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Military Firearm Restoration Corner

Corrosion On Stainless Browning A-Bolt


bobmoffett

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My cousin pulled out his stainless steel Browning A-bolt for this year's deer season, only to find it had surface corrosion on the action and barrel as well as the blued steel scope rings and mounts. The stainless steel trigger guard and magazine however showed no signs of any corrosion. Not sure why the gun corroded as he claims he cleaned and put it away after last year's hunt. He cleaned off the worst of the corrosion on the stainless with steel wool, but the stainless steel now has an almost tan color where the corrosion was. The stainless had a matte or bead blasted appearance before the corrosion took hold. What is the best way to return the stainless to its original matte silver color? Looking for any and all suggestions. Thanks

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Casey's has a bluing remover that also removes rust, if I remember correctly. My local gun store carries it, or it did.

 

Naval jelly might work. You could try a small section and see what happens.

 

Bead-blasting would work too, provided you taped-off machined, internal areas.

 

I'm a fan of those small bronze/metal wire brushes; you know the kind that look like a tooth brush that you get at hardware stores. Using those with some good penetrating oil can get into crevices that sandpaper can't.

 

If both the bottom metal and receiver are stainless and only the receiver rusted, you're looking at two different metals. 400 series stainless - despite it's name - WILL rust if it's not wiped down and oiled. 300 series stainless is very resistant to corrosion, but lacks the tensile strength, toughness, and heat treat-ability for use in containing cartridge pressures.

 

400 series IS magnetic; 300 series is slightly magnetic, to the point of being negligible.

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I work in stainless a lot. I'm building a whole car from scratch out of it. You do not want to use steel wool on stainless. You will be embedding little bits of carbon steel into the stainless. The carbon steel will rust and it will look like the stainless is rusting. Done right, you want a stainless or brass/bronze wire brush that you only use on stainless metals. If you use it on steel/iron, then on stainless, you can put little bits of steel/iron on your stainless and you're stuck again. Most of the time I don't worry about it, as a tiny bit of rust on a car frame is really cosmetic and can be cleaned up when it shows, if it shows, but that's the "professional" way to do it.

 

To get the mat finish, it's going to have to be bead blasted. If you want a polished finish, some emory cloth will do.

 

Some stainlesses will rust. I suppose they will all rust, depending on your definition of rust and how much time you are willing to wait, but 50K years might be a bit much for us. Anyway, some stainlesses rust, just rust (stain) LESS than other metals.

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Thanks to both replys. I was thinking about naval jelly also. Its been a long time since I used any but as I remember it creates a pretty dull surface finish. Good advice about the steel wool rusting. I doubt if the brass brush is going to do any more than the steel wool did. I suspect I will have to remove the top surface of the stainless to get back to a bright/matte finish. Bead blasting might be the final solution, but I am hesitant to go that way if there is another possible solution.

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  • 2 years later...

I know that it has been a long time since anyone contributed to this thread, but I thought that passivation needs to be mentioned. In any critical application (and at any mill that produces stainless steel) they need a fast and reliable way to remove undesirable contaminants so that the surface will not show staining "in the field". That is accomplished by passivation. Basically a very good degreasing, rinse, then all contaminants are removed with an acid etch.

 

This website affers some commentary on stainless steel passivation: http://www.finishing.com/466/18.shtml

Very important - the stainless part should remain completely oil free for at least a few hours, to allow the natural chromium oxide layer to re-develop. Protecting it from oxidation too soon is inviting future problems.

 

Quote below:

 

Passivating Stainless Steel with Citric Acid

 

 

+++++++ What are the risks of using Citric acid rather than Nitric acid on Stainless Steel manufactured products? Oxidation was mentioned? Also does Citric Acid remove less than Nitric Acid? Would a fall out occur because of this?

 

Ellyce Chrisbaie

QC Manager - Westwood, Massachusetts

 

First of two simultaneous responses -- +++++++

 

Personal opinion. Citric and nitric are a "wash" on 300 series SS. On 400 series, the citric will blow nitric out of the water. That is assuming that you are using a citric from a good company and not a home brew. The major advertiser of citric at this site has a product that I like, and I am not on their payroll.

 

James Watts

- Navarre, Florida

Second of two simultaneous responses -- +++++++

 

Passivation is the controlled "oxidation" of the nickel on the surface of stainless steel".

 

Citric Acid removes free iron, PERIOD.

 

Nitric Acid (and sometimes with dichromate depending on the alloy) also removes the free iron BUT then control oxidizes the surface to prevent further oxidation (unless exposed to a reducing liquid or chloride).

 

robert_probert.jpg Robert H Probert

Robert H Probert Technical Services

support.GIF

Garner, North Carolina Editor's note:

Mr. Probert is the

author of Aluminum How-To / Aluminio El Como +++++++ Quite the contrary, the risks are in using nitric. Safety risks, risks to surrounding equipment from fumes, risk of etching the surface of your parts.

 

Citric removes "less" than nitric in the sense that it removes the iron only and leaves behind the chromium and other metals. This is beneficial both from a waste disposal standpoint and from a corrosion resistance standpoint, as the citric leaves a deeper chromium-enriched layer than nitric.

 

And yes, the chrome oxide layer is formed not in the bath but in the air afterwards. This does not prevent citric from delivering equivalent or even superior corrosion resistance results.

 

Passivation of stainless steel as defined by ASTM A967 [link is to spec at TechStreet] is the removal of the free iron from the surface, which enables the passive chrome oxide layer to form. Though yes, from a general chemist's perspective, the passivation is the formation of the unreactive oxide layer itself.

