Oxidation of 316L(N) stainless steel in liquid sodium at 650 °C

JOURNAL OF NUCLEAR MATERIALS

卷:500

Article

Rivollier, Matthieu^1,2  Courouau, Jean-Louis¹  Tabarant, Michel³  Blanc, Cecile³  Giorgi, Marie-Laurence² 

[1] Univ Paris Saclay, CEA, Den Serv Corros & Comportement Mat Environm SCCME, F-91191 Gif Sur Yvette, France

[2] Univ Paris Saclay, Cent Supelec, Lab Genie Procedes & Mat, 3 Rue Joliot Curie, F-91192 Gif Sur Yvette, France

[3] Univ Paris Saclay, Den Serv Etud Analyt & React Surfaces SEARS, CEA, 3 Rue Joliot Curie, F-91192 Gif Sur Yvette, France

关键词: Liquid sodium;    Austenitic steel;    High temperature corrosion;    Selective oxidation;   

DOI  :  10.1016/j.jnucmat.2017.12.037

来源: Elsevier

【 摘 要 】

The corrosion of an austenitic steel in liquid sodium containing 189 mu g g(-1) of oxygen was investigated at 650 degrees C as a function of time (122, 250 and 500 h). The steel samples were characterized by means of complementary techniques, namely scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectroscopy and transmission electron microscopy. The characterizations showed that a NaCrO2 oxide scale forms at the steel surface. Under this oxide scale, iron and molybdenum rich M6C carbide particles together with NaCrO2 in the grain boundaries and cavities filled with sodium were observed. The stainless steel substrate and/or the chromite scale were dissolved in parallel with the formation of chromite and carbides. Thermodynamic calculations showed that NaCrO2 and M6C are equilibrium phases in such a system. NaCrO2 is formed by the reaction of chromium diffusing from the steel bulk with sodium and dissolved oxygen (external selective oxidation). Mo segregates to the steel surface where it reacts with Fe from the steel and C dissolved in liquid sodium. The dissolution of stainless steel occurred since the liquid sodium bath is not saturated in the dissolving species (pure metals and oxides such as NaCrO2, Na4FeO3). As for the cavities, vacancies are created at the steel/NaCrO2 interface by Cr oxidation, carburization and dissolution of the other elements present in the stainless steel. The vacancies become supersaturated and this leads to the nucleation of the cavities observed. Part of the vacancies created by Cr oxidation or steel dissolution is annihilated at sinks like dislocations leading to the translation of the oxide/metal interface towards the metal bulk. (C) 2018 Elsevier B.V. All rights reserved.

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