The characterization of the Grade 91 steel welded joints during creep is an important topic in the energy field. The microstructure in the Heat Affected Zone (HAZ) is complex and leads to premature creep failure in the InterCritical Heat Affected Zone (ICHAZ). For this purpose, interrupted creep tests are performed with industrial creep parameters (600 °C and 100 MPa) in order to follow the evolution of the ICHAZ microstructure. Employed characterization techniques include hardness mapping, electron microscopy (SEM and TEM), electron diffraction (EBSD) and spectroscopy (EDS) analyses. The results provide quantitative evolution of the different microstructure factors during the creep test until the fracture: the disappearance of fine precipitates, substructure and solid solution elements. This change accelerates the plastic deformation, favouring the recovery/recrystallization of the ICHAZ leading to equiaxed fine grains microstructure.