I have read about casting stainless steel in the firearms industry.
From what I learned, stainless steel can not be melted into a liquid,
or even a pasty state. The method used is to mix powdered stainless
steel with a binding paste, inject that into lost wax moulds, bake
the binding paste to solidify the casting, remove the casting then
heat to near melting point in order to burn out the binding paste and
sinter or fuse the stainless steel particles. There is a lot of
shrinkage in the last process, but the industry boffins have it
worked out so that the final product is amazingly accurate and well
finished. The resulting stainless steel is very strong, but is
microscopically porous and not completely "stainless". Cold or hot
working may eliminate the porosity.
Try seaching for "lost wax sintered casting", I believe it is also
used for casting other non-castable metals like tungsten.
Good luck in your endeavour,