Effect of Thermal Aging on Microstructural Evolution in Ferrite of Duplex Stainless Steel in Nuclear Power Plant Applications

Z3CN20-09M duplex steels are thermally aged at 400oC for up to 20,000 h. The mechanical properties have been characterized by Charpy V-notch impact test and nanoindentation test. It is found that the nanohardness in ferrite increases and the impact toughness decreases with aging time. Moreover, the distribution of alloying elements has been carefully characterized using atom probe tomography (APT). The results indicate that the ferrite decomposes into Cr-rich α' and Cr-lean α phase during the thermal aging and Ni-rich G-phase forms in ferrite. The effect of aging time on solute nanostructure has been investigated systematically.