Blackrock Foundry is spread into 3 wings bosses each, then Warlord Blackhand is in "The Crucible" by himself.

Wing 1 - Slagworks (Gruul, Oregorger, The Blast Furnace)
Wing 2 - The Black Forge (Han'sgar & Franzok, Flamebender Ka'graz, Kromog)
Wing 3 - Iron Assembly (Beastlord Darmac, Operator Thogar, Iron Maidens)

Please note the Iron Maidens appear on "The Black Forge" part of the map, but they are the final boss of the "Iron Assembly" wing.