The aim of this study concerns the effect of multi-pass shielded metal arc welding (SMAW) on the corrosion behavior of CW6MC cast nickel alloy. Using optical and SEM techniques the welded joint is analyzed. Vickers microhardness mapping and potentiodynamic polarization in NaCl and H₂SO₄ solutions are also evaluated. Both the Laves phase and NbC-type carbides are identified in the base metal (BM) and weld metal (WM) regions. The main microstructural difference observed between these regions is the morphology aspect and fineness of the dendritic arrays. The welding process promotes the finer columnar grains formation with refined intermetallic particles in the WM than equiaxed grains of the BM, which in turn results in higher microhardness values in the former region. However, no substantial changes were observed in the corrosion behavior between the BM and WM regions, considering both acid and saline media. Nevertheless, during the multi-pass SMAW process, some non-metallic micrometric inclusions (Mo and S-rich regions) can be constituted to occur in the WM region. This is associated with a significant drop in the corrosion performance of this region when the electrochemical tests are evaluated.

The purpose of this work was to evaluate the microstructural alterations associated to the aging thermal treatments performed at 450, 475, 800 and 850°C, for 1, 3 and 12h, besides evaluating the influence of the precipitation of the alpha line phase on corrosion resistance. The samples were characterized by scanning electron microscopy, energy dispersion spectrometry, X-ray diffraction, feritscope, hardness, microhardness, in addition cyclic potentiodynamic polarization and double loop electrochemical potentiokinetic reactivation. In the agings performed at 450°C for 1h and 475°C for 12h, there was precipitation of the alpha line phase inside the ferrite and there was no significant effect on the resistance to pitting corrosion and the phenomenon of sensitization was not promoted. In the aging at 800 and 850°C for 1, 3 and 12h, the sigma phase was formed from the consumption of ferrite, and in the aging at 850°C there was the precipitation of the chi phase, promoting the increase in steel hardness. In agings for 12 h at 800 and 850°C, there was resistance to pitting corrosion decrease and the phenomenon of sensitization was moderated promoted at 800°C, with just the sigma phase precipitation and promoted at 850°C with sigma and chi phases precipitation.

With technological advances in the several areas of knowledge, the constant search for materials with characteristics that meet certain applications has been growing, especially in the chemical and petrochemical industries, where materials capable of withstanding the conditions of corrosion in aggressive environments are required. The aim of this paper was to analyze the influence of the alloy element molybdenum on the microstructure and the resistance to corrosion of two duplex stainless steels identified as A (with molybdenum) and B (without molybdenum), after solution-treated under the following conditions: heating at 1100ºC for 30, 120 and 240 minutes. The steels were characterized by SEM, EDS, DRX and microhardness. The rise in solution treatment time fostered an increase in the volumetric fraction of the ferrite phase, in both steels. The solution treatment at 1100ºC for 120 minutes, for steels A and B, provided good resistance to pit corrosion, as well as the development of a passivating film in the solution of lithium chloride (120,000 ppm of chloride ions).