| Fe-6.5wt.%Si high-silicon steel has excellent soft magnetic properties such as high magnetic permeability,high resistivity,low iron loss.near-zero magnetostriction,etc.These features are conducive to improving equipment efficiency,reducing noise,miniaturizing devices,and saving energy.However,due to the presence of ordered phases like B2 and DO3,the room-temperature brittleness exists,making the alloy very difficult to be deformed,and thus seriously restricts the industrialization and application of Fe-6.5wt.%Si high-silicon steel.Due to the fact that fast cooling can effectively inhibit the formation and growth of ordered phases,melt-spinning technology is beneficial to improve the room temperature ductility of Fe-6.5wt.%Si high-silicon steel with large cooling rate.In this thesis,the Fe-6.5wt.%Si high-silicon steel ribbons with good quality were successfully prepared through melt-spinning method.The as-spun microstructure and properties,effect of heat treatment on microstructure evolution and magnetic properties,and preparation of insulating layers were studied.The Fe-6.5wt.%Si high silicon steel ribbons were also assembled and tested as cores in high-frequency reactors and motors.The main conclusions are as follows:(1)Continuous Fe-6.5wt.%Si high-silicon steel ribbons with a maximum width of 60 mm and thickness of 30-40 ?m can be successfully prepared by melt-spinning process.The ribbons exhibit very fine microstructure and good room-temperature ductility.The surface of the ribbons contacting the cooling roller is composed of equiaxed grains with grain size of 1.7 ?m.while the free surface is composed of columnar grains with grain size of 2.4 ?m.The columnar grains are tilted 20° toward the spinning direction,exhibiting a near {100} texture parallel to the surface of the ribbon.The melt-spun ribbons own unique low iron loss at high frequencies above 20 kHz.(2)After heat treatment at 400 ?,500 ?,and 600? for 5 h.the grain size and the orientation of the free surface of the ribbon rarely change.while the DC performance is significantly improved.For the AC properties,the iron loss is reduced under low frequencies below 5 kHz,and increased under high frequencies above 10 kHz.For the heat treatment below 600?,although the grain size rarely change.the defects such as dislocation density reduces,resulting in reduction of the resistance to the magnetic domain motion,i.e.resulting in improvement of DC performance and also the AC properties under low frequencies.For the iron loss at high frequencies,the increment of the eddy current loss resulted from the reduction of the electric resistance would be responsible for the increment of the total loss.(3)After heat treatment at 850?,the grain size is dependent with the annealing time.For the annealing time lasting from 10 min to 5 h.the grain size is fitted well to the grain growth kinetic equation of D3-D03 = 2971t,in which the grain growth exponent is 3,deviating from the classical grain dynamics theory.The preferential orientation of<100>turns toward to the normal direction(ND)of the surface.After heat treatment at 850?.DC magnetic properties are improved together with the grain growth.The coercive force He and the permeability ?mcomply with Hc =529436/?m.(4)After heat treatment at 1000 ?.the grain boundary has the ability to jump through the deep "corrosion groove",and the grain size is further increased.After 3 h,the grain size is 33.2 ?m,and the DC and AC properties are further improved.With longer annealing time,the grain size reaches saturation and rarely changes.(5)Based on Steimentz law,a new method for prediction of iron loss is proposed:Pt = ktBN,in which kt and N are in dependent with frequency,kt = k0 + afm,N = N0 + bf2 + cf,index m,coefficients a,b,c are related to the microstructure.Based on some tested iron loss data,the relationship between kt,N and frequency can be revealed,and the iron loss under other conditions can be predicted.The prediction results are in good agreement with the measured results.(6)The oxide layer preventing adhesion of the ribbons during high temperature heat treatment was invented and fabricated successfully.After heat treatment in air at 500 ?,a pre-oxide layer with a thickness of 16-21 nm is formed on both surfaces of the ribbons.The oxide layer consists of Fe2O3 and SiO2,and the layer can prevent adhesion of the ribbons during high temperature heat treatment.The ribbons with pre-oxide films have better magnetic properties after heat treatment at 1000 ? for 3 hours than that without pre-oxide layers.(7)The ribbons were assembled and tested as cores in high-frequency reactors and motors.Compared with reactors assembled by Fe-based amorphous ribbons,the noise of the reactors can be decreased by 30%.Compared with the high-speed motors assembled by ordinary non-oriented silicon steel,the torque was increased,and the iron loss can be decreased by 67%. |
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