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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
+++++++ -- 1st of two
simultaneous entries
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
+++++++ -- 2nd of two
simultaneous entries
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
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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.
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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


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