As far as I can remember my physics lessons, the state of an element (Solid, Liquid, Gas) depends on temperature and pressure in such a way (approximatively): p ^ | + + | + L + | + + | + + | G + + | + + | ++ | * S | + | + +-----------------------> T where * is the "triple point", that is the only couple (T,p) where the three states exist together. I don't know where we could find this diagram for iron to see how pressure can influence melting and boiling temperatures (that is to put values on this diagram).