Influence of Cutting Speed on Chip Formation and Hardening in the Deep-Hole Drilling Process of VTM-PLUS Tool Steel

This study aimed to evaluate the effect of v_c on the hardening of chips formed during the deep drilling process in VTM-PLUS tool steel, in the annealed state. The deep drilling was carried out with gun drills having straight channels, internal coolant, high speed steel shank, carbide tip and 7.8 mm diameter, with the ratio L/D = 26. The v_c of 60 and 70 m/min were analyzed. To evaluate the influence of cutting speed on the hardening of the chips they were analyzed via microscopy and Vickers hardness test. From the results obtained, it was observed that the formed chips were are segmented for both speeds and that the increase in the cutting speed caused an increase in its hardness. Hardness values increased in the condition of v_c = 70 m/min (321 ± 18 HV) when compared to the annealed condition (223 ± 3 HV). For the condition v_c = 60m/min there was also an increase in hardness values (309 ± 12 HV), although smaller, when compared to those of higher cutting speed. With the results obtained, it was possible to conclude that the increase in the deformation rate, imposed by the higher cutting speed, led to an increase in the hardness values due to the increase in work hardening.