A study on the selective dissolution behavior of duplex stainless steel in systems containing nitric acid

Duplex stainless steel is composed of ferritic and austenitic phases, which have different crystal structure and element component, thus in different solutions, ferrite and austenite demonstrate different dissolution rate, that is, selective dissolution. In this investigation, the potentiodynamic polarization experiment was carried in nitric acid and hydrochloric acid mixture, and mixture of nitric acid and sodium chloride, nitric acid and ferrite chloride as well. After the experiments, SEM and EDS were used to distinguish and analyze the morphology differences of the two phases. The results show that in the solutions containing nitric acid, adding hydrochloric acid and sodium chloride will enhance the selective dissolution of two phases, while adding low concentration of ferrite chloride will decrease the corrosion difference between ferrite and austenite, but the phenomena vanish with the increasing of the concentration of ferrite chloride.