| Gear is widely used in wind power,high-speed railway,helicopter and other equipment manufacturing industries.With the rapid development of industrial technology,higher requirements are put forward for the wear resistance and service life of gear surface.Magnetic deep cryogenic treatment is an effective treatment method to improve material properties,which can greatly improve the wear resistance of the material.Even so,tooth surface wear is still inevitable.With the continuous development of wear,the stability and transmission efficiency of gear power transmission will be seriously reduced,and the gear wear failure will be accelerated.The maintenance and replacement of high-performance gears such as wind power,high-speed railway and helicopter will consume a lot of human,material and financial resources.Therefore,effective monitoring measures need to be taken to monitor the wear process of tooth surface in time.In this thesis,18 Cr Ni Mo7-6 carburized steel,a common material for high-performance gears,is taken as the research object to explore the influence of magnetic deep cryogenic treatment on its mechanical properties and microstructure,in order to obtain a reasonable magnetic deep cryogenic treatment process.Collecting the acoustic emission signal in the wear process,analysing the change law of the characteristic parameters of the acoustic emission signal in the wear process of the specimen,and studying the wear process monitoring method based on the acoustic emission signal,in order to realize the effective monitoring of the tooth surface wear.The research on magnetic deep cryogenic treatment of 18 Cr Ni Mo7-6 carburized steel is another development in the field of magnetic deep cryogenic treatment in China.Through the organic combination of the high-performance gears’ magnetic deep cryogenic treatment process and effective gear wear monitoring,the wear resistance of gear can be improved,its service life can be prolonged and the reliability of gear service can be improved.This is of great significance to break through the bottleneck restricting the healthy development of China’s major equipment and high-end equipment,and improve the profit margin and international competitiveness of the high-end equipment industry.The main work of this thesis is as follows:(1)Influence characteristics of magnetic deep cryogenic treatment on mechanical properties of materials: Considering the five factors of magnetic field strength,deep cryogenic holding temperature,deep cryogenic alternating times,deep cryogenic cooling rate and deep cryogenic holding time,the orthogonal test of magnetic deep cryogenic treatment is designed to explore the influence characteristics of various process factors on the impact toughness,hardness and wear resistance of 18 Cr Ni Mo7-6 carburized steel,and the optimal magnetic deep cryogenic treatment process parameters of toughness and hardness are obtained by range analysis.The results show that the impact toughness,Rockwell hardness and wear resistance of the material can be greatly improved by the magnetic deep cryogenic treatment.The magnetic field strength is 1T,the cryogenic temperature is-190℃,the alternating treatment is not carried out after cooling for 16 hours,and the cooling rate is 2℃/min,which is the optimal process group of this orthogonal test.Compared with conventional heat treatment,the impact toughness,Rockwell hardness and wear resistance were increased by 38.08%,9.49%and 65.87% respectively.The influence order of various process factors on impact toughness is magnetic field strength > cryogenic alternating times > cryogenic temperature > cold holding time > cooling rate;The order of influence on Rockwell hardness is alternating times > magnetic field strength > cryogenic temperature > cooling rate > cold holding time.(2)Action mechanism of magnetic deep cryogenic treatment: Using the optical microscope analysis these sample’s microstructure and their grain size for exploring why magnetic deep cryogenic treatment can improve the 18 Cr Ni Mo7-6 carburized steel material’s mechanical properties.Analysing results show that magnetic deep cryogenic treatment can promote the transformation of retained austenite and it can increase bainite’s content and martensite’s content.It can increase the precipitation of carbon particles and refine the martensite matrix structure.The mechanical properties of the material can be improved by refining the microstructure grains.(3)The acoustic emission model in the process of friction and wear is established to explore the relationship between friction speed,loading load,asperity radius,grain size and surface quality and the root mean square value of acoustic emission,and the simulation results are calculated.The simulation results show that the root mean square value of acoustic emission is directly proportional to the friction speed and the square of loading load;It has a negative correlation with the radius of asperity radius and a positive correlation with the grain size.The acoustic emission characteristic values produced by friction are also different with different surface quality.(4)Friction and wear monitoring of 18 Cr Ni Mo7-6 carburized steel based on Acoustic Emission Technology: Collecting the AE signal during the wear process of the specimen,analysing the AE characteristic parameters(amplitude,energy and root mean square value)of the material in time and frequency domain,and summarizing the variation law of AE signal characteristic parameters during the wear process of the specimen.It is found that the higher the hardness and wear resistance of the material,the smaller the characteristic value of acoustic emission during friction.When the load is constant,the characteristic parameters of acoustic emission are positively correlated with the relative sliding velocity of the surface.The consistency between the RMS value and energy value of acoustic emission is verified by experiments.And the accuracy of acoustic emission model is verified. |
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