Cold rolled non-oriented silicon steel with high reduction rate
Abstract: Microstructure and texture are important factors affecting the properties of non-oriented silicon steel. In order to improve the product properties, the effects of cold rolling reduction rate (71.7%~87.0%) on the microstructure, texture, magnetic properties and mechanical properties of high grade non-oriented silicon steel were studied. The results show that the average grain size decreases first and then increases with the increase of cold rolling reduction rate. The Gaussian and cubic textures weaken, γ fibers strengthen, α fibers change into stronger α*({h, 1, 1} < 1/h, 1, 2 >) texture, and strengthen with the increase of cold rolling reduction rate, and its peak value gradually moves towards the {111} plane. Power frequency iron loss P1.5/50, high frequency iron loss P1.0/400 and magnetic polarization strength J5000 decreased at the same time, the yield strength changed little, and the surface hardness gradually increased. When the reduction rate of cold rolling is increased from 84.7% to 87.0% and the thickness is reduced to 0.30mm, the decrease of high frequency iron loss is 11 times that of power frequency iron loss, and the increase of surface hardness is larger. The above research results provide a good guide for the optimization of texture and structure of silicon steel after thinning.
Key words: cold rolling; Reduction rate; High grade non-oriented silicon steel; High frequency iron loss; Power frequency iron loss; Yield strength; Surface hardness
quotation
Problems such as exhaust pollution and oil safety have prompted new energy vehicles to become the mainstream of future motor vehicles, and high-grade non-oriented silicon steel, as an important soft magnetic material, is widely used in high-end home appliances, new energy vehicle drive motors and efficient industrial motors and other fields. Benefiting from the stable development of the power industry, the implementation and promotion of frequency conversion technology in the home appliance industry, the rise of the new energy automobile industry and the development of motor energy saving and high efficiency, the domestic demand for high-grade non-oriented silicon steel will continue to rise significantly. In the past 10 years, due to the rapid promotion of new energy vehicles, high grade non-oriented silicon steel is required to have higher magnetic induction, lower iron loss and thinner thickness. Improving the magnetic properties of non-oriented silicon steel has always been the focus of research in the field of silicon steel. Due to cost and efficiency, most enterprises tend to use the cold rolling method when producing non-oriented silicon steel. The content of alloying elements, the quantity and distribution of inclusions, the structure, texture, plate thickness and surface quality all have significant effects on the magnetic properties of non-oriented silicon steel. Texture and grain size are the two most important factors affecting magnetic properties and mechanical properties of non-oriented silicon steel under the condition of constant composition and plate thickness. In actual industrial production, in order to meet the different needs of the market, silicon steel needs to prepare a variety of thickness specifications, and the thinner the specifications, the greater the cold rolling reduction rate. Changing the reduction rate of cold rolling will affect the deformation microstructure and texture, and thus affect the formation and development of recrystallization texture. Many scholars have focused on the influence of thickness reduction on product structure, texture and magnetic properties. For 2.69%Si non-oriented silicon steel, Dong Hao et al. prepared 0.20mm thickness silicon steel by secondary cold rolling, and found that when the reduction rate of secondary cold rolling was more than 55%, the texture groups of {111} < 112 > and {111} < 110 > which were unfavorable to magnetic properties gradually strengthened. De Dafe SFS et al. studied the effect of cold rolling reduction rate on the recrystallization texture of Fe-3%Si alloy, and found that good η recrystallization texture and good magnetic properties could be obtained when the cold rolling reduction rate was 64.3%~72.2%. Quadir MZ et al. studied the effect of cold rolling reduction rate on the deformation of IF steel. When the cold rolling reduction rate was 50%, γ-recrystallization texture would be formed after annealing. When the reduction rate increased to 80%, γ-recrystallization texture would gradually become stronger, and when the reduction rate increased to 95%, γ-recrystallization texture would gradually become stronger. The recrystallization texture of {111} < 123 > ~{554} < 225 > and the weaker {114} < 481 > texture are obviously unfavorable to the magnetic properties. The thickness specifications of the above research are limited, and for the thin non-oriented silicon steel prepared by one cold rolling, the magnetic properties and mechanical properties of the product have not been systematically analyzed after the reduction rate is large and the thickness is reduced.
Therefore, in this paper, 2.54%Si high grade non-oriented silicon steel normalized plate produced by TISCO was selected and rolled into products whose thickness basically covered the common specifications of silicon steel market (0.65, 0.50, 0.35, 0.30mm) with a high reduction rate of more than 70%. The effects of microstructure and texture of annealed sheet on magnetic properties and mechanical properties of different frequencies under high reduction rate were systematically analyzed, which provided technical support for the development of high grade non-oriented silicon steel products and the selection of motor materials in different fields.
Concluding discussion
(1) The number of recrystallization nucleation increases, the average grain size decreases, and the grain size distribution becomes uniform with the increase of cold rolling reduction rate of high grade non-oriented silicon steel. When the cold rolling pressure is increased to 87.0% and the thickness is reduced to 0.30mm, the heating rate of the steel plate during annealing is accelerated, the average grain size increases, and the grain size distribution is uneven again.
(2) With the increase of the cold rolling reduction rate of high grade non-oriented silicon steel, the cube texture and Gaussian texture strength of annealed sheet weaken, the γ fiber texture increases, the α fiber texture is deflected to form a strong α* fiber texture, and the peak component moves towards the {111} plane.
(3) Power frequency iron loss P1.5/50, high frequency iron loss P1.0/400 and magnetic polarization strength J5000 all decreased with the increase of cold rolling reduction rate. The decrease of high frequency iron loss P1.0/400 is higher than that of power frequency iron loss P1.5/50. When the reduction rate of cold rolling increased from 84.7% to 87.0% and the thickness decreased to 0.30mm, the decrease of power frequency iron loss slowed down, and the decrease of high frequency iron loss increased, and the decrease of high frequency iron loss was 11 times that of power frequency iron loss.
(4) With the increase of the cold rolling reduction rate of high grade non-oriented silicon steel, the yield strength increases first and then decreases with the change of grain size, but the overall change is little; The hardness increases with the increase of cold rolling reduction rate. When the cold rolling reduction rate increases from 84.7% to 87.0% and the thickness of steel plate decreases to 0.30mm, the hardness increases greatly.
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