Study On Residual Stress And Deformation Of Alloy Steel By Laser Melting Deposition

Laser Melting Deposition(LMD)technology is based on the basic principles of rapid prototyping,selects metal powder as the raw material,uses a high-energy laser as the energy source,and melts the metal powder supplied synchronously according to a predetermined processing path,solidifying rapidly and deposited layer-by-layer to achieve direct manufacturing of metal parts,the application prospect is very broad.However,LMD forming is a non-steady state process of local laser action,which causes complex temperature and stress fields.Especially for large-scale components,it is more likely to cause larger residual stresses,cracks and other defects,which affect the performance of components.In this paper,the background of the LMD technology for the manufacture of nuclear power emergency diesel engine camshafts,and the use of 12CrNi2 alloy steel materials for camshafts as the research material,the LMD forming cam surface forming process is typically LMD forming surface multi-layer multi-channel,using numerical simulation and experiments method,using the ABAQUS software to write the surface moving heat source program,and using the birth and death unit technology to achieve the simultaneous deposition of the deposition layer,the establishment of the LMD surface forming process temperature and stress field finite element model,studied the temperature field,stress field and deformation distribution law of LMD surface forming process under different process parameters(laser power,scanning speed,preheating temperature,scanning method and interlayer cooling time).A single-pass experimental study of 12CrNi2 alloy steel LMD was carried out,the process parameters of the initial study were drawn up,and the macro and micro-morphology of the single-pass deposit were observed and analyzed.The study found that a laser power of 2000 W,a printing speed of 5 mm/s,and a powder feed rate of 11.6 g/min are more appropriate;The top of the single-layer deposit is an equiaxed crystal,the middle and lower part are columnar crystals with epitaxial growth characteristics,and the structure of the deposit is lath martensite;In order to obtain accurate material properties,sample preparation,testing and analysis were carried out to obtain thermal physical properties such as high temperature mechanical properties,fracture morphology and specific heat capacity of the material.The study found that the increase in temperature decreases the strength of the material and improves the plastic properties.The elastic modulus and yield limit of the material gradually decrease;Both the ductile fracture at 200?and 400?,and the creep fracture at 600? and 800?;In order to verify the accuracy of the temperature field,a single channel LMD numerical simulation was carried out,and the size of the molten pool obtained by the simulation and the experimentally tested molten pool were compared.The errors of the melting width and the melting depth were 4%and 9.6%,respectively.Fits well with experiment.The cam deposition is typically formed as a curved multi-layer multi-layer deposition.Based on the thermo-elastic plastic method,the finite element analysis model of the curved multi-layer multi-channel LMD process is established using ABAQUS finite element software,and the melting of the curved LMD multi-layer multi-layer deposition is analyzed.The law of peak temperature,pool life,temperature field distribution,temperature change rate,thermal stress evolution,residual stress and deformation distribution.The results show that with the increase of the number of scanning channels,the life of the molten pool is increasing,and the size of the molten pool is gradually increasing;the maximum equivalent stress after cooling is 686 MPa,which appears at the boundary between the substrate and the deposited layer;The residual stress is approximately symmetrical with respect to the scanning direction(ROT plane)and ROZ plane,respectively.The maximum stress is 719 MPa and 751 MPa,respectively;the larger residual stress is mainly concentrated in the lower part of the sedimentary layer,and the residual stress of the entire sedimentary layer is relatively small.The maximum average deformation is 0.217 mm,which mainly appears in the sediment layer area,and finally shows the inward shrinkage deformation of the sediment layer.The effects of different process parameters,that is,laser power,scanning speed,preheating temperature,scanning method and interlayer cooling time on the peak node temperature,melt pool life,temperature change rate,residual stress and residual deformation of the laser-melted and deposited components law.The results show that as the laser power increases or the scanning speed decreases,the peak temperature and melt pool life gradually increase;increasing the laser power and preheating temperature helps to reduce the residual stress in the deposited layer area,and at the same time correspondingly increase the residual stress at the boundary between the deposition layer and the substrate and the area outside the deposition layer;increasing the scanning speed will increase the residual stress in the area of the deposition layer,and at the same time will reduce the residual stress in the area outside the deposition layer;arc profile compared with the axial parallel scanning method,the scanning method has the largest thermal stress in the process and the residual stress after cooling are relatively small.The increase of interlayer cooling time can increase the residual stress in the deposited layer area to a certain extent,and the stress change in the area outside the deposited layer is small;along the pathl path,as the laser power and preheat temperature increase,the deformation gradually increases as the scanning speed and cooling time between layers increase,the deformation gradually decreases.