White layer changes in cBN tools when turning hardened steel

The paper presents experimental results of investigations in turning of hard Machin able steels (60 - 62 HRC) with cutting tools made of cubic boron nitride (cBN) - based polycrystalline super hard material. Modeling of temperature distribution was performed using the finite element method (FEM). Experimental results for tool wear indicate the presence of oxidation process and changes of physical- chemical properties in the cutting tool white layer. Oxidation of the tool white layer, directly next to the tool-chip zone, leads to the increase of tool hardness and decrease of its strength, which ultimately results in the occurrence of tool composite micro fracturing, and thereby rapid tool wear.