In order to appreciate the effects on an element of changing
the temperature and pressure, a phase diagram must be consulted.
Figure 5.7 shows the phase diagram for Fe; each line
on the diagram is a phase boundary and crossing a boundary
(i.e. changing the phase of the metal) requires a change of
temperature and/or pressure. For example, at 298K and
1 bar pressure, Fe has a bcc structure (a-Fe). Raising the
temperature to 1185K (still at 1 bar) results in a transition
to g-Fe with an fcc structure. A transition from a- to g-Fe
also occurs by increasing the pressure on Fe maintained at,
e.g., 800 K.