Punching Property And Punching Process Optimization Of New Zirconium Alloy Sheet Strip

Zirconium alloy has excellent nuclear properties.Under the working conditions of high temperature,high pressure and water vapor,zirconium alloy has good corrosion resistance and neutron radiation resistance,moderate mechanical properties,good processing properties and good compatibility with uranium fuel.Therefore,zirconium alloy has become an important material for thin plate strip for nuclear fuel assembly frame.In this thesis,taking the new zirconium alloy sheet and strip as the research object,by means of numerical simulation,process test and microscopic analysis,on the basis of studying the relationship between forming quality and punching forming and material microstructure of sheet and strip,the relationship between forming quality and punching forming and microstructure of sheet and strip is studied by means of numerical simulation,process test and microscopic analysis.Based on the orthogonal test,the punching process parameters are optimized,and the stamping forming quality of sheet and strip is significantly improved.The results of this thesis can provide theoretical reference and technical support for promoting the localization of new zirconium alloy sheet strip for PWR nuclear power plant.Firstly,the three-dimensional tensile test of the new zirconium alloy sheet and strip is carried out in this thesis,and the basic mechanical properties of the material required for numerical simulation are obtained.It is found that the main failure modes of the new zirconium alloy sheet strip specimen are drawing and burst,and the deformation modes of the corresponding specimen are drawing and bulging,and the second phase in the new zirconium alloy is analyzed by transmission electron microscope?TEM?.It is found that the second phase is mainly distributed in the grain boundary and intragranular,and the Nb content of the second phase distributed in the grain boundary is much higher than that in the second phase,while the Cr content in the second phase distributed in the grain boundary is much lower than that in the second phase.There are twins in the new zirconium alloy,but the second relative slip and twinning affect the plastic deformation of the thin strip of the new zirconium alloy.The microstructure of the new zirconium alloy is analyzed by electron backscattering diffraction?EBSD?technique.It is found that the grain size of the new zirconium alloy is coarser,the average grain size is 8.25?m,the tensile test shows that the hardening index of the new zirconium alloy is lower,and the grain boundary distribution of the new zirconium alloy is lower than that of the new zirconium alloy.The proportion of small angle grain boundary is 22%,and that of large angle grain boundary is 78%.The blocking effect of grain boundary on slip is obvious.The forming quality of the new zirconium alloy specimen is closely related to the deformation mode in the stamping process,the grain size of the strip and the second phase material factors.Secondly,the influence of stamping process factors on the forming limit diagram of thin sheet and strip is explored in this thesis.It is found that among the technological factors affecting the stamping of new zirconium alloy sheet and strip,the influence of stamping speed and blank holder force is small,and the influence of friction coefficient is greater.On the other hand,the clearance of punch and concave die has a significant effect on the clearance of punch and concave die.Finally,based on the orthogonal experiment,the punching process parameters are optimized from the point of view of process supplement.It is found that when the stamping speed is 1 000 mm·s^-1,the blank holder force is 20kN,the friction coefficient is 0.125,and the clearance of punch and concave die is 0.5484mm.The maximum thinning rate of the new zirconium alloy sheet strip is reduced by 22.2%,the maximum principal strain is reduced by 14.7%,and the safety margin is increased by 1.5%.The simulation calculation and experiment show that the fracture rate of the new zirconium alloy sheet and strip is greatly reduced,and the punching forming quality of the sheet and strip is significantly improved.