ISSN:
1573-4889
Keywords:
IRON BASE ALLOYS
;
MULTIPHASE ALLOY OXIDATION
;
RESERVOIR EFFECT
;
CARBIDE DISSOLUTION
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Ferrous alloys containing significant volumefractions of chromium carbides were formulated so as tocontain an overall chromium level of 15% (by weight) buta nominal metal matrix chromium concentration of only 11%. Their oxidation at 850°C inpure oxygen led to either protectiveCr2O3 scale formation accompaniedby subsurface carbide dissolution or rapid growth ofiron-rich oxide scales associated with rapid alloy surface recession, which engulfedthe carbides before they could dissolve. Carbide sizewas important in austenitic alloys: an as-castFe-15Cr-0.5C alloy contained relatively coarse carbides and failed to form aCr2O3 scale, whereas the samealloy when hot-forged to produce very fine carbidesoxidized protectively. In ferritic alloys, however, evencoarse carbides dissolved sufficiently rapidly to provide the chromium flux necessary to formand maintain the growth of a Cr2O3scale, a result attributed to the high diffusivity ofthe ferrite phase. Small additions of silicon to theas-cast Fe-15Cr-0.5C alloy rendered it ferritic and led toprotective Cr2O3 growth. However,when the silicon-containing alloy was made austenitic(by the addition of nickel), it still formed aprotective Cr2O3 scale, showing that the principal function of silicon was inmodifying the scale-alloy interface.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1018880019395
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