EXPERIMENTAL STUDIES OF OPERABILITY OF HARDENED CUTTING EDGES OF PARTS
Keywords:thermo-hardening, plasma, parts, cutting edge, spiral drill, resistance
The operability of machine and tool parts is often determined by the state of the working surface. It is on the surface that cracks arise, wear and corrosion processes begin. The presence of defects, the degree and depth of hardening, the level of residual internal stresses, the structure, the nature of the transition to the base material, most often determine the reliability and service life of parts and structures. Based on a critical review of hardening methods, it was found that one of the promising ones is the effect on the treated surface of a plasma jet of different power density. To ensure wear resistance of the working edges, the surface was treated with low-temperature plasma at an indirect arc plasmatron installation. The work investigated the phase and structural transformations after plasma coating on model samples of steel 65G, studied the structure and built microhardness profiles. Optimal parameters of plasma processing of articles are determined: distance from plasmatron - 30 mm, rotation speed - 10 s-1, heating time - 10 s. The established optimal modes of hardening treatment were used for plasma hardening using the example of an instrument (spiral drills made of steel grades R6M5, R6AM5 and 11R3AM3F2) under production conditions. For all types of drills, it was possible to obtain a hardened layer of 1-1.5 mm deep from the surface. According to the results of metallographic analysis, the microstructure of the hardened layer contained a white, non-etchable in acids zone with a high microhardness of up to 12000 MPa, the depth of which reached up to 0.4 mm; then there was a structure consisting of martensite and residual austenite with a microhardness of up to 9000 MPa. Tests of experimental drills for resistance, carried out in production conditions, showed an increase in their resource by 2 times compared to a tool that did not undergo plasma hardening, confirmed the possibility of multiple regrind within the hardened layer.