Dis-Hell's Crucible.

[TheMenacer]

Personally, I'd cut the straight demonic units. I really like the theme of hell's forges on earth, but I think I'd be a bit happier with it if it was a human nation that was made up of these fantastic smiths and machinists that pay a terrible price for their talents, or perhaps a people that worships their machinery and invites demons to possess it although that might be a little too blatantly inspired by Warhammer 40K's Machine Spirit, something like that. Maybe there could be plenty of demon units, but I'm seeing recruitable demons as fitting more into an early-middle age nation and given the mechanical theme I'm seeing this as a late age nation.

The furthest I'd go in having recruitable demons is the manes, which sounds like a pretty cool unit, and I'd definitely make them sacred to reduce their numbers.

Other than that, the summons sound cool as hell, infernal machine and furnace golem especially. I also really like the idea of a unit that you can only get via PD.