mechanical welding of stainless steel fasteners

[Tom80]

I have an application in which a 10-24 stainless steel allen head screw is fitted to a stainless steel plate nut. I am experiencing a failure mode in which the allen head screw becomes stuck or welded to the nut. I am not using any loctite or other threadlocking material. The weld is so strong that a mechanical forced removal of the screw results in stripped out threads when considerable force is used to separate the two parts. A cross section of a failed part showed some evidence of the welding. My question, is this a documented failure mechanism of stainless steel hardware, and what can I do to prevent the mechanism. The application is aviation equipment and vibration is possible.

Thank you.

 

[kenvlach]

This process is know as 'galling.' Stainless steels are characterized by a very thin, invisible oxide layer. When SS-to-SS threads are tightened, this oxide gets sheared away and cold-welding of the 2 SS parts occurs. Very common. Methods of preventing include lubrication, plating of the male threads, choosing SS alloys of dissimilar microstructure (e.g., austenitic & martensitic), adding N to the alloy (basis of Carpenter Technologies' 'Gall-Tough' alloys), nitriding the male fastener, etc.

See THREAD GALLING
thread367-31365

Galling on stainless steel thread under seawater condition
thread338-52413

 

[boo1]

Anti-sieze should be used or change hardness of one of the parts. Consider changing fastener material to Nitronic 60 for superior gualling resistance. Wear and Galling resistance are increased using this material, especially when self mated. Corrosion resistance is similar to 304, with twice the strength of 304 or 316. See

http://www.gocarlson.com/AlloyPDF/Nitronic60.pdf

 

[Tom80]

Thank you for your replies. It is most appreciated!

Tom80