Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

ASTM A967 spec says passivate it, but AMS2759/8 note says depassivate it

Q. I have once again come across an old drawing that calls out two conflicting finishing notes. One note says to passivate per ASTM A967 and a note further down the drawing says to ion nitride per AMS2759/8 60-65 HRC with a finished case depth of .0025-.0030 on each surface. (Note: De--passivate all parts prior to nitriding).

I am not a finishing expert, but it is confusing when a drawing says to passivate then depassivate for ion nitriding!
I am guessing that I can get rid of the ASTM A967 note & just go with the ion nitride note for finishing. Can these two processes co-exist? Is there a need to?

A. Denny

If I recall correctly, nitrided surfaces should not be subjected to passivating solutions, and be performed after passivation. I believe the 'de-passivation' refers to the areas to receive the nitriding- "....0025-.0030 on each surface".

If the entire part is to be nitrided, then the initial passivation ensures an iron free surface to apply the nitride to, after de-passivation.

Q. Willie,
Thanks for the input, but I am still confused. Let us set up a scenario. You have a piece of Stainless machined to print. You (usually) send the part out for finishing work. It reaches the finishing company, they passivate the part then turn around and de-passivate the part for ion nitriding. Is that how it is done? Do finishing companies passivate then de-passivate for ion nitriding even if you don't call it out on the drawing? Do you have to perform the pass/depass steps to get an SAE-AMS2759/8" --> finish? (p.s. the whole part is being ion nitrided)

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