No abstract

DIN 1.4110 martensitic stainless steel is largely used in the cutlery industry due to its high corrosion resistance associated with high mechanical resistance. However, when this material works under corrosion and wear conditions at the same time, their synergistic effect can accelerate the degradation process of the alloy. Cryogenic heat treatments have been proposed to improve the dimensional stability and mechanical properties, since they minimize the amount of retained austenite. The aim of this work is to study the effect of deep cryogenic heat treatment at -80 ºC and at -196 ºC on the corrosion resistance and tribocorrosion behavior of DIN 1.4110 martensitic stainless steel. The microstructure, hardness, corrosion resistance and tribocorrosion behavior were evaluated. Although the heat-treated samples presented higher hardness and lower corrosion current density (i corr ) compared to samples in spheroidized condition, their material removal under tribocorrosion conditions increased, which demonstrated the synergy between corrosion and wear.

Flexible risers are critical equipment for the production of oil and gas in offshore fields around the world. The annulus region may condense acidic water containing H 2 S exposing the tensile armour steel wires to a sour environment, which may promote sulphide stress cracking (SSC) and/or hydrogen-induced cracking (HIC). This work aims to evaluate through electrochemical and constant displacement tests the effectiveness of thermal spray aluminium (TSA) coating to mitigate SSC and HIC in high strength steel used to manufacture the tensile armour of a flexible riser. Electrochemical tests confirmed the anodic behaviour of the coating against the steel and estimated a service life of 2.5 years. The constant displacement test indicated that the non-coated samples failed by SSC although some cracks were also found in the samples mid-section due to HIC. For Al-coated samples, no signs of SSC and HIC were observed. The TSA coating showed a dual barrier effect, hindering either corrosion of steel or hydrogen up-taking, and neither SSC nor HIC was observed. Samples with a coating defect were cathodically protected and no HIC was observed.

ResumoAs superligas de níquel apresentam boa combinação de resistência à corrosão e à oxidação, resistência mecânica, resistência à fadiga e à fluência, além de conseguirem operar em temperaturas elevadas, mantendo tais propriedades. A liga Inconel 625 vem sendo estudada como revestimentos, obtidos por cladeamento ou aspersão térmica, para tubos de aços ao carbono utilizados nas indústrias de petróleo e gás. Esses tubos poderão ser unidos pela técnica de soldagem, quando então se obtém uma junta Inconel-Inconel, e isso pode acarretar modificações nas propriedades dessas superligas. O presente trabalho objetiva obter uma junta soldada da liga Inconel 625 empregandose o processo de soldagem a arco utilizando eletrodo revestido Ni-Cr-Mo 3 e caracterizar o cordão de solda quanto à microestrutura, à dureza e à corrosão. A microestrutura foi avaliada por microscopia óptica; para dureza foi realizado perfil de microdureza Vickers ao longo da junta soldada; quanto à corrosão foram realizadas curvas potenciodinâmicas em três diferentes soluções: 3,5% NaCl, 3,5% NaCl + 0,01M Na 2 S 2 O 3 e 3,5% NaCl + 1N H 2 SO 4 . Os resultados obtidos mostraram que a zona fundida tem microestrutura dendrítica, sendo a zona afetada pelo calor de aproximadamente 1,2 mm de extensão. A solda não alterou significativamente as propriedades de corrosão e dureza. Palavras-chave: Inconel 625; Soldagem; Corrosão; Microestrutura. MICROSTRUCTURE AND CORROSION RESISTANCE OF WELD JOINT INCONEL 625 AbstractNickel-based superalloys show a great combination of strength, corrosion, fatigue, creep and oxidation resistance, in addition to the ability of operate in high temperatures. Alloy 625 has been investigated recently like a coating on carbon steel tubes utilized in oil and gas industry utilizing cladding or thermal spray process. These tubes can be joint by welding, however, this process may changes some properties in weld joints InconelInconel. So, the main target of this work is to perform the Inconel 625 weld joint by shielded metal arc welding process with ERCrNiMo-3 and characterize the microstructure, corrosion resistance and hardness. The microstructure was investigated by optical microscopy. Microhardness Vickers profile was done across the joint transverse section. Electrochemical polarization techniques were used to characterize the corrosion resistance in three different solutions: 3.5% NaCl, 3.5% NaCl + 0.01M Na 2 S 2 O 3 e 3.5% NaCl + 1N H 2 SO 4 . The results show that fusion zone microstructure is dendritic and the heat input modified the base metal around 1.2 mm. The weld did not significative modification of corrosion resistance and hardness.