Abstract: The influences of the cutting speed on the three-component cutting forces, cutting temperature, surface roughness, machined surface morphology, tipping morphology of the cutting tool and chip form in low, medium and high speeds dry hard turning of the high hardness, strength and wear resistance hardened steel Cr12MoV(60±1HRC) by utilizing the PCBN inserts were experimentally investigated.The experiments were carried under the feed of 0.15 mm/r, depth of cut of 0.25 mm, and cutting speeds of 50, 250, 450, 650, 850 m/min.The results showed that the radial force is higher than the main cutting force, and the feed force is lowest, that the highest temperatures in the cutting zone vary from 142 to 288 ℃, and that the sudden change of the radial force does occur at the cutting speeds of 250 and 650 m/min.The surface roughness linearly decreases with the increase of the cutting speed, and the machined surface quality is the best at the cutting speed of 850 m/min.The tipping of the PCBN tool easily happens in the case of a 850 m/min cutting speed.The chip forms are the continuous chip, incompact helix chip, granulated chip, filamentary chip and continuous chip with increments of the cutting speed.

Key words: high speed, dry hard, turning, hardened steel, cutting force, cutting temperature, surface roughness