Estudo sobre corrosão localizada em junta de aço inoxidável duplex para uso em dessalinizador: efeito do gás proteção e temperatura de pré-aquecimento

Abstract

Recent studies show that the welding of duplex stainless steel sheets with preheatingallows a more efficient control of the phase balance, thus providing better characteristicsof the welded region. However, welding promotes microstructural changes that include themodification in the balance between ferrite and austenite, in proportions of approximate50 % each, in addition to the precipitation of secondary phases, such as the phase𝜎and the chromium nitride. In this context, the objective of this work is to evaluate themicrostructural changes and the corrosion resistance of duplex stainless steels subjected towelding process. The autogenous GTAW welding process was performed on UNS32205stainless duplex plates exposed to room temperature and preheated to 200∘C and 300∘C.After the welding, the plates were sectioned, prepared for the metallographic analysisof the morphology of austenite formed and for the quantification of the phases. Themicrostructural characterization was evaluated by optical microscopy and scanning electronmicroscopy (SEM). Besides this, double-cycle potentiodynamic electrochemical reactivation(DL-EPR) tests were performed to evaluate the corrosion resistance of the steel. The resultsshowed the presence of grain - bound allotriomorphic austenite, Widmanst ̈atten austeniteand intragranular austenite. It was observed that the preheating temperature and theshielding gas influenced the microstructural balance and the corrosion resistance. Finally,there was no evidence of pitting corrosion in samples immersed in the saline solution