Tool wear and surface roughness analysis in hard turning of AISI 4340 steel with coated carbide inserts

The performance of CVD-coated carbide inserts (TiCN/Al₂O₃) in hard turning AISI 4340 steel at cutting speeds of 60, 95, 180, and 250 m/min, under both dry and wet conditions are investigated. The goals were to evaluate tool wear, surface roughness, and wear mechanisms over different machining conditions. Surface roughness Ra value was noticed, and it dropped to Ra = 0.30 μm at 180 m/min but increased at 250 m/min due to vibration, edge instability, and wear. Flank wear rose with cutting speed: 186 μm at 60 m/min, 265 μm at 180 m/min, 542 μm at 250 m/min (dry), and 692 μm (wet), exceeding ISO tool life (VB = 300 μm) due to edge breakage, flaking, and adhesion. The examination of the tool surface by SEM and EDS revealed abrasion and slight coating delamination at low speeds, adhesion and oxidation at intermediate speeds, and catastrophic tool failure at high speeds.