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.

I learned this using my Leatherman Super Tool in the ocean at Nantucket Island, MA. I cut some line, a couple of pieces of bait, and my brother (almost a native) said my knife would rust unless I immediately flushed it with fresh water.

I didn't, and it did. Just a bit of surface rusting, but it stayed stained for 20 years...