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Hydrogen Embrittlement Relief Required After Passivation?


Q. We accidentally passivated 416 SS in ASTM A967 [affil. link] Nitric 2 instead of Nitric 1. The surface looks fine, there is no evidence of etching or pitting. My question is, have we induced hydrogen embrittlement by using a more concentrated acid solution?

Kevin Livingston
- Nova Scotia, Canada

simultaneous 2005

A. The reaction between ferrous based materials and nitric acid are backwards - the more concentrated the nitric, the less active it is to steels including stainless. The fact that you've used MORE CONCENTRATED nitric during passivation should not be deemed as deleterious! As long as it tests OK as passivated, you should be fine.

milt stevenson jr.
Milt Stevenson, Jr.
Anoplate Corporation
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Syracuse, New York
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A. Kevin, if they look OK (no pitting or etching as you said) then I'd buy them off in a heartbeat. Any problem with the different solution would show up on the surface.

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York

Is there danger of hydrogen embrittlement from acidic passivation of titanium?

November 19, 2008

Q. Is there a need for hydrogen release after passivating titanium in acids (nitric or citric)?

Dan Moor
product designer - Israel

November 25, 2008

A. Hydrogen embrittlement is known to happen with titanium, although tests with citric acid products formulated correctly have not been know to cause this. We do not have any data with nitric acid, but you could search the internet for data on this.

lee kremer
lee kremer sig
Lee Kremer
Stellar Solutions, Inc.
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McHenry, Illinois
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December 9, 2011

Q. Currently have Medical Instruments 465ph parts tested with hydrogen embrittlement.
Passivated (per customer prints) in house with CitriSurf 2250.
Outsourced for Chrome coat.

AMS2460 [affil. link], ASTM A967 [affil. link] , ASTM A380 [affil. link] and ASTM B254 [affil. link] all kinds of contradictions of each other.
AMS2460 [affil. link] says "acid cleaning shall not be used"?
ASTM B254 [affil. link] Says "Activation immediately before plating" (I assume this is activating the passive layer?).

1. Does the CitriSurf enable hydrogen embrittlement by itself? And should we be doing a 24-hour post bake to defuse hydrogen? Some parts are EDM'ed and we use nitric for those (parts that don't get chromed).

2. I know the Chrome coat pre-clean "should" reactivate the passive surface but what if it doesn't, but they do a 23-hour post bake after chrome per ASM2460? Could there be hydrogen "trapped" by the passive layer that the post bake after chrome isn't able to diffuse? So technically do I have to passivate before chrome and will the pre-chrome "acid clean" remove free irons?

3. Is chrome coat considered a "Passivation"?

Don Crowley
Engineer - Bartlett, Tennessee

December 23, 2011

A. In the aerospace industry it is highly unusual to bake for hydrogen embrittlement relief after passivation. I won't say it's never done, because I don't know what everybody does, but we don't, nor do my colleagues at Boeing, Lockheed, United Technologies, Rolls-Royce, etc. So I would say no, baking after CitriSurf is unnecessary.

If the chromium plating covers all the surfaces, I would not bother to passivate beforehand. If the chromium plating is partial, then I would passivate the entire part before plating. The plating shop will activate the surface appropriately, allowing the chromium to stick to the stainless steel.

Chromium plating is not considered a passivation.

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York

January 5, 2012

A. We haven't seen hydrogen embrittlement problems with stainless passivated with CitriSurf. It seems to be an issue only when passivating with nitric.

I agree with Lee on not bothering to passivate if the entire surface is getting plated. For that matter, if the entire surface is getting plated, I wouldn't even bother using stainless.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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January 10, 2012

A. This discussion is going on and on. For medical parts the best option is electropolishing, which provides optimal passivation and appearance. Even for surgical instruments, the passivation layer is so strong, that strong acids do not destroy it for an extended period of time.

Any metal shop can have electropolishing installed. No fumes. Contact us for more information.

Anna Berkovich
Russamer Lab
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Pittsburgh, Pennsylvania
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To minimize searching & thrashing, multiple threads were merged; please forgive repetition, chronology errors, or disrespect of other responses (they probably weren't there) :-)

Is Hydrogen Embrittlement Relief Required After Electropolishing or Passivation by AMS2759 [affil. link]?

March 22, 2012

Q. Table 1 of AMS2759 [affil. link] requires hydrogen embrittlement stress relief baking of certain low-alloy and stainless steel, heat treated/hardened alloys following "Chemical Processing" or "Etching". Note (3) of that table lists the chemical processes as "etching, stripping, pickling, and milling", but as I understand it, it really applies to any acid treatment on the metal surface, which I would think would include passivation and electropolish as well.

Is that interpretation correct, even though those latter 2 processes aren't specifically listed in the note (3) list of processes?

Mike Palatas
Management - Gardena, California, USA

March 23, 2012

A. That's an interesting question to me, Mike. Electropolishing per se wouldn't seem to me to be capable of creating hydrogen embrittlement since the parts are strongly anodic and drowning in oxygen. And passivation in oxidizing acids like nitric and chromic would seem somewhat similar. But hopefully someone with actual experience in implementing or not implementing embrittlement relief after passivation will chime in.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

April 1, 2012

A. Hi Mike!
Generally, the efforts to insert a hydrogen embrittlement (HE) bake requirement into AMS2700 [affil. link] for passivation get defeated in committee because of the lack of evidence that passivation causes an HE problem. Remember that passivation is done only for stainless steels, so the ones that are at risk are 440C, 420, BG42, other martensitic stainless steels, and the precipitation hardening grades like 17-4 and 13-8. These generally aren't as susceptible to HE as are the high carbon (acicular) martensite alloy steels like 4340 and AerMet 100.

Electropolishing is a different animal. HE is bad in electroplating as you are making your part a cathode, sucking in positively charged hydrogen ions. But in electropolishing, you're making the part an anode. You're not going to drive positively charged hydrogen ions into a positively charged part. So no, we'll never require an HE relief bake for electropolishing.

If you need to discuss this further, Ted has my contact information. Or just look- I'm not hard to find.

Good luck!

lee gearhart
Lee Gearhart
metallurgist - E. Aurora, New York

April 4, 2012

thumbs up signTed and Lee, thanks for your replies!

My takeaway is that it isn't required for electropolish at all, and that since there are contrary opinions on the passivation process and since 90% of the parts that I process are aerospace parts which may or may not be flight critical, I will err on the conservative side and bake out only the 440C, 420, BG42, other martensitic stainless steels, and the precipitation hardening grades like 17-4 and 13-8. Thanks again.

Mike Palatas [returning]
- Gardena, California, USA

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