Summary for 440c passivation callout Discussion
passivation callout for 440c parts: Sean asks what to specify for hardened 440C stainless steel when the machine shop suggests ASTM A967. The reply says ASTM A967 will probably be a good specification if the parts are not orthopedic implants or aerospace parts, but warns that you should not call out a spec you have not read because it can place obligations on the buyer as well as the vendor. The answerer explains this with a hydrogen-embrittlement example from plating, where buyers had to notify shops that parts were hardened and needed baking. The response also notes that ASTM A967 includes options such as citric acid versus nitric acid passivation, so the buyer may need to choose the method that fits the application. The practical advice is to review the spec before using it and decide whether a specific passivation method should be required.
Q. I have a part that is made from 440c (then hardened 56-60Rc) that I want to have a passivation callout. My question is what should be the correct callout. The machine shop suggested ASTM A967. I do not have that spec so I cannot tell if I need to specify anything other than just the spec #.
Thanks,
Sean L [surname deleted for privacy by Editor]
– Mountain View, California, USA
2005
A. Hi Sean. If your parts are neither orthopedic implants nor aerospace parts, then ASTM A967 will probably be a good spec for your parts.
That spec and others are available for instant downloading from the authoring body and from clearing houses. You should never call it out without seeing it though. One of the practical reasons is that such specs can obligate you, not just the vendor. For example, some time ago there was a huge fiasco of components fracturing in the field, with all the attendant costs & dangers, due to hydrogen embrittlement from electroplating. Why aren’t all parts baked for embrittlement relief after plating? Because it costs money and is only required for hardened parts … and a lot of parts (if not most) aren’t hardened. Why didn’t the plating shops know that the parts were hardened and required baking? Because according to the spec that caused the problem, it was not their job to do hardness testing, it was the buyer’s job to notify the plating shop that the parts were hardened and required baking.
The spec you mentioned also includes options such as citric acid vs. nitric acid passivation. There may be a reason for your to specify one vs. the other for your specific parts. And hey, be careful out there :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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