How do I get this “crust” and rust off of here?
Have you tried a paste of baking soda and water? I’ve had good results with that on other kinds of cookware - leave the paste on for a half hour or so, and then scrub it off. I usually use salt as a scrub for my cast iron. (And soap, sometimes, shhh.)
I haven’t done anything.
Based on my (little) experience…
Surface rust comes off with water, very little soap, and a non-scratch scubbie pad. Dry and lightly the oil IMMEDIATELY.
That crust probably ain’t coming off unless you use some pretty drastic measures to strip seasoning (which you can find on the internet). Even taking a sander will not work (at least, it didn’t for my partner).
Some of those methods are vaguely dangerous, so, if the inside of the pan is smooth and non-rusted, I’d leave well enough alone, TBH.
I haven’t tried this myself, but a friend swears by external soaking of the pan in Coca-Cola for 28-72 hours. Apparently the relatively acidic pH of Coca-Cola (at a pH of 2.52) does wonders.
Again, just passing on a a tip from someone else - one I haven’t used myself in the past. Caveat emptor: YMMV.
I have used the second method here,https://kentrollins.com/how-to-restore-cast-iron/, with good results. Just be aware that you will have to completely reseason your pan.
Of course let it cool off completely before you touch it!
Some other methods: