Abstract
2-dimensional finite-difference calculations have been undertaken to examine the depletion of chromium at specimen edges and ribs in a 20Cr–25Ni–Nb steel which is being selectively oxidized. The calculations have been performed for parabolic oxidation kinetics and for temperatures in the range 800–1200°C. It is found that under re-entrant features, e.g. interior edges, the extent of depletion is less than under a planar surface but the converse holds for exterior edges. For this latter case, it is shown how the initial severe depletion can fill in with time by the supply of chromium from the bulk of the specimen. This process, however, results in the propagation of the “edge effect” away from the corner with kinetics that scale as (Dt)1/2. Rectangular ribs contain both types of geometric features but it is found that the two exterior edges forming the rib tip lead to extensive depletion in this region which gradually propagates along the length of the rib. Similar calculations for a trapezoidal rib are also given and, in this case, are compared with SEM/EDX chromium concentration measurements for samples oxidized at 1000°C in a CO2/1%CO environment.
Similar content being viewed by others
References
Wagner C. (1952) . Journal of the Electrochemical Society 99:369
Whittle D. P., Evans D. J., Scully D. B. (1967) . Acta Metallurgica 15:1421
Whittle D. P. (1972) . Corrosion Science 12:869
H. C. Cowen and S. J. Webster, in Corrosion of Steels in CO2, D.R. Holmes et al., eds. (British Nuclear Energy Society, London, 1974) p. 349
Evans H. E., Donaldson A. T., Gilmour T. C. (1999) . Oxidation of Metals 52:379
Evans H. E., Hilton D. A., Holm R. A., Webster S. J. (1980) . Oxidation of Metals 14:235
Lobb R. C., Evans H. E. (1984) . Corrosion Science 24:385
Gleeson B., Li B. (2004) . Materials Science Forum 461–464:427
Vossen J. P. T., Gawenda P., Rahts K., Röhrig M., Schorr M., Schütze M. (1997) . Materials at High Temperatures 14:387
W. M. Pragnell, Modelling Solute Depletion during the High Temperature Oxidation of Alloys, PhD thesis (University of Birmingham, Birmingham, UK, 2005)
W. M. Pragnell, H. E. Evans, D. Naumenko and W. J. Quadakkers, Materials at High Temperatures 22(3/4), 399 (2005)
Crank J. (1975). The Mathematics of Diffusion. Oxford University Press, Oxford UK
J. A. Nesbitt, COSIM - A Finite-Difference Computer Model to Predict Ternary Concentration Profiles Associated With Oxidation and Interdiffusion of Overlay-Coated Substrates, NASA Report: NASA/TM-2000–209271, USA (2000)
Evans H. E. (1988) . Materials Science and Technology 4:415
Smith A. F., Gibbs G. B. (1969) . Metal Science Journal 3:93
Barin, I., Thermochemical Data of Pure Substances, (VCH Verlagsgesellschaft mbH , Weinheim, Germany, 1993)
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Pragnell, W.M., Evans, H.E. Chromium Depletion at 2-Dimensional Features during the Selective Oxidation of a 20Cr–25Ni Austenitic Steel. Oxid Met 66, 209–230 (2006). https://doi.org/10.1007/s11085-006-9039-5
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11085-006-9039-5