After the magnet test, carefully scrape the edge of them to see what the base metal is. Based on that, you can decide which method is best to remove the outer crust.
Seriously, those do look like some sort of coinage, but that looks like iron rust, not precious metal. I wonder if they may have been tokens of some sort -- possibly political or advertising tokens. Maybe game pieces like checkers? Just throwing out some ideas.
Hmm, as said above my first thought was electrical knockouts. But those are way too thick and of the wrong material. As for coins.... any precious metal wouldn't be covered in rust like that. Definitely try to clean them up and see what's underneath, though. They may be junk, or they may be a good find. This is the only thing I could find that could be a possibility. Thoughts? https://www.store-chateauversailles.com/en/child/toys-and-games/cast-iron-disc-game