I tried a few days ago to find on the web properties of X40 cobalt superalloy, which is also known as Stellite 31, also on the Stellite site. I found almost nothing...
here some references :
Superalloys II, SIMS C.T., STOLOFF N.S., HAGEL W.C.( Editors), J. Wiley &Sons (1987)
Metals Handbook...