Crystal Plastic Finite Element Modeling Of The Deformation Process Of Ferritic Stainless Steel

Ferritic stainless steel(FSS),as a typical nickel-saving stainless steel,with the improvement of smelting technology in the steel industry,it can effectively reduce the interstitial content of carbon and nitrogen,and by adding micro alloy elements such as niobium and titanium,its corrosion resistance can reach the level of austenitic stainless steel.In addition,ferritic stainless steels have excellent anti-stress corrosion performance,high thermal conductivity,magnetic properties and other special properties,making them widely used in home appliances,automobiles,construction and other industries.At the same time,ferritic stainless steel is also a typical material whose texture affects its performance,while the structure changes during deformation and recrystallization,the crystal orientation will also change to form a texture,studies have shown that an increase in the <111> // ND recrystallization texture content in the finished sheet is beneficial to improve the deep-drawing properties of ferritic stainless steel,and the surface wrinkling defects in the forming process were also considered to be related to the micro-region texture distribution.Therefore,the study of plastic deformation characteristics of ferrite polycrystals has important theoretical significance and application value for the analysis of deformation texture and deformation anisotropy.In this paper,combined with experimental research and crystal plasticity theory,the plastic deformation mechanism of ferritic stainless steel crystals and the texture formation rules of ferritic stainless steel finished plates are analyzed through deformation and recrystallization annealing experiments;The Plastic Finite Element Model(CPFEM)analyzes the influence of micro-orientation on surface ridging during plastic deformation of ferritic stainless steel finished plates,and realizes the quantitative prediction of stress-strain response and surface ridging of ferritic stainless steel during deformation.The specific research contents include:1)Research on evolution law of microstructure and texture of ferrite stainless steel during cold rolling deformation and recrystallization annealingThe micro-orientation and structure of the cold-rolled sheet with a deformation amount of 30%,50%,and 70% were detected by using Electron Backscatter Diffraction(EBSD)technology.The orientation after deformation is mainly ? texture and ? texture.With the increase of the amount of deformation,the strength of the ? texture increased,the structure was stretched into a fibrous shape,and the small-angle grain boundaries and energy storage increased.Meanwhile,by comparing the sizes of ?-texture and ?-texture deformed grains in the ND direction after deformation,it is proved that ?-texture has better formability than ?-texture.The grain size after recrystallization will be gradually refined with the increase of the deformation amount,which is beneficial to the improvement of the material propertiesThe quasi-in-situ tracking technology was used to study the recrystallization process of cold-rolled samples at different annealing times,and the evolution of the microstructure and micro-orientation of the entire process from recrystallization to complete recrystallization was successfully obtained.It shows that the nucleation position in the recrystallization process is in the order of ? texture ? other orientations(non-?,? texture orientation)? ? texture,and the small-angle grain boundaries of the nucleation position disappear.And due to the orientation nucleation mechanism,the new grain orientation will partially retain the original deformed grain orientation,thus forming a recrystallized texture.2)Detection and analysis of micro-orientation characteristics of ferritic stainless steel sheetIn order to give the crystal plastic finite element real orientation,the surface and center microdomain orientation of the RD-ND cross section and RD-TD cross-section surface and central micro-area orientations were examined by EBSD,and the micro-region texture and grain boundary distribution characteristics were analyzed.It is clear that the micro-orientation of ferritic stainless steel is mainly concentrated on the ? texture and the ? texture.The orientation of the central position has a tendency to be distributed in grain clusters along the rolling direction,And the difference in texture strength between the center position and the surface position makes it a texture gradient along the thickness direction.3)Construction of crystal plastic finite element modelBased on the crystal plasticity theory,using the material deformation subroutine UMAT in the Abaqus finite element software,on the basis of the Huang Yonggang single crystal plastic program framework,a body-centered cubic ferrite polymorphic deformed crystal plastic finite element model was compiled.Based on the rate-dependent model,the deformation hardening model of ferritic stainless steel is characterized.Through consulting literature and stress-strain curve fitting,the crystal plastic constitutive parameters of ferritic stainless steel were determined.By calculating the classic theoretical model of wrinkling on the surface of ferritic stainless steel proposed by Chao,Takechi and Wright,it is clarified that the grain cluster is an important reason for ridging of ferritic stainless steel.In addition,the experimentally obtained EBSD data of ferrite stainless steel crystal orientation distribution is imported into the constructed crystal plastic finite element model,and the corresponding relationship between crystal orientation distribution and ridging in the surface layer and the central layer microzone,as well as the effect of texture gradient on ridging were analyzed.The calculated results were consistent with the experimental results.Through calculation,the positive strain(E33)and shear strain(E13)are determined to be the important factors that determine the difference between the deformation of grain clusters and the surrounding region,thus causing the deformed surface to ridge.Finally,the true stress-strain curves obtained by simulation and experiment are compared to verify the correctness of the simulation results.