Effect of ferrite on pitting corrosion of Fe20Cr9Ni cast austenite stainless steel for nuclear power plant pipe

Abstract

The ferrite content and grain size in a Fe20Cr9Ni (wt-%) cast austenite stainless steel which has been widely used in primary coolant pipes of nuclear power plants were found to vary due to nonuniform solidification of the large pipe with a thickness of 95 mm. The pitting corrosion of Fe20Cr9Ni cast austenite stainless steel with five ferrite contents, i.e. 13, 11, 10, 9?5 and 8 vol.-% and different ferrite grain sizes was investigated in a 0?5 mol L 21 NaCl solution by means of potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Both pitting potential and charge transfer resistance value of specimens increased with the decreasing ferrite content and grain size, indicating that few and small ferrite grains were beneficial for improving pitting resistance. The passive film properties studied by EIS correlated well with the polarisation results. Electron probe microanalysis results showed that the difference in the Cr concentration between ferrite and austenite decreased with a decreasing amount of ferrite phase. Accordingly, the composition microsegregation was reduced, and passive film homogeneity of the specimens was improved.

Microstructures and properties of high-entropy alloy films and coatings: a review

“…Based on the aforementioned reports in Section 4.2, the HEA films and coatings exhibit the superior corrosion resistance. A comparison of the corrosion behavior between HEA films (coatings) and other corrosion-resistant alloys, including stainless steels, Al alloys, Ti alloys, Cu alloys, Ni alloys and the HEAs [33,131,[153][154][155][156][157][158][159], in salt water (3.5 wt.% NaCl) is shown in Figure 16. E pit is the parameter, which can represent the resistance to pitting corrosion, and I corr is relevant to the corrosion rate obtained through polarization tests in the 3.5 wt.% NaCl solution at room temperature.…”

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

“…So, it might be concluded that the change in fraction and size of α ′ phase thermally aged for longer than 7000 h is not insignificant. Pitting corrosion resistance of stainless steels is significantly affected by metallurgical variables such as microstructure, inclusions, precipitates, alloy composition and heat treatment [19][20][21]. The fraction and morphology of ferrite in specimens will not change with thermal aging time.…”

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

“…Pitting corrosion, the localized dissolution of a passivated metal in the presence of a solution of certain anionic species, is a major cause of failure of stainless steels owing to pits perforation or acting as an initiation site for cracking 14 . Generally, any factor whose can bring the defects in passive film or cause chemical or physical heterogeneity at the surface, such as inclusions, second phase particles, solutesegregated grain boundaries, flaws, mechanical damage, or dislocations, will be considered as the possible reasons for pitting corrosion 4,[15][16][17][18][19] . Thermal aging embrittlement induced by the spinodal decomposition of ferrite phases into coherent Cr-enriched α′ and the precipitation of G-phase in ferrite can also degrade the pitting resistance of DSS.…”