Coordinated Regulation Of Microstructure And Residual Stress Of Pure Iron Spherical Shell

In precision machining,the microstructure and residual stress distribution of materials with the same composition have significant effects on the mechanical properties and machining deformation of the workpiece.Therefore,it is of great scientific significance and engineering value to put forward the method of coordinating the microstructure and residual stress of pure iron and study the effect of mesoscopic properties of pure iron on machining deformation.Based on the theory of dislocation evolution,considering the effect of pure iron recrystallization on dislocation density during heat treatment,the microstructure and the residual stress prediction model of pure iron spherical shells were established.Combined with finite element simulation,a coordinated control technology of microstructure and stress is proposed to provide guidance for the elimination of residual stress and the control of workpiece distortion.The detailed research is listed as follows:In this paper,quasi-static compression of DT4 E pure iron at room temperature and heat treatment were carried out to study the effects of initial deformation,heat treatment temperature and holding time on the microstructure evolution of pure iron.The material parameters of the recrystallization model and grain growth model of pure iron were obtained by fitting the experimental data.At the same time,A modified creep model based on the dislocation density evolution was established and the evolution of dislocation density was affected by the initial hardening,the recovery and the static recrystallization.The stress relaxation behavior of pure iron samples with different initial hardenings at different temperatures was studied and finally the parameters of the stress relaxation model were fitted.Based on finite element simulation software ABAQUS,the finite element model of the cold-forging process for pure iron and heat treatment process were established.The microstructure evolution model and the stress release model were written into CREEP subroutine to predict the microstructure evolution and the Residual stress release of cold-forging spherical shell during the heat treatment.In order to study the influence of residual stress on machining deformation,stress mapping method and the birth and death element technology were used to predict the deformation of pure iron spherical shell caused by residual stress relaxation in the FE software ABAQUS.It was found that eliminating residual stress by heat treatment can effectively reduce machining deformation.