Restoration of laser technology for hardening and restoration of products from steel and alloys

Abstract

In this paper, we consider: methods for hardening the working surface of cylinder sleeves of an internal combustion engine, their advantages and disadvantages; materials from which engine cylinders are manufactured by world manufacturers, demerit in the production technology of gray cast iron cylinders. Currently, in order to increase the wear resistance of friction surfaces in modern engineering, laser heat treatment is becoming widespread. This is due to certain advantages of this method of heating compared to traditional energy sources used in the restoration and hardening of parts. These include, first of all, the possibility of a high concentration of energy per unit area (with a certain combination of LHT radiation power and laser beam speed), and the corresponding possibility of heating and cooling at ultrahigh speeds in a practically unlimited temperature range. The influence of laser processing modes on the structure and phase composition, as well as the physicomechanical properties of the inner surface of cylinder liners of a KAMAZ engine, was investigated. Tests for wear resistance (test time was 100hours) of templates cut out of cylinder liners after laser thermal strengthening, it was shown that their wear resistance increases 2.2-4.5 times as compared with the standard version of hardening (high-frequency quenching) the highest wear-resistance results were obtained with hardening of 70-80% of the working surface of the liner without melting or with local melting of the surface. The LHT of the working (inner) surface of the liner was carried out using a single-turn helix obtained by simultaneously rotating and longitudinally moving the laser beam along the liner, and the cylinders were processed using a «Comet-2» continuous-wave CO2 installing in the 0.8 - 1.2 power interval kW, the radius of the laser spot 2-4mm. To obtain different power densities of laser radiation and, as a consequence, different depths of thermal influence, the linear processing speed was changed at a constant power level and the size of the radiation spot. Various hardening schemes for the inner working surface of the liner were implemented by changing the speed of the longitudinal movement of the beam in the LHT process. A method is proposed for the diazotisation (decomposition) of the surface layer in parts by laser beam treatment, which reduces the amount of mechanical processing and also causes the coating to be applied with further restoration without disturbing the straightness of a long piece. A mathematical substantiation of LHT modes of machine parts and equipment for layer decomposition after chemical-thermal hardening has been performed. Based on the mathematical calculations, laboratory and experimental studies, the optimal parameters of laser treatment of the inner working surface of the cylinder liner were determined, both for their hardening and for the process of dissociation of nitrides in the parts to be restored to previously subjected to nitration.