Study On Temperature Field Evolution Behavior Microstructure And Mechanical Propertities Of Direct Laser Deposition Of 12CrNi2Y Alloy Steel

Shaft parts,as a key component to ensure the operation of electromechanical equipment,have complex structure and strict service conditions.The surface should have high hardness,high wear resistance and internal strength-ductility matching performance.Direct laser deposition(DLD)enables rapid prototyping of complex parts,simplifies production processes while maximizing material utilization,and has become one of the iconic technologies in advanced manufacturing.Alloy steel was used to manufacturing the shaft parts.However,the DLD alloy steel is mainly composed of non-equilibrium phase transition of bainite.Its morphology and substructure are diverse.The temperature field evolution is complicated under the complex interaction of laser process,and the heat input of the cycle is different.It is difficult to control the structure during the rapid melting/solidification process,which brings great difficulties to the research,and thus restricts the improvement of the tough matching performance of the alloy steel parts.In this paper,the temperature field evolution behavior and microstructure of DLD12CrNi2Y alloy steel are studied.ABAQUS is used to establish the temperature field numerical model and analyze the thermal behavior of the forming process.High-density block samples were prepared by DLD forming system,combined with temperature field simulation results,high temperature tissue growth in situ observation(LSCM)and XRD,SEM,EPMA,EBSD and TEM methods.The phase composition,size,nucleation growth process,the fine substructure evolution and the second phase precipitation mechanism were systematically studied.The high-resolution X-ray tomography was used to observe the three-dimensional morphology of the defects,and the influence mechanism of the microstructure on the hardness and tensile properties of the alloy steel was analyzed.The experimental results show that growth behavior of bainite nucleation in DLD alloy steel accords with the new Bainite rapid cooling one-dimensional nucleation growth kinetics model under KJMA model theory.The scanning speed is improved to promote the fine structure of bainitic ferrite sub-laths.The low-angle grain boundary increases.The high temperature tempering generated by the thermal cycle causes fine Cr7C3 to be dispersed.Under the combination of substructure refinement and second phase strengthening,the full-dense sample(density 99.55%)has an average hardness of 384±11 HV0.2,and the tensile strength,yield strength and elongation after fracture can reach 1084±20 MPa,respectively.1024± 18 MPa and 11.8±0.3%,the performance is higher than the value of forging.The laser power mainly affects the morphology of granular bainite in DLD alloy steel.With the increase of power,the M-A islands are strip-shaped parallel to the bainite ferrite slab(Bg2)and are distributed in a granular form to the ferrite matrix(Bg 1),and the bainitic ferrite sub-laths are thin.The diffuse distribution of M-A islands and fine substructures made the sample average hardness 342±9 HVo.2,and the tensile strength,yield strength and elongation after fracture were 901±16 MPa,702±14 MPa and 15.2±0.6%,respectively.Higher than the value of quenching and tempering performance.By optimizing the process,the purpose of preparing high-performance 12CrNi2Y alloy steel with strong toughness matching by DLD technology was preliminarily realized,which provide a theoretical and technical foundation for the manufacturing of high-performance alloy steel components by laser additive manufacturing.