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07467 Effect of Mo Addition on the Oxidation Behavior of Fe-25Cr-20Ni Alloy in a Water Vapor Containing Atmosphere

Picture for 07467 Effect of Mo Addition on the Oxidation Behavior of Fe-25Cr-20Ni Alloy in a Water Vapor Contain
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Product Number: 51300-07467-SG
ISBN: 07467 2007 CP
Author: Hiroshi Yakuwa, Norio Takahashi, and Shin Inagaki
Publication Date: 2007
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The influence of the addition of molybdenum on the oxidation behavior of Fe-25Cr-20Ni alloys was studied in an N2-H2-H2O gas mixture at 700 to 900oC. The mass gain followed a near-parabolic rate law or a slightly slower rate law for all the specimens. The mass gain of the Mo-added alloys tended to be smaller than those of the non-Mo-added alloy at 700oC, though the mass gain of the Mo-added alloys became rather greater than that of the non-Mo-added alloy at 900oC. Relatively thick oxide scale, the thickness of which was uneven, was formed on non-Mo-added and 1-mass% Mo-added alloys especially at 700oC. On the other hand, thin Cr-rich oxide scale, the thickness of which was even, was formed on 3.5- and 7-mass% Mo-added alloys. A Mo-Cr-rich phase precipitated within the substrates on the 3.5- and 7-mass% Mo-added alloys, resulting in smaller grain sizes. It could be concluded that the smaller grain size promoted the preferential diffusion of Cr toward the alloy surfaces and the Mo-Crrich phase also played a role as a Cr-supplier, contributing to the maintenance of the Cr-rich protective oxide scale.
The influence of the addition of molybdenum on the oxidation behavior of Fe-25Cr-20Ni alloys was studied in an N2-H2-H2O gas mixture at 700 to 900oC. The mass gain followed a near-parabolic rate law or a slightly slower rate law for all the specimens. The mass gain of the Mo-added alloys tended to be smaller than those of the non-Mo-added alloy at 700oC, though the mass gain of the Mo-added alloys became rather greater than that of the non-Mo-added alloy at 900oC. Relatively thick oxide scale, the thickness of which was uneven, was formed on non-Mo-added and 1-mass% Mo-added alloys especially at 700oC. On the other hand, thin Cr-rich oxide scale, the thickness of which was even, was formed on 3.5- and 7-mass% Mo-added alloys. A Mo-Cr-rich phase precipitated within the substrates on the 3.5- and 7-mass% Mo-added alloys, resulting in smaller grain sizes. It could be concluded that the smaller grain size promoted the preferential diffusion of Cr toward the alloy surfaces and the Mo-Crrich phase also played a role as a Cr-supplier, contributing to the maintenance of the Cr-rich protective oxide scale.
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