Studenets S. Improving the performance of cutting broaches from high-speed steels for processing cast iron parts by modifying the surface layer by hydrogen-free ion nitriding

As a result of the work, a scientific and technical task was solved, which is im-portant for mechanical engineering, which is to improve the performance of cutting broaching tools used in the processing of cast iron parts, by modifying the working surfaces of the tool with anhydrous ion nitriding ion nitriding (AIN). Studies have shown that the use of AIN to modify the working surfaces of cut-ting broaches made of steel P6M5 provides an increase their tool life up to 12 times when machining holes in cast iron parts (HB 1.6 - 2.2 GPa). It is established that the greatest increase in the performance of the tool occurs during the formation by AIN on its working surfaces of a modified surface layer with a thickness of ~ 80 μm in the composition: γ'-phase (Fe4N) - 20%, ε-phase (Fe2N + Fe3N) - 70%, 10% - other compounds. The method of X-ray spectral analysis shows that by varying the parameters of the AIN mode it is possible to obtain in the modified layer different levels of residual microstresses, which directly affect the formation of microcracks when applying to the contact surface of the tool workloads. It is proved that the increase in the stability of the tool is explained by the for-mation on its working surfaces of a stable (active) build-up, which protects the tool from wear and ensures stable accuracy of the hole and the roughness of the treated surface. Qualitative differences in the wear of nitrided and conventional broaches have been experimentally established, namely, the period of tool life of the nitrided tool is divided into three distinct stages, which differ in wear intensity: initial (tool running), normal wear and catastrophic wear. In conventional broaches, the intensity of wear during the entire period of stability does not change. Further development was the provision on the crucial role of the characteristics of the processed material Sk (true fracture stress) in determining the cutting force. An equation based on it is used to calculate the tensile strength when machining holes in cast iron parts. It is established that the use of nitrided cutting broaches provides the formation of the roughness of the treated surface Ra 2,7 – 3,8 μm (2 times less than when using conventional broaches) while maintaining a stable nature of the formation of such roughness throughout the period of economic tool life of the tool. The results of the work were tested and industrial in the conditions of the enter-prise PJSC "Hydrosila APM" Kropyvnytskyi.