Influence Mechanisms Research Of Rare Earth On The Magnetic Properties Of High Grade Non-oriented Silicon Steel

High grade non-oriented silicon steel is the main soft magnetic material for the manufacture of large motor and generator core.Its magnetic properties are one of the key factors affecting the core loss of large motor and generator.Improving the magnetic properties and stability is of great significance for reducing core loss and improving energy efficiency of large motor and generator.Based on the production process of high grade non-oriented silicon steel（3.0%Si-0.85%Al-0.27%Mn）,the formation mechanism of rare earth inclusions was studied by means of theoretical analysis,industrial experiment,laboratory experiment and detection analysis;the influence of rare earth content on their inclusions（type,size and distributions）,the effect of rare earth treatment on the refinement of solidification structure of continuous casting billet,and the effect of rare earth treatment on process organization and texture evolution were studied.The mechanism of the effect of rare earth treatment on the magnetic properties of high grade non-oriented silicon steel is further discussed.The main research conclusions are as follows:（1）The formation thermodynamics of inclusions in smelt-continuous casting process and the detection and analysis of inclusions in production process show that the endogenous inclusions in high grade non-oriented silicon steel mainly include Al₂O₃,m Ca O·n Al₂O₃,m Al₂O₃·n SiO₂ and unavoidable m Mg O·n Al₂O₃ inclusions.The secondary oxidation of steel mainly generates Al₂O₃ and Ca O·2Al₂O₃ and some low melting point 2Ca O·Al₂O₃·SiO₂ and 12Ca O·7Al₂O₃.The Ca introduced by the alloy promoted the transformation of Al₂O₃ to calcium aluminate,and replaced the Mg element in Mg O·Al₂O₃ to the low melting point Ca O·Mg O·Al₂O₃ composite inclusions.（2）The theoretical and experimental study of rare earth treatment of metamorphic inclusions shows that the effect of rare earth metamorphic inclusions is mainly reflected in the reaction of rare earth with Ca O·2Al₂O₃ and 12Ca O·7Al₂O₃ in Al₂O₃ and m Ca O·n Al₂O₃ inclusions,and the product is（La,Ce）Al O3,the metamorphic effect of rare earth on Al₂O₃·SiO₂ and Mg O·Al₂O₃ inclusions in steel is weak;With the increase of rare earth content,rare earth inclusions change from angular（La,Ce）Al O₃ to spherical or near-spherical（La,Ce）₂O₂S;The decrease of molten steel temperature and the secondary oxidation of steel promote the formation of（La,Ce）₂O₂S;Al₂O₃ and Mg O-Al₂O₃ in the steel nucleate and grow on the surfaces of La Al O₃,Ce Al O₃,La₂O₂S,and Ce₂O₂S,forming composite inclusions such as（La,Ce）Al₂O₃,（La,Ce）Al₂O₃-（La,Ce）₂O₂S,and（La,Ce）₂O₂S;Nitrides precipitated during steel solidification exist in the form of composite inclusions such as Al N-（La,Ce）Al₂O₃,Al N-（La,Ce）Al₂O₃-（La,Ce）₂O₂S,and Al N-（La,Ce）₂O₂S.（3）According to the heterogeneous nucleation theory,the calculation of“edge-edge matching”model and the industrial test,the results show that:1)rare earth treatment promotes the desulfurization of molten steel and the deterioration of Al₂O₃,Ca O·2Al₂O₃ and 12Ca O·7Al₂O₃;2)The reason for the fine of the equiaaxial crystal in the center of the casting billets is that（La,Ce）₂O₂S is the core of heterogeneous nucleation ofδ-Ferrite.（4）Research based on density functional theory and industrial experiments indicates that when treating with 26ppm of rare earth elements,the excess amount of grain boundary layers per unit area(1?^-2)is 0.13;the average grain size of the finished plate increases by 6.3μm;the content ofγ-fiber texture（{111}<112>）decreases by10.8%,while the content ofα*-fiber texture（{100}<120>～{114}<481>）increases by12.8%.The magnetic properties show significant improvement,with the P_1.5/50reduced by 0.07W/kg and B₅₀ increased by 0.005T.When treating with 38ppm of rare earth elements,the excess amount of grain boundary layers per unit area(1?^-2)is 0.16.The average grain size of the finished plate increases by 4.1μm;the content ofγ-fiber texture（{111}<112>）increases by 4.4%,while the content ofα*-fiber texture（{100}<120>～{114}<481>）decreases by 7.8%.The P_1.5/50 decreases by 0.03W/kg,and the B₅₀ decreases by 0.005T.It is proved that the grain boundary segregation of rare earth elements has two sides on the magnetic induction intensity.（5）The recrystallization experiment of cold rolled plate with rare earth content of 38ppm shows that the rare earth segregation is the reason that the recrystallization starting temperature of cold rolled plate increases from 620℃to 640℃,and the grain size of the annealed plate treated with rare earth is smaller than that without rare earth treatment in the low temperature recrystallization zone（760～860℃）.The effect of rare earth segregation inhibits the grain growth at the low temperature annealing stage of the finished product,and then promotes the development ofγ-fiber texture.