# Why does Chloride attack CrO?

In certain applications some sorts of stainless steel (V2A, 1.4301) corrode when exposed to $\small{\ce{Cl^-}}$ in water, or at least it is strongly advised to use other steels.

The conditions that were explained to me as being especially bad were: redox potential >0, acidic environment.

Under these conditions, why do I need $\small{\ce{Cl^-}}$ to corrode steel? I would think that any electrolyte would have a bad effect.

Edit to add 26.7: Most stainless steel contains chrome, a layer of $\ce{CrO}$ is what's protecting the steel. Most articles mention that $\ce{Cl^-}$ damages this layer. More resistant steels use $\ce{Ni}$ (and are more expensive because of that). So, to narrow down the question, how does $\ce{Cl^-}$ attack the passive layer?

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Perhaps chromium can form a chloride-containing complex e.g. $\left[ \ce{Cr \cdot 2 Cl \cdot 4 H_2O}\right]$. (I know copper forms an analogous complex, but only at high concentrations of $\ce{Cl^-}$.) The possibility of forming this complex would make chromium oxide more soluble in water in the presence of chloride than in its absence.