Originally Posted by KnhoJ

Cutting that lock took a fair bit of work, the cut shows a lot of impatient seesaw action with the saw. The surface of the cut also suggests that the material was removed very slowly, that saw wasn't knocking loose nice clean chips, more like little grainy specks, I'd bet. And over enough time to reduce at least some of the kerf to powder, which would produce that rust right away. You can even see the rusty dust worked into the plastic of the lock.