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Citric Acid Passivation Of Laser Etched Stainless Steel

Citric Acid Passivation Of Laser Etched Stainless Steel

Citric Acid Passivation Of Laser Etched Stainless Steel

We currently laser etch stainless steel (17-4) for medical applications.  After laser etching, we follow with Type II nitric acid passivation at ambient condition/temperature.  The intent of the passivation is to remove free iron from laser etched area, which could create a rusting issue if left in nonpassive state.  

In an attempt to reduce hazards and flexibility, we are looking at citric acid passivation per ASTM A-967.  In testing, we are noticing that the citric acid is not as effective as the Type II nitric acid passivation on the laser etched areas.  The laser etched areas don't pass the copper sulfate test.  We have had some samples that have passed the copper sulfate test, but the laser etch is completely removed.

Here are my questions.  Has anybody dealt with this issue before?  Is it possible to achieve success with citric acid passivation of laser etch?  If so, then how is then done in a way not to completely remove the laser etch?  Is there an adititive used like a mixed acid blend to have success?  You input is appreciated.  

RE: Citric Acid Passivation Of Laser Etched Stainless Steel

Lots of people have this problem, but there's no easy solution.  Technically, the presence of laser etch marking (unless masked off) violates passivation requirements -- all high T oxidation should be removed before or during passivation.

Some people passivate before laser marking, handle carefully (white cotton gloves) during marking, and then only do a 'light' passivation afterwards.

Others play around with laser settings.

Suggest asking Stellar Solutions how to citric acid passivate w/o removal of  laser marking.  They have several passivation formulae:

RE: Citric Acid Passivation Of Laser Etched Stainless Steel

Are you using a prepared Citric solution with sufactants and chelating agents?
If not try one.  CHP CitriSurf is one that comes to mind.
Even heated it will not do the same job as nitric.

You aren't just passivating.  Your situation requires that you actually lightly pickle the part edges.  If all oxide and Cr depleated metal was gone then the citric would work fine.

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