Figure 5: Changes in the neutron diffraction signal as a function of time and temperature for a HT-9 steel (after [63]). Some diffraction peaks of the ferrite (bcc) and austenite (fcc) phases are indicated. The disappearance of the ferrite and concurrent appearance of austenite peaks with increasing temperature as well as the change in peak positions due to temperature changes are visible. Data analysis allows to quantify these effects, for example, determination of volume fractions and lattice parameters/coefficients of thermal expansion of the two phases.