Study On Residual Stress Of Fuse-adding Considering Solid-sate Phase Transformation And Elimination Of Stress By Mechanical Peening

Wire and arc additive manufacturing(WAAM)is widely used in repair and manufacturing of the hot forging die,the distribution of residual stress have significant influence on the success of the additive and the dimensional reliability of the mold in service.Since it is difficult to obtain the distribution of residual stress by experimental means,finite element method(FEM)can display the distribution of residual stress field in all dimensions.But it might bring a large error in finite element simulation if the solid-state phase transformation(SSPT)effects were neglected for some Fe-base alloy,such as application of RMD248 deposited metal wire to 45 steel substrate.Therefore,in order to study the effect of SSPT on residual stress,finite element simulation of WAAM considering SSPT was carried out based on MARC software.The main contents and conclusions of this paper were as follows:(1)The effect of volume change,yield strength variation and transformation induced plasticity(TRIP)on residual stress were discussed,which laid a foundation for analyzing the effect of SSPT on residual stress of WAAM.The simulation results show that the volume change and yield strength change have a great influence on the formation of residual stress,while TRIP have a relaxation effect on the tendency of stress variation during phase transformation.(2)Based on the MARC finite element software,a multi field coupling model considering SSPT effect was developed to calculate the temperature,microstructure and residual stress of single-layer single-pass and single-layer multi-pass WAAM of RMD248 deposited metal wire to 45 steel substrate.Through observing the microstructure and measuring the micro-hardness of the WAAM,the accuracy of the model were verified.The residual stress of surfacing was measured by X-ray diffraction method,and the validity of the model was verified by comparing the experimental value with the simulated value.(3)The research results of single-layer single-pass WAAM show that: The peak temperature,cooling rate and thermal cycle time of the materials at different positions are different.The martensitic transformation occurs mainly in the welding seam,the ferrite transformation and pearlite transformation occurs mainly in the heat-affected zone(HAZ),and the solid phase transformation does not occur in the matrix.Compared with that without considering the effect of SSPT,the peak value of transverse and longitudinal residual stress is significantly higher than the yield strength of base metal at ambient temperature.Meanwhile,we can see that considering the effect of SSPT,the distribution of residual stress in the WAAM is more uniform,especially for transverse residual stress.(4)The research results of single-layer single-pass WAAM show that: the cover passes have more important effects on the temperature,microstructure and residual stress than the former passes.Moreover,the cover passes increases the holding time of bainite transformation temperature and reduces the proportion of martensitic transformation.We can see that considering the effect of SSPT,the residual stress presents tensile-compressive distribution in the surfacing layer and the HAZ.Furthermore,the elimination and redistribution of residual stress in the cover passes are weakened.(5)Considering the effect of SSPT,a finite element simulation of single-layer single-pass WAAM by trailing peening was carried out.Results indicate that different peening intervening temperature correspond to different peening contact microstructure.When the peening intervening temperature is medium temperature,most of the corresponding microstructure are austenite,and the effect of peening treatment is best.Meanwhile,The effect of peening treatment under different peening loads were simulated and analyzed.The results show that With the increase of peening load,the effect of increases first and then decreases.