Oil stains after heat treating

Blacksmithing Troubleshooting
1

Hey there, I’ve been making some knives and I recently heat treated and tempered my blades, but I made the terrible mistake of using burnt motor oil to do so and the oil stained my steel, huge stains the I have not been able to remove. Does anybody know how to remove them? Has it ever happened to anyone?

Thebes for reading and I appreciate any advice I can get

2

Have you tried a metal wire wheel on it? I use spent oil pretty often, but it doesn’t cake on. It’s it pretty thickly caked on? Any pictures of it?

3

Etch over night in white vinagre, and the scales comes straight off by gently rubbing