Metal finishing Q&As since 1989

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Shot peening with stainless shot, then electropolishing?

2006

Dear All

We are currently produce 304 stainless steel furniture with stainless shot peened surface.

We passivate them with Nitric acid, carefully follow ASTM A967, but the result is not yet satisfying. We cannot change the grade to 316 because of the cost issue.

So we are heading toward "Passivation by electropolishing" after shot peening.

Have anyone tried to do this kind of thing before?

As far as I know electropolishing will make the surface smoother....The major problem is we do not want the surface to be shiny chrome-like...We really want it look like the way it is but a bit shinier and improve its corrosion resistance.

How can we make a shinier and more corrosion resistance without smoothing the whole surface?

Really need some advice.

Kelly J.
Furniture - Thailand

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2006

Kelly,
It is true that electropolishing improves the anti-corrosion properties of stainless steel, though of course it is through a different mechanism than what acid passivation provides. citric acid based passivation can offer better corrosion resistance than the nitric equivalent without affecting the surface finish the way that nitric passivation or electropolishing will. Let us know if we can help you.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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2006

Glass bead blasting will give a smoother, more corrosion resistant surface than peening. Still textured enough to hide fingerprints and diffuse reflections.
Follow with either nitric or heated citric passivation.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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2006

Thanks for all your suggestion.
The problem is our customer doesn't want us passivated by Nitric or Citric anymore.So we really need to do electropolishing,eventually.

It's just my curiosity that if the surface is not totally shine and smooth, as the usual electropolished finished should be, will it have any effect on the corrosion resistance?

Thanks again for your support.

Kelly
- Thailand

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Dear Sir

Although I haven't seen the process done personally, I am looking into it for some automotive accessories that I'm manufacturing in Thailand. I'll be able to confirm this to you in the near future. From what I've seen it will increase the shine but not remove the sandblasted effect (satin finish).

Kirk Riddell
- Banpong, Ratchaburi, Thailand
2006