Non-oriented Electrical Steel Sheets Research Articles

Effects of Processing Routes on Recrystallization Texture Development and Magnetic Properties of 0.10 Mm Ultrathin Non-Oriented Electrical Steel Sheets for High-Frequency Application

Effects of Processing Routes on Recrystallization Texture Development and Magnetic Properties of 0.10 Mm Ultrathin Non-Oriented Electrical Steel Sheets for High-Frequency Application

Textures of Non-Oriented Electrical Steel Sheets Produced by Skew Cold Rolling and Annealing

In order to investigate the effect of cold rolling deformation mode and initial texture on the final textures of non-oriented electrical steels, a special rolling technique, i.e., skew rolling, was utilized to cold reduce steels. This not only altered initial textures but also changed the rolling deformation mode from plane-strain compression (2D) to a more complicated 3D mode consisting of thickness reduction, strip elongation, strip width spread and bending. This 3D deformation induced significantly different cold-rolling textures from those observed with conventional rolling, especially for steels containing low (0.88 wt%) and medium (1.83 wt%) amounts of silicon at high skew angles (30° and 45°). The difference in cold-rolling texture was attributed to the change of initial texture and the high shear strain resulting from skew rolling. After annealing, significantly different recrystallization textures also formed, which did not show continuous <110>//RD (rolling direction) and <111>//ND (normal direction) fibers as commonly observed in conventionally rolled and annealed steels. At some skew angles (e.g., 15–30°), the desired <001>//ND texture was largely enhanced, while at other angles (e.g., 45°), this fiber was essentially unchanged. The formation mechanisms of the cold rolling and recrystallization textures were qualitatively discussed.

Characterization Methods along the Process Chain of Electrical Steel Sheet-From Best Practices to Advanced Characterization.

Non-oriented (NO) electrical steel sheets find their application in rotating electrical machines, ranging from generators for wind turbines to motors for the transportation sector and small motors for kitchen appliances. With the current trend of moving away from fossil fuel-based energy conversion towards an electricity-based one, these machines become more and more important and, as a consequence, the leverage effect in saving energy by improving efficiency is huge. It is already well established that different applications of an electrical machine have individual requirements for the properties of the NO electrical steel sheets, which in turn result from the microstructures and textures thereof. However, designing and producing tailor-made NO electrical steel sheet is still challenging, because the complex interdependence between processing steps, the different phenomena taking place and the resulting material properties are still not sufficiently understood. This work shows how established, as well as advanced and newly developed characterization methods, can be used to unfold these intricate connections. In this context, the respective characterization methods are explained and applied to NO electrical steel as well as to the typical processing steps. In addition, several experimental results are reviewed to show the strengths of the different methods, as well as their (dis)advantages, typical applications and obtainable data.

Grain Size Influence on the Magnetic Property Deterioration of Blanked Non-Oriented Electrical Steels.

Non-oriented electrical steel sheets are applied as a core material in rotors and stators of electric machines in order to guide and magnify their magnetic flux density. Their contouring is often realized in a blanking process step, which results in plastic deformation of the cut edges and thus deteriorates the magnetic properties of the base material. This work evaluates the influence of the material’s grain size on its iron losses after the blanking process. Samples for the single sheet test were blanked at different cutting clearances (15 µm–70 µm) from sheets with identical chemical composition (3.2 wt.% Si) but varying average grain size (28 µm–210 µm) and thickness (0.25 mm and 0.5 mm). Additionally, in situ measurements of blanking force and punch travel were carried out. Results show that blanking-related iron losses either increase for 0.25 mm thick sheets or decrease for 0.5 mm thick sheets with increasing grain size. Although this is partly in contradiction to previous research, it can be explained by the interplay of dislocation annihilation and transgranular fracturing. The paper thus contributes to a deeper understanding of the blanking process of coarse-grained, thin electrical steel sheets.

Prediction of Kerf Width in Laser Cutting of Thin Non-Oriented Electrical Steel Sheets Using Convolutional Neural Network

Kerf width is one of the most important quality items in cutting of thin metallic sheets. The aim of this study was to develop a convolutional neural network (CNN) model for analysis and prediction of kerf width in laser cutting of thin non-oriented electrical steel sheets. Three input process parameters were considered, namely, laser power, cutting speed, and pulse frequency, while one output parameter, kerf width, was evaluated. In total, 40 sets of experimental data were obtained for development of the CNN model, including 36 sets for training with k-fold cross-validation and four sets for testing. Compared with a deep neural network (DNN) model and an extreme learning machine (ELM) model, the developed CNN model had the lowest mean absolute percentage error (MAPE) of 4.76% for the final test dataset in predicting kerf width. This indicates that the proposed CNN model is an appropriate model for kerf width prediction in laser cutting of thin non-oriented electrical steel sheets.

