The following is a discussion of the article entitled "Oxidation of 21Cr-6Ni-9Mn Stainless Steel in Molten Lead Oxide and Static Air" by R. O. Slonaker and G. W. Powell, published in Corrosion, 26, 363 (1970) September. G. W. Powell's and R. O. Slonaker's reply follows the discussion.
The authors have observed a subsurface cellular phase in the austenite below the external scale, after oxidizing 21Cr-6Ni-9Mn in static air and in molten lead oxide. With what appears to be a minimum of direct evidence, Slonaker and Powell conclude that “the subsurface phases…..are cubic oxides and are probably either FeMn2O4, FeCr2O4 and/or MnCr2O4.”
When I saw the authors’ photomicrographs (Figures 1 and 2), I was immediately struck by the similarity of these subsurface phases to the lamellar chromium-rich nitrides with which I am familiar (M2N or Cr2...
