How the heck does stainless steel get pitted?

[jtcarm]

I've been perusing online auctions way too much lately and have seen several SS Smiths described with pitting and what looks like corrosion on the frames & barrels.

I know SS isn't bulletproof, but what kind of neglect and abuse could cause that? Keeping it on a saltwater vessel?

 

[Alk8944]

Stainless steel is somewhat rust resistant, not rust proof. Simple neglect, like believing it doesn't need to oiled and leaving it in any type storage container that may retain moisture for a long period will do it. I have only 2 stainless steel S&W revolvers which were purchased used. BOTH of them had some pitting on the exterior. A 60-4 was pitted and rusted behind the left recoil shield,around the thumb piece and under the factory Uncle Mikes stocks. My 629 Mountain Revolver has deep pitting on the frame and barrel which looks like electrolytic corrosion.

The answer is to care for a stainless gun just like a blued one, it certainly will do no harm!

 

[Boge]

Stainless is not bulletproof. It just needs a little more time to rust/corrode in a bad scenario, which is usually owner neglect.

 

[OKFC05]

"Stainless" steel is resistant to corrosion, but several things can affect this resistance.
First, stainless surfaces are treated or "pickled" to remove the iron atoms from the surface and reduce oxidation potential. However, scrubbling and sanding can remove the more inert surface and get down to where there are more iron atoms.
Second, the presence of catalysts can accelerate corrosion, even on stainless, and salt is one possibility, even from sweat.

So I clean my new stainless guns of all foreign solvents, oils, etc., and apply wax, renewing periodically. Leaving the pickled surface intact and using wax makes a difference.

 

[STCM(SW)]

"The answer is to care for a stainless gun just like a blued one, it certainly will do no harm!"

That is the answered.

 

[Sebago Son]

It's Stain-LESS not Stain-FREE.

Most grades of stainless have a good deal of carbon remaining.

 

[jtcarm]

Hmm, seen plenty of blued & nickel finishes that look like road kill, but few stainless. To me letting an SS finish corrode is kinda like breaking crow bar

 

[jaymoore]

Blood or ketchup do it in fairly short order (As a couple of examples that come to mind immediately.). Plus some sweat, but usually only in areas away from sight, such as under the grips. The mechanism is somewhat different than rusting of blued steel, hence the intense localized corrosion versus a more generalized shallow corrosion. If air or water are in constant motion over stainless, it usually won't corrode appreciably. The area needs to be "stagnant" (Like under a layer of blood, etc.)

So your revolver is fine for trips hunting all day in the rain or for swimming in reasonably fresh water, but not so much being enclosed with no oil, etc. protection.

 

[Nemo288]

I work at an indoor swimming pool (YMCA) and you should see what
some of the supposedly stainless steel looks like after being exposed
to the toxic atmosphere for a year or 2. Actual red rust as well as
some white corrosion in places. We had to replace the hydro lift
chair because it rusted out. It was made of stainless. Some of the alloys
are better than others and I don't know why some of the manufacturers
use the insti-rust ones.

I have a few stainless handguns (in fact they all are) and have never
seen any corrosion on them. I do wipe them with an oil rag before
putting them away after a clean and lube.
I won't be storing them at the pool anytime soon

---
Nemo

 

[hangnoose]

CHLORINE

If it's a chlorine pool, theres your answer.

 

[Fessor]

"Stainless" steel is resistant to corrosion, but several things can affect this resistance.
First, stainless surfaces are treated or "pickled" to remove the iron atoms from the surface and reduce oxidation potential. However, scrubbling and sanding can remove the more inert surface and get down to where there are more iron atoms.
Second, the presence of catalysts can accelerate corrosion, even on stainless, and salt is one possibility, even from sweat.

So I clean my new stainless guns of all foreign solvents, oils, etc., and apply wax, renewing periodically. Leaving the pickled surface intact and using wax makes a difference.

Very well said from a metallurgical standpoint. I will ad that different series of stainless such as the 300 vs. 400 series have different corrosion resistance.

 

[WR Moore]

Good example of neglect: keeping a model 60 in a leather pocket holster and neglecting to remove both weapon and holster from the pocket and separate the two to dry during a hot summer. Add failure to wipe down the handgun occasionally.

You can get much the same result-different areas of the weapon- by leaving the piece in a duty holter for an extended time. Gear out of the locker, worn on duty, rehung in the locker (regardless of weather conditions). Repeat over time.

 

[kwselke]

I've been perusing online auctions way too much lately and have seen several SS Smiths described with pitting and what looks like corrosion on the frames & barrels.

I know SS isn't bulletproof, but what kind of neglect and abuse could cause that? Keeping it on a saltwater vessel?

Go hunting, Get blood on your stainless gun. Put gun in holster and do not clean until three months later. That will do it.