Analytical Study on Core Loss Reduction of Segmented Stator Core Motor in Consideration of Rolling Direction of Nonoriented Electrical Steel Sheet

This article proposes the core loss reduction of a surface-mounted permanent magnet motor with a segmented stator core. First, it is shown that the core loss of a motor is decreased by the segmentation of a stator core made of a nonoriented electrical steel sheet. The nonoriented electrical steel sheet used as the segmented stator core has an anisotropy, which is easy to magnetize in the rolling direction. Therefore, it is important to investigate the core loss of the segmented stator core in consideration of the rolling direction of the electrical steel sheet. The rolling direction of the steel sheet can be taken into consideration in magnetic field analysis by using the Enokizono & Soda (E&S) model, which is one of the vector magnetic property utilization techniques. Accordingly, the finite-element method, which introduced the E&S model, is used to evaluate the core loss of the motor. Second, the core loss of the segmented stator core is further reduced by applying a corner radius to each tooth root. Finally, the relation between the core loss and the rolling direction in the segmented stator core applying corner radius is investigated.

Two-Dimensional AC Magnetic Properties of Electrical Steel Sheet with Two-Dimensional DC-Biased Magnetization

To estimate the magnetic properties with two-dimensional AC-magnetization with two-dimensional DC-biased magnetization, three different grades of non-oriented electrical steel sheets with two-dimensional DC-biased magnetization were prepared. As a result, in the high grade specimen, the difference in the magnetic properties depending on the excitation direction (AC excitation direction is parallel to DC excitation direction) was larger than in the low grade specimen, and the magnetic properties were the best when the excitation direction was the rolling direction. Non-oriented electrical steel sheets have small magnetic anisotropy. High grade non-oriented electrical steel sheets have a large magnetic anisotropy to compare with low grade non-oriented electrical steel sheets. It is thought that magnetic anisotropy increased in the high grade non-oriented electrical steel sheets because the B-H loops under DC-biased magnetization were minor loops. In addition, the increase rate of the H widths and the increase rate of the iron losses depending on the excitation direction were relatively consistent. Since the iron loss is proportional to the area of the B-H loop, it is considered that the iron loss increased at the same rate as the H width of the B-H loop.

Angular magnetic Barkhausen noise of incline- and cross-rolled non-oriented electrical steel sheets

Magnetic Barkhausen noise (MBN) analysis is a relatively new technique used to characterize the magnetic properties of electrical steels. Not only has it been utilized to evaluate the overall core loss of electrical steel sheets, but it has also been employed as a non-destructive testing (NDT) tool to assess the magnetocrystalline anisotropy of ferromagnetic materials. In this study, non-oriented electrical steel sheets produced by inclined and cross rolling were characterized by both MBN and electron backscatter diffraction (EBSD). The angular MBN measured on the surface of the steel sheet was directly compared to the magnetocrystalline anisotropy energy (MAE) calculated from the measured crystallographic texture. The MBN energy corresponding to the saturation-to-remanence part of the hysteresis loop was evaluated, which had been reported to have a close correlation to the MAE in pipeline steels. The results in this study showed that such a relationship did not exist in any of the electrical steel samples examined (including deformed, partially recrystallized, and completely recrystallized), although in some samples the polarities of the MBN and MAE partially coincide. It was shown that the residual stress in the material played an important role in determining the polarities of the angular MBN, which had been ignored in the previous studies when comparing the MBN to the MAE. Possible reasons that caused the discrepancies between the results of this study and those of the previous studies were given.

Experimental evaluation on weld zone of thin–laminated stacked sheets post-GTA weld of CRNO electrical steel

Electric motor industries widely use cold-rolled non-oriented (CRNO) electrical steel sheets (ESSs) as the magnetic core. The sheets are of low carbon–silicon, thin (0.5 mm), and laminated and joined as a stack with gas tungsten arc (GTA) welding. A weld zone is affected by the welding heat and dependent on welding current (30–110 A). The fusion zone (FZ) and heat-affected zone (HAZ) of the weld zone are analyzed for variation in the base metal (BM) and microstructural properties using a scanning electron microscope (SEM) and optical microscope (OM). The effects of weld depth, weld width, stress–strain relationship, filler material, and grain size are investigated with a weld current change. Tensile and micro-hardness testing in FZ and HAZ revealed a change of failure in zones, maximum fracture load, and micro-hardness. The effect of grain size and completely ferritic phases (α-phase and γ-phase) in the weld zone is also studied. All the properties variations are compared and correlated to the input welding heat on the thin–laminated, non-grain-oriented stack on ESS.

