone was the most critical zone for pitting corrosion for all samples. The results were associated to the microstructural features of the materials. Generally, the breakdown potential of the top regions of welds was higher in acidified glycerin than the weld root for welds fabricated with two different filler metals. Basically, all the welded samples exhibited similar or higher corrosion resistance, compared with the corresponding base metal.

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Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualq'uer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Assessment of the TMCP Shipbuilding EH36 Steel Weldability of High Heat Input Submerged Arc Welding JointAbstract: The welding with high heat input is one of the main strategies used by shipyards in the world to increase their productivity in joining operation activities. However, the thermal cycles due to the welding process may affect the microstructure features and be deleterious to the toughness in the heat affected zone (HAZ). The aim of this study was to evaluate the microstructure and the mechanical properties of the HAZ of the EH36 steel produced by controlled rolling and accelerated cooling compared to a conventional steel of the same grade, both welded with submerged-arc welding with two heat inputs: 76 to 130 kJ/cm. It was observed that the presence of a more refined microstructure in the different regions of the HAZ, associated with a fine base metal grain size and lower carbon equivalent value, were the main factors that contributed to the excellent HAZ toughness of the TMCP steel compared to conventional steel. The results of this study showed that it is possible to obtain welded joints with excellent mechanical properties even using high heat input levels by employing TMCP steel , and its use may be a strategy to optimize the production time and cost in the shipbuilding industry.

ResumoA soldagem com elevado aporte térmico é uma das alternativas adotadas pelos estaleiros para aumento da produtividade nas operações de união de materiais. No entanto, os ciclos térmicos gerados durante a soldagem podem provocar transformações microestruturais prejudiciais à tenacidade na zona afetada pelo calor (ZAC). Este estudo teve como principal propósito realizar a caracterização microestrutural e avaliar as propriedades mecânicas da ZAC do aço naval Sincron EH36 produzido na Usiminas por laminação controlada seguida de resfriamento acelerado em comparação com um aço de mesma classe de limite de escoamento produzido convencionalmente, ambos soldados pelo processo ao arco submerso em dois níveis de aporte térmico: 76 e 130 kJ/cm. Foi observado que a presença de uma microestrutura mais refinada nas diferentes regiões da ZAC, associadas ao menor tamanho de grão do metal base e ao menor carbono equivalente, foram os principais fatores que contribuíram para a excelente tenacidade da ZAC do aço Sincron em comparação ao aço convencional. Os resultados obtidos mostraram que é possível obter juntas soldadas com excelentes propriedades mecânicas ao se empregar aço Sincron para a soldagem com altos aportes de calor, e sua utilização pode ser uma estratégia para otimização dos tempos e custos de fabricação na indústria naval. Palavras-chave: Soldagem; Aços TMCP; Resfriamento acelerado; Elevado aporte térmico. ASSESSMENT OF THE TMCP SHIPBUILDING EH36 STEEL WELDABILITY OF HIGH HEAT INPUT SUBMERGED ARC WELDING JOINT AbstractThe welding with high heat input is one of the main strategies used by shipyards to increase their production. However, the thermal cycles due the welding process may affect the microstructure features and the toughness in the heat affected zone (HAZ). The aim of this study was evaluate the microstructure and the mechanical properties of the HAZ of the Usiminas steel Sincron EH36 produced by controlled rolling and accelerated cooling compared to a conventional steel of the same yield strength grade, both welded with submerged-arc welding with two heat inputs: 76 to 130 kJ/cm. It was observed that the presence of a more refined microstructure in the different regions of the HAZ, associated with a smaller base metal grain size and lower carbon equivalent value, were the main factors that contributed to the excellent toughness of the HAZ Sincron steel compared to conventional steel. The results of this study showed that it is possible to obtain welded joints with excellent mechanical properties by employing Sincron steel with high heat input welding, and its use may be a strategy to optimize the time and cost of production in the shipbuilding industry.

Low-temperature plasma assisted carburizing (LTPC) is an efficient method to provide improvement on surface mechanical properties of stainless steels, with a consequent improvement on its tribological behavior. The application of this treatment on martensitic stainless steels is recent and there are many aspects that deserves attention, including the treated surface corrosion resistance. Among various electrochemical techniques, critical pitting temperature (CPT) has been widely used to characterize stainless steels corrosion resistance due to its good reproducibility, sensitivity and efficiency. In this context, the purpose of this work was to apply LTPC thermochemical treatment on AISI 410 martensitic stainless steel, aiming to determine the influence of the treatment temperature in the treated surface microstructure, hardness and corrosion resistance employing TCP technique. The carburizing treatments were carried out at 300, 350, 400 and 450 °C during 6 hours, using a gas mixture containing 99.5% of (80% H 2 + 20% Ar) + 0.5% de CH 4 (in volume). The gas mixture flow rate and pressure were fixed at 1.67 x 10-6 Nm 3 s-1 and 400 Pa. The treated samples were characterized using X-ray diffractometry, optical microscopy, and microhardness measurements. The treated surfaces corrosion resistance was evaluated using OCP and CPT measurements. For the treated surfaces an increase in hardness and a displacement of XRD martensite peaks was observed, indicating that the carburizing processes were succeeded. The