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Q&As since 1989
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Cast 17-4 material does not passivate well
Intro / synopsis: Investment cast parts are difficult to passivate, but it can be done with citric acid solutions. However, passivation should not be done until after heat treatment.
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Q. We receive cast 17-4 handles from an investment caster. We bead blast the handles to achieve an ok surface finish. If we passivate at that point the handles get a frosty look causing us to bead blast again. But this time the bead blasting gives us a very nice appearance. What is happening to the 17-4 at passivation? They have not been heat treated.
Can I skip passivation after I have bead blasted?
Thanks.
connector products - Waynesboro, Virginia, USA
2005
A. Investment cast 17-4PH parts can be a real problem to get passivated so that they will not corrode and discolor, but it can be done. We have been very successful at many companies in getting the bead blasted parts passive using special citric acid formulations. Standard passivation formulations do not seem to work well normally.
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
A. If they haven't been heat treated, they are still in un-useable condition. They do not have the intended mechanical properties or corrosion resistance potential until they have been heat treated. Heat treatment will destroy the effects of passivation, so you should delay passivation until last.
Bill Reynolds [deceased]
We sadly relate the news that Bill passed away on Jan. 29, 2010.
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