Cutting ceramics for turning of specialised stainless hard-to-machine steel

This study shows the possibility of using cutting ceramics as a turning tool. Replaceable standard cutting plates made of VOK-60 and VOK-71 cutting ceramics are used. In the work, based on simulation modelling in the DEFORM software environment, the possibility of high-speed processing with the specified cutting ceramics is substantiated and then experimentally confirmed. Additionally, the authors propose to apply hardening coatings by condensation with ion bombardment, which ensures an increase in the cutting speed to 100 m/min and more with an increase in the service life of the cutting ceramics from 3 to 3.8 times. The maximum stresses in the tool material and the deformation rate of the process material are studied. To select rational solutions in simulation modelling, the authors used the “temperature in the cutting zone”, “stresses in the tool material”, and “tool wear” parameters, which characterise the combined tension of the tool material. The transition from these parameters to the predictive design of cutting ceramics was performed by measuring the cutting force during natural cutting. The measured values of the cutting force components were used to calculate the stresses in the tool material. The study confirmed the hypothesis that the cutting ceramics is capable of operating under the conditions of processing viscous hard-to-machine corrosion-resistant specialised stainless steels such as 09H17N7Yu (C-0.09; Cr-17; Ni-7; Al-1) grade (EU 1.4568, X7CrNiAl17-7), which have a high content of chromium (16–17.5 %) and nickel (7–8 %). The authors propose original technological methods to improve the performance of the cutting ceramics through special heat treatment and coating deposition. In particular, heat treatment in a vacuum at a temperature of 1100–1400 °C for 20–40 min increased the bulk strength of the ceramics, and additional thermochemical treatment by ion nitriding performed at the final stage of heat treatment made it possible to alloy the bond.