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Buscail H.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Issartel C.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Nguyen C.T.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Perrier S.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Fleurentin A.,CETIM Senlis
Materiaux et Techniques | Year: 2010

A comparison of the high temperature oxidation behaviour has been performed between blank 330Cb and carburized 330Cb specimens. Before oxidation, carburized specimens contain NbC and Cr7C3 carbides. Kinetic results show that the oxidation follows the same rate on blank and carburized 330Cb specimens. The best oxide scale adherence is observed on carburized 330Cb specimens after 160 h oxidation in air. After oxidation, the only spalled areas are observed on the reach niobium nodules present on the alloy surface. On all specimens, manganese chromite is located at the external interface. The main oxide scale only contains Cr2O3. No iron is detected in the oxide scale. This is due to some silicon and niobium segregation at the internal interface, which acts as an iron diffusion barrier. After oxidation, carbon precipitates in the alloy due to carbides decomposition by the chromium oxidation process. This does not appear to be detrimental to a good oxide scale adherence because the carbon nodules are formed along the alloy grain boundaries and not at the internal interface. © 2010 EDP Sciences. Source


Issartel C.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Buscail H.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Wang Y.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Rolland R.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | And 2 more authors.
Oxidation of Metals | Year: 2011

The 4509 alloy (Fe-18Cr-Nb-Ti) was oxidised in dry and wet air in the 800-1000 °C temperature range. Results showed that the formation of a chromia layer acts as a good diffusion barrier under isothermal conditions at 800 and 900 °C, under 7.5 vol.% water vapour and dry air. Nevertheless, a breakaway is generally observed at 1000 °C, under wet air 7.5 vol.% H 2O. It is proposed that the oxidant H +/OH - species react at the internal interface with iron in the chromium-depleted alloy zone. Wüstite reacts with Cr 2O 3 to form FeCr 2O 4. Outward iron diffusion leads to Fe 3O 4 and Fe 2O 3 formation. The chromia scale was consumed by reaction with wüstite, but chromia also internally forms owing to a chromium oxidation process with the inner chromium-rich alloy area. © 2011 Springer Science+Business Media, LLC. Source


Issartel C.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Buscail H.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Nguyen C.T.,Laboratoire Vellave sur lElaboration et lEtude des Materiaux LVEEM | Fleurentin A.,CETIM Site de Senlis
Materials and Corrosion | Year: 2010

The 330Cb alloy (Fe-35Ni-18Cr-1Nb-2Si) has been oxidized, in air, in the 800-1000 °C temperature range. Results show the formation of a chromia layer acting as a good diffusion barrier under isothermal conditions. Nevertheless, some oxide scale spallation is generally observed after cooling to room temperature. A fine and adherent chromia scale is only obtained after short-term oxidation at 800 °C. In this case, the scale is probably too fine to expect a protection against carburization. At 900 °C we have observed that the scale spalled off on the niobium rich alloy areas. At 1000 °C the scale adherence is very bad. This study shows that the oxide scale adherence is decreased when the 330Cb alloy oxidation duration is increased. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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