The corrosion behavior of austenitic stainless steels (UNS S30400/S30403, S30800) with machined, electropolished, or temper filmed surfaces was tested in deaerated, pH adjusted water at 500 °F (260 °C), 550 °F (288 °C) and 620 °F (327 °C) for up to 10,000 hours. Test specimens were subsequently analyzed by X-Ray Diffraction, Auger Electron Spectroscopy, and Electron Spectroscopy for Chemical Analysis to determine oxide composition, thickness and structure. The resultant corrosion rate of the machined specimens exhibited an inverse temperature dependency, with the rates decreasing by an order of magnitude from the lowest to highest test temperature. Corrosion of electropolished specimens was only slightly sensitive to temperature effects, and was similar to machined specimens at the highest temperature. Temper filmed materials had distinct phases of slow or rapid corrosion with different durations depending on the test temperature. Corrosion films on all specimens consisted of varying degrees of iron-rich spinel crystals covering a smooth layer of chromium-rich oxide, most likely Fe3O4 and/or FeCr2O4, with some Fe2O3. The temper films consisted of Cr2O3, which persisted throughout the test. The elemental composition of the films, particularly the nickel content, varied with increasing temperature.

Subject
X-ray diffraction, Films, Materials, Ions, Composition, Corrosion rate, Oxides, Autoclaves, Oxide films, Metal oxides, Oxide surfaces, Sputter deposition, Corrosion coupons
Keywords:
Corrosion, austenitic stainless steel, electropolish, temper film, oxide
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2019
Association for Materials Protection and Performance (AMPP)
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