One of the leading areas of research in the energy sector is the improvement already established and much applied materials, with a focus on exploring new ways to extend the life of materials in demanding environments. Unique properties such as high corrosion resistance, mechanical properties and machinability are required for materials used in various energy materials applications, including fusion. Recent years have also seen the development of magneto-optical characterisation techniques, in particular the magneto-optical Kerr effect (MOKE), to investigate the microstructural and correlative mechanical properties of steels. The method allows the study of magnetic properties emanating from the surface of the material and allows correlation with the bulk magnetic properties of the material. In addition, the use of cryogenic processing (CP) is a novel process for improving the properties of various stainless steels. During CP material is exposed to sub-zero temperatures, which are fundamentally causing changes to the properties (hardness, toughness, strength, corrosive resistance, magnetism etc.) for instance of stainless steel. This study investigates the induced microstructural changes of ferritic-martensitic stainless steel in relation to changes in corrosion and magnetic properties. Results on corrosion performance and magnetic properties indicate the importance of microstructure for explaining changes induced by CP. We present, that high-resolution MOKE microscopy can be applied on stainless steels for microstructural characterization such as morphology of ferrite/martensite, identification of austenite and carbide grains without using etchants. Furthermore, the increased precipitation and restructuring of the matrix within the CP samples is expected to play an additional role in potential weak points during exposure to corrosive environments. As such, the newly obtained microstructure has higher dimensional stability, which could also play an important role in prolonged functionality of stainless steels in high demanding environments, such as fusion. Finally, the CP modified material has unique properties that can only be achieved with CP, when considering the processing time and energy.