Evaluation of pitting corrosion in duplex stainless steel Fe20Cr9Ni for nuclear power application. (15th September 2020)

• Record Type: Journal Article
• Authors: Chen, Yuefeng; Yang, Bin; Zhou, Yangtao; Wu, Yuan; Zhu, Huihui
• Is Part Of: Acta materialia. Volume 197(2020)
• Page Start: 172
• Page End: 183
• Publication Date: 2020-09-15
• Subjects: Duplex stainless steel -- Spinodal decomposition -- G-phase -- Pitting corrosion -- Strain field; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2020.07.046
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: A spinodal decomposition is often carried out in the austenite-ferrite duplex stainless steel Fe20Cr9Ni during long-term service at a temperature in the range from 280 to 320°C, resulting in a decrease of pitting corrosion resistance. Fe-rich α phase rather than G-phase has been suggested as the major reason for the deterioration in pitting corrosion resistance of the thermally-aged steel. Here, we found that ∼76.8% of the decline in pitting resistance for the duplex stainless steel Fe20Cr9Ni was attributed to G-phase, and ∼23.2% to Fe-rich α phase after the spinodal decomposition. In this study, a suitable thermal aging treatment was introduced to obtain a larger size of the G-phase and to study the role of the phase in the corrosion process. Through immersing thermally-aged TEM specimen treated at 475°C for 3000 h in NaCl solution, the preferential position of corrosion pits formed in the ferrite was obtained. The composition changes and strain field distribution around the G-phase were analyzed by TEM-EDS, 3DAPT and GPA techniques. We further found that, although the concentration difference of Cr element between α and α' phases was as high as 60 at.%, corrosion pits were initiated at the interface between the G-phase and the ferrite matrix rather than in the Fe-rich α phase, indicating that the Cr-depleted theory could not explain the aforesaid phenomenon. The strain energy at the interface between the G-phase and the ferrite matrix was found to be the largest. The atoms at the interface have higher energy than in the intracrystalline, and thus easily react with Cl − ions in the solution to form pits finally. Graphical abstract: Image, graphical abstract