Surface hardening of steel alloys can also be achieved through mechanical treatments. Grinding of steel material under appropriate conditions has been shown to lead to surface hardening comparable to the traditional heat treatment [1] and [2]. Similarly, machining operation of steel material under severe conditions has been shown to produce a hardened layer on the surface [3]. Other mechanical surface hardening methods that have been applied to steel materials include explosive impact, high energy shot peening, etc. [4]. All these techniques involve severe plastic deformation of surface layer that is undergoing hardening treatment. The heat generated by the process of severe plasticity can raise the temperature of the surface layer above the austenitizing temperature. Rapid cooling through heat dissipation into the bulk material can be fast enough for the formation of martensitic phase and consequent hardening of the surface layer. Thus, the basic mechanism of surface hardening of steel material by mechanical treatments also involve phase change, similar to traditional thermal treatment.