The Investigation Of The Effects Of Electrically Assisted Forming On The Microstructure And Properties Of Non-oriented Silicon Steel And Its Mechanism

Non-oriented silicon steel is among the most ouput in metallic functional material at present,mainly used in the manufacturing of motor and generator cores.Its magnetic properties directly influence motor efficiency and are closely related to the loss of electric energy.Improving its magnetic properties is an important way to achieve energy saving and carbon emission reduction.In recent years,the development of modern industries such as new energy vehicles and robot industry and others makes the requirements of non-oriented silicon steel sheet with thinner thickness,higher magnetic induction intensity,and lower magnetic anisotropy and iron loss.The poor plasticity of non-oriented silicon steel leads to the edge crack of thin specification which makes rolling fail.And the rolling force of thin specification is a heavy load for rolling mills.These problems limit the thickness reduction of silicon steel sheet.Improving the plasticity of non-oriented silicon steel and reducing its deformation resistance while keeping better magnetic properties is urgently needed.It is more and more difficult for traditional means to solve these problems.Investigations showed that electrically assisted forming can change microstructure,improve plasticity,and reduce deformation resistance.It may have a great potential to be applied in the processing of non-oriented silicon steel.Therefore,it is of great significance to study the effects of electrically assisted forming on microstructure and properties of non-oriented silicon steel and its mechanism.In this research,the non-oriented silicon steel containing 0.5wt.%silicon was used.Electrically assisted tensile tests and static current heating tests were carried out under different electric current densities and cooling conditions.Metallographic,electron back-scatter diffraction(EBSD),and X-ray diffraction(XRD)measurements were carried out.The effects of electrically assisted tensile forming(EAF)on mechanical properties,magnetic properties,and microstructures and its mechanisms were studied.The research about the effects of EAF on mechanical properties show that,compared with tensile forming without electric current(TF),in EAF the plasticity of the material was improved under natural cooling with current density of 7.5 A/mm~2～10 A/mm~2 and under water cooling with current density of 10 A/mm~2～16 A/mm~2.And elongation was increased by 64%at most.The deformation resistance was significantly reduced.The variation law of stress drop in EAF was revealed and the constitutive models of EAF were established.The effects of EAF on magnetic properties were analyzed and the results show that,compared with TF,EAF reduced magnetic anisotropy and promoted magnetic induction intensity.Magnetic anisotropy was reduced by 92%and magnetic induction intensity was increased from 1.735 T to 1.751 T at most.Under suitable deformation conditions,EAF reduced iron loss.The effect of electric current on magnetic properties is much larger in the direction parallel to electric current than in the direction perpendicular to electric current.Compared with TF,EAF enhanced cube and Goss texture.The volume fraction of Goss texture was increased by 3.3 times at most.Under suitable deformation conditions,EAF enhanced rotated cube texture andθ-fiber and reducedγ-fiber.The microstructure evolution and mechanism of mechanical property changes during EAF were studied.The results show that EAF promoted grain size,the axial ratio of grains,grain boundary curvature,triple junction curvature,and the degree of deviation from the equilibrium of triple junctions and reduced microstructural defects and geometrically necessary dislocation density(GNDs).The mechanism of mechanical performance changes reveals that the elongation variation in EAF is attributed to that the effects of electric current on the special grain boundary fraction and the triple junction distribution result in the change of the size of special grain boundary cluster and electric current promotes grain size which both cause the change of microcrack propagation,and the decrease of microstructural defects causes the variation of microcrack initialization.The decrease of the deformation resistance in EAF is attributed to serval aspects,that is,the increase of grain size and grain axis ratio promotes the grain boundary spacing along the tensile direction,the increase of grain boundary curvature promotes the migration ability and migration rate of grain boundaries,and the increase of triple junction curvature and the degree of deviation from the equilibrium of triple junctions reduces the resistance of triple junctions in deformation.The texture evolution and mechanism of magnetic property changes during EAF were studied.The analysis reveals that the enhancement of Goss texture is due to the preferential nucleation and growth of Goss grains which is attributed to the influences of electric current on many factors,such as the increases of the Goss grain size,the Goss grain boundary curvature,theΣ3 andΣ9 coincidence site lattice(CSL)boundaries,and the microstrctural defects of Goss grains.The study of the mechanism of magnetic changes reveals that the increase of magnetic induction intensity is attributed to the change of textures.The reduction of magnetic anisotropy can be attributed to the change of textures,the decrease of microstructural defect density and GNDs,and the decreased gradient of the internal stress.The reasons for the reduction of iron loss in some EAF specimens are the increase of grain size and the reduction ofγ-fiber.This study proved that under suitable deformation conditions EAF can improve the plasticity,reduce the deformation resistance,enhance the magnetic induction intensity,and reduce the iron loss and magnetic anisotropy of non-oriented silicon steel.The research provides a new effective method for developing thinner and better performance silicon steel,and supplies a theoretical reference for the application of EAF in silicon steel production.