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topic 56819

Discoloration from Hydrogen Embrittlement Relief after Plating

A discussion started in 2011 & continuing through 2017 . . .

February 23, 2011

Q. We have been cadmium plating steel parts of Landing Gear components. Recently we have acquired a new oven for de-embrittlement relief.
However after 23 hours at 375 °F baking the parts show local and severe discoloration as seen on the photos.

56819-1 56819-2

If you can guide us about the possible reasons or a way to identify root cause,we would be grateful.

Note: The issue has not been observed with the "old" oven, which suggests the problem is about the "new" oven.

Ozgur Erdal

Ozgur Erdal
Plating Shop Employee - Istanbul, TURKEY

February 28, 2011

A. Ozger,

I would start by putting 5 or 6 thermocouples in various spots inside the oven. You may be experiencing localized hot spots and this method will tell you.

Trent Kaufman
Trent Kaufman
Galva, Illinois

simultaneous March 1, 2011

A. Since it is an aircraft part, the new oven was supposed to have an oven temperature survey done before it was used.

The part should have 1 or more certified thermocouples attached to the part.

I would have another oven survey done, since you are having problems.

James Watts
- Navarre, Florida

March 2, 2011

A. Hi Ozgur,

As Trent has stated you need to check out for hot spots. The discolouration really does look like an overheating problem, something cadmium is quite sensitive to. Has your oven been calibrated at all? If not you need to get it calibrated in accordance with AMS2750 [link by ed. to spec at TechStreet] or BS 2M54, depending on who your customers are. As far as I am aware all aerospace companies require ovens to be calibrated in accordance with one of these specifications.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom

March 2, 2011

A. We de-embrittle tubes after cadmium plating, they often have similar staining, our specs allow us to dip the components in 0.1%v/v sulphuric acid for a few seconds.
This does get rid of the staining and reactivate the cadmium surface for dichromate passivation.
Hope this helps.

Mark Lees
- Isle of Man, Great Britain

March 7, 2011

Q. Our specs also favors a reactivation agent such as sulphuric acid or sodium cyanide.

However we are not sure how serious the stains could be and try to avoid extra work (cause the "old" oven with ventilating duct do not have such complications).

As a summary,
- We have closed the flap of the "old" oven and finally observed similar discoloration, which strongly suggests the case could be about air quality/ventilation.

- For the local hot spots, I will use 3M temperature recorder tapes on the parts. (Thermocouple do not seem practical and cheap :))

I will inform once the "experiments" are finished.
Please inform if you will have additional comments/advices.


Ozgur ERDAL [returning]
- Istanbul, Turkey

De-embrittlement, alkaline zinc

March 19, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am struggling to get a good aesthetic finish on zinc plated high-tensile parts. They look good after zinc plating, but after de-embrittlement (8 hrs at 200 °C) they come out of the oven blotchy.
I then colour passivate them but the blotches are still visible.
The zinc is not coming off and the problem is just a cosmetic one, but the customer is not happy.
How can this be rectified?

daniel hunt
- england

simultaneous March 20, 2017

A. Hi Daniel,

A better description of the blotchy finish would be helpful, maybe even a picture or two.

If I was to take a guess I would suggest that the final rinse has been in tap water and the parts have been placed in the de-embrittlement oven wet. The temperature has then baked on the stains. Make sure the final rinse is de-mineralised or distilled and that the parts go into the oven dry, or at least mainly free of rinse water.

Brian Terry
Aerospace - Yeovil, Somerset, UK

March 20, 2017

A. Hi Daniel,
The staining after de-embrittlement is quite common. Often small amounts of plating residue coming out of the surface, or just an oxidation reaction with air. This can be removed by a few seconds dip in ~1m/l sulphuric acid solution.
This is often done to reactivate the surface prior to chromate passivation, both in zinc and cadmium plating.
I hope this is of use for you.
Best regards
Mark Lees

Mark Lees
- Cold rock in the Irish Sea

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