I thought fel iron was corrupting because it radiates fel energy?Eh, let's not be underestimating the new metals that start forming as a result of everything that went on. Fel Iron is basically safe to use as long as you don't put it to use for demonic purposes, and Adamantite is really nice. Khorium is also incredible.
I mean, taking aside the constant progression of stuff, Khorium-alloy is one of the toughest, most magically conductive materials in the setting. Elementium is the only thing in it's league.