Valve seizure in automotive application (stellite galling issue)

[andyrich]

Hi,

I am experiencing a problem with a valve seizure on a high temperature (600ºC) automotive application. The shaft is stellite 6 which is being used in a 420V vanadium stainless steel bushing. The valves are seizing, and examination of the surfaces seems to show that this is due to galling.

Has any one seen any similar issues or these materials, or has anyone any ideas on a more suitable material choice?

Thanks
Andrew

 

[JimCasey]

Usually Stellite 6 is quite resistant to galling, even when running against Stellite 6. I am surprised to hear of your problem particularly with dissimilar metals.

Have you looked at your coefficients of thermal expansion? Possibly your clearances are closing up as the assembly heats up.

 

[btrueblood]

What hardness is the 420 bushing? If you can increase it above ~ 45 Rc, you might try that.

Also, consider changing the bushing to a Nitronic 60 alloy. If you can get ahold of a copy of Electralloy bulletin E-60, "Nitronic 60 Stainless Steel", it has a wealth of information on galling resistance of various materials. Interestingly, N-60 has somewhat worse gall resistance than Stellite 6B at room temp., but much better resistance than 6B at high temperatures (1000 F). Unfortunately, the bulletin lists no data for type 420.

 

[btrueblood]

Oh, and you may want to try posting your question in the tribology and/or metallurgy forums, both of which might get a bit more traffic from people with a lot more knowledge in the area of gall reistance.