Abstract
The microstructures, solute concentration distribution, and pitting corrosion resistance have been investigated in duplex stainless steel SUS329J1 weld metals with different nitrogen content (0.066, 0.142, and 0.207mass%). Ferrite content decreases and critical pitting potential shifts to the noble direction with increasing nitrogen content. For the weld metals with low nitrogen content (0.066 and 0.142mass%), not only CrN within the ferrite grains but also Cr2N along the ferrite/austenite interfaces is observed; in contrast, for the weld metal with high nitrogen content (0.207mass%), only CrN precipitates within the ferrite grains. Cs-TEM/EDS analyses revealed that Cr-depletion in the vicinity of Cr2N is deeper than that of CrN. Additionally, Cr-depletion decreases with increasing nitrogen content. Increment of nitrogen content promotes the nucleation and growth of austenite phase, which has high solubility limit of nitrogen, thereby decreasing nitrogen concentration in ferrite phase. Diffusion-controlled growth simulation of Cr-nitrides in ferrite phase indicated that Cr-depletion is suppressed by decrement of initial nitrogen concentration in ferrite phase. Hence, nitrogen addition improves pitting corrosion resistance owing to the suppression of Cr-depletion.
