SiFe Electrical Steel Research Articles

Magnetic Properties of Fe-Si Electrical Steel after Laser Scribing

Improvement of magnetic properties of electrical steel can be achieved by reduction the size of magnetic domains. The application of local stresses through laser scribing leads to reduced core losses. In order to determine the effect of laser refinement conditions of magnetic domains on the properties of the soft magnetic material, four samples with a thickness 0.23 mm were refined. The refinement of each sample was carried out using different line energies of the laser beam. Estimation of the magnetic domain size was performed using the Jeffries method, the magnetic viewer was used to reveal the domain structure. The measurement of the magnetic properties was performed at a frequency of 50 Hz and an induction of 1.5 T. The analyzed results presented in this work indicate impact of laser refining on magnetic properties of grain oriented electrical steel depending on used laser beam energy.

Additive manufacturing of Fe-6.5 wt.%Si transformer steel toroidal cores: Process optimization, design aspects, and performance

Fe-Si electrical steels are conventionally popular materials for transformer application. Although higher Si (4wt.%<) content is favorable for increasing the resistivity and improving the soft magnetic properties, fabrication of transformer core with higher Si containing electrical steels is difficult by conventional wrought processes due to an increase in its brittleness. Additive manufacturing provides a novel alternative plausible way to fabricate transformer cores with higher Si content and unique design features. The current work focused on process optimization and design aspects of laser powder bed fusion additive manufacturing of Fe-6.5wt.% electrical steel. Additively manufactured components with 99.5% relative density were produced. The optimally fabricated component contained columnar grains of α-FeSi phase morphologically oriented in the build direction. The optimally fabricated Fe-6.5wt.% component was also subjected to annealing treatment at 1150∘C for 1 h in Ar resulting in multi-fold grain growth and improved soft magnetic response. Based on optimal laser processing parameters, 3 different designs for toroidal cores with slit patterns for varying degree of cross-sectional areas were additively fabricated. The toroidal cores were subjected to same annealing treatment as that of the additively fabricated component. Core with least cross-sectional area exhibited improved magnetic performance compared to the other designs.

Variables Affecting the Evolution of the {100}&lt;0vw&gt; Texture Induced by Surface Nucleation During γ → α Phase Transformation in Fe–Si Electrical Steel

Variables Affecting the Evolution of the {100}&lt;0vw&gt; Texture Induced by Surface Nucleation During γ → α Phase Transformation in Fe–Si Electrical Steel

A Novel Dynamic Hysteresis Model for Grain-Oriented Electrical Steels Based on Magnetic Domain Theory

A novel approach is adopted to model the hysteresis phenomenon of grain-oriented electrical steels (GOESs), by incorporating a variation of the domain patterns associated with ferromagnetic materials during magnetization and demagnetization. The ensuing model treats the anisotropic and isotropic components separately, together with the coupling effect of the excitation field. Its ability to replicate experimentally obtained dynamic hysteresis loops (DHLs) for Epstein size laminations of GO 3% SiFe electrical steels, for different magnetizing frequencies and peak flux densities, and facilitate the straightforward evaluation of the energy loss in GOESs is demonstrated for the case of controlled sinusoidal magnetic induction. Close agreement is found to exist between the predicted energy loss and corresponding bulk measurements, with the maximum difference being less than 2%.

Variables Affecting the Evolution of the {100}&lt;0vw&gt; Texture Induced by Surface Nucleation During Γ → Α Phase Transformation in Fe-Si Electrical Steel

Variables Affecting the Evolution of the {100}&lt;0vw&gt; Texture Induced by Surface Nucleation During Γ → Α Phase Transformation in Fe-Si Electrical Steel

Correlation between Cutting Clearance, Deformation Texture, and Magnetic Loss Prediction in Non-Oriented Electrical Steels

Manufacturing the magnetic cores in electrical machines impacts the magnetic performance of the electrical steel by inducing stresses near the cutting edge. In this paper, energy loss behaviour in non-oriented electrical steels punched with different cutting clearances before and after annealing is investigated. An experimental shear cutting tool was employed to punch the ring-shaped parts from electrical steels in a finished state with four different values of cutting clearance corresponding to 1%, 3%, 5%, and 7% of the sheet thickness. The effect of cutting clearance on the magnetic losses is derived and analysed by the statistical theory of losses and associated loss separation concept including the analysis of movable magnetic objects. In this framework, this paper assesses the combined effect of cutting clearance, frequency, and heat treatment on the hysteresis loops and iron losses in non-oriented FeSi electrical steels. Measurements have been performed from quasi-static to 400 Hz at peak induction Bp = 1.0 T. Both states before and after heat treatment have been considered. The excess loss is observed as the most sensitive loss component to cutting clearance and its magneto–structural correlation is quantified.

