Metal treatment – Compositions – Heat treating
Patent
1978-07-21
1979-09-18
Kendall, Ralph S.
Metal treatment
Compositions
Heat treating
148 315, C23F 702
Patent
active
041681843
ABSTRACT:
A method of making surface layers, with improved corrosion properties, on articles of iron-chromium alloys, and the article produced thereby. The article is heated in an oxygen containing gaseous atmosphere with a total vacuum of about 10.sup.-1 down to 10.sup.-8 mm Hg, preferably about 10.sup.-5 mm Hg, to a temperature, at which diffusion of the most reactive alloy component or components, primarily chromium, with respect to the tendency of combining with oxygen, to the surface becomes perceptible, at which temperature the remaining properties of the alloy substantially are maintained. For most iron-chromium alloys that temperature is between 300.degree. C. and 600.degree. C. The aforesaid condition of treatment, is maintained until a surface layer containing oxidized chromium has grown to a thickness of preferably 10.sup.-9 -10.sup.-7 m, and with respect to structure and composition is transformed from a condition on the surface to a condition in the matrix of the metal alloy.
REFERENCES:
patent: 2269601 (1942-01-01), Perrin
Hickman et a., An Electron Diffraction Study of Oxide Films Formed on High Temperature Oxidation Resistant Alloys, Electrochemical Society, Preprint 91-32, 1947, pp. 467-476.
Hultquist Gunnar
Leygraf Christofer
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