This paper presents a study of the impact of FSP on surface hardening and the associated impact on the friction and wear behavior of alloy 4140 steel material. The results showed that the steel can be successfully hardened to a level superior to the conventional heat treatment and quenching procedure. While the friction behavior of the baseline, heat hardened and FSP materials are similar, significant improvement in the wear performance was observed with FSP. Hardening processes, both conventional FSP, reduced wear but the wear with FSP is less than half of the conventional method. It also appears that wear in FSP material is less dependent on the contact load, when compared to the baseline and other heat treatment. FSP also changed the wear mechanisms in the 4140 steel material. All these improvements in wear behavior is attributed to the effect of FSP on the microstructure of near-surface layer of the material. The extreme grain refinement resulting from FSP resulted in the formation of ultrafine martensite phase in the processed material.