Effects of cryogenic cooling on the surface integrity in hard turning of AISI D6 steel

Methods able to enhance surface integrity of machined components have been one of the emerging areas in manufacturing engineering, and a technique that has been providing satisfying results in the last years is cryogenic machining. Besides promoting surface integrity improvement, it is considered an alternative to the use of conventional cutting fluids, which is in accordance with the latest global trends for sustainable means of production. In this sense, replacing grinding operation, which uses large volumes of conventional cutting fluids, by hard turning assisted by liquid nitrogen, for example, could be a good choice. The aim of this work was to investigate the effects of cryogenic cooling on the surface integrity of quenched and tempered AISI D6 tool steel after turning operation. Dry and cryogenic turning trials with polycrystalline cubic boron nitride tools were performed and the results of surface integrity (surface roughness and topography, microhardness and residual stresses, as well as the modified microstructure of the deformed layer) were analyzed for comparison. The results showed that cryogenic cooling played an important role in modifying the workpiece surface integrity, providing low values of surface roughness (similar to those obtained in grinding operations), as well as higher values of surface microhardness and compressive residual stresses as compared to the dry condition.