This quest is not available in game.
Collect a Core of Iron from the engine of the Grimrail Depot train [Heroic only.]
There's no point in getting a Core of Flame without any way to focus its power. Somehow, the goblins figured out how to do it - the technology is used in the "Iron Star" engines that the Iron Horde is using extensively throughout Draenor. We're gonna need the biggest engine core that we can find.
Our best bet is to derail one of their trains and crack open the engine compartment. I suggest a raid on the Grimrail Depot...