17-4PH corroded after EDM. Fix by Passivating? 1

[NuclearNerd]

Hi all

I've run into a new problem. We often spec 17-4PH for hardened parts that must stay operate in a fresh water environment. For the first time, I machined the part using EDM before heat treatment (to H1025). After immersion, the EDM surface shows significant corrosion, as shown in the picture.

I'm assuming the high temperature process sensitized the surface of the metal, in the same way that welding does. We normally passivate parts after welding, but is that enough in this case? Should I be trying to pickle the parts to remove more of the affected material? Will that be enough to restore the corrosion resistance of the EDM'd surface?

 

[EdStainless]

Significant? All I see is some surface blushing. Is there pitting?
Yes, it is related to surface damage from the arcing, probably not sensitization from EDM but more likely related to the surface texture.
You should clean before aging, perhaps even pickle. I don't know if a passivation will be enough.

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Plymouth Tube

 

[NuclearNerd]

Right, it is only surface blushing now (no pitting), but it's only been submerged for a few months. The expected life is many years. I'll try the pickling route.

 

[EdStainless]

You might also look at a light mechanical surface prep (flap wheel?) and then passivate, doing this prior to aging.

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Plymouth Tube