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Brass staining as result of annealing

C371 brass parts are machined and annealed at 1100 F for 2 hr in nitrogen.
Rapid air or nitrogen cool. The parts (1200 month) are received with black stains.
Can you help me with cause and corrective action.

Steve Ennis
valve and coupling mfgr. - Chestertown, Maryland, USA
2003

What kind of stains are you seeing on the parts? Is the whole part colored? (which implies that you don't have a proper inert atmosphere in the oven) or are there definite stains of another type?

Mark Camilleri
- Malta
2003

First thought is that there is some residue on the parts, possibly cleaning material and probably organic. Second thought is that the furnace operator is not properly purging the furnace before starting the run, or there is a leak in the N2 line . Even tho' it is under pressure, a leak can venturi effect air into the inert atmosphere. With no more information, it is a wild guess.

James Watts
- Navarre, Florida
2003