Research On The Technology And Residual Stress Of 12CrNi2 Metal By Laser Metal Direct Forming

Laser metal direct forming technology is a new laser additive manufacturing technology based on laser cladding and rapid prototyping.Due to the manufacturing features of its layer stacks,traditional 3D material reduction can be converted into 2D additive fonning.This technology has the advantages of high processing accuracy,good economics,simple modeling,short processing cycle,etc.It has wide range of research prospects and is listed in the "Made in China 2025" plan.This topic uses the laser additive manufacturing of the nuclear power system camshaft as the background,the direct metal forming technology of 12CrNi2 powder laser metal "shape","performance" and stress analysis of the three aspects of the study,to obtain a defect-free and good performance of the process parameters,and using finite element and actual testing to analyze the residual stress of the formed specimens.Through macroscopic metallographic analysis and penetrant inspection,the stainless steel SUS304 and Q460E substrate materials,the powder feed rate at different rotational speeds,and the different laser power parameters were determined in the process window.At the power of 1300 W or more,no non-fused sample was obtained.The Q460E substrate was used to obtain a crack-free shaped test piece.A powder of 8g/min was used to obtain a higher layer thickness and a defect-free shaped test piece.Based on the determination of the process window,the ABAQUS software finite element analysis technique was used to numerically simulate the temperature field and residual stress distribution of the three parameters of laser power,preheating temperature,and scanning speed,and obtained the parameters for the molten pool.The influence of the maximum temperature,temperature gradient,cooling rate,and residual stress,and guide the next test.The densities of the formed specimens of each parameter were higher than 95%,and the density decreased slightly with increasing scanning speed and laser power.The surface structure is bainite,martensite and acicular ferrite,and the inner layer is granular bainite and ferrite.The strength of each specimen is higher than standard strength 790MPa.The parameter of 1400W,preheating 150?,and speed of 8mm/s are the best.The highest tensile strength is 911MPa,which is higher than the national standard 15%.The cross-sectional hardness distribution decreased from the surface layer to the inner layer,the hardness of the specimens with preheating at 300? and scanning speed of 6mm/s decreased significantly.As the laser power increases,the scanning speed decreases,and the preheating temperature decreases,the residual stress increases.The longitudinal stress is between 176MPa and 293MPa,the transverse stress is between 173MPa and 281 MPa.Longitudinal stress concentrates tensile stress in the rear-end deposition channel region,and lateral residual stress concentrates tensile stress in the region along the longitudinal direction of the test piece.