 

ray_kremer.jpg Ray Kremer

Stellar Solutions, Inc.

support.GIF

McHenry, Illinois

+++++++ Regarding ASTM A 967. In between "free iron from the surface --- and which enables" ALSO appears what was left out, namely "with a mild oxidant". Citric Acid is not an oxidizing agent, nitric acid at the recommended concentrations for the various alloy IS an oxidizing agent. Let's quote the whole sentence.

 

robert_probert.jpg Robert H Probert

Robert H Probert Technical Services

Garner, North Carolina

 

+++++++ It's certainly not wrong to call attention to a misquote or selective quote, Robert, but after 12 years of countless postings on the subject here, I admit I too am weary of this "debate" between proponents and opponents of citric acid passivation.

 

A decade ago I asked for references to independent studies showing that citric acid "worked", and I immediately received them. I don't feel the shoe is on their foot anymore, but on the other foot; that those who remain opposed to citric acid passivation should quote some recent independent studies showing that it wasn't a satisfactory substitution.

 

For my part I've had too much experience with parts being destroyed in nitric acid, hazardous plant evacuations when steel parts were accidentally put into passivating tanks, and harassment from regulators with their nonsense that passivation shops are nitrate factories, to want to continue to use nitric acid for passivation unless there is actual evidence that it remains necessary.

 

mooneybeach2.jpgtedsig.png

Ted Mooney, P.E.

finishing.com

Brick, New Jersey

First of two simultaneous responses -- +++++++

 

Not to belabor the point with petty bickering, but while the citrate ion is not an oxidizer, hydrogen ions, and by extension every type of acid, are. Iron atoms are oxidized in order to remove them from the metal surface as iron ions, by both citric and nitric acid. The oxidation of the chromium occurs in the air later on, which is also explicitly stated in A967.

 

Regardless of the exact mechanism, if it didn't work, people wouldn't be using it.

 

ray_kremer.jpg Ray Kremer

Stellar Solutions, Inc.

McHenry, Illinois Second of two simultaneous responses -- +++++++

 

Citric acid is the reducer and promote de-passivation of the surface. Passive film formed after citric acid treatment is very thin. Further increase in thickness of such passive film take place during rinsing and drying. Such operations are hard to control. Therefore citric acid is very effective in removing free iron, but not sufficient enough in actual passivating. We recommend that after citric acid treatment stainless steel is treated in nitric acid solution or other more environmentally friendly solutions with high redox-potential in order to create thick passivating film. http://en.wikipedia....ction_potential Such film will increase corrosion resistance and reliability of corrosion protection.

 

We have developed such passivating solution for 300-steel for food and medical industry. We also have passivating solution for 400-steel which deploy both functions removing of fee iron and passivating film formation.

 

anna_berkovich.jpg

Anna Berkovich

Russamer Lab

support.GIF

Pittsburgh, Pennsylvania

+++++++ I have been following this thread with quite a bit of interest. As we have been having the perennial problems with 416 and 440C on a very intermittent basis we were advised that citric acid may well be the way to go as the potential for attack was greatly reduced (correct me if I'm wrong).

 

My problem is that when I read such polar views I am disinclined to investigate too much further.

 

So, in general, are we for or against passivation with citric acid? Please give me something to go on instead of the "it works/no it doesn't" arguements.

 

Looking forward to seeing some reasoned arguments, preferably backed up with some more literature sources.

 

Brian Terry

Aerospace - Yeovil, Somerset, UK

 

+++++++ From my experience, Anna has presented the most accurate information. Let me just share some personal experience from a non-biased perspective. Citric acid indeed behaves differently than nitric acid in the way that it helps achieve passivation. The comparison of the resulting passivation layer thicknesses is key here. The thickness of the layer helps determine corrosion resistance. The one thing that many are overlooking is the application you are using the SS for. For many applications Citric is sufficient and the difference is negligable. However, I have first-hand experience using both citric and nitric for metal injection molded (MIM) parts, as well as some other medical device applications and nitric sometimes out-performs citric. This is especially important if cosmetic finish is a factor. It also depends on how smooth your surface is pre-passivation.

 

Dwayne Bell

- San Jose, California, USA

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That's interesting on the citric acid. Nitric acid is some seriously bad stuff. I would not want that around the house/shop. I would rather have stained/rusted stainless than nitric around. Citric isn't too bad.

 

What about some easy DIY techniques for "bluing" (not really bluing, but blackening, staining, whatever you want to call it) 300 series? Like if you want a stainless knife to have a dark finish or something.

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  • 2 months later...

That's interesting on the citric acid. Nitric acid is some seriously bad stuff. I would not want that around the house/shop. I would rather have stained/rusted stainless than nitric around. Citric isn't too bad.

 

What about some easy DIY techniques for "bluing" (not really bluing, but blackening, staining, whatever you want to call it) 300 series? Like if you want a stainless knife to have a dark finish or something.

 

Citric acid is also easy to obtain and reasonably cheap - I got some (powdered) in the canning section at WM the other day because the Bulk Store was out. Just under a half pound for just under $5. That's "expensive" relative to what you can find it for online in larger quantities. Very safe to use AND dispose of.

 

Oddly, everywhere I asked about it, I got fearful "whadd'ya need THAT for?!" replies, so it's not like it would be any better than trying to buy nitric I suppose. Ignorance has few bounds but I am still surprised at times. Just tell them you are canning tomatoes. :P

 

Here is an excellent (and long) thread about using citric acid to clean cartridge brass. It also speaks of stainless and the effects of citric acid solutions on the same, so there is a lot of useful information here. At least one of the posters is a chemist and others have significant experience. I have used this forum for a long time and there is very little Internet ignorance infused.

http://castboolits.gunloads.com/showthread.php?t=83572&highlight=citric+acid+passivation+brass

 

I have not used it on stainless myself yet.

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