Abstract AISI D6 tool steel and AISI 304 stainless steel are among the most widely used material in the industry. However, this application field can still be expanded through the coatings deposition. In this regard, the objective of this work was to evaluate the impact of coatings application by cathodic cage technique using Hastelloy’s cathodic cage, on corrosion resistance of these steels. Two treatment temperatures were compared. The samples were characterized by Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, X-Ray Diffraction with the application of the Rietveld routine and corrosion test. The results showed the formation of multiphase layers that contributed to corrosion potentials reduction for treatments at 400 °C, being more effective when applied on AISI D6. It was observed that the corrosion resistance is influenced by the temperature, which was attributed to the precipitation of chromium nitride and iron oxide at 450 ºC.

RESUMO Em dutos que operam em regime turbulento, o processo corrosivo é acelerado e diretamente responsável por inúmeros prejuízos em plantas industriais, tais como paradas nas linhas de produção, falhas em equipamentos e elevados custos de manutenção. Embora haja poucos estudos laboratoriais nesta condição de escoamento, há um consenso entre inúmeros pesquisadores que o monitoramento e investigações nesta condição são essenciais, uma vez que simulam condições representativas da realidade industrial. Este trabalho investigou a influência do fluxo do meio eletrolítico sobre os parâmetros eletroquímicos do aço ABNT 1020 em solução NaCl 3% submetido a diferentes velocidades (0,21, 0,42, 0,62 e 0,84 m.s-1), relacionando os resultados obtidos por Espectroscopia de Impedância Eletroquímica (EIE) e Polarização Potenciodinâmica Linear (PPL). Os ensaios eletroquímicos foram realizados a partir de uma plataforma experimental construída para tal finalidade e acoplada às conexões do potenciostato, a fim de se obter curvas experimentais enquanto o eletrólito fluía dentro da célula e interagia com a superfície do metal. Os resultados mostraram que a variação da velocidade provoca mudanças notáveis nos principais parâmetros do ensaio e que as técnicas eletroquímicas corroboraram entre si mesmo em condições turbulentas de escoamento na plataforma de testes.

ABSTRACT In pipelines that operate in turbulent conditions, the corrosive process is accelerated and directly responsible for numerous losses in industrial plants, such as downtime in production lines, equipment failures and high maintenance costs. Although there are few laboratory studies in this flow condition, there is a consensus among countless researchers that monitoring and investigations in this condition are essential, since they simulate conditions representative of industrial reality. This work investigated the influence of the flow of the electrolytic medium on the electrochemical parameters of ABNT 1020 steel in 3% NaCl solution submitted to different speeds (0.21, 0.42, 0.62 and 0.84 ms-1), relating the results obtained by Electrochemical Impedance Spectroscopy (EIE) and Linear Potentiodynamic Polarization (LPP). The electrochemical tests were performed from an experimental platform built for this purpose and coupled to the connections of the potentiostat, in order to obtain experimental curves while the electrolyte flowed inside the cell and interacted with the metal surface. The results showed that the variation in speed causes notable changes in the main parameters of the test and that the electrochemical techniques corroborated each other in turbulent flow conditions in the test platform.

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 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.