Microstructure and pitting corrosion in simulated heat-affected zones of duplex stainless steels

The effects of nitrogen contents and cooling rates on the microstructure and pitting corrosion in the simulated heat-affected zone (HAZ) of 2205 duplex stainless steels (DSSs) were investigated. The results showed that the grain size of the α phase and the amount of Cr2N precipitates in the simulated HAZ decreased as the content of the γ phase was increased. Electrolytic extraction analysis demonstrated that Cr2N precipitation in the α phase became pronounced with a reduction in the nitrogen content and an increase in the cooling rate in the temperature range of 800–500°C. The results of cyclic polarization tests indicated that the pitting corrosion resistances of simulated HAZs in 3.5 wt.% sodium chloride (NaCl) solution were inferior to those of the solution annealed DSSs. Pitting corrosion was not found in regions where the precipitation of Cr2N was less likely to form, e.g. the precipitate free zone (PFZ) and the grain boundary austenite (GBA). Clearly, the presence of Cr2N in the simulated HAZs was the main cause of the deterioration in the pitting resistance of DSSs.