Estudo do efeito de parâmetros do processo GTAW pulsado na resistência à corrosão intergranular e por pite do aço inoxidável duplex UNS S32304

• Autor(a) principal: Palácio, Felipe de Oliveira
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Federal do Espírito Santo (riUfes)
• Texto Completo: http://repositorio.ufes.br/handle/10/4175
• topic: Stainless steel; Corrosion; Electrochemistry; Welding; Engenharia Mecânica; Aço inoxidável; Corrosão; Eletroquímica; Soldagem; 621

The duplex stainless steels, as well as austenitic and ferritic, are susceptible to intergranular corrosion. The chromium depleted regions adjacent to precipitates that can be formed in these steels is the most accepted mechanism for describing this phenomenon. Welding processes and heat treatments can cause such a mechanism and it is said that the material is sensitized. The welding processes generate inhomogeneous thermal cycles and this makes the material undergoes microstructural changes often unwanted. Regions near the fusion zone (FZ) are considered critical due to favoring the precipitation of new phases and microconstituents. The called heat affected zone (HAZ) can suffer a thermal cycling over a temperature range that favors the kinetics of formation of new phases. Several industrial processes adopt a post-weld heat treatment to minimize or even abolish these effects. This study aims evaluate the effect of welding process parameters GTAW (Gas Tungsten Arc Weld) pulsed on the resistance to pitting and intergranular corrosion of a duplex stainless steel UNS S32304. For this reason, polarization curves were performed and the method of double loop electrochemical potentiodynamic reactivation version (DLEPR) was also employed. It were obtained ten fillets weld without deposition of material on steel plates studied. A condition studied was conventional GTAW, and the parameters evaluated in the process pulsed were frequencies between 1 and 4 Hz, and the pulse on time. The mechanical properties were evaluated by microhardness testing and microstructural characterization of the material was performed by optical microscopy and scanning electron microscopy. The welded regions showed less susceptibility to intergranular corrosion when compared to the metal base (MB). And this in turn presented a higher pitting potential to others. The formation of precipitates in the HAZ did not cause a drastic effect on intergranular corrosion resistance, but on the other hand, the resistance to pitting corrosion was affected.