46079

440C parts rust ten minutes after citric acid passivation  

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Hi, I'm having parts made of 440C passivated following A967 [link is to spec at TechStreet] -01 Citric 4, after being blasted with glass shot. They rust all the time after 10 minutes of cleaning in deionize water and Liquinox in an ultrasound bath.
What is wrong with the procedure? Could electropolishing do a better job than glass shot?
Or is it the passivation that needs to be revised?
Thanks

Marc Thebo
Product designer - Montreal, Canada

In addition to the question, our pieces need to be laser engrave, that is why we are not using nitric passivation.

Marc Thebo
- Montreal, Canada

Your sentence construction makes me wonder if the citric acid is after or before the glass bead.
What is the possibility that the glass bead and the cabinet are contaminated with iron/rust?
Proprietary citric acid works better than home brew. Electropolish works very well on 400 series, but it is another chemical process to maintain and keep up. Time for a cost benefit analysis.

James Watts
- Navarre, Florida

James is correct. There is no reason for the 440C to rust if it is hardened correctly and passivated correctly according to ASTM A967-01 Citric 4. This is done all the time with proprietary citric formulations with excellent results. When done correctly it will not remove the laser marks but will produce excellent corrosion resistance. What hardness are you running??

Contact us if you need help.

Lee Kremer Stellar Solutions, Inc. McHenry, Illinois

So as I am reading, is it safe to assume that once the 440C is heat treated [approx. 45 RcC] that regular Citrisurf passivation will work and no rusting will occur on 440C?

I have had rusting on 440C after blanking and on an "annealed" end of a heat treated part. [Both rust conditions occurred on Non- ht treated material.]

Thank you for your help,
Ted Bouck

Ted Bouck
Medical Devices - Middlefield, Ohio, USA