Pitting corrosion of thermally aged cast duplex stainless steel for primary coolant pipes of nuclear power plants

Abstract

The pitting corrosion of thermally aged Z3CN20.09M cast duplex stainless steel (CDSS) was investigated using potentiodynamic polarisation and electrochemical impedance spectroscopy. Both pitting potential and charge transfer resistance values of thermally aged specimens became less positive with aging time, while passive current density increased, indicating that thermal aging causes degradation in pitting corrosion resistance. The pitting potential of thermally aged specimens after annealed is higher than that of thermally aged specimens revealing that the pitting corrosion resistance of annealed specimens has been improved. The α' phase precipitation during thermal aging in ferrite brings the Cr-enriched and Cr-depleted zone microstructures which mainly induced the degradation of pitting corrosion resistance. The microsegregation of Cr element or Cr enriched and Cr-depleted zones will be alleviated or even removed due to the Cr-rich α' phases dissolution during the process of annealing. So, the pitting corrosion resistance of annealed specimens is improved.

Corrosion Evaluation of Duplex and Superduplex Stainless Steel Friction Stir Welds Using Potentiodynamic Measurements and Immersion Tests in Chloride Environments

“…The repassivation potential (E rp ) was higher for the BM than for the SZ, indicating an easier repassivation process. Undesired phases can precipitate under hot operational conditions or during welding, which can lead to disruption of the phase balance of the ferrite and austenite phases, with precipitation of intermetallic phases causing decreased corrosion resistance [4].…”

“…However, undesired phases can precipitate under hot operational conditions or during welding, which can lead to loss of corrosion resistance [2]. Fusion welding of duplex (DSS) and super duplex (SDSS) stainless steels can lead to disruption of the equilibrium of the ferrite and austenite phases, with precipitation of intermetallic phases reducing the corrosion resistance and fracture toughness of the welded joint [3][4][5]. Use of the friction stir welding (FSW) technique has been shown to be able to reduce some of the problems related to fusion of the material, because this process enables the joining of materials below their fusion temperatures [6].…”

Probing the Anti-Corrosion Behavior of X65 Steel Underwater FSW Joint in Simulated Seawater

“…As shown in Table 4, the corrosion potential of the four kinds of samples changed from −728 to −586 mV after 0.5-h immersion. With the increase of duty ratio, the corresponding corrosion potential value of the three samples with Ni coating keeps moving forward, and the corrosion current density keeps decreasing, indicating that the corrosion resistance is continuously enhancing (Wang et al, 2017). After being immersed for 24 h, the corrosion potential of the samples changed from −926 to −792 mV, and the reaction corrosion rule was similar to that after immersion for 0.5 h. Combined with the immersion conditions of 0.5 and 24 h, it can be seen that the corrosion potential of Ni-coated samples moves negatively and the corresponding corrosion current density increases.…”

Pitting Corrosion of Thermally Aged Duplex Stainless Steels at Different Temperature for Long Time

“…Thermal ageing induces the precipitation of Cr-rich α′ phases in ferrite and brings the Cr-depleted zones around them. The interface between Cr-enriched α′ phase and Crdepleted zone could become the preferential sites for pits initiation, subsequently, pits grew in ferrite 13,28,29 . The more the precipitation of α′ phases and Cr-depleted zones, the worse the pitting resistance of DSS specimens revealing by the lower E p value.…”

“…However, they will be subjected to thermal aging embrittlement and sensitization when they are exposed to the temperature range of 320 -1000 ℃ mainly due to the formation of several undesirable precipitates such as α′, G, M 23 C 6 , σ, χ, etc in ferrite phase 2,7-10 . These precipitated phases not only severely decrease the toughness of steels but also negatively impact corrosion resistance, especially localised corrosion [11][12][13] .…”