The ultrafine grained 2205 duplex stainless steel with an average grain size of 300 nm was obtained by cold rolling down to 95% reduction in thickness and reversion annealing at 900 degrees C for 200 s. The ultrafine grained sample showed higher corrosion resistance than coarse grain one in borate buffer solution at room temperature, indicating that the passive film formed on the surface of the ultrafine grained 2205 duplex stainless steel is more protective. Comparing the doping concentrations between coarse grain and ultrafine grained samples from the Mott-Schottky plots, higher corrosion resistance of ultrafine grained sample was probably attributed to lower donor density and the thicker passive film in borate buffer solution. The results of electrochemical impedance spectroscopy were further supported by Raman spectra and XPS analysis. (C) 2015 Elsevier B.V. All rights reserved.