I doubt anyone on here has tried this, so i will share.
I bought an Oxford disc lock a few years back for my stepson (who never uses it). I have bought myself a Yamaha 115 Delight to get to work and back. I used the Oxford disc lock and found that the pin was a bit big to go through the hole in the disc, but I pushed it in and it locked.
Went to unlock it this morning and because it's such a tight fit, it wouldn't pull the pin back. No room whatsoever to get anything in there and I had to get to work, so I got out my angle grinder. It took me 20 minutes, and nearly a whole grinding disc to get through it. I was very impressed (but annoyed that I'd actually forced it on there in the first place!).
There were no sparks, so it must be some sort of metal mixed with something that can resist an angle grinder very well. I would buy another one to replace it but I'll have to get a different style to fit through my tiny scooter brake disc