17-7 PH Stainless as a Contact Material?

Hello,

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?

Thanks,

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.

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.