Hydrogen Embrittlement vs. Electroless Nickel Plating

A. Hi Patanwala,
1000 mpa (145 ksi) is high strength steel. Per earlier postings on this thread, it is subject to hydrogen embrittlement, especially from anodic cleaning and acid activation ... but, yes, from the plating step as well.

Perhaps the component is blasted (which does not cause embrittlement) in lieu of electrocleaning and acid activation. In that case you need be concerned only about the plating step per se. But if the parts are non-critical and you have a history of them being okay with electrolytic nickel, they're probably okay with electroless nickel. Still, baking is probably a good idea. Luck & Regards,


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

A. Hi Mr. Patanwala!

Tubes with internal threads may be electroless nickel plated without concern, as they have ~25-34 HRC and internal threads don't have the concerns of the external threads and bolt heads cracking because of the stress failure of H-E.

We make some Class 10 ISO nuts, and they don't have any concern with H-E failures post plating, but bolts are another history.

Baking EN plated parts will improve significantly the performance of the coating, but if you don't do it, it is a valid alternative for electrolytic nickel plating.

Best of luck!

A. Not totally true. EN produces less than an electrolytic nickel, but that does not produce all that much either. The real culprit is the acid etch prior to the plate. It generates a considerable amount and then plating over it traps most of it that is in the surface of the metal.

Baking is a tradeoff. The more expensive the part is to make or to replace in the field or the higher the liability for a failure is, baking is ultra extremely cheap.

The higher the hardness of the metal or the abruptness of the fillets and etc. further promote failure. So, "it depends".

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A. Hi

H₂ ions are produced during EN plating which produces porosity in the plating. The plating may also contain 6-12% phosphorus (if the plating bath is phosphite-based)which in combination with H₂ could cause H₂ embrittlement. (At least this is my theory anyways!)

A. ENP coating is amorphous in structure in the "As Coated" state. Baking would make the surface harder and, depending on the time and temperature, the structure could be transformed to crystalline. Since crystalline structure offers less corrosion resistance than the other one, this point has to be considered while baking the part. I used to work with some components used as load carrying elements. We did not carry out baking of the parts and we did not have any complaints.

A. Michael,

I suggest to read the ASTM B 656-84 [Ed. note: withdrawn in 2000] and MIL-C-26074 [on DLA]C. H2 embrittlement will be present always in EN coating.

A. Atomic hydrogen will be present but hydrogen embrittlement may not be. Two more conditions must be met before hydrogen embrittlement will occur: 1) the material must be a relatively high strength alloy (e.g. high strength steels or nickel based alloys like some Inconels or age hardened k-monel) and 2) it must be stressed (even just for a short time) to a significant percentage of its yield strength. If baking is needed, it doesn't have to be at a very high temperature (say, 400° F.), but the trade off for temperature is duration (don't cut it short). Sorry about the vagueness but it all depends on the alloys and the hydrogen concentrations.

Hydrogen ions are produced during the process of pretreatment as well as in EN process. To increase the hardness and corrosion resistance is the basic advantage of baking of EN plated products.

The symbol for the element of Hydrogen is H not H2. - H2 would state that there are 2 parts of hydrogen. Have a great day!

A. Hi, Mohammad. Electroless nickel should be able able to withstand temperatures far higher than are required for hydrogen embrittlement relief baking.

It sounds like your plating is not properly done; please tell us about it.

Regards,

Sorry Mohammad, but after 2 postings I still don't know much about your problem. Apologies, but I cannot understand whether you are saying that the screws never had any plating on them, or whether you are saying that the baking operation destroys the plating. I guess my first question is: do the screws look proper before baking? And the second question is: what temperature did you bake them at and for how long? Thanks!

Regards,

A. Hi Javad. You're moving on, without acknowledging previous posts & clarification requests :-(

1. Yes, it is my understanding that it can be more difficult to achieve hydrogen de-embrittlement if the coating is thicker, because the hydrogen can't as easily escape through it during baking. As an example of the recognition of this fact, Ti-Cad plating is sometimes used whereby a titanium powder is occluded into the cadmium plating to build a structure through which the hydrogen can escape.

2. When you speak of "different chromates", you may be talking about a different type of plating than electroless nickel. Please try to detail your actual situation rather than asking abstract questions because it is very easy to misunderstand and then mislead.

Regards,