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Laser etch coming off after nitric passivation

I work as a manufacturing engineer for a medical device job shop.

We are required by our customers to passivate stainless steel parts before and after laser etch. We are having trouble with the etch being removed after the post laser etch passivation process.

We have the problem mainly with parts made from 17-4 and 455 stainless steel, both normally heat treated to H900 condition. In any particular lot of parts typically 50-1000 pieces), we may see all of them have the problem, some of them, or none. Similarly, sometimes some of the etch on a particular part is removed, while the rest of the etch is unharmed. The problem has been very sporadic and difficult to diagnose.

We have a passivation line set up with Citrisurf products, and this solution works, but we are required by some customers to use nitric. The solution we are using is 45%-55% nitric acid, followed by deionized water rinse and over dry. The time in the nitric acid is 5-30 seconds.

Any suggestions on how to eliminate this problem would be greatly appreciated!

Chris Swailes
Manufacturing Engineer - Sault Ste. Marie, MI, USA
April 22, 2008

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April 25, 2008

Chris

If your passivation process is robust...

Consider tweeking with the laser, or reducing your acid concentration and/or temperature, if the specification will allow it. With a 5 second immersion time, you will have significant variations in exposure time from top to bottom of your rack.

Willie Alexander
- Colorado Springs, Colorado