It’s not warped or cracked ... it’s just got this pebbley, blistered stuff on the interior surface.
Some of it is light and flakey and I dusted that stuff off...no problem underneath it.
I have a chain-mail-wrapped-around-a-sponge for nasty crusty mess.
Works great. Then a stiff brush, some canola oil, and some time in the oven.
Was it a polished surface or a plain cast surface?
You might start with a wire brush on right angle grinder. It might remove some of the damaged metal. I’ve done this where old cast iron skillets had irregular seasoning coat. I brushed the seasoning coat away and re-seasoned the surface.
I have one cast iron skillet that had a crack on outside edge when I bought it. Did not notice it at first. So I used a nickel alloy welding rod and welded the break and ground the surface smooth. Still works fine.
If that does not polish it up, you might try polishing it with a very fine flap disc on the right angle grinder.
What ever approach you use, you will have to season the surface again.
I have used a mixture of 9% vinegar and TSP and soaked old corroded axe and hammer heads and even pliers and wrenches. I usually soak then from 2 days to a week or more. rinse them and polish with a wire brush.
That technique will also clean and sharpen old files. They will cut much better, but the stock removed is irregular, they will load up with metal more quickly.