The literature review shows few studies concerning the turning of hardened steels using carbide tools. A research in this case can provide a better understanding and an option of inserts with less cost than usually applied ceramic and CBN (cubic boron nitride) inserts. Thus, the objective is to investigate the tool-life of ISO P and ISO S grade coated carbide inserts and average roughness (R a) of the machined surface generated with these tools in the hard turning of AISI 4140 steel under dry and minimum-quantity of lubrication (MQL) conditions. Comparing the ISO P and ISO S grades tool life in two different cutting speed levels (60 and 120 m/min), the higher cutting speed generated the lowest R a values. Relating the lubri-cooling conditions, dry turning resulted in lower R a values. When the tool nose wear does not change during the passes, the R a remains constant. In addition, ISO S grade coated carbide insert has shown a possibility for this hard turning due to the low tool nose wear at a relatively high cutting speed.