welding stellite to stainless steel

First reaction would be to TIG weld using an Inconel or Hastelloy filler rod. Hastelloy W is my favorite filler for joining dissimilar metals.

You might be better off brazing. Depends on what it is being used for.

What kind of heat or physical stress is it going to experience?

Have you considered contacting Stellite

and asking, they were quite helpful recommending a grade when I asked and told them what I was doing. The answer may also depend on the type of stellite you have as a casting.

I have a call into manufacturer and hope to learn more. The first fellow was kind of a dead end.... that is why I went to the guys that have done it....

Thank you for your comments. Robby