Pits on Plating of 440 Stainless Steel

M

MantleMickey

#1
Greetings, I have a question I would like to pose to all of
you intelligent people out there.
After turning and processing our 440 material, we plate it.
Before plate, no pits, after plate, some pits.
Any ideas on how to stop this, is it humidity, dipping solution?
Any thoughts would be appreciated.
Enjoy your day!
 
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dickgent

Involved In Discussions
#4
If this is SS then you can order the steel passivated. This will reveal any imperfections in the surface of the material.

HOWEVER If the plater cleaning baths are too strong (including type and Ph) - OR - he does not succeed in his first attempt at plating the stripping his and re-plating process will remove impurities (all SS has them) continue to attack the material and create the pitting you see.

I would ask for the chemistry analysis of the run (process chemicals; ph check; temp titrate etc.) and compare the "GOOD" run analysis to the "Pitted" run. The plater will tell you it is the material, Check his processes to be sure or split a batch into two suppliers.

Hope this helps with limited information.
 

Wes Bucey

Quite Involved in Discussions
#5
Pitting in the base metal is usually due to contamination when the base metal is SS.

The steps I would follow in root cause analysis:

  1. assure base metal is smooth and clean - passivating before plating can remove microscopic contaminants which get flushed out in the plating process. (The contaminants come from tool bits used to machine the base metal.) I sometimes had my parts electropolished to provide smooth substrate for plating.
  2. contaminants in the plating bath can cause pitting - some platers are less fastidious than others - this is part of the approval process to really check when doing supplier approval with platers.
  3. Consult third party metallurgist to examine the products, plating, etc. - there are some technical things having to do with electrical hookups, racking, chemistry, etc. which only an expert (or the plater) can discern and check which can cause myriad plating flaws.
Let's hear what the plating is and its function - there may be other options which have less propensity to cause pitting which can deliver same or similar function.
 
M

MantleMickey

#6
A little more specifics, 440A annealed ground,
after machining, we dip parts in nickel watts bath,
then diamond plate head,
After this process, parts are removed, and we notice
that SOME parts are pitted on the O.D. Very frustrating.
Thanks for your help
MM
 

Wes Bucey

Quite Involved in Discussions
#7
A little more specifics, 440A annealed ground,
after machining, we dip parts in nickel watts bath,
then diamond plate head,
After this process, parts are removed, and we notice
that SOME parts are pitted on the O.D. Very frustrating.
Thanks for your help
MM
I gather from your phrasing you are doing this plating process in house. If you have control, check the nickel chloride component of the bath - too high a concentration contributes to corrosion, even in SS.

As I said in my earlier post, there may be options to explore which will eliminate this pitting condition entirely and still give you the function you desire from the plating.

A major problem we encountered in electrolytic plating was "dog boning" on sharp edges and tapered features of high precision components. When the protection and appearance of nickel was required, we resorted to electroless nickel plating. We found the uniform deposition and durability to be superior to electrolytic nickel. Even better, in functions where components had moving contact with other parts, we found that a preparation with Teflon would eliminate galling.

Plating is not my business - I counted on research and experts to help me solve problems and make my life easier and more profitable.

In the past, I have found reliable leads to solving problems which I then further explored with experts from the manufacturers of the plating chemicals. One source I recommend is reading and participating in discussion in metalfinishing
 
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