 

[BigBill]

Stainless Steel isn't as tough as some think it is. Your body sweat while using an in the pants holster first will tarnished the s/s finish. Now even if we wipe the gun down were still sticking it back in the damp holster. I do
not use in the pants holsters in the hot weather. I'd rather use shoulder holsters were I can. If it's just tarnished the Simi chrome polish will return it to a new looking finish again. I've also seen the nickel finished tarnished from body sweat too. I'm not sure what to do with the sweat still in the holster?

 

[gm272gs]

I work at an indoor swimming pool (YMCA) and you should see what some of the supposedly stainless steel looks like after being exposed
to the toxic atmosphere for a year or 2. Actual red rust as well as some white corrosion in places. We had to replace the hydro lift chair because it rusted out. It was made of stainless. Some of the alloys are better than others and I don't know why some of the manufacturers use the insti-rust ones...

Architects & Engineers often get this wrong. You want to use aluminum in and around pools, not stainless steel. It is indeed the chlorine that does it. I saw some stainless steel urinal screens (the low "privacy" walls between urinals) that were a rusty mess, once. It turned out that they were cleaning the restroom with "The Works". The main ingredient of that cleaner is hydrogen chloride. When you mix hydrogen chloride with water, you get hydrochloric acid. That's what we call "bad" for stainless steel.

 

[JDBoardman]

The "pickling" for most stainless steels passivates the surface, providing a surface rich in chromium oxide. It is this passive layer that actually provides the alloy's corrosion resistance. When 300 series stainless steels are elctropolished, the chemical etching process removes some of the ferric material, as well as much of the surface contaminants left over from the machining and forming processes, even further enhancing the corrosion resistance of the material. When used in a harsh envionment, 304L or 316L (the 'L' designates low carbon) are preferred for corrosion resistance. At the same time, as the carbon content decreases, while corrosion fighting increases, the ultimate physical strength is reduced and the yield strength also decrease. "There ain't no such thing as a free lunch", so if one property is improved, another property is decreased, so there is always a tradeoff.

Corrosion (rusting) is an electrochemical process involving galvanic reations, so anything that can reduce the number or severity of "cells" at or near the surface will improve the resistance to corrosion. If the embedded contaminants are removed, and a chromium-rich surface layer is produced (by pickling, passivation or electropolishing), the number of galvanic cells is reduced and the corrosion resistance increases. Conversely, if you "activate" the surface by exposing it to such items as chlorine ions (sweat, blood, salt water), or other halogens, you will alter the chromium oxide protective film and the stainless teel will corrode, or pit, in the regions where the film is damaged or removed.

 

[jaykellogg]

When you machine stainless steel it is a fair bet you use a high carbon tool steel for the cutters. This leaves minute particles of carbon steel behind and this is why some stainless is passivated by dipping in acid.

18-8 stainless (304) is probably the most corrosion resistant, but it cannot be heat treated. I doubt that much of that is used in firearms.

In a highly corrosive atmosphere it is advisable to use titanium if possible. I have highly acid skin oils and I wear titanium glasses frames.

One disagreeable aspect of stainless is it tends to gall when it wears against itself.

There is a galvanic scale for prediction corrosion resistance. Steel and stainless steel are not close on the galvanic scale. That is why during the late '50s automakers switched from stainless trim to aluminum. If you take off a fender spear from an early '50s car you will see the outline of it in small pits in the fender. what actually happens is in the presence of an electrolyte (Salt water) small batteries are formed and the metal is eaten away. Today's cars have very little stainless. The exhaust systems and some fuel lines, but these are usually insulated with rubber.

 

[jaymoore]

When you machine stainless steel it is a fair bet you use a high carbon tool steel for the cutters. This leaves minute particles of carbon steel behind and this is why some stainless is passivated by dipping in acid.

...

I can't remember the last time I used HS steel on stainless aside from possibly some drill and tap operations and of course edge breaks with a file. (usually 17-4 or 15-5 at the 180-200kpsi HT.) Carbide tooling, generally coated inserts.

But I've heard that steel wool and stainless aren't a good combination. No first hand experience, though.

BTW, blood can pit in a day:


Deer blood, at any rate!

 

[Rpg]

Obviously, lots of the folks who responded to this thread know much more about metallurgy than I. I respect their views and they are all certainly correct.

My experience is that stainless steel in a firearm is, at best, a short term (hours, not days) benefit.

You have to care for your so called stainless firearms just as you woul for blued.

I wouldn't buy a 'stainless steel' firearm because of the supposed 'stainless' quality. I've seen too many instances where they corrode very rapidly.

Stainless requires the same care as blued in firearms. To think otherwise is to invite disappointment

 

[hanken]

Type 316 is used in all medical equipment and instruments and has the most resistance, but it is some of the hardest to machine. Tooling does not last very long, so it cost a lot more to produce goods made with it.


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