Corrosion resistance of Al-alloying high Cr-ODS steels in stagnant lead-bismuth

Takaya, Shigeru  ; Furukawa, Tomohiro  ; Inoue, Masaki ; Fujisawa, Toshiharu*; Okuda, Takanari*; Abe, Fujio*; Onuki, Somei*; Kimura, Akihiko*

Oxide dispersion strengthened (ODS) ferritic steels with excellent high-temperature strength are the candidates for fuel cladding tubes. But, the compatibility with lead bismuth eutectic (LBE) is one of the key issues in accelerator driven system and LBE cooled fast reactors. Addition of Al and increase in Cr may have beneficial influence on the compatibility. Addition of Al, however, causes a decrease in high-temperature strength. A significantly higher Cr concentration results in aging embrittlement. Therefore, we need to find their optimal amount to balance corrosion resistance with high-temperature strength. In this study, the cross sections of the samples after 3,000 h of exposure to LBE with 10 wt% oxygen at 650 C are examined in detail using scanning electron microscope and Auger electron spectroscopy. The observation shows that very thin Al oxide layer is formed continuously between multiple oxide layer/internal oxide zone and matrix, and that such Al oxide layer suppresses further growth of multiple oxide layer/internal oxide zone. The average oxide layer thickness shows a tendency to get thinner by increasing in Al content from about 2 to 4 wt%, although significant dependency on Cr content is not recognized. Furthermore, the additional corrosion test for 5,000 h is conducted. These materials show good corrosion resistance even after 5,000 h of exposure to LBE containing 10 wt% at 650 C. Addition of 3.5 wt% Al is very effective in improving corrosion resistance.