To study the influence of shear deformation on the evolution of the microstructure and the mechanical strength in rail steels, three steels with different microstructure (two pearlitic, one bainitic) were deformed by High Pressure Torsion (HPT). In order to evaluate in addition the effect of the strain path, a cyclic form of HPT was applied. The mechanical strength was determined by means of in-situ measurement of the flow stress and microhardness measurements. The differences of the mechanical strengths between the monotonic and cyclic deformed samples clearly indicate that a monotonic deformation promotes higher dislocation densities and leads to the assumption that dissolution of the cementite takes place more pronounced.