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420 corrodes around laser etching

I am having a problem with corrosion on surgical instruments. We make cutting instruments using SS 420 which is machined, laser marked and then citric passivated. We are having a hard time getting the laser marked areas passive. We are getting the corrosion after repetitive autoclave (steam sterilization) cycles. Any ideas?

Chip Rauch
- Fort Lauderdale, Florida, USA
 

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Chip:

You need a more aggressive passivation process. Citric will not do anything to an area that has heat scales such as the etched areas of your product.

Dan Weaver
- Toccoa, Georgia
 

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Chip:

You need to use the correct citric acid formulation. Major surgical instrument companies have found that proprietary citric acid formulations give 80% reduction in corrosion and rejects. There are companies that specify ONLY citric formulations for their surgical instruments. Contact us and we can tell you how to do it.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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So Dan,

What do you recommend as a more aggressive passivation. We used Nitric previously without achieving any better results. We also tried Citric based product, and that didn't help either.

Chip Rauch
- Fort Lauderdale, Florida, USA
 

There really is no way out of the corrosion problem that you are seeing with the 420 as it is inherent in the laser marking process. You could laser mark hardened and passivated 17-4, which is more corrosion resistant than 400 series, and you get the same problem. When I design instruments, I typically only laser mark in non-critical areas unless the material is 304 or 316. Even with those, you can still get corrosion. It really is only a question of how many autoclave cycles until it becomes a problem.

Martin Padget
- Valencia, California, USA