Effect of aging at 850 degrees C on pitting corrosion of UNS S31803 duplex stainless steel was examined in chloride Received 10 September 2008 solution by potentiostatic critical pitting temperature (CPT) measurements. The quantitative metallography coupled with X-ray diffraction technique was employed to follow the microstructure evolution. the initiation and propagation of pitting corrosion had been imaged in relation to microstructure variations using scanning electron microscopy (SEM). The results demonstrated that the corrosion behavior is strongly dependent on the microstructure, namely the presence of sigma phase. A deterioration of pitting corrosion resistance is found after aging 4 min, resulting in a drop in CPT. In particular, the metastable current transients during CPT test can clearly reflect the initiation of pitting process. Pitting nucleates preferentially in the austenite phase for the solution-annealed specimen, while the initiation of pitting corrosion takes place around sigma phase, in the newly formed secondary austenite for the aged specimen. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.