Intergranular corrosion mechanism

Figure 2. Microfractographic particularities the intergranular corrosion mechanism, x 400.

Wilson, F. G., Mechanism of Intergranular Corrosion of Austenitic Stainless Steel , Br. Corros. J., 6, 100 (1971)... 

Fig. 28. Micrographs of a fractured specimen, showing numerous small cracks on the gauge length (enlarged in (b)), and intergranular fracture (c) enlargement of fracture surface [57]. Copyright 1991. Electric Power Research Institute/EPRl ER-7247. Intergranular Corrosion of Stainless Steel. Vol. 1 Mechanism of Crack Initiation. Reprinted with permission.

Intergranular Corrosion of Stainless Steel, Vol. 1 Mechanism of Crack Initiation, EPRI ER-7247, Electric Power Research Institute, Palo Alto, CA (March 1991). 

Nevertheless at exploitation of airplanes during 15 years, in spite of insignificant stresses, cases of failures of the parts by means of a corrosion mechanism (intergranular brittle fracture) and by means of a combined corrosion-fatigue mechanism had taken place. 

Susceptibility to intergranular corrosion also can occur in ferritic stainless steels (Ref 86-90). As with the austenitic stainless steels, the extent of the susceptibility is a function of the chemical composition and the thermal history of the steel. Also, the mechanism of intergranular attack is essentially the same for both classes of stainless steels, specifically, attack of lowered-chromium-content regions adjacent to precipitated chromium-rich carbides and nitrides. However, there are... 

Because of the broad variation in composition and response to thermal treatment of the nickel-base alloys, it is not possible to generalize mechanisms responsible for developing susceptibility to intergranular corrosion. Therefore, the following discussion of the behavior of a Ni-Mo-Cr alloy is used to illustrate the complexity of an interrelationship between alloy composition, heat treatment, corrosion environment and corrosion rate. The alloy has the nominal composition in weight percent of 14.5 to 16.5 Cr, 15 to 17 Mo, 3 to 4.5 W, and 4 to 7 Fe with maximum limits on carbon and silicon. The alloys for which the corrosion data are shown in Fig. 7.59 contained 0.045 to 0.06 wt% carbon and 0.53 to 0.80 wt% silicon and were initially quenched from 1225 15 °C (2235 25 °F), which produced a dispersion of M6C type carbides (M = Mo, W, Si) in austenite (Ref 94). These carbides were not involved in the subsequent corrosion behavior or heat treatments. Heat... 

Table 7.8 Gradual transition from one mechanism of failure to another, intergranular corrosion to brittle fracture...

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