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Re-Machining of part that has been passivated to ASTM A967

Gentlemen:
I have a situation where a finished passivated part needs to be reworked (re-machined) in a few locations. I need to know if I use a "Tungsten Carbide" cutting tool and no cutting fluid, is the part still acceptably passivated (to ASTM A967 ) since we will not be introducing any "Ferritic" materials to the surface of the part? The material is 13-8MO, stainless steel. It was heat treated to condition H1100 after machining but before passivation. Is there any specification that can be specifically cited regarding this situation?
Sincerely,

Jon B. Shereshaw
tool company - Branchburg, NJ
2005

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I believe you will find that all passivation specifications require that passivation be done after all machining has been done, so if you do additional machining, you will have to repassivate. It isn't just the removal of iron which has been smeared onto the surface, but also iron which may have been exposed during machining.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2005

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Machining with carbide tooling should give surfaces that are free of "free iron", and thus the surface of a good grade like this should be pretty good. HOWEVER, it will not meet the requirements of ASTM A967, since this requires passivation after machining.

As the previous responder has stated, passivation is a combination of a lot of things, not just removing free iron smeared onto the surface in processing. It is cleaning and chromium enrichment of the surface. If you want the optimum in corrosion resistance you will always passivate to optimize the chromium content of the surface. In a grade like 13-8MO you have a lot of factors helping to give you good corrosion resistance, but passivation is always recommended.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2005