I decide to test whether or not this thing is invulnerable. I set up what can only be described as complete ownage, then put a hellstone titan in the middle. and then:
It melts.
I am disappoint. Must've got the raws wrong.
Anyway, it was disappointing. For the short period it did not melt, They lopped off limbs like nobody's buisness.
The hellstone code goes into your inorganic_stone_mineral folder. The titan code goes easiest into your creature_standard folder. Make sure you copy the entirety of both codes. You miss a line, it won't work right.
And for the burning blood? No, blood is weakness. Bleeding to death can kill, and blood makes it a living thing, not a construct. Giving it blood reduces it's defense (making it a shell over the less dense blood). A thinner shell could be broken open with sufficient force (bronze colossi can punch fingers and toes off, so while ultra dense and sturdy, Hellstone is not unbreakable). A bronze colossus could crack it open with sufficient effort. Oh, and last I checked, the max temp for anything is 60000 degrees Urist, according to the wiki. I may be wrong.
Oh, and if you can make truly heatproof armor, then make Hellstone hammers and equip your warriors with them. You can have an army of dwarves that melt enemies while they fight. You know you want to.