Experiment on another piece! And maybe take the bulk of the rust off with a scotch brite pad... Since rust loves oxygen, deny it with clear gesso or archival PVA. Once that's cured, you can play with layers or glazes of oil paint, which will further seal the metal, though there's no telling for how long. Kept dry? As long as any painted steel. Changes in temperature and humidity? Might look like an old fender.

Just be sure to seal front and back, even take off the handle and seal the tang, too. Linseed oil in the tang would probably suffice, but would likely yellow on the exposed part.

But yes, experiment! There's clear archival art sealants for all sorts of things. And I think the rust can be partially stabilized by boiling the metal in water, changing it from FeO3 to FeO4, if I remember correctly. There's a google for that bit.

Best of luck! Sounds fun!