Austenitic stainless steels passivity models

For some material-environment combinations it has been shown that accelerated anodic dissolution of yielding metal is the significant mechanism. This is the case for austenitic stainless steels in acidic chloride solutions. In these steels, plastic deformation is characterized by a dislocation pattern giving wide slip steps on the surface. For such systems, Scully [7.50] has proposed a model for initiation and development of stress corrosion cracks, which has been supported by other scientists [7.51]. The model in its simplest form is illustrated in Figure 7.52. A necessary condition is that flie surface from the beginning is covered by a passivating film (A). 

On stainless steels and on nickel-based stainless alloys, the passive film can be described by the bilayer model already presented. The concentration of Cr " in the inner oxide layer is much higher than the nominal chromium content of the alloy. The compositions of passive films formed on ferritic (Fe-Cr) and austenitic (Fe-Cr-Ni) stainless steels, and on Alloys 600 and 690... 

---