An experimental study of the white layer formation during cryogenic assisted hard machining of AISI 52100 steel

Abstract

White layers seem to be detrimental to the performance of products since they can reduce the lifetime of bearing significantly. It is generally believed that white layer formation is mainly due to the thermal loads during hard turning. Cryogenic cooling is proposed in this paper to restrain the formation of white layer by reducing the influence of temperature in cutting process. Several experimental machining tests of hardened AISI 52100 steel are conducted under dry and liquid nitrogen cooling conditions using cubic boron nitride (CBN) cutting tools. The characteristics of the white layer is observed using scanning electron microscope and the phase analysis is carried out using X-ray diffraction method. It is found from the experimental results that cryogenic cooling can help reduce the thickness of white layer and increase the surface hardness especially at high cutting speed. Meanwhile, the weight fraction of retained austenite is also reduced rapidly. Moreover, it shows that severe plastic deformation also has a significant effect on the white layer formation compared to the thermal dominant through cryogenic processing, mainly at the change of surface hardness and retained austenite content.