It is proposed that the lattice parameter change at high temperature is measured for a mix of 316L and SA508 grade 3 steel powders, by means of neutron diffraction in High Resolution Powder Diffractometer (HRPD). The change in lattice parameter occurs as a result of the diffusion of substitutional elements from 316L to SA508. The temperature and dwell time of the experiment are selected in order to simulate the conditions present during the Hot Isostatic Pressing (HIP) manufacturing process, with the aim of predicting the time required for homogenisation of the microstructure.