Macro-scale Simulation Of 24CrNiMo Alloy Steel For Selective Laser Melting Fabricating High-speed Railway Brake Disc

As one of the core technologies of Intelligent Manufacturing,Additive Manufacturing(AM)has been rapidly warming up in the world in recent years.Selective Laser Melting(SLM),as a precise metal forming technology,has become the focus of extensive research in the industry,and has been gradually applied in petrochemical,aerospace,automotive,medical,die and other fields.Because of the complex physical metallurgical processes such as multi-field coupling and multi-scale,it is difficult to fully reveal the mechanisms and laws of the process by experimental means,so macro-scale simulation methods such as finite element method(FEM)have become an important means to study SLM process.After establishing the temperature field theory based on multiple heat transfer mechanism and the stress field theory based on thermo-elastic-plastic method,the SLM multi-layer and multi-track FEA model is established by ABAQUS.The material parameters of 24CrNiMo powder and solid are determined by theoretical calculation,experimental measurement and numerical calculation by Jmatpro.The sequential activation process of forming layer is realized by model change function,the transformation process from powder to solid is realized by USDFLD subroutine,and the moving loading process of heat source model is realized by DFLUX subroutine.The single track and bulk forming experiments of 24CrNiMo high alloy steel are carried out with SLM equipment.The morphology is observed by optical microscope(OM).The process parameters with better forming quality(laser power 200W-300W,scanning speed 150-250mm/s)are obtained.By fitting the structure size of molten pool,the parameters of double ellipsoid heat source model(a=y=120um,c=160um,η=0.35)are determined,which verified the accuracy and reliability of FEA modelThe simulation technology of SLM is studied comparatively.It is found that the temperature field obtained by the method of gradual activation,large substrate and powder paving is more reasonable and close to the actual process.The variation and distribution of temperature/stress field in selective laser melting of 24CrNiMo alloy steel and the influence of different process parameters on it are described.The results show that the peak temperature of the molten pool is above 2000℃,and the residual stress after cooling is about 350 MPa.Within a certain range of process parameters,with the increase of laser power or the decrease of scanning speed,the temperature increases with the increase of heat input;with the increase of laser power or scan speed,the stress increases with the increase of temperature gradient.Subarea scanning,the interlayer scanning angle change and preheating of the substrate are helpful to reduce the residual stress and crack generation.The laws of residual stress and deformation of high-speed railway brake disc is analyzed by using MSC Simufact Additive software,a special software for SLM.The results show that under the default process parameters,the high-speed rail brake disc is manufactured in different forming directions,and there is a large stress concentration in the flange structure edge and the area near the radiating rib.Heat treatment process can greatly reduce the residual stress of friction surface and installation hole position of brake disc structure,contact position between brake disc structure and base plate,thus reducing the tendency of cracking.