Investigations on Magnetic and Corrosive Characteristics of Thin Cold-Rolled Nonoriented Electrical Steel Sheets Post Gas Tungsten Arc and Laser Welding

Abstract Thin sheets (0.5 × 10−3 m) of cold-rolled nonoriented (CRNO) electrical steel are widely used for rotating electrical machines. Gas tungsten arc (GTA) and, recently, laser welding are used for welding M-43 grade CRNO steel. The performance of CRNO is thus explored because of changes in low-carbon, high-silicon content and thin insulation coatings post welding. The welding current for GTA varied from 30 to 110 A, whereas a laser of 800 W was used to estimate the heat affected zone (HAZ), fusion zone (FZ), and weld characteristic ratio. Ferritic phases with polygonal grain size, percent silicon content, magnetic losses, and welded corrosive samples corrosion rate (in mils penetration per year) are compared with the base material (average grain size 55 ± 12 μm). Five different corrodent (NaCl, NaOH, HCl, H2O, H2CO3) environments were created for 2,000 h as per ASTM B895-16(2020)e1, Standard Test Methods for Evaluating the Corrosion Resistance of Stainless Steel Powder Metallurgy (PM) Parts/Specimens by Immersion in a Sodium Chloride Solution, and ASTM G31-72(1999), Standard Practice for Laboratory Immersion Corrosion Testing of Metals standards. The GTA weld samples revealed much-increased weld geometry with welding current, and a significant increase in grain sizes up to 189.2 ± 4 μm for GTA and 187 ± 3 μm for the laser sample near the weld zone is observed. Microhardness variation is found to be in the range of 55 HV for GTA and 51 HV for laser samples in the FZ region with reference to the base metal hardness of 227 HV. In addition, the increase in core loss of 58.72 % for GTA and 39.82 % for laser samples with reference to nonwelded samples is observed.

A New Structure of a Gap-Reactor to Reduce Electromagnetic Vibrations

Magnetostriction is an inherent property of an electrical steel sheet (ESS). Experimental measurements have revealed that the magnetostrictions of Grain-oriented and Non-oriented ESSs are mostly opposite in their directions. Based on this, a novel structure of gap reactor is suggested to reduce the mechanical vibration of the reactor. The new structure follows the conventional manufacturing process, and is built by stacking Grain-oriented and Non-oriented cores alternately while a conventional one is by only Grain-oriented or Non-oriented core. In order to verify the effectiveness of the proposed structure, the electromagnetic vibration, stress and displacement of the reactor are analyzed based on the magneto-elastic coupled analysis. The measured magnetization and magnetostriction data of the ESSs are adopted during the numerical calculation. Prototypes of new and traditional structures with the same design parameters were also built and electromagnetic-induced vibration were measured and analyzed. Both the computational and experimental results showed that the proposed structure made much less electromagnetic vibration than the conventional one. Moreover, the noise level around the reactors were measured and the average noise level around the improved prototype was reduced by 16.7%.

The Origin of the Cube ({001}) Texture in Non-oriented Electrical Steel Sheets

Although cube ({001}<100>) is a preferred final texture in non-oriented electrical steel (NOES) sheets, this texture is rarely produced in commercial NOES products. The major texture of fully processed NOES is usually the unfavorable <111>//ND (normal direction) fibre, which originates from the deformed <111>//ND texture. To reduce/eliminate the <111>//ND texture and promote the cube texture, one method is to change the initial texture before cold rolling. In this research, two electrical steels containing 0.88 wt% and 2.8 wt% Si are cold rolled with the initial textures rotated by 60° around the ND before cold rolling. This rotation leads to the rotated Goss ({110}<110>) texture in the deformed microstructure. Within the shear bands of the rotated Goss grains, crystallites with cube orientation are formed. Regions of these crystallites may have lower stored energy than their neighboring areas. During annealing, these crystallites preferentially nucleate and grow, and form a strong cube texture in the final steel sheets.

Anomalous Loss and Hysteresis Loop in Electrical Steel Sheet

This article presents an algorithm for identification of anomalous magnetic field and loss in silicon steel sheet (SSS). Since the magnetic field in an SSS consists of static hysteresis, eddy current, and anomalous magnetic fields, the anomalous magnetic field is extracted from the measured hysteresis field by excluding the static hysteresis and eddy current fields. In order to predict the anomalous magnetic field for an arbitrary B-waveform, an artificial neural network model with deep learning algorithm is suggested. Through comparisons with experimental measurements over a non-oriented electrical steel sheet, 35PN440, the proposed algorithm is validated.

