Destroy a Fel Reaver in Hellfire Peninsula and plunge the Unfired Key Mold into its remains. Bring the Charred Key Mold to Dumphry in Honor Hold.
It's not working, lad . I cannot give it enough heat... the materials will not be properly tempered.
You know, the fel reavers used by the Burning Legion are powered by a scalding core of fel fire - it burns much hotter than normal fire.
If you could find enough people to take one down, you could heat the mold in the insides of the fallen reaver. Beware, <class>, those fel reavers pack quite a punch.