Sustainable hard turning of gas carburized SAE 8620 steel: comparative analysis of PCBN tool performance and surface integrity under dry and MQL conditions

The manufacturing industry is increasingly seeking sustainable alternatives to traditional grinding processes for finishing hardened components. This research presents an in-depth evaluation of the hard turning process applied to carburized, quenched, and tempered SAE 8620 steel employing polycrystalline cubic boron nitride (PCBN) inserts. Induction-hardened SAE 1045 steel served as a benchmark for comparative purposes, owing to its widespread use in similar industrial contexts of SAE 8620. The research compares dry machining and Minimum Quantity Lubrication (MQL) conditions, analyzing their respective effects on tool performance and surface integrity. The experimental methodology comprised the systematic monitoring of machining forces, flank and crater wear, surface roughness, chip morphology, and white layer formation. The results indicate that the specific microstructure of SAE 8620, resulting from the carburizing process, induces wear patterns distinct from those observed in other steels of equivalent hardness. The application of MQL effectively mitigated both flank and crater wear compared to dry cutting, although it significantly altered the surface topography and the metallurgical characteristics of the white layer. It is concluded that the replacement of grinding by PCBN hard turning is a viable and efficient strategy for gas carburized SAE 8620 steel. Furthermore, MQL proved superior to dry machining in extending tool life by suppressing thermal and tribological mechanisms, though it necessitates rigorous control over roughness parameters and surface integrity.