Why Does Stainless Steel "Rust"?

Move to the country and pump water from your own well, and you won't have a chlorine problem.

We have 30 year old utensils made with SS and no rust.
Back in CA we had one of the best water (no profit) utility Co, but getting close to a year in Las Vegas where water is famous for being ugly, SS holds well.

Thank you for the information. Here in SA every time the readings for water is off they add chlorine to the water. I have a water softener and have had to replace the resin already. Seems chlorine dissolves the resin (had particles in the screens on the taps). Had to flush out the lines and the water heater. Had to also add a filter coming into the house with a chlorine filter to stop the resin from dissolving.

My mistake I should have titled it "If you're stainless steel rusts :))"

The only Chlorine down down here comes in a Chlorox bottle and a brand of dishwashing soap called Tri-Cloro.

Stainless only means it stains less, not that it won't stain or rust. :(

Haven't experience rust on SS yet and have never used well water so everything gets washed in chlorinated water. Maybe I am lucky or maybe my SS isn't really SS.

Or soaked the stuff in hot heavily chlorinated water.

Heating water, especially boiling removes the Chlorine PDQ. As you may know there are different types of stainless, some types aren't very 'stainless'. Type 316 is the most common corrosion resistant type, but it isn't that strong nor does it hold an edge well. 400 series SS are harder and stronger but the are not as corrosion resistant.

Normally chlorine is a concern in inter-granular corrosion not surface corrosion. At least in industrial usage. I spent 30+ years as an industrial/environmental chemist and had lots of experience with corrosion prevention.

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..

Its called Stainless, not rust free, it is just that "Stain LESS". and depending on the type, some stainless will get a good surface rust. Look at stainless exhaust systems.

It has nothing to do with how "good" or "bad" the stainless is or how "cheap" or not the stainless is, it has to do with what properties and applications the steel has been designed for.

Where looks and esthetics are important, the stainless puts that first, other qualities like, strength, edge holding, sharpness on the back burner. Where longevity and heat resistance is priority, surface rusting takes a hit.

And, not all stainless is non magnetic either.