Three-dimensional wear parameters and wear mechanisms in turning hardened steels with PCBN tools

Hard turning has been applied in a wide range of mechanical components based on ferrous materials. The application of these components is a function of mechanical properties and microstructure - that also has manufacturing process influences, i.e., cutting mechanism. This research aims to discuss the tool wear level and the correlation with the wear mechanisms in turning with PCBN tools, which deals with three steel alloys (AISI 4340, AISI 52100 and AISI D2) and considers six levels of hardness (on the interval from 35 to 60 HRC), applying the novel three-dimensional wear parameters based on Focus Variation Microscope (FVM) to wear evaluation. Considering the wear parameters that represent the amount of material removed from the tool (WRM) and tool affected area (WAA), tool wear intensity and abrasion wear mechanisms have a decreasing trend with the increase of hardness in the range of 35-50 HRC. Above 50 HRC, however, there is a tendency of increased tool wear intensity when steel hardness is increased. The fraction volume of carbides in the steel microstructures intensifies the abrasion wear mechanism. The adhesion wear mechanism showed a reduction with an increase of the steel's hardness - identified by wear parameters WAM (adhered material volume on the tool). Based on crater wear formation, the diffusion wear mechanism had an inverse behavior when compared to adhesion. Better results concerning tool wear can be achieved when turning steels with 50 HRC. It was evidenced that the three-dimensional wear parameters applied open new possibilities to understanding complex and specific phenomena occurring in machining processes, particularly in the machining of hardened steels.