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  for Metal Finishing since 1989
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Re-passivation of coated stainless steel

I have a brushed stainless steel 301 or 304 part of which I want to be able to hide fingerprints. It has been suggested to me that if I coat this part with a clear coating of some sort that the inherent re-passivation process that occurs in air will be inhibited and the part can possible rust or corrode. Any truth to this?

Thanks,

Adam Steinman
- Glen Allen, Virginia

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Imagine taking a pice of ordinary carbon steel and clear coating it. Will it rust more or rust less? This is the limiting case of how stainless steel will perform when robbed of its passive layer.

Unfortunately this is the short answer. How your stainless steel will hold up will depend on the actual environment in which it is used. The clear coat will stop oxygen from reaching the surface and will stop the autopassivation from taking place. If the part is clear coated and passive to start with, then the passive surface on the stainless steel will remain and autopassivation will not be needed anyway. If the part is to be immersed in water then the situation may well change and the clear coat may not be a good idea and if the part is exposed to a high chloride environment and periodic water then the clear coat is contraindicated.

In short, if the part will remain mostly dry and free of cholorides then the clear coat will be fine.

Good luck

John Holroyd
- Elkhorn, WI

Adam:

You will not defeat the passivation effects if you coat it after the chrome oxide layer has been formed on the surface. However, you always need to be careful when coating any surface. First, you need to use a coating that will not fingerprint in its own right, and the coating many times will peel off after a time and cause an ugly looking surface that is hard to repair with removing the coating completely.

Second, if you get a pinhole in the coating and the surface is exposed to a corrosive atmosphere, you can get an anodic effect that will make the corrosion in the weak spot MUCH greater.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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A clear coating will not harm the repassivation of stainless. You're not the first person in the appliance industry to want to get rid of finger prints on stainless.

The first coating which claims to do this has just been advertised at AK Steel. It's called Agion, I think. It also has an anti-microbal action. Some major appliance people are designing it in.

Dr. Michael McGuire
- Pittsburgh, Pennsylvania, USA