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Passivation of Stainless Steel after Chrome Plating
adv.
Q. Dear Readers,
Can I eliminate the passivation treatment of 17-4PH cast stainless steel after heat treatment, at the casting house, if the machined parts are going to be chrome plated? Doesn't the chrome plating process strip off the passivation layer during pretreatment and then re-occur during the final stages of the chrome plating process? Some regions of the part are chrome plated.
Thanks for your response,
Aerospace - Greenville, Ohio
2003
A. You do not need to passivate the stainless steel casting prior to chrome plating.
Toby PadfieldAutomotive suspension modules - Michigan
2003
A. Chemical cleaning may be helpful for this process, but passivation is not needed. You are right in that the passive layer will be removed in the activation treatment before plating.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
2003
A. The OP notes that some regions are plated, which I take to mean that some areas will be masked off. If a region is masked off, and thus protected from the bath, I suspect that there will be surface iron that will allow rust spotting more readily than a passivated piece.
Wyndon Evans- Lago Vista, Texas
August 8, 2016
Q. If there are masked areas that require passivation can it be done after chrome plating?
Ruth Neal- Farmingdale, New York, USA
August 21, 2017
A. Hi Ruth. Although it might be possible to put chrome plating into a passivating solution with minimal damage, I'm not sure, and it would probably depend on the type and thickness. Hopefully another reader has experience with it. Please explain your situation because it strikes me as more practical to passivate the whole item, mask the areas you don't want chrome plated, do the chrome plating, then remove the masking. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 2017
Q. Hi Ted,
Our plater overlooked passivating before plating; we are hoping to avoid having to strip the parts just to ensure a small exposed area has passivation. Thanks for your help!
- Farmingdale, New York, USA
August 22, 2017
A. Ruth,
I don't see why not. You'll have less risk of damaging the chrome using citric passivation rather than nitric passivation.
Chrome plating stainless steel they way you describe seems like a curious thing. Is there any reason it couldn't be mild steel with 100% coverage of the chrome plating, or stainless steel that is electropolished rather than plated?
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
August 23, 2017
Q. We are having staining on our parts but only on C-455 components. We are at a loss as to what's causing the staining after passivation.
My question is, the parts are ALREADY chrome plated. Is there a need to passivate them?
Arthrex - Walnut, California, USA
September 11, 2018
A. Hi Ron. Your question is a bit brief and thus perhaps subject to misinterpretation. The component is chrome plated (no nickel underlayer?) over its surface (100% of the surface, no exposed stainless steel)? Then you passivate the chrome plated surface (nitric acid or citric acid)? And it becomes stained (rust colored, black, white, yellow)? And you are asking whether the passivation step can be skipped to prevent that staining? Thanks.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2018
Q. Thanks Ted. I actually misspoke. I got the wrong information. Our parts are NOT getting passivated after chrome plating.
As far as your other questions are concerned, we do use citric acid to passivate and the staining looks like rust but it is not red oxide in appearance. The C-455 gets darkened. It only happens on the C-455 components whether it is being passivated by itself or with 17-7, 17-4. We tried to change the cleaning solution more often and the passivation solution more often but we get mixed results with some stained and some perfectly fine parts. We've tried not changing the solutions and we get similarly mixed results. Appreciate any feedback you can provide.
- Walnut, California, USA
September 11, 2018
A. Ron,
Passivation in this context means removing iron from the surface. This is necessary for stainless steel and for non-ferrous alloys that have been contaminated with iron by an outside source. However, a freshly plated part should have a surface composition of only the plated material. Therefore since there is no iron to remove, a passivation treatment is superfluous.
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois
September 14, 2018
adv.
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