The use of cbn tools for dry turning hardened steel should  follow the following principle:

Select a large depth of cut as far as possible under the rigidity of the machine tool, so that the heat generated in the cutting zone softens the metal in the front of the edge 

and can effectively reduce the wear of PCBN tools. 

In addition, PCBN tools should be used as much as possible during small cutting. Due to the poor thermal conductivity of the CBN tool, makes the heat in the cutting zone have 

not enough time for the diffusion. The shear zone can also produce a significant metal softening effect and reduce the wear of the cutting edge.