Papers by Keyword: Non-Oriented Electrical Steel

Abstract: Cube texture ({001}<100>) is a desired final texture in non-oriented electrical steel sheets used as magnetic cores because it contains two easy <100> axes in the sheet plane, which is beneficial to the magnetic properties. However, the cube texture is very difficult to form in non-oriented electrical steels through conventional rolling and annealing. It has been shown that after conventional rolling, the deformed <111>//ND (normal direction) grains provided nucleation sites for the unfavourable <111>//ND texture during recrystallization, leading to a final <111>//ND texture. To eliminate the <111>//ND texture and promote the {001}<100> texture, an uncommon rolling process, i.e. inclined rolling, was adopted in this study. By rotating the hot rolling direction by 60° around the ND, an uncommon initial texture, the rotated Goss ({110}<110>), was intentionally generated. This was intended to change the orientation flow during plastic deformation, and suppress the formation of the conventional <111>//ND texture in the deformed microstructure. Plane-strain compression (rolling) of the rotated Goss grains produced shear bands within these grains due to their large Taylor factor. Electron backscatter diffraction (EBSD) characterization of the shear bands illustrated that, crystallites with the cube orientation were formed within these shear bands. During recrystallization, the shear bands provided preferential nucleation sites, and the cube crystallites preferentially nucleate within the shear bands. These cube crystals can then grow into the deformed matrix, and lead to the formation of a strong cube texture in the final annealed steel sheets.

Abstract: In this paper four non-oriented electrical steel grades M400-50A, M400-65A, M300-35A and NO20, utilizing a laboratory single sheet tester, were analyzed. For the magnetic measurements the peak magnetic polarization of 1 T was chosen. The frequency was variated between 3 Hz and 400 Hz. The isotropic electrical steel sheets were cut through punching technology, along the rolling direction. The experimentally determined energy losses were decomposed, using the loss separation theory, into hysteresis, classical and excess components. The relative magnetic permeability was analyzed and its parts, real and imaginary permeability were computed. The non-oriented alloy magnetic properties’ variation as a function of frequency was plotted and explained in the paper.

Abstract: Non-oriented electrical steel sheets are the most commonly used material for the manufacturing of magnetic cores for electric motors and generators. The microstructure and texture of the steel after final annealing have a significant effect on the magnetic properties of the lamination core. To investigate the effect of cold rolling and annealing on the magnetic properties of the steel sheets, a 0.9 wt% Si non-oriented electrical steel was cold rolled at different angles to the hot rolling direction (HRD) and annealed at various temperatures (600°C to 750°C) to produce dissimilar microstructures. The progress of recrystallization was characterized by electron backscatter diffraction (EBSD), and the magnetic response of the steel at various stages of recrystallization was evaluated by magnetic Barkhausen noise (MBN). A number of MBN parameters, e.g. the root mean square, the smoothed envelope, the peak, the full width at half maximum (FWHM) of the envelope, the time integral of the MBN signals and the MBN energy, were analyzed with respect to the fraction of recrystallization during annealing. The results show that cold rolling at different angles to the hot rolling direction induces various deformation microstructures and stored energies, which, in turn, lead to considerably different recrystallization behaviours during annealing. The difference in recrystallization of these materials is also reflected in the MBN parameters.

Abstract: Non-oriented electrical steel, as the core magnetic material, is firstly blanked into lamination in motor manufacturing. As for the newly developed steel, there is a general tendency toward thinner and coarser-grained. Due to blanking clearance and thickness are both down to the sub-millimeter scale, grain size becomes an important role in formation of blanked edge quality, which mainly determines the deterioration level of magnetic properties. This paper aims to systemically investigate the influence of blanking clearance and grain size on blanked edge quality. In this research, non-oriented electrical steel sheets of the same chemical composition, 3 thicknesses and 3 grain sizes are prepared for blanking tests over the conventional relative blanking clearance range. The blanking edges are quantitatively examined by means of optical microscopy to visualize the distribution of plastic deformation. The results show that there exists an optimum clearance that leads to a fine blanked edge. In further study, an approximate linear equation of the ratio of clearance/grain size (c/D) vs. D is found for optimizing the blanked edge quality. This research thus provides an in-depth understanding and guidance for optimum blanking clearance determination influenced by size effect.

