Stainless Steels and Alloys: Why They Resist Corrosion
and How They Fail*
In addition to the dependence of alloy composition, the
chromium content in the passive film is also dependent on the passivating
potential. Fig. 7 shows that the passive film formed at a higher passivating
potential (+920 mV) has a higher chromium content than that formed at a
lower passivating potential (+750 mV).
Fig. 7 The potential dependence of chromium content in
passive films An interesting observation for the nickel-containing stainless
steel is that nickel was actually depleted in the passive film and in some
cases was found to be enriched in the metallic form immediately beneath
the passive film. Surface analysis results in Fig.8 showed that chromium
was enriched in the passive films while nickel was depleted in the nickel-containing
steel. 
Fig. 8 Enrichment of chromium and depletion of nickel
in the passive films
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