Hard turning is considered as a new machining process aimed at turning hardened steels with high surface qualities. This process is a good alternative for many grinding applications which were previously done hrough traditional machining processes. The goal of this paper is to test the empirical feasibility of using this new method instead of grinding in many industrial applications, and to determine the effects of independent arameters such as hardness of parts and cutting speeds on the surface quality and tool wear in hard turning operations. Hence parts made of AISI 4140 alloyed steel are exposed to different thermal treatments to chieve different hardness rates in the range of hard turning operations. These parts are then machined with BN cutting tools and CNC lathing machines at different cutting speeds, and results are compared in terms of urface roughness.

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