17-7 PH Stainless as a Contact Material?(2001)
I am working on a new part which is composed of a stamped spring made of 17-7 PH stainless in contact with a chromated aluminum tray. Though this does not have to be a high reliability electrical contact, I am relying on some degree on conductivity (ground return path).
The material is formed dead soft, then heat treated to a Yield of around 150 KSI. The heat treatment is supposed to be done in an inert gas environment.
After heat treatment, the surface of the metal changes from a normal bright stainless color to a dull grey (military looking) finish.
Does anyone know if the heat treatment significantly effects the conductivity of 17-7 stainless, especially on the surface where discoloration is apparent? If there is a surface effect, is there a process which could be used to restore surface conductivity?
Finally, has anyone out there seen 17-7 used in an application that requires electrical performance or any degree?
- Pullman, Washington, USA
The dull grey is usually an oxide layer. This will definitely lower the conductivity of the surface. Abrasive cleaning may remove this tenacious layer.
To keep a stainless clean, do not simply use a "nitrogen" atmosphere because the water vapor will react with the steel. I would suggest a reducing atmosphere with at least 75% hydrogen. This will keep the surface bright and reduce the thickness of the oxide layer to a minimum. Many heat treaters have this capability. If your local one does not check around on the net for the closest one that does.Paul Bruessow
Eaton - Myakka City, Florida, USA
Hydrogen is not that great of a reducer at the aust. or aging temp. a vacuum of 5x10-5 torr or less will produce a much cleaner part.Mike Momo
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