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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.

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The microstructure, crystallographic texture, strain hardening in the hole edge‐punched and stretch‐flangeability of hot‐rolled multiphase sheet steel is investigated by scanning electron microscopy, electron backscatter diffraction, and microhardness measurements. The results show that the strain hardening in the hole edge‐punched is not the main factor that influences the hole expansion ratio. The bainite fraction, average grain area, and kernel average misorientation distribution mean are microstructure factors that improve the hole expandability and reduce the effect of strain hardening in the hole edge‐punched on the hole expansion ratio. The crystallographic texture affects the hole expandability. The high intensity of {332}<113>α and {111}<112>α components that have higher normal anisotropy (rtrue¯) also reduces the effect of strain hardening at the hole edge‐punched. The cracks propagate through the interfaces following the banded microstructure direction at the hole edge‐punched during the punching process. The gamma distribution analysis of the kernel average misorientation distribution indicates that there are different energy transfer (β parameter) and dislocation densities due to different cooling rates.

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