Friction stir processing (FSP) is an off-shoot of friction stir welding which is a process used to joint metallic material in solid state via severe plastic deformation and mechanical mixing. In FSP, the process is not to join two pieces of materials, but to modify the microstructure of the surface layer of metallic material work piece [5], [6] and [7]. FSP has been applied to many metallic materials and alloys to produce improvement in ductility, fatigue resistance and eliminate microstructural defects [8], [9] and [10]. The FSP process involves plunging of a non-consumable rotating tool to the surface being processed until the tool shoulder contacts the work piece. This is then followed by lateral translation to cover area of interest. Significant heating is generated in the processed layer by the high strain rate severe plastic deformation of the processed area and the rubbing of the tool and workpiece material. Because of the ease of their plasticity, the bulk of investigations on application of FSP have been on low-melting point and soft alloys such as aluminum, magnesium and bronze. Increasingly more studies are being conducted on the application of FSP process to various grades of steel materials [11] and [12]. In terms of tribological application, FSP was recently applied to AISI 1080 steel [13] and AISI 420 steel [14] as a means to harden the surface and thereby enhance the friction and wear performance of the materials.