Silicon and Chromium Depletion During the Long-Term Oxidation of Thin-Sectioned Austenitic Steel
Silicon and Chromium Depletion During the Long-Term Oxidation of Thin-Sectioned Austenitic Steel
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薄断面奥氏体钢长期氧化过程中硅和铬的损耗
DOI：
10.1023/a:1018808925756
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发表时间：
1998
影响因子：
2.2
通讯作者：
A. Donaldson
中科院分区：
文献类型：
--
作者：
H. Evans;A. Donaldson
本文报道了20 Cr-25 Ni-Nb稳定的奥氏体钢在900 ~ 950°C温度范围内，在CO_2/1%CO环境中氧化最长约40,000小时后，在0.38 mm薄切片中残余硅和铬浓度的电子探针显微分析（EPMA）测量结果。发现由于在较厚的氧化铬表面层下面形成的二氧化硅夹层的增厚速率较低，硅的耗尽发生得很慢。这一点，再加上钢内相对快速的扩散，导致了一个平坦的耗尽轮廓。相比之下，铬的氧化越快，在氧化物金属界面附近合金中该元素的浓度梯度就越大。在每一种情况下，溶质浓度在这个界面是非常大的比，为平衡与各自的氧化物，表明氧化动力学是由内部的氧化物层，而不是在钢中的传输。在所有研究的例子中，理论分析产生了良好的协议与消耗测量使用氧化速率常数与金相测量和扩散系数的类似值在文献中报道的一致。
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.