In this study, the effect of severe plastic deformation on grain size refinement and mechanical properties of a coarse-grained steel was investigated. The experimental material used in the present investigation was advanced tungsten modified 9 %Cr P92 steel. The coarse-grained state of P92 steel was deformed at room temperature by high-pressure sliding or high-pressure torsion. The microstructure was investigated using Tescan Lyra 3 scanning electron microscope equipped with an electron-back scatter unit. Severe plastic deformation at room temperature led to grain size reduction down to sub-microscopic level. The grain size and hardness exhibited significant changes to the equivalent strain of about 10, and slight changes between the equivalent strains of 10-20. Equivalent plastic strains higher than 20 only led to insignificant changes in the mean grain size and hardness. The creep behaviour of the ultrafine-grained state exhibited the minimum creep rate of about two orders of magnitude greater when compared to the coarse-grained P92 steel.