I posted earlier in this thread that I just throw rusted chains in the bottom of my gunk tank and let them lie there for months and check them later. Well, I was looking for a misplaced part this weekend and discovered two chains I had forgotten about. Pulled them out and got almost all of the links freed up just by working them by hand. Threw them back in. They will be good enough to run on a bar for the final cleaning and then I'll sharpen them. These are chains I found in a half filled bucket of water lying in the woods of an area I was cleaning up for a friend. Seems a shame people don't take better care of their assets. They are dull but have lots of tooth left or they would have already been in my scrap bin. I'm sure i have a saw and bar they will fit although I don't know what size they are yet.
What I have used (not recommended for saw chains) to clean up small rusted parts such as large quantities of screws or nails is a concrete mixer. Just dump them all in and tumble them for 20 minutes (dry). works like a charm. I had acquired boxes of nails that someone left outside and they got pretty rusted. This made them useable again.