STEEL
1: Put Iron ore/ingot in blast furnace(with limestone and coal)
2: Put resulting gray iron in bloom with coal

MITHRIL
1: Put Mithril ore in blast furnace(With limestone and coal)
2: Put result in bloom with Zyrridum clump
3: Put again with Coal

IGNOTUMITE
1: Put Ore on anvil and hit with hammer
2: Put result dust in blast furnace(with limestone and coal)
3: repeat step 2
4: put in bloom with coal

IRON
1: Smelt ore into wrought iron
2: Wrought Iron + limestone = Iron

Temperatures for ingot heating
Bronze:Any
Iron/Steel/Mithril: Coal with bellows
Ignotumite/Dragonforge: Lava or maybe blazerods with bellows