Passivation of 304, 305 and 384 Steel

Question:

If this is true then what is recommended? And why? (Aerospace application). J.K.

We manufacture (or have manufactured) fasteners for many different applications including military, aerospace and automotive. One fastener that we produce can be made of 304, 305 or 384 steel. The part calls for passivation per QQ-P-35 TYII. These parts have been produced for a few years now and passivated, by outside venders, and they have certified to the QQ-P-35 TYII specification. We have now moved to a new vendor and they are stating that you cannot passivate this material to QQ-P-35 TYII.

Is the statement true that you cannot passivate the 304, 305 or 384 steel to QQ-P-35 TYII? (Vender is recommending using TYVI or TYVII)

Answer:

I was not familiar with that specification and had to do a little searching to find information about it. As it turns out, it could be that both shops are correct. At the time you started having this passivating done by the outside jobshop, it is possible that they were performing the process to the QQ-P-35 specification. The search that I did, however, indicated that the specification was cancelled on September 11, 1998. So that is likely why the new vendor indicated that they cannot passivate the material to that specification. The cancellation notice indicates that future references should be made to ASTM A967 or SAE-AMS-QQ-P-35.

From the information I found, it looks like the original QQ-P-35 specification was for a nitric acid-type passivation only. The 1999 version of A 967 contains table X1.1 in the appendix that recommends passivation treatments for various types of stainless steel. All options noted are nitric acid based only. More recent investigations have focused on the more environmentally friendly and worker safe citric acid for passivation. The ASTM A967 specification does allow for the use of citric acid passivation procedures, however it is not clear if that is allowed for DoD or aerospace use, as this was the primary audience for such federal specifications in the past.

Note that the conclusion of research recently done at Boeing stated “Citric acid solutions used in this evaluation are as good as or better than Type II and VII nitric acid solutions specified in AMS-QQ-P-35 for removing iron particle contamination and passivating wrought stainless steel alloys.” (Gaydos, Plating and Surface Finishing, March 2003, p. 20-25). It was also explained that the Type II solution contained sodium dichromate in addition to the nitric acid. Considering the hazards and potential environmental risk of the use of this chemical, that could be the another reason for the other jobshop to not offer the process.

Update: For more information on this topic Click here.