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The Influence of Water Vapor on the Corrosion of Chromia-Forming Steels
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2001
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Materials ScienceCorrosion TechnologyChemical EngineeringCorrosion ProtectionEngineeringCorrosionOxidation ResistanceCorrosion RateMechanical EngineeringGas VelocityChromia-forming SteelsHigh Strength Low Alloy SteelWater VaporChemistryCorrosion ResistanceCorrosion Inhibition
The effect of gas velocity on the oxidation of three chromia-forming steels; X20 (11%Cr), 304L (18%Cr) and 310 (25%Cr) in O 2 +40% H 2 O at 600°C is reported. The samples acre investigated by a number of surface analytical techniques including grazing angle XRD, SEM/EDX, and SAM. At low gas velocities a protective chromium-rich oxide forms on X2() and 310 while 304L shows partly protective behavior. With increasing gas velocity, the oxide tends to becomes more iron-rich and, consequently, less protective. The influence of gas velocity in O 2 /H 2 O environment is explained by the loss of chromium from the oxide through evaporation. The volatile species is suggested to be CrO 2 (OH) 2 . The different behavior shown by the three materials is explained in terms of the supply of chromium from the substrate to the oxide. Chromium depletion results in an increase in corrosion rate with gas velocity for all three materials and to breakaway corrosion in the case of X20.