RJ wrote:
I've always thought that stainless steel
was impervious to corrosion.
....

Stainless steel ??

No real difference other than it isn't so much "grade" of SS as it is
the particular alloy--there are a zillion recognized/numbered-lettered
SS alloys and an infinite number of possibilities beyond that for ad hoc
formulations.

All the "SS" designation alone really indicates is some minimal Ni/Cr
content.

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