Improving Global Ferromagnetic Characteristics of Laminations by Heterogeneous Deformation

During electrical machine manufacturing, the process may induce plastic mechanical strains, especially in the magnetic core. However, magnetic properties are highly sensitive to the material mechanical state. Thus, the performances of electrical machines, which also rely on the magnetic material properties, are often deteriorated. This article proposes an approach to reduce the impact of the forming process on the magnetic core performances by creating high localized heterogeneous deformations instead of having a low homogeneous deformation distributed on the whole structure. A NO (non-oriented) FeSi (1.3%) electrical steel (M330-35A) is characterized after uniaxial tensile test. Samples are deformed either in heterogeneous or in homogeneous ways while keeping the same global deformation. Experimental measurements show that, for the same displacement value, the heterogeneous configuration, with localized strain, deteriorates less the global magnetic properties than the homogeneous configuration. These results are supported by a magneto-mechanical modeling approach that predicts accurately the physical behavior of the test samples.

Use of Time-Frequency Representation of Magnetic Barkhausen Noise for Evaluation of Easy Magnetization Axis of Grain-Oriented Steel.

The paper presents a new approach to non-destructive evaluation of easy/hard magnetization axis in grain-oriented SiFe electrical steels based on the Barkhausen phenomenon and its time-frequency (TF) characteristics. Anisotropy in steels is influenced by a number of factors that formulate the global relationship and affect the Barkhausen effect. Due to the observed high variability in the dynamics of magnetic Barkhausen noise (MBN) over time, obtained for various directions in grain-oriented steel, it becomes justified to conduct MBN signal analyses in the time-frequency domain. This representation allows not only global information from MBN signal over entire period to be expressed, but also detailed relationships between properties in time and in frequency to be observed as well. This creates the opportunity to supplement the information obtained. The main aspect considered in the work is to present a procedure that allows an assessment of the resultant angular characteristics in steel. For this purpose, a sample of a conventional grain-oriented SiFe sheet was used. Measurements were made for several angular settings towards the rolling and transverse directions. A data transformation procedure based on short-time Fourier transform (STFT) as well as quantitative analysis and synthesis of information contained in the TF space was presented. Angular characteristics of selected TF parameters were shown and discussed. In addition, an analysis of the repeatability of information obtained using the proposed procedure under various measurement conditions was carried out. The relationship between the selection of calculation parameters used during transformation and the repeatability of the obtained TF distributions were demonstrated. Then the selection of the final values of the calculation parameters was commented upon. Finally, the conclusions of the work carried out were discussed.

Identification and analysis of static and dynamic magnetization behavior sensitive to surface laser treatments within the electromagnetic field diffusion inside GO SiFe electrical steels

Surface laser treatment of soft magnetic materials, such as GO SiFe electrical steels, is mainly used to reduce iron losses by modifying the static and the dynamic magnetic properties. Laser treatment effect on mesoscopic electromagnetic properties of soft magnetic materials is presented. An experimental procedure using the Single Sheet Tester is performed on a magnetized sheet with specific exciting induction level and frequency. Transient average magnetic flux density through the sample cross-section and its corresponding applied magnetic field are measured. Data are identified in the time-domain with numerical results obtained by solving the diffusion equation using a 1-D discretization approach. The identification strategy requires a material law that includes both non-linear static and dynamic properties and describes the magnetic behavior due to domains and walls dynamics. Next, parametric and physical studies are performed on materials submitted to different laser treatments in order to determine and interpret their effects on the identified magnetic properties and the time response in the sheet’s depth. The results show that the static and the dynamic properties can be simultaneously improved. This analysis help to understand the impact of laser treatments on the static and the dynamic behaviour in order to improve the material magnetic performances within magnetic circuits inside electrical machines and transformers.

Mechanistic approach of Goss abnormal grain growth in electrical steel: Theory and argument

The first Si-Fe electrical steel was produced in 1905, and the grain-oriented steel was discovered in 1930 after Goss demonstrated how optimal combinations of heat treatment and cold rolling could produce a texture giving Si-Fe strip good magnetic properties when magnetised along its rolling direction. This technology has reduced the power loss in transformers greatly and remains the basis of the manufacturing process today. Since then many postulations reported on the mechanism on abnormal grain growth (AGG) which is the key for Si-Fe superior magnetic properties, however, none have provided a concrete understanding of this phenomenon. Here, we established and demonstrated a new theory that underlines the fundamental mechanistic approach of abnormal grain growth in 3% Si-Fe steel. It is demonstrated, that the external heat flux direction applied during annealing and Si atom positions in the solid solution disordered α-Fe cube unit cell that cause lattice distortions and BCC symmetry reduction are the most influential factors in the early stage of Goss AGG than what was previously thought to be dislocation related stored energy, grain boundary characteristics and grain size/orientation advantages.

