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Problems Electroless Nickel Plating B7 Alloy Bolts


Q. Am experiencing a problem where a local plater is having difficulty depositing electroless nickel on B7 alloy bolts (ASTM A193 [affil. link] ). The result is poor adhesion, with the plating flaking off in small pieces. I suspect the root cause of the problem to be related to a poor surface preparation/cleaning operation prior to plating? Can anyone tell me if the B7 alloy poses a problem for the electroless nickel process or should this material plate-up without issue?

Denis Moles
- Foxboro, Massachusetts

"Electroless Copper and Nickel-Phosphorous Plating"
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A. I have no clue as to what B7 is, but another possibility is that it is a metal that requires a strike plate before the EN.

James Watts
- Navarre, Florida


A. I don't know what a B7 alloy is. Assuming it is a hardened and or high strength steel it needs to be pretreated and plated under different conditions than would be acceptable for low carbon steel.

Todd Osmolski
- Charlotte, North Carolina, USA


A. B7 is a specification for high strength steel fasteners normally made up of 4140 or similar alloy heat treated steel. It should be given a Wood's nickel strike prior to EN and a post-bake to release hydrogen. Other preparatory steps per conventional procedures.

Guillermo Marrufo
Monterrey, NL, Mexico

March 5, 2014

Q. Did you ever find a solution to this problem?

I have a similar problem with plating Nickel onto ASTM A193 [affil. link] B7 fasteners. I believe it is due to the black coating that is on the parts following the heat treating of the 4140 steel to satisfy the B7 standard.

I remove the black material (unknown metal oxides?) with 10% HNO3 but it leaves quite a bit of smut. I assume this black smut to be elemental carbon, but 4140 is such a low-carbon alloy that I find this hard to believe as well.


Typical Chemistry
Carbon 0.42%
Silicon 0.30%
Molybdenum 0.20%
Manganese 1.00%
Chromium 1.00%

It has been suggested that the carbon smut is a result of the oil quenching process which can leave much carbon on the surface. However, I cannot verify this.

I would like to know if anyone has had a similar problem and a good solution?

My attempts were to use a HNO3 desmut and an HNO3/NH4F*HF desmut. Both worked *somewhat* but not fully (even at high concentration).

Any ideas?

Rick Morgan
- Seattle, Washington USA

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