Research On Laser Cladding Repair Mechanism And Microstructure And Properties Of Die Steel Surface

Aiming at the problem of mold wear failure caused by factors such as cracking of the cladding layer surface and hot working die face due to large cyclic stamping load and friction and wear,this paper combines the characteristics of laser cladding and laser remelting to prepare the cladding in laser cladding.Based on the laser cladding to prepare the cladding layer,combined with the laser remelting method,the mechanical properties of the cladding layer are further improved,and the cladding layer cracking is improved.Through numerical simulation and experimental research,the temperature field,microstructure properties and crack formation mechanism of Ni50A cladding layer were studied to provide theoretical guidance for crack suppression.The specific work and main conclusions are as follows:(1)Using the finite element analysis software ANSYS to analyze the temperature field of single laser cladding and multiple overlap laser cladding during the laser cladding process,the influence of different laser process parameters on the temperature field was obtained,and the model was analyzed.Corresponding experimental comparison and verification of the rationality of the molten pool are shown.The comparison and verification results of the morphology of the molten pool show that the morphology of the experimental molten pool and the simulated molten pool are basically the same.The depth of the simulated molten pool is slightly greater than the depth of the experimental molten pool.The error between the experimental and simulated values is less than 5%.The comparison and verification results of the YZ plane structure of the cladding layer section show that the experimental results of the YZ plane structure are basically consistent with the simulation results.The results prove the rationality of the model.(2)Through a single factor experiment,the effect of process parameters on the crack sensitivity of the cladding layer was explored.Within the range of power allowed by the laser,as the laser power increased,cracks The number and total length of the cracks decrease accordingly;with the increase of the scanning speed,the number of cracks and the total length of the cracks increase significantly.In addition,within a certain range(-5mm?f?+5mm),the larger the absolute value of the defocus amount,the higher the susceptibility of the cladding layer to cracking,and the susceptibility of the cladding layer crack obtained by the negative defocusing process is lower than that of the positive The cladding layer obtained under the coke process.(3)The crack formation mechanism of Ni50A cladding layer was studied,and it was found that Ni50A cladding layer mainly includes the following three types of cracks:thermal cracking due to defect aggregation,cracking due to component segregation,and liquefaction cracking.Based on the laser cladding process,a surface crack-free cladding layer was obtained on the surface of the H13 steel substrate using laser parameters and process optimization.The experimental results show that the structure at the bottom of the laser remelt cladding layer is more uniform and finer,the size of the precipitate phase is reduced and the distribution is more uniform,the degree of element segregation and the cracking sensitivity of the cladding layer are strongly suppressed.(4)The main structure of the Ni50A cladding layer is composed of a?-(Ni,Fe)solid solution matrix phase and a strengthening phase.The strengthening phase is mainly Ni3Si2,Ni₆Si₂B₁,Cr₂₃C₆,Cr B₂,and Cr B.With the increase of scanning speed,the type of boride increased and the content of precipitated phase decreased.In the cladding layer prepared by the low scanning speed process,a large number of lamellar eutectic structures and granular structures are distributed at the bottom of the cladding layer,and a small number of columnar dendrites are locally distributed.With the increase of scanning speed,the growth morphology of the cladding layer changed,the chrysanthemum eutectic structure disappeared,the interfacial organization changed from cell crystals to planar crystals,and the bottom tissue of the cladding layer consisted of a large number of columnar crystals,dendrites,and a few cell crystals.(5)When other process parameters are unchanged,within a certain range,the hardness of the cladding layer decreases as the scanning speed increases.When the scanning speed is 1.5 mm/s or less,the wear volume of the cladding layer is the smallest.The wear resistance of the cladding layer can be increased up to 5 times of the substrate under the same wear conditions.As the scanning speed increases,the depth of the wear scar decreases first and then increases,and the width of the wear scar increases first and then decreases.The wear mechanism gradually changed from slight abrasive wear to adhesive wear and peeling wear.(6)After the laser remelting process is applied(when the laser remelting power is less than or equal to the laser cladding power),the bottom structure of the cladding layer is mainly a large number of fine hard phase particles dispersed and distributed on the?-(Ni,Fe)matrix in.The distribution of the hard phase is more fine and uniform,and the crack propagation resistance increases.In addition,when the laser remelting power is lower than the laser cladding power,the hard phase and structure in the cladding layer are refined,and the average hardness of the cross section of the remelted layer is increased by 5.8%.