The effect of nitriding on the properties of VK10 hard alloy

Nitriding of VK10 hard alloy was carried out and the influence of different process modes on its properties was studied. Nitriding was carried out in a vacuum furnace VARP NVF-9915. The temperature of the ammonia dissociator was 850 ± 10 оC. The nitriding process included several stages. At first, voltage of 300–400 V was applied to clean the part and glow discharge was induced. As cleaning progressed, the voltage was increased to 500 V. The cleaning time was 1 hour. Heating to the temperature of isothermal exposure was carried out for 1 hour, then isothermal exposure was performed. After that, nitriding was done. Then, for 1 hour, the charge was cooled to 280 оC without removing the discharge. The approximate cycle duration (without isothermal exposure) was 4 hours. Nitriding of hard-alloyed samples was carried out at a temperature of 900–1000 оC, the duration of isothermal exposure was up to 2 hours. After nitriding, the hard-alloyed tool acquired the silvery-white color. The longer the process, the more saturated the white color became. The aim of the work was to study the effect of the nitriding process on the mechanical and operational properties of VK10 hard alloys. During the experiment, samples such as billets measuring 5×5×35 mm, foursided diamond-shaped plates made of VK10 hard alloys were used. The thickness of the diffusion layer after nitriding varied within 2.5 microns and did not depend on temperature in the range of 900–1000 оC. Microhardness studies showed that the maximum values were achieved at a temperature of 1000 оC and processing time of 1 hour. At the same time, the average values of microhardness significantly exceeded those of the source material. Despite a slight decrease in tensile strength, the data obtained on an increase in microhardness and wear resistance allow us to conclude that the nitriding process is advisable to improve the properties of VK10 hard alloy. Thus, the experimental results confirm the effectiveness of nitriding as a technology that can not only improve the performance of this material, but also be successfully implemented in the processing.