On the Use of Repeated Low-Temperature Nitrocementation for Effective Hardening of the Crankshafts of KAMAZ Vehicles, Ground to Repair Dimensions

Abstract

Purpose of research the aim of the work is to develop an effective technology for surface hardening of the crankshafts of KAMAZ 740 engines, restored by re-grinding to repair dimensions, by means of their accelerated low-temperature nitrocementation in the conditions of car service (car repair) enterprises.Methods. Nitrocementation of the samples was carried out in a nitrogen-carbon paste. The samples with a nitrocementating coating were heated in a laboratory furnace with a vertical load of SSHOL-12-M3-U4. The nitrocemented samples were subjected to metallographic analysis using an Axio Observer.A1m optical microscope and a Quanta TM 3D200i electron scanning microscope. Phase analysis of diffusion layers on samples nitrocemented according to various modes was carried out on an XRD-7000S X-ray diffractometer. The microhardness of the nitrocemented samples was measured using a Duramin-5 microhardness meter with a computer and software. The hardness of the nitrocemented samples was measured on a TK-2M (Rockwell) hardness tester on the "A" scale according to the standard method.Results. The technology of low-temperature nitrocementation of nitrided crankshafts of KAMAZ vehicles after their repair by grinding with the removal of the hardened layer from the surfaces of the root and connecting rod necks is presented. It is shown that nitrocementation of 42HMFA steel, from which crankshafts are made, at a temperature of 520...580 °C for 3 hours in a highly active paste ensures the production of hardened layers in depth, structure, phase composition and hardness are almost identical to nitrided layers. Such nitrocementation can be a full-fledged and effective replacement for the re-nitriding of the restored shafts provided for in the technical documentation for the repair of KAMAZ engines, categories E-2, E-3 and E-4.Conclusion. The low labor intensity and technological simplicity of nitrocementation will allow it to be used to strengthen the crankshafts of all seven repair sizes provided for these parts, which can give a very large economic effect.