Corrosion behavior of high chromium steels in flowing lead-bismuth at 823K underactive oxygen control

None

古川 智弘  ; Konys, J.*; Mller, G.*; 青砥 紀身 

Furukawa, Tomohiro; Konys, J.*; Mller, G.*; Aoto, Kazumi

2種の高クロムマルテンサイト鋼(12Cr鋼、ODS(M))の酸素濃度制御823K流動鉛ビスマス中における5,000hまでの腐食試験を実施した。鉛ビスマス中の溶解酸素濃度の制御は、鉛ビスマス中へのH2/H2O混合ガスのバブリングにより試みた。しかしながら、酸素センサーによる測定結果は、目標値(10-6wt%)に対して試験開始から連続して低下し続け、一時的にマグネタイト形成に必要な酸素濃度を下回った。このため、約3500h以降は、部分的にAr-Air混合ガスをLBE中に注入することにより、目標値近傍に酸素濃度を制御した。この鉛ビスマス条件下に曝された両鋼は、おおよそ同様な腐食挙動を示した。800hおよび2,000h終了後の試験片の観察の結果、部分的にFe、CrおよびOから成るスピネル酸化物が形成され、5,000h浸漬後にはこの酸化物が連続的に試験片表面に形成されていた。酸化皮膜の成長厚さを調べた結果、本試験条件では、800h以降、大きな成長は観察されず、酸化皮膜形成による良好な耐食性が両鋼ともに観察された。さらに、本試験条件下では、材料構成元素の鉛ビスマス中への直接溶解やエロージョンは観察されなかった。

Two kind of high chromium martensitic steels named as 12Cr-steel and ODS-M, proposed for use in fast breeder reactors were subjected to corrosion tests in flowing lead bismuth eutectic (LBE) under active oxygen control at 823 K for up to 5,000 hours. The concentration of dissolved oxygen in LBE was controlled by H2/H2O mixture gas bubbling into LBE to keep at 10-6 wt%. However, the oxygen concentration was degreased with increasing of operation time, and temporarily reached below the value necessary for magnetite formation. Then, after 3,300 hours of effective operation time, oxygen concentration was controlled near the target value by periodically adding argon and mixtures of argon and technical air to the H2/H2O mixture gas stream through the oxygen control system. Both steels exposed in LBE under the condition showed approximately the same corrosion behavior. Double-layer structure composed of Fe-Cr spinel and diffusion zone were observed on the surface of the steels exposed for up to 2,000 hours. After 5,000 hours of exposure, it changed to single-structure composed of Fe-Cr spinel. Results of thickness measurement of the oxide layers, the total thickness of oxidized zone was approximately constant during test periods from 800 hours to 5,000 hours. It meant that the steels showed good corrosion resistance under this tested condition. In addition, both erosion and dissolution attack called as liquid metal corrosion were not observed on the all tested specimens.