Board Thread:Lore Discussion/@comment-12481512-20130717104617/@comment-30388866-20151224064204

If I had to make speculation, the metal could have possibly be something that can withstand magma, as the Forgemaster did.

So, it could have been something that involves iron, nickel, titanium, tungsten or even a combination of these. Though, to be fair, this could just be referring to the Forgemaster's own construction as it could withstand the heat, but the other machines in the same area around the Atherium Forge were warped.

Perhaps the "lower tier" machines were made with less sturdy materials while more important ones (such as the Forgemaster) were created using stronger materials.