fig4

A review on pitting corrosion and environmentally assisted cracking on duplex stainless steel

Figure 4. The effect of environmental variables on the passive film. (A) The passive film in the open air is constituted by a two-layer structure, specifically, the Cr-rich inner layer and the Fe-rich outer layer. (B) When immersion in the solutioncontaining chlorides, the CrOOH disappears[28]. (C) When the temperature increases, the passive film thickens and becomes more enriched in Cr[35]. (D) When the hydrostatic pressure increases, less Cr2O3 is detected[37]. (E) Removing oxygen decreases the point defects in the passive film and lowers the film/solution potential drop[35]. (F) Hydrogen sulfide accelerates the film dissolution process and local acidification processes[38]. (G) Increasing the anodic potential transforms the passive film from p-type to n-type[36]. (H) Hydrogen charging makes the passive film more conductive and imparts it with a larger OH-/O2- ratio[39,40]. (I) Stress creates more point defects and more soluble CrO3 in the passive film[41,42].

Microstructures
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