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.

The influence of the prior cold work (0, 10, 30, and 30% thickness reduction) on the microstructure evolution and corrosion resistance of UNS S32304 lean duplex stainless steel (LDSS) welded by gas metal arc welding (GMAW) process was investigated. The cold work promotes flattening of the ferrite and austenite bands, deformed regions in the austenite and increase of the hardness of the material. The welding of the cold‐worked steel generated, besides the typical regions of the welded DSS joints (fusion zone (FZ), heat‐affected zone (HAZ), and base metal zone (BM)), an annealed region around the HAZ, that showed partial recovery of the microstructure and hardness reduction. The HAZ presented excessive ferritization and precipitation of chromium nitrides. The cyclic potentiodynamic polarization tests, in an aqueous solution of 3.5 wt% NaCl at room temperature, showed for the only cold‐worked samples an increase of the pitting corrosion resistance up to a level of 30% thickness reduction and a decrease of the localized corrosion for 50% thickness reduction. The welding of the cold‐worked samples promoted the reduction of pitting corrosion resistance for all levels of thickness reduction evaluated.

The effect of the welding GMAW, with heat input of 1.4 kJ/mm, on the microstructure and corrosion resistance of the steel UNS S32304 prior cold worked (0, 10, 30, and 30% thickness reduction) was evaluated. The welding process generated, in the weld joint, the regions: fusion zone (FZ), heat‐affected zone (HAZ), an annealed region around the HAZ, and the metal base zone (BM) deformed by cold working. Excessive ferritization and high precipitation of chromium nitrides in the HAZ were identified. The corrosion resistance of the welded joints was not significantly changed for low deformation levels by cold work (up to 30% thickness reduction). However, for 50% thickness reduction a decrease in the corrosion resistance of the welded joint was observed. The annealing of the BM around the HAZ increased its corrosion resistance, making this region immune to localized corrosion. The heat input used in this study promoted higher ferritization and precipitation of chromium nitrides, lower annealing of the base metal near the HAZ and lower corrosion resistance when compared with the higher heat input used in our previous work (about 2.5 kJ/mm).