Iron stains bleeding thru silver plate on 410 SS

[capntom62]

Hello:
Newbie here.
We are an Aerospace mfg and just received parts back from Silver plate (AMS 2410) and we are seeing what appears to be iron oxide bleed thru in the root of the threads on the inside diameter. Diameter is Ø 7.000. I sent one piece out for chemical analysis to see whether it is Iron oxide or some other contaminant.
Any suggestions ?
We also are seeing similar spots on the parts after they have been stripped of coating.
If it is free iron oxide, can we passivate before plating to clean the surface ?
Of course the plater says his tanks are "clean" and nothing has changed.........

 

[hacksaw]

it has iron in it so you can get iron oxide on the surface but generally considered harmless

 

[bimr]

Contamination by Mild Steel

Corrosion initiation from mild steel contamination may occur when the protective oxide film on the stainless steel is broken when carbon steel has contacted the stainless steel. This contact creates a mild steel/stainless steel interface which is a corrosion cell.

The carbon steel contamination may be at the outer surface of the oxide film on the stainless steel. Then, under moist conditions, the mild steel will corrode and cause both oxygen depletion and ionic concentration beneath the ferrous deposit. These latter effects destabilise the adjacent oxide film on the stainless steel, which then readily corrodes.

http://www.azom.com/article.aspx?ArticleID=1143