Why Does Stainless Steel "Rust"?

MEXICOWANDERER wrote:
I thought it weird. My knives rusted in the USA but they don't rust down here -- even in a salt air environment.

It ain't the chili...

Turns out the culprit is Chlorine.

Even as little chlorine as contained in tap water. Like any other chemical process, reaction is modified (accentuated) by heat and length of exposure time.

Chlorine tends to remove the protective coating stainless steel forms on it's finish. Chlorinated water is weak, but if it is heated and utensils spend time soaking in the sink, then this changes the scenario.

Ive got a few pricey 440c stainless knives that I would rather not have to deal with. So now I know. I avoid chlorine (my regular liquid dish-washing soap contains it). And I need not keep the blade smeared with cooking oil.

18-10 flatware is also sensitive to chlorine.

CHEAP "Stainless" will rust no matter what.

GOOD "Stainless" will not.

Cheap stainless contains much less Chromium than good stainless.

Stainless steal must have 12%-30% Chromium in order to be called "Stainless Steel"..

Stainless also must contain nickel and manganese but Chromium is the key element to preventing rust.

Yes, in "theory" Chlorine may attack the Chromium boundry weakening the effect of the Chromium layer and rust may develop..

But, unless your city water has an unusually high (and possible hazardous) concentration of Chlorine I doubt it is the cuplrit in your case.

Be aware, that the use of steel wool scrubbing pads can "embed" microscopic pieces of steel into the Chromium layer which then will cause rust to show..

So don't ever use those steel wool cleaning pads on stainless..

I have a all stainless gas grill on my back porch, it HAS rust streaks ON SOME PARTS BUT NONE ON OTHER PARTS and it was never exposed to Chlorine, directly or indirectly from city water..

I also have a bunch of Revere Ware stainless pots and pans with copper bottoms, lots of stainless knives and even a stainless steel sink.. None of any of that has ever shown rust..

But we don't use Steel wool pads.

I have well water which is not treated with Chlorine but is softened via a water softener which uses salt to regenerate the filter..