Ferritic/Martensitic materials such as T91 (9Cr–1Mo) and HT-9 (12Cr–1Mo) are candidate materials for nuclear reactor fuel cladding. In order to ensure a full understanding of these materials microstructure in this study a comprehensive characterization of these alloys was conducted. A heat of HT-9 and T91 was produced and the micro-structural changes from the as cast state to the final heat treated sheet product were characterized. Metallography revealed an overall picture of the different microstructures while neutron diffraction performed during the materials heat treatment revealed insight about texture, thermal expansion and transition temperatures. 3D atom probe showed the exact overall composition and the local composition the carbides formed in the material.