Effect of workpiece sulphur content on the degradation of a PCBN tool material

Tool degradation may be significantly different depending on small variations in chemical compositions of the workpiece material. The present study is an in-depth microstructure investigation of worn low content polycrystalline cubic boron nitride tool materials after dry hard turning of steels with low and high sulphur contents. The results illustrate the important role of sulphur content on the degradation of the crater zone. Sulphides tend to adhere on the wear surface and form layers that protect the tool from workpiece ingress. In the absence of sulphides in the workpiece material, no protective layer can form and iron compounds make their way into the tool microstructure already at lower cutting speeds (150 m/min) and preferably attack cBN grains compared to Ti(C,N) grains.