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

Highlights: • No zone depleted in chromium is detected in the matrix around (Cr, Fe)2N particles. • Pitting corrosion is observed at particles. • Particles first dissolve and a crevice is formed. • The bare substrate is exposed to the aggressive solution and large pits propagate. - Abstract: 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.