Oxidation of Metals

, Volume 14, Issue 3, pp 235–247 | Cite as

The development of localized pits during stainless steel oxidation

  • H. E. Evans
  • D. A. Hilton
  • R. A. Holm
  • S. J. Webster
Article

Abstract

A study of the localized pitting attack of 20% Cr/25%Ni stainless steel and a similar alloy containing a dispersion of titanium nitride particles has been made over the temperature range 1023 to 1173 K. Pitting is initiated when localized spoiling of the protective chromic oxide film occurs. Rapid oxidation of the chromium-depleted substrate then proceeds with the formation of an iron-rich oxide mound on the alloy surface and spinels containing nickel, chromium, and iron within the pit itself. A silica layer which, in general, remains on the alloy surface acts as a diffusion barrier during this stage of the reaction. With increasing depth of attack the local chromium concentration in the alloy at the base of the pit attains a critical value (∼16%) for a protective chromium oxide film to reform; the pitting attack then effectively ceases, although a a subsequent slow rate of growth continues through the protective film at the base. The observed maximum depth of pitting as a function of time is consistent with the parabolic variation predicted by the proposed mechanism. There is no significant difference in the kinetics of attack between the alloys examined.

Key words

stainless steel high-temperature oxidation chromium depletion pitting 

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Copyright information

© Plenum Publishing Corporation 1980

Authors and Affiliations

  • H. E. Evans
    • 1
  • D. A. Hilton
    • 1
  • R. A. Holm
    • 1
  • S. J. Webster
    • 2
  1. 1.Berkeley Nuclear LaboratoriesCentral Electricity Generating BoardBerkeleyUK
  2. 2.Spring fields Nuclear Power Development LaboratoriesU.K.A.E.A.Salwick, PrestonUK

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