Magnetic properties of Fe-1.5wt% Si high-frequency powder cores

Electro-magnetic devices, such as motors and inductors, have been continuously required to increase their operation frequency for high efficiency. To satisfy this requirement, Fe-Si powder cores with high electrical resistance have been attracted much attention although they have lower permeability than Fe-Si electrical steels. With increasing the Si content, the ductility of Fe-Si alloy sharply decreases, which further lowers the density and magnetic properties of cores. In this study, we aimed to fabricate Fe-Si powder cores with higher saturation magnetization and lower loss in 1 ∼ 10 kHz range compared with commercial products. As a result, fabricated Fe-1.5wt% Si@Fe3(PO4)2 cores reached a 98% theoretical density and showed a magnetic flux density of 1.65 T at 10000 A/m and a core loss of 176.8 W/kg at 1 T @ 2 kHz.

Evaluation of the interdependency of mechanical cutting and magnetic anisotropy on the magnetic properties of FeSi electrical steel

Evaluation of the interdependency of mechanical cutting and magnetic anisotropy on the magnetic properties of FeSi electrical steel

Mechanistic Approach of Goss Abnormal Grain Growth in Electrical Steel: Theory and Argument

The first Si-Fe electrical steel was produced in 1905, and the grain-oriented steel was discovered in 1930 after Goss demonstrated how optimal combinations of heat treatment and cold rolling could produce a texture giving Si-Fe strip good magnetic properties when magnetised along its rolling direction. This technology has reduced the power loss in transformers greatly and remains the basis of the manufacturing process today. Since then many postulations reported on the mechanism on abnormal grain growth (AGG) which is the key for Si-Fe superior magnetic properties, however, none have provided a concrete understanding of this phenomenon. Here, we established and demonstrated a new theory that underlines the fundamental mechanistic approach of abnormal grain growth in 3% Si-Fe steel. It is demonstrated, that the external heat flux direction applied during annealing and Si atom positions in the solid solution disordered α-Fe cube unit cell that cause lattice distortions and BCC symmetry reduction are the most influential factors in the early stage of Goss AGG than what was previously thought to be dislocation related stored energy, grain boundary characteristics and grain size/orientation advantages.

Abnormal growth of {100} grains and strong Cube texture in strip cast Fe-Si electrical steel

High-grade non-oriented electrical steel was successfully processed by controlling texture using strip casting technology. Remarkable abnormal grain growth of {100} grains occurred in the as-cast strip after isothermal annealing. This phenomenon is considered to be the synergistic effect involving the size advantage of coarse columnar grains and surface energy, where the normal grain growth was inhibited by thermal grooving in the surface layer. Special rotation path was identified during the cold rolling process and metastable {118} 〈110〉–{113} 〈110〉 texture dominated the deformation texture. The final annealed sheet exhibited strong Cube texture together with significantly superior magnetic properties.

Effects by the microstructure after hot and cold rolling on the texture and grain size after final annealing of ferritic non-oriented FeSi electrical steel

The magnetic properties of fully processed non-oriented FeSi electrical steel are characterized by their magnetization behavior and specific magnetic losses. The magnetic properties are determined by the texture and microstructure. Less gamma fiber intensity and a high intensity of preferable texture components, especially cube fiber texture, are desirable to obtain an excellent magnetizing behavior. Furthermore, large grain sizes are necessary to reach low values of the specific magnetic losses. The fabrication route of the fully processed non-oriented electrical steels comprises a heavy cold rolling of the hot rolled material before final annealing. To fulfill the requirements on large grain size for low loss materials, grain growth, which appears after complete recrystallization, plays an important role. In this paper we will analyze the influence of different microstructures of the hot strip and the resulting microstructure after cold rolling on the appearance of recrystallization and grain growth after final annealing. The evolution of texture reflects the present ongoing softening processes: recovery, recrystallization and finally grain growth at the given annealing conditions. It will be shown that the image of texture at recrystallization is remarkable different from the texture at grain growth. Substantially grain growth is obtained at lower annealing temperatures for an optimum microstructure of the hot rolled material.

