Friction stir processing (FSP) has been shown to be effective in the microstructural modification. In this study, 2507 super duplex stainless steel was subjected to multipass FSP and the processed samples were investigated. Refinement in grain size of both ferrite and austenite was observed in the stir zone of the processed samples. Increased number of passes led to further reduction in grain size. Anodic polarization studies in 3.5 wt% NaCl solution showed that the processed samples possessed improved corrosion resistance. The Mott-Schottky analysis confirmed that the charge carrier density in the passive oxide layer is decreased with decreasing grain size. © 2017, The Minerals, Metals & Materials Society.