Corrosion behavior of austenitic steels 1.4970, 316L and 1.4571 in flowing LBE at 450 and 550 ℃ with 10~(-7) mass% dissolved oxygen

摘要

Corrosion behavior of austenitic steels 1.4571,1.4970 and 316L was investigated in flowing oxygen-controlled LBE (2 m/s,10~7 mass% O) at 450 and 550 ℃ for up to 8766 and 2011 h,respectively. The corrosion modes and material loss were analyzed qualitatively and quantitatively. Steels underwent both oxidation accompanied by formation of a thin (≤0,5 μm) Cr-based oxide film and selective leaching of Ni and Cr that resulted in formation of a layer-type ferrite zone and deeper local damages with pit-type appearance both penetrated by Bi and Pb. The corrosion loss increases with time and temperature providing that the oxygen content is constant (10~7 mass%). Detailed quantitative analyses of corrosion loss showed that at 450 ℃ metal recession of steels ranged from 4 to 27 μm after 8766 h. Maximum depth of local attack reached 114,183 and 210 μm for 1,4571,1.4970 and 316L steels, respectively. At 550 ℃metal recession ranged from 23 to 60 μm after 2011 h that correlates well with thickness of ferrite layer formed. The maximum depth of local attack reached 587,207 and 158 μm for 1.4571,1.4970 and 316L steels, respectively. The effect of composition, surface state and bulk micro-structure on the corrosion response of steels is discussed. The results are compared with those obtained in LBE with higher oxygen concentration, i.e., 10~6 mass% O.