OBSERVATIONS ON COATED CEMENTED CARBIDE TOOLS AFTER TURNING OF A TEMPERED LOW ALLOY STEEL.

The results of observations of cemented carbide cutting tools (a plain ISO P 25 grade and two varieties obtained by deposing either TiC or TiC/TiN on a P 25 base by chemical vapor deposition) employed in the turning of a low alloy spring steel tempered to 1000 to 1100 MN/m**2. The TiC/TiN coated inserts ensured a much longer life span (all the tools had not yet failed after 50 pieces) whereas the standard P 25 tools had to be replaced after an average of 20 worked items because dimensional tolerances were no longer met; the TiC coated tools did not behave as well as the TiC/TiN coated inserts in this particular application, their average life being 30 parts. The superior behavior of the TiC/TiN coated tools results from the fact that the TiN film acts like a boundary, hence preventing the adhesive phenomena which would otherwise occur between the rake face and the sliding chip.