Surface integrity and machinability analysis in dry hard turning of X38CrMoV5-1 steel using coated and uncoated ceramic tools

This study investigates the machinability and surface integrity of hardened X38CrMoV5-1 steel (50 HRC) during dry hard turning using coated and uncoated mixed ceramic cutting tools (Al₂O₃/TiC). The influence of cutting speed, feed rate, depth of cut, and nose radius on surface roughness (Ra), cutting force (Fc), specific cutting force (Kc), and material removal rate (MRR) was analyzed using Taguchi design, Response Surface Methodology (RSM), and Analysis of Variance (ANOVA). Experimental results showed that Ra varied between 0.18 and 1.51 μm, Fc between 25.57 and 207.45 N, and Kc between 1423 and 3925 MPa within the selected cutting conditions. Feed rate and depth of cut were identified as the most significant parameters affecting surface roughness and cutting forces. Uncoated ceramic tools consistently produced lower cutting forces, improved surface finish, and longer tool life compared with TiN-coated tools under identical dry machining conditions. The maximum tool life reached 41 min for the uncoated insert (r = 1.2 mm), while the coated insert reached 28.5 min under the same parameters (Vc = 150 m/min, f = 0.08 mm/rev, ap = 0.30 mm). Two-dimensional and three-dimensional surface analyses, along with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), revealed that abrasion was the dominant wear mechanism, with adhesion and diffusion contributing to crater formation. The developed RSM models demonstrated high goodness of fit within the studied parameter range. This work provides a comparative evaluation of coated and uncoated Al₂O₃/TiC ceramic tools for sustainable dry hard turning of hardened steel, highlighting the influence of machining parameters on surface integrity and tool performance.