Theory chromium depletion

Ceilings, P. J. and de Jongh, M. A., Grain Boundary Oxidation and the Chromium-depletion Theory of Intercrystalline Corrosion of Austenitic Stainless Steels , Corros. Sc/., 7,413 (1967) Armijo, J. S., Impurity Adsorption and Intergranular Corrosion of Austenitic Stainless Steel in Boiling HNOj-KjCrjO, Solutions , Corros. Sci., 7, 143 (1967)... 

A quantitative model was developed by Strawstrom, Hillert and Tedmon et al. [35,36]. This further strengthened the chromium depletion theory. Figure 4.31 shows a comparison of Cr-C-Cr23C6 chromium carbide equilibrium data for 304 stainless steel with experimentally obtained corrosion data for several temperatures. The bulk carbon concentration is shown on the abscissa. The chromium content in equilibrium with Cr23C6 in the steel is shown as the ordinate. 

On the basis of chromium depletion theory, a uniform attack occurs on both sides of the grain boundary carbide. Therefore, the observation that the knife-line attack (knife-line attack occurs in a very narrow band in the parent metal immediately adjacent to the weld), occurs only on one side of the carbide, austenite interface cannot be explained by the chromium depletion theory. The knife-line attack arises as a result of strains... 

From the above description, it is dear that the electrochemical theory [41] is controversial and it does not present a better picture of intergranular corrosion than predicted by the chromium depletion theory. 

The above model is based on the chromium depletion theory described earlier. The mechanism proposed by Hodges [50] is based on the following observations on high purity ferritic steels. 

Which of the following assumptions regarding the chromium depletion theory for stainless steels has more evidence in support of it ... 

State four salient characteristics of the model of grain boundary attack based on chromium depletion theory. 

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