Effects of Chromium Content and Sodium Velocity on the Compatibility of High-Cr Ferritic Steels in a Sodium Environment

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  • Mutoh Isao
    National Research Institute for Metals. Tsukuba Laboratories
  • Suzuki Tadashi
    National Research Institute for Metals. Tsukuba Laboratories

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Other Title
  • 高Crフェライト鋼のナトリウム中の共存性に及ぼすCr量とナトリウム流速の影響
  • コウ Cr フェライト コウ ノ ナトリウムチュウ ノ キョウソンセイ ニ オ

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To obtain fundamental data on the compatibility of high-chromium ferritic steels in sodium, high-purity Fe-0.1C-1Mo-5, 9 or 13Cr ferritic steels were prepared by vacuum melting. Test specimens of these steels which were normalized and tempered and a reference type 316 stainless steel (316 ss) were exposed to two sodium-velocity regions for periods up to 10.8 Ms in a sodium loop system which had a direct resistance main heater and was made of SUS 316. The test temperature, the maximum temperature, of the loop system in this work was 873 K, the oxygen content of sodium was 1-2 ppm, and the sodium velocities were about 4.0 and 0.02 m/s. The specimens exposed to the high sodium-velocity region revealed that corrosion loss at a zero downstream position of the three kinds of ferritic steels was smaller than that of the reference 316 ss; about one fifth for the 5 and 9%Cr steels and one half for the 13%Cr steel. The surface analysis showed deposition of Ni that dissolved at upstream for all the ferritic steels, deposition of Cr for the 5%Cr steel, and selective dissolution of Cr for the 9 and 13%Cr steels. The ferritic steels without Ni and with less amounts of Cr than the reference 316 ss would result in their smaller corrosion loss than the 316 ss. Transfer of carbon, nitrogen and oxygen was not remarkable, except the carburization of the 5%Cr steel. The specimens of the three kinds of ferritic steels which were exposed to the low sodium-velocity region revealed much smaller corrosion loss than that in the high velocity region, deposition of both Ni and Cr, and no transfer of carbon, nitrogen and oxygen except for slight carburization of the 13%Cr steel.

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