Effect of cryogenic oils-on-water compared with cryogenic minimum quantity lubrication in finishing turning of 17-4PH stainless steel

17-4PH stainless steel is widely used for applications of critical importance owing to its favorable property profile. However, the great mechanical performance of 17-4PH stainless steel is at the cost of its unsatisfied machinability. Exploring suitable cooling method becomes an effective way to improve its machinability. This study aims to explore the applicability and feasibility of oils-on-water (OoW), which is a hybrid cooling/lubrication technique, compared with minimum quantity lubrication (MQL) in the finishing turning of 17-4PH stainless steel mixed with different cooling media, namely, cryogenic air (CA, -50 degrees C) and liquid nitrogen (LN, -178 degrees C). A comprehensive investigation of the cutting temperature, cutting forces, tool wear characterization and surface quality were studied. The result showed that CA or LN mixed with OoW (CAOoW/LNOoW) achieved the lowest flank wear compared with CA or LN mixed with MQL (CAMQL/LNMQL). Besides, CAMQL had the lowest friction force and coefficient of friction, thus resulting in significant surface roughness, which diminished by 38.4% when compared with dry cutting. The greatest anti-abrasion capability was acquired under LNOoW, wherein the addition of water improved the strength and longevity of the lubrication layer. It was found that the anti-adhesion capacity of the cutting tool increased with the decrease in environmental temperature. Even at cryogenic environment, it is still vital to provide cooling and lubrication to the tool-chip interface for further improving cutting performance.