| Gear is a key part of the mechanical transmission system.Carburizing treatment is needed to meet the requirements of internal toughness and external hardness,so that it can obtain high hardness and wear resistance.Vacuum low pressure carburizing technology effectively solves the defects of ordinary gas carburizing technology.It has the characteristics of good quality,low energy consumption,clean and high efficiency.It is a truly environmental protection and green technology.In order to meet the high requirements of new energy vehicle transmission system for gear wear resistance and fatigue resistance,it is necessary to optimize the vacuum low pressure carburizing process to improve the service life of gear.In the actual vacuum low pressure carburizing production,multiple carburizing experiments will be carried out through empirical analysis to determine the best process scheme.However,due to many influencing factors of vacuum carburizing,the process is complex,and there are few optimal schemes,which bring difficulties to process formulation and optimization.Therefore,it is necessary to introduce a controllable and predictable numerical simulation into the vacuum carburizing technology to accurately describe the microstructure and performance changes in the vacuum carburizing process.The optimum vacuum conditions are explored to replace the expensive and time-consuming experimental trial-and-error method,which provides scientific guidance and technical support for the optimization of vacuum carburizing process scheme and provides a theoretical basis for improving the life of key components in the field of mechanical manufacturing.In this paper,20 Mn Cr S5 steel,20 Cr Mn Ti steel and 20 Cr Mo steel,the typical sample materials of gear in high-speed transmission system of new energy vehicles,were taken as the research objects.The microstructure evolution law and properties of vacuum carburizing process were studied by combining simulation and experiment,and the vacuum carburizing process parameters was optimized.The main research work of this paper is as follows :(1)The vacuum low pressure carburizing heat treatment experiments were carried out on three kinds of gear steels.The relationship among carbon content-microstructure-properties under different processes was investigated.The effects of different strong carburizing time and diffusion time process parameters on the carbon content distribution,microstructure and hardness distribution from surface to interior were analyzed.(2)A complete nonlinear parameter databases of three kinds of gear steels for heat treatment materials was established.A multi-field multi-scale model was established based on the temperature-diffusion-phase transformation-stress coupling theory and different scale simulation methods to simulate the vacuum carburizing process.The carbon concentration distribution,microstructure evolution and hardness distribution in the vacuum carburizing process can be quantitatively calculated to realize the accurate prediction of the vacuum low pressure carburizing process of gear steel.Simulation results of vacuum low pressure carburizing were compared with the experimental results,and they were in good agreement,which verified the effectiveness of numerical simulation,indicating that the multi-field and multi-scale coupling model of vacuum carburizing heat treatment was reliable.(3)The numerical simulation of different vacuum low pressure carburizing processes of20 Mn Cr S5 steel was carried out.The influence of the two process parameters of strong carburizing time and diffusion time on the carbon concentration of the workpiece after carburizing was discussed,and the process parameters of vacuum low pressure carburizing process parameters were optimized.(4)The nonlinear mapping relationship model of vacuum low pressure carburizing process-performance of 20 Mn Cr S5 steel was established.The model was trained and tested by using the sample data under different process parameters of vacuum low-pressure carburizing process,and the generalization ability of the model was verified.Finally,a visual neural network optimization process parameter prediction system for vacuum low pressure carburizing was established,and the practicability of the designed prediction system was confirmed.The prediction results were relatively accurate,which was open a new way for the improvement of the actual production process of vacuum carburizing heat treatment,and had certain engineering practical significance. |
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