Shear Banding in Rotated Goss Grains and its Effect on the Formation of Cube Texture in Non-Oriented Electrical Steel

Cube texture ({001}&lt;100&gt;) is a desired final texture in non-oriented electrical steel sheets used as magnetic cores because it contains two easy &lt;100&gt; 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 &lt;111&gt;//ND (normal direction) grains provided nucleation sites for the unfavourable &lt;111&gt;//ND texture during recrystallization, leading to a final &lt;111&gt;//ND texture. To eliminate the &lt;111&gt;//ND texture and promote the {001}&lt;100&gt; 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}&lt;110&gt;), was intentionally generated. This was intended to change the orientation flow during plastic deformation, and suppress the formation of the conventional &lt;111&gt;//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.

Local Vector Magnetic Measurement in Iron Core of EI Type Reactor Under Out-of-Plane Stress

Magnetic property of an electromagnetic steel sheet which is used for an iron core of electrical machinery and apparatus changes due to the external stress. Although several researches under out-of-plane stress are reported, those all are investigations for a measurement sample. An investigation of magnetic property by applying stress to an iron core of electrical machinery and apparatus directly is very important for future electrical machinery and apparatus development. Additionally, magnetic flux density B and magnetic field intensity H are vector quantities and a spatial phase angle θBH is between those. The spatial phase angle θBH is an important factor to calculate iron loss. Therefore, in this paper, local vector magnetic measurement in iron core of EI type reactor under out-of-plane stress is reported. The iron core is non-oriented electrical steel sheet. As a result, it is clarified that iron loss decreases because the phase difference θBH decreases by applying of stress from out-of-plane.

Examination of Evaluation Method of Permeability Tensors in Non-Oriented Electrical Steel Sheet

Examination of Evaluation Method of Permeability Tensors in Non-Oriented Electrical Steel Sheet

Fatigue Strength of Punched High-strength Non-oriented Electrical Steel Sheets

Fatigue Strength of Punched High-strength Non-oriented Electrical Steel Sheets

An improved real-time temperature control for pulsed laser cutting of non-oriented electrical steel

An improved method based on fuzzy gain scheduling (FGS) control is developed in this study to tune the PID parameters and precisely control the working temperature in situ during laser cutting of non-oriented electrical steel sheets. Experiments on laser cutting of thin electrical steel sheets are performed to compare the cutting quality of kerf features using an open loop controller with a constant power, a conventional PID controller, and the proposed FGS controller. An unstable and inconsistent cutting quality of kerf with a larger heat affected zone (HAZ) and dross attachment is observed under open loop control due to a significant variation of working temperature and kerf width along the cutting path. The FGS controller shows better cutting performance and tracking response than the conventional PID controller by reducing the settling time as well as enhancing the control stability in the steady period. A better quality of finer and uniform kerf width with parallel kerf edges of a smaller HAZ and dross attachment are thus produced by the improved FGS control through real-time tuning of control parameters. Finally, the average kerf width is well correlated with the set-point temperature in FGS control by a linear equation.

An Improved Anisotropic Vector Preisach Model for Nonoriented Electrical Steel Sheet Based on Iron Loss Separation Theory

An improved anisotropic vector Preisach model is proposed in this paper to describe the hysteresis properties of nonoriented (NO) electrical steel sheet (ESS) under 50 Hz rotating magnetic fields. The proposed model consists of three components, static hysteresis component, eddy current component, and excess component, which is based on the iron loss separation theory. The static hysteresis component is constructed by the static vector Preisach model. The proposed model is identified by the measured hysteresis properties under 1 Hz and 50 Hz magnetic fields. Finally, the experimental results prove the effectiveness of the proposed anisotropic vector hysteresis model.

Design and performance of an additively manufactured high-Si transformer core

Additive manufacturing (AM) of functional alloys has become a promising area of research for the development of novel devices with complex geometric features that cannot be manufactured using conventional methods. In this work, we investigate the additive manufacturing of Fe3Si and Fe6Si benchtop scale transformer cores. A novel design inspired by a Hilbert curve was developed to exploit the geometric complexity of AM, and cores of each alloy were successfully printed, heat treated, machined, pickled, and assembled. The microstructure and magnetic performance of the cores were characterized and compared to additively manufactured components with simpler square cross-sections as well as to conventionally laminated non-oriented electrical steel sheet. The AM cores showed performance roughly comparable or better than the conventional non-oriented sheet, but higher power losses than Goss oriented steel. The increased Si content of the Fe6Si alloy resulted in a significant reduction in core losses. The transformer cores had higher losses than the similarly manufactured simple cross-sections, which was attributed to defects in fabrication and assembly that resulted in air gaps between the transformer legs. The performance was also rationalized relative to nanoscale carbide and oxide inclusions.