| 42CrMo steel is used as the raw material of the tension-straightening roll and has good hardenability,strength and toughness.However,42 CrMo steel that has not undergone heat treatment has poor hardness,wear resistance and fatigue resistance,and the pores and cracks often appear in the steel body.There are many defects in the internal structure.The chemical composition in the grains is uneven,and the composition is segregated seriously.Large content of materials,etc.,will lead to premature failure of the tension-straightening roller.Therefore,the optimization of the laser surface melting modification of 42 CrMo steel can significantly improve the structure and performance defects.However,the fused layer after only laser surface melting treatment is still not perfect,and the surface layer carbon and compounds will burn out,and the structure distribution caused by component segregation will be uneven.In view of this,this research introduces electromagnetic field and ultrasonic field to carry out electromagnetic/ultrasound-assisted laser surface melting research.Using a combination of finite element simulation and experimental research to explore the structural characteristics and mechanical properties of the electromagnetic/ultrasonic-assisted laser fused layer,and systematically study the improvement effect of electromagnetic/ultrasound on the structure and performance of the laser fused layer,and provide for the improvement of the performance of 42 CrMo steel Theoretical basis.After 42 CrMo steel undergoes laser surface melting treatment,three areas will be formed on the substrate: melting zone,phase transition zone,and heat-affected zone.The main structure of the melting zone is mainly martensite and some retained austenite plus ledeburite.The phase transition zone is mainly composed of fine strip martensite and tabular martensite integrated structure.And the heat-affected zone is mainly tempered sorbite,pearlite and a large number of massive carbides.When the process parameters of P=1400w and v=5mm/s are used for laser surface melting treatment,a fused layer with fewer pores,high hardness and uniform distribution can be obtained on the substrate.At this time,the internal structure of the fused layer is highly refined,The content of martensite is large,and the content of oxides is small,and the diffusion of carbon and compounds is good.The finite element software COMSOL is used to simulate electromagnetic assisted laser surface melting and analyze the distribution of electric field,magnetic field and electromagnetic force in the matrix,then by coupling the calculated electromagnetic force with heat transfer and laminar flow,the influence of the electromagnetic field on the flow field and temperature field of the molten pool is obtained.The simulation found that the addition of an electromagnetic field will reduce the maximum temperature of the molten pool,but the flow rate of the molten pool will increase by about 20%.Then conduct an experimental study on electromagnetic assisted laser surface melting.It was found,under the same laser process parameters,the area of the molten pool added with electromagnetic field is increased,the number of pores is reduced,and the surface burning phenomenon is obviously alleviated;in terms of mechanical properties,the hardness is increased and the distribution is more uniform,and the wear resistance is improved;the internal structure of the fused layer is refined The degree is increased,the segregation of components is reduced,and the oxide content is also reduced.The ultrasonic-assisted laser surface melting is simulated by COMSOL,and the sound field in the matrix and the influence of the sound field on the molten pool are analyzed.Simulation discovery,the sound field sound pressure gradient diffusion form is similar to Marangoni convection,it promotes the flow of the molten pool,the flow rate of the molten pool is increased by about 50%,and the maximum temperature of the molten pool is also reduced.By adding ultrasonic field to assist the experimental study of laser surface melting,it is found that under the same laser power,ultrasonic field can increase the area of the molten pool(similar to the simulation results),reduce the number of pores in the fused layer,improve the overall hardness and wear resistance of the fused layer,make the structure of the fused layer more dense,and reduce component segregation,especially the oxide content The reduction is obvious.This paper conducts experimental research and simulation on electromagnetic field and ultrasonic field assisted laser surface melting.Analyze the mechanical properties and microstructure of the fused layer.Explored the physical auxiliary field to solve the existing problems of the fused layer,and provide a certain reference for the physical field-assisted laser surface melting research... |
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