Corrosion behaviour of sites containing (Cr, Fe)2N particles in thermally aged duplex stainless steel studied using capillary techniques, atomic force microscopy and potentiostatic pulse testing method

The microstructure and corrosion behaviour of sites containing (Cr, Fe)2N in UNS S32202 duplex stainless steel after heat treatment at 900 °C were studied in 2 M NaCl using surface observation techniques at the micro- and nanoscale, the electrochemical microcell technique at the microscale and the potentiostatic pulse testing method. No zone depleted in chromium was detected in the matrix around (Cr, Fe)2N. Although there is no depleted zone, pitting corrosion was observed at particles. It is shown that particles first dissolve. A crevice is formed and the bare substrate is exposed to the aggressive solution. Large pits propagate.