Tribological performance and energy savings in sustainable machining of duplex stainless steel via hybrid Cryo-MQL

Abstract The most reliable industrial uses of duplex stainless steels (DSS), including energy systems, maritime engineering, and chemical processing, are on the rise due to the material’s exceptional corrosion resistance and high mechanical strength. Tool wear is rapid, surface integrity is poor, and energy demand is high when machining these materials due to their bi-phase microstructure and high alloy content. This work analyzes the performance of these four cooling and lubrication techniques and compares their effectiveness in improving the machinability of DSS turning: dry, Minimum Quantity Lubrication (MQL), cryogenic cooling, and the hybrid Cryo-MQL (CMQL). Extensive tests for tool wear, surface roughness, microhardness profiles, chip morphology, and machining energy consumption were carried out. CMQL was found to be the best among all methods, reducing tool wear by 54%, surface roughness to a lower level of 0.558 µm, and energy consumption by 32.3%, while increasing the subsurface microhardness by 31.7%. The results support the use of CMQL as an eco-friendly, high-efficiency alternative for the precision machining of DSS parts.