The Influence Of Punching And Annealing On Microstructure And Magnetic Properties Of Electrical Steel Sheets

The effect of punching and annealing process on microstructure and magneticproperties of electrical steel sheets was investigated. Microstructure, hardness distribution,residual stress distribution and magnetic properties were observed and measured by meansof ultra-depth three-dimensional microscopes, micro-hardness tester, X-ray residual stressanalyzer and single sheet tester. The punching samples were750℃×1h vacuum annealingin order to obtain the degree of recovery of power loss and magnetic induction ofelectrical steel sheets. The main research results are as follows:(1) The influence of punching process on striped non-oriented microstructure is notobvious, but no matter for non-oriented steel sheets or oriented steel sheets, there is a400μm strain hardening region near cutting edge due to punching process,400~600μm isweakened strain hardening region, in which hardness and residual stress are bigger thanthat in center region.(2) Magnetic properties of electrical steel sheets have a significant deteriorationowing to large residual stress near cutting edge after punching, the iron losses of electricalsteel sheets increase up to10%and magnetic induction decreases up to50%in weakmagnetic field, while magnetic induction nearly constant in strong magnetic field.(3) Magnetic properties of non-oriented are still different along different direction,the power loss and coercivity are smaller along rolling direction than that along transversedirection.(4) Microstructure of toothed steel sheets near cutting edge has a severe deformationdue to its own configuration and dimensions. The grains near cutting edge are larger thanthat near center because of great deformation energy resulting from severe deformation.There also is a400μm strain hardening region near cutting edge due to punching process,400~600μm is weakened strain hardening region. Hardness and residual stress are bigger near sharp and corner region than than that straight cutting edge, the iron losses P1.5increases up to12%.(5) The effect of750℃vacuum annealing on microstructure of striped samples isnot obvious, however, on toothed samples is apparent. Recovery and recrystallization willoccur due to severe deformation for the toothed samples resulting in grains near cuttingedge grow, grains size near center region almost constant. Meanwhile, deformation andstrain hardened region are reduced after annealing, residual stress also greatly decreases,which lead to power loss decreases and magnetic induction increases, but magneticproperties of punching samples are not fully recover after annealing.