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Passivation Of 416 Steel

Hello Passivation Experts,

When I do passvation on 416 steel to QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil] type II the parts always come out discolored "like a Dark Black" and not very goodlooking cosmeticly. Is this normal for 416 steel or should I try another type of passivate on the 416 steel that would pervent discoloration?

Thank You in Advance,

Hello Kevin!

You first want to check out the FAQ on the topic, at www.finishing.com/faqs/sstpass.html where you'll find you are not alone. Reading the FAQ, you'll also notice that all of the problems are occurring in Type II baths- the one with the dichromate added. So, we've gone to a type VIII bath: no dichromate, no etching problems, fine stain test results.

Good luck!

Kevin:

Excellent results can also be attained without discoloration by using the correct citric acid formulations. Citric 4 in ASTM A967 (which replaced QQ-P-35c) works well with the correct solution.

We would be happy to help you with this if you need it.

Regards,

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