Abstract: In the present research work the determination of residual stress distribution in welded non-oriented electrical steel samples is discussed. Tungsten Inert Gas and Electron Beam Welding were used as the welding methods. The residual stresses induced by welding estimated by the magnetic, non-destructive method of Barkhausen noise and were compared with the values resulting from the semi-destructive method of X-ray diffraction Bragg-Brentano (XRD-BB). In order to evaluate accuracy and reliability of the magnetic methods applied, the steel samples were subjected in both compressive and tensile stress and the magnetic noise values were correlated to residual stress values through an appropriate calibration curve. Furthermore, the fluctuations of the residual stresses in the welding zones of the welded samples were discussed on the basis of the experimental evidence and the microstructural changes occurring during welding. It was found that the residual stress determined by MBN method was in good agreement with the XRD-BB results. However, the residual stress determined by magnetic permeability method was not in good agreement with the XRD-BB results. In contrast to the XRD-BB method, the magnetic techniques required a precise calibration procedure in all zones with noticeably different microstructure.

Abstract: In this paper the microstructure evolution of an iron-silicon alloy with 3.2 wt.% silicon throughout the manufacturing stages hot rolling, cold rolling and annealing is presented. Starting with a 35 mm thick feedstock, which was hot rolled to 1 mm, with different cooling conditions, the material was cold rolled to a final thickness of 0.3 mm and final annealed under same conditions to show the influence of the hot rolling on the texture and microstructure of the final annealed material.

Abstract: Effects of RE addition on deoxidation and desulphurization efficiency, precipitation behaviors of the inclusions, microstructure and magnetic properties of the finished sheets have been investigated for no-oriented electrical steel produced in industrial scale. The most suitable addition amount of RE alloy added in the electrical steel bearing is proposed for excellent deoxidation and desulphurization efficiency. RE added into the steel can form larger and higher melt point RE oxides, RE sulfides and RE oxysulfides inclusions removing from the bath by floating which decreases the numbers and increases the size of the fine inclusions. The average size of the inclusions remained in the steel is 0.8μm~1.4μm. RE content affects grain size by influencing number and size of fine inclusions in the finished steel sheets. The magnetic flux density of the finished steel sheets dereases with the increase of RE content while the lowest core loss of it has an optimum RE content in the steel. In the steel bearing 1.15wt% Si, the content of RE should be strictly controlled in the range from 20×10^-4 wt% to 60×10^-4 wt%.

Abstract: A Fe-1.3% Si non-oriented silicon steel strip was produced by twin-roll strip casting process, and subsequently treated with cold rolling and annealing. The effect of heating rates on the recrystallization and precipitation behavior of second phase particles (AlN and MnS) was investigated by MMS-200 thermal mechanical simulator. It was found that the recrystallization area fraction decreased obviously with the increase of heating rate. At the heating rate of 5 °C/s, the recrystallization rate gradually decreased with the extension of holding time, but it increased at the rapid heating rates. The particle’s sizes mainly concentrated in 50~200 nm at the heating rate of 5 °C/s during annealing. The number of particles under 50nm increased gradually and the number of precipitates between 50~400 nm reduced significantly when the heating rate was increased to 50~300 °C/s. The results indicated that the rapid heating rate could refine the size of precipitates and decrease the number of particles above 50nm.

Abstract: Texture change during grain growth in Fe-3%Si non-oriented electrical steel was investigated. Cold rolled steel, 0.35mm in thickness, was annealed and recrystallized as an initial structure. Normal grain growth and abnormal grain growth occurred by additional annealing. {111} was dominant in the initial texture. However {100} component, which was not in majority in the initial structure, became stronger after normal grain growth. It was revealed that an average grain size of {100} in the initial structure was bigger than those of other components by analysis of the EBSD data,. Therefore, it is concluded that {100} strengthened after normal grain growth due to its size advantage. On the other hand, {111} components became more stronger after abnormal grain growth. It is inferred that another mechanism of the texture change worked in abnormal grain growth.

Abstract: In order to improve the magnetic properties, copper was added to cold-rolled non-oriented electrical steel with low carbon and low silicon. The grain sizes and precipitates in hot-rolled bands of the investigated steel were quantitatively studied. The results show that the recrystallization of deformed grains has been completed in the coiled bands and the recrystallized grains are fine due to low coiling temperature and pinning effect of precipitates. But grains grew up obviously after normalizing annealing at 850°C for 1h because the mobility of grain boundary is so good at elevated temperature that pinning effect of precipitates can’t prevent the migration of grain boundary. Thus, normalizing annealing is necessary to obtain large grains in hot-rolled band. In addition, the typical morphologies of precipitates in hot-rolled bands are square, rectangular, hexagonal and triangular and they are identified as AlN phase based on EDS and SEAD analysis, which can form by epitaxial growth mode. For the hot-rolled bands coiled at 550°C, the increase of average size and volume fraction of AlN particles with coiling time is mainly related to the growth of AlN particles, whereas for the hot-rolled bands coiled at 650°C, the decrease of average size and the increase of volume fraction of AlN particles with coiling time are chiefly attributed to the precipitation of many small AlN particles. The volume fraction of AlN particles increases with coiling temperature because they precipitate more quickly at 650°C than at 550°C.