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Passivating Stainless Steel

I operate a small Anodising plant. Lately we have been getting requests from clients to start doing passivating of stainless steel.

I would prefer to do this with Nitric acid as it is always available. 1. What strength should the mixture be and does it vary for different grades of stainless. 2. What immersion period should I use and at what temperature.

Willem Kleinschmidt
- Strand, South Africa

Yo, Willem!

You want to go to astimage.daps.dla.mil/quicksearch/ and get your copy of QQ-P-35C [from DLA] , the old, cancelled, but still informative US Federal Specification on Passivation. It will give you the information you seek. Then, if you decide to continue, you'll want to get a copy of a current specification. In the States they are ASTM A967 or AMS2700, and these are available from the ASTM and the SAE websites. I don't know the European specification for passivation.

You'll also want to take a look at Ted's fine FAQ on passivation of stainless steels.

Good luck!

Lee Gearhart
metallurgist - E. Aurora, New York

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