Accurate determination of the number density of G-phase precipitates in thermally aged duplex stainless steel

• Published in: Philosophical magazine (Abingdon, England) England), 2012-08, Vol.92 (22), p.2716-2732
• Main Authors: Hamaoka, T., Nomoto, A., Nishida, K., Dohi, K., Soneda, N.
• Format: Article
• Language: English
• Subjects: 3DAP; aging; Cross-disciplinary physics: materials science; rheology; duplex stainless steel; Exact sciences and technology; G-phase; Materials science; phase boundary; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; TEM
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786435.2012.674222

G-phase precipitation in the ferrite phase in thermally aged duplex stainless steel (DSS) was investigated. A needle-shaped sample of DSS aged at 673 K for 5000 h was observed by transmission electron microscopy (TEM), and subsequently by atom probe tomography (APT). The precipitates of the G-phase observed by TEM corresponded well to clustering atoms observed by APT. On the other hand, regarding the precipitates of the G-phase that formed in an earlier stage of aging, the present study suggests that not all the precipitates can be detected by TEM. A large area of DSS aged at 673 K for 5000 h containing both the ferrite and austenite phases was observed. The number density of precipitates of the G-phase in the ferrite phase was small in the vicinity of the phase boundary and increased with the distance between the phase boundary and each field of view. The number density reached an almost constant value at a distance of approximately 4 µm from the phase boundary. The suppression of G-phase precipitation in the vicinity of the phase boundary is discussed in terms of the depletion of alloying elements that comprise the G-phase.