Study On Micromechanical Behavior Of 304 Ultra-thin Stainless Steel Strip In Rolling Deformation Zone

Precision ultra-thin stainless steel strip is widely used in high-end fields such as aerospace,defense,and military industries.Therefore,more stringent requirements are put forward for its dimensional accuracy,microstructure and mechanical properties.The size of ultra-thin stainless steel strip has reached to microscale,and there are only a few layers or single-layer grains in the thickness direction.So the anisotropy of material increases and the size effects become significant.Crystal plasticity theory depicts the plastic anisotropy and evolution of metal materials,and essentially describes the plastic deformation behavior of metal materials.In this paper,the micromechanical behavior of the rolling deformation zone of 304 ultra-thin stainless steel strip is analyzed through the finite element simulation and experimental research based on the crystal plasticity theory.Moreover,the influence of rolling process parameters and size effect on the rolling deformation behavior of 304 ultra-thin stainless steel strip are explored.The main research contents are as follows:1.Based on ABAQUS finite element software for secondary exploration,the user-defined material constitutive subroutine is compiled.The Voronoi polycrystal model generation system is developed,and GUI interface of twodimensional and three-dimensional polycrystal model of controllable crystal core coordinate point is established based on MATLAB software.Random grain orientations are generated based on the Eulerian space subdivision method,and Python software is used to compile the polycrystal material attribute assignment program.Finally,the polycrystal plastic finite element model is established in ABAQUS / CAE through inputting the INP file.2.Using the above method to establish the polycrystal plastic finite element model,the RVE uniaxial tensile model is established.The influence of the number of grains,the number of elements in the grains and the regularity on the simulation accuracy is analyzed by using the model.The unknown crystal plastic parameters of 304 ultra-thin stainless steel strip are calibrated by comparing the stress-strain curves obtained from tensile experiments and simulations.The RVE model is used to study the micro inhomogeneous deformation of 304 ultra-thin stainless steel strip with different random initial grain orientations under the same engineering strain.The results show that the type,number,sequence and motion state of the active slip systems are different when the initial orientation of the grains is different,which results in different deformations of the grains,uneven distribution of cumulative slip amounts,and the shear strain of each slip system varies greatly in different regions of the grains.3.According to the experimental conditions,a 304 ultra-thin stainless steel strip rolling model is established.The accuracy of the finite element simulation of rolling crystal plasticity is verified by comparing the simulation results with the microscopic characterization results.Using the above model,the effects of tension and reduction rate on rolling deformation are analyzed.The results show that increasing the tension can promote plastic deformation and reduce the rolling force of the ultra-thin strip.The shear deformation of the slip system at the center of the rolling deformation zone is significantly larger than the upper and lower surfaces,and the shear deformation at each position decreases slightly with the increase of tension.With the increase of reduction rate,the rolling force increases significantly,but the stress,strain and cumulative slip in the rolling deformation zone increase slightly,and the distribution tends to be uniform.The slip shear strain at each position increases significantly.4.The influence of size effects(ultra-thin strip thickness and grain size)on the deformation characteristics of 304 ultra-thin stainless steel strip is analyzed by using a crystal plastic rolling model.The results show that with the decrease of the ultra-thin strip thickness,the affected area of the surface grains increases,the anisotropy of the grains is significant,and the rolling force fluctuates obviously.And the restraint effect of the roll surface increases,the cumulative slip strain increases and it gradually expands from the grain boundary to the grain interior.With the decrease of grain size,the volume ratio of surface grains decreases,the number of grains increases,the action area of grain boundaries increases,and the restraint effect of adjacent grains increases,which is easy to form narrow shear bands that run through the thickness direction and are 45°from the rolling direction.