ISSN:
1573-4889
Keywords:
AUSTENITIC STEEL
;
OXIDATION
;
FINITE THICKNESS SAMPLES
;
CHROMIUM AND SILICON DEPLETION
;
EPMA MEASUREMENTS
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Electron-probe microanalysis (EPMA) measurementsare reported of the residual silicon and chromiumconcentrations in thin sections (0.38 mm) of a20Cr-25Ni-Nb-stabilized austenitic steel oxidized in aCO2/1% CO environment for maximum periods of around40,000 hr at temperatures in the range 900 to 950°C.The depletion profiles obtained have been analyzed usingthe theoretical treatment of Whittle and Cowen-Webster. It is found that silicon depletion occursslowly because of the low rate of thickening of thesilica interlayer formed below the much-thicker,chromia-surface layer. This, coupled with relativelyrapid diffusion within the steel, leads to a flatdepletion profile. By contrast, the more rapid oxidationof chromium develops large concentration gradients ofthat element in the alloy in the vicinity of the oxidemetal interface. In each case, the soluteconcentration at this interface was very much largerthan that for equilibrium with the respective oxide,indicating that the oxidation kinetics were determined by transport within the oxide layer rather thanin the steel. In all the examples studied, thetheoretical analysis produced good agreement with thedepletion measurements using oxidation rate constants consistent with the metallographic measurementsand diffusion coefficients of similar value to thosereported in the literature.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1018808925756
Permalink
