Corrosion rate of ferritic ODS stainless steels in a supercritical water environment

Full text of publication follows: The corrosion behavior of several ODS (Oxide Dispersion Strengthened) steels (Fe-xCryAl-zW-Y2O3) were studied. A corrosion experiment was performed up to 1000 hrs in 510 deg. C and 25 MPa pure water environments. The dissolved oxygen content was controlled by exposing the test solution to laboratory air at the start of the test. The weight gain of each sample was used to estimate the amount of corrosion assuming dissolution rates to be small. Low angle X-ray diffraction method was applied for characterizing the surface oxide resulting from corrosion reactions. further, the cross section area was observed by FESEM-EPMA to reveal the morphology and composition of the oxide. The weight gain increased with time and after a certain time, it reached a steady state. Using the weight gain data, we estimated the corrosion rate defined as the ratio of weight gain and the test interval. The corrosion rate decreased with time, which reflected that the oxide film became protective for all the ODS steels. From XRD and FESEM-EPMA studies, the oxide layers were examined to be Cr rich spinel at the early test period and to become Cr oxide (Cr2O3) after a certain time due to phase transformation. The Cr oxide formation inhibited further corrosion, reaching the steady state. No exclusive aluminum oxide layer was formed in the test condition. Nonetheless, the summation of Cr and Al content represented the corrosion resistance of ODS steels. (authors)