Study On Recrystallization、texture And Precipitation Behavior Of High Strength Non-oriented Silicon Steel During Normalization

Due to the continuous deterioration of the environment,new energy vehicles have become the development trend in the world automobile industry.As the core material of the rotor of new energy vehicle driving motor,non-oriented silicon steel is the guarantee of high efficiency and high power density of vehicle motor.Due to the high speed of the driving motor of new energy vehicles and the high torque requirements of vehicle starting and acceleration,the non-oriented silicon steel used in the rotor is required to have excellent mechanical properties while meeting the requirements of high magnetic induction intensity and low iron loss.In the production process of non-oriented silicon steel,normalizing treatment after hot rolling and crimping is one of the indispensable processes.The recrystallization structure,texture and precipitation behavior after normalizing treatment have genetic effects on subsequent processes and affect the properties of finished products.The study of recrystallization structure,texture and precipitation behavior of steel plate in the process of normalization has important guiding significance for improving the performance of non-oriented silicon steel used in the rotor of new energy vehicle.In this thesis,the evolution of recrystallization,texture and precipitation behavior of non-oriented silicon steel during the process of normalizing has been studied with 3.0%Si,0.8%Al,0.15%Nb and 15ppm Ce as composition systems by Zeiss metallographic microscope,X-ray diffractometer and transmission electron microscope.In this thesis,through adding Nb elements in the traditional orientation of silicon steel,The strength of unoriented silicon steel was improved employing solid solution Nb drag on dislocation and grain boundaries and Nb-rich secondary precipitates pinning grain boundaries,However,too much NB-rich second phase pinning grain boundaries makes it difficult for grains to grow,hinders the movement of magnetic domains,and leads to severe damage of magnetic properties,Therefore,it is very important to control the size and quantity of Nb-rich second phase by reasonable process optimization.In this thesis,the evolution of recrystallization,texture and precipitation behavior of non-oriented silicon steel during normalization has been studied utilizing Zeiss metallographic microscope,X-ray diffractometer and transmission electron microscope.The results show that the precipitates of non-oriented silicon steel hot rolled plate used for driving motor of new energy vehicle are mainly Fe₁₆Nb₆Si₇,Nb₇P₄,Nb C and a small amount of Mn S.At the beginning of normalization treatment,with the increase of normalization temperature from 850℃to 1100℃,the degree of coarsening and remelting of NB-rich second phase precipitates gradually increased,and the effect of inhibiting grain growth gradually decreased.The recrystallization structure gradually replaced the deformation fiber structure of hot rolled plate,and the recrystallization behavior occurred preferentially on the surface layer of the sample.Orientation in new energy vehicles drive motor,hot-rolled silicon steel plate texture mainly brass texture,rotating cube texture and gauss texture is given priority to,a normative sample texture type and texture of hot rolled states type basic same,sample processing,often the second phase particle coarsening rich Nb back to dissolve,recrystallization grain growth,makes the remarkable increase of eta orientation line texture and texture gamma orientation line greatly weakened;Recrystallization is more likely to occur in the sample with lower final rolling temperature during normalization,and the texture strength of the hot rolling sample with lower final rolling temperature along theηorientation line is higher under the same normalization process.