Soft magnetic composites based on hybrid coated Fe-Si nanocrystalline powders

The preparation and characterisation of soft magnetic composite compacts based on hybrid coated nanocrystalline Fe-Si powder are presented. The Fe-Si powder was prepared by mechanical milling of Fe-Si electrical steels sheets up to 20h. The hybrid coating consists in an electrically insulating phosphate and a polymer layer that covers the Fe-Si particles. The influence of phosphating duration on the particles surface was investigated by SEM, EDX, XRD, and FTIR investigations. The saturation magnetisation of the powders phosphated for 60s decreases with 17% as compared to the uncoated powder. The influence of the compaction pressure, as well as the phosphating duration, on initial relative permeability and power losses of the compacts was investigated. It was found that increasing the compaction pressure leads to the increase of the compact's permeability and a decrease of the hysteresis losses. A shorter phosphating duration leads to a partial coating with phosphate of the Fe-Si particles and to compacts with higher density characterised by high magnetic permeability.

Evolution of Optimum Grain Size for Low Loss Ferritic FeSi Steels

The magnetic properties of non‐oriented Fe–Si electrical steels are characterized by their magnetization behavior and specific magnetic losses. The magnetic losses are the most important property for selection of material grades at a given application. The magnetic properties are determined generally by the texture and microstructure. There is a strong link between the specific magnetic losses of the fully processed electrical steel and the grain size. Large values of grain size are necessary to reach low values of the specific magnetic losses. This is in contrast to conventional steels with high strength, where low values of grain size are preferable. To fulfill the requirements on large grain size for low loss materials grain growth plays an important role. In this paper, the authors will analyze by optical microscopy and EBSD investigations the influences of different microstructure of the hot strip and the resulting microstructure after cold rolling on recrystallization and grain growth after final annealing of Fe–2.4 wt% Si. The image quality plus rotation angle map and the misorientation angle frequency are used to access the degree of microstructural changes during processing.It will be demonstrated that the microstructure of the used hot band effects remarkable the onset of grain growth.

Quantifying Effects of Cutting and Welding on Magnetic Properties of Electrical Steels

The magnetic properties, namely the iron losses and the relative permeability, of SiFe electrical steel laminations after guillotine shearing and cutting by means of fiber and CO 2 lasers are studied. The magnetic measurements are conducted on the Epstein frame for lamination strips with 1, 2, and 3 additional cutting edges along their length, in order to increase the cutting effect and the characterization data. The quantified effects of manufacturing (cutting and welding) are presented for three different material grades: M270-50A, M400-50A, and a nonoriented electrical steel of gauge 0.2 mm called NO20. Usage of the Epstein frame method allows any electrical steel company to reproduce the measurements for any specific grade. Data presented in normalized values facilitate utilization of the presented results and comparison between materials. An original model that incorporates the cutting effect considering homogenously damaged areas is developed and implemented in a finite-element method-based motor design software. Its originality is that it includes dependence on the geometry, included in the material magnetic properties. Simulations made for an industrial low voltage induction motor indicate a more than 15% increase in the iron losses compared with a model that does not consider the mechanical cutting effect. In the case of laser cutting, this increase reaches 30% to 50%, depending on laser settings. These relatively large increases of iron losses justify the implementation of the effect of cutting in industrial finite-element design tools, using a method that does not increase the simulation time.

Fe-Si 전기강판 폐스크랩을 이용한 3원계 Fe-9.8Si-6.0Al 합금의 연자성 특성

Fe-Si 전기강판 폐스크랩을 이용한 3원계 Fe-9.8Si-6.0Al 합금의 연자성 특성

Amorphous Soft Magnetic Core for the Stator of the High-Speed PMBLDC Motor With Half-Open Slots

Several papers have appeared in recent years on the application of the amorphous soft magnetic materials in the stators of the electric motors. In our previous work, we demonstrated that the replacement of a slotless stator from the FeSi electrical steel with the stator from an amorphous alloy Metglas 2605 SA1 in a high-speed permanent magnet brushless direct current (PMBLDC) motor resulted in a substantial decrease of power losses in this stator, even by three times at the rotary frequency of 70 000 r/min. This paper was concentrated on the development of the cores for stators with half-open slots, which are technologically more difficult to produce than the slotless cores. The cores were made by cutting out suitable amount of $25~\mu \text{m}$ -thick rings from the FeSiB amorphous ribbon by a laser technique, followed by stacking up the rings and their consolidation, and suitable heat treatment of the compressed stacks. Next, the measurements of the magnetic properties of the sample cores with half-open slots were made using the Remacomp C-1200 hysteresisgraph and the Lakeshore 450 Gaussmeter. Based on the results of measurements, the sample cores of different heights (17.5 and 10 mm) were selected for application in a stator of the prototype high-speed PMBLDC motor, 800 W in rated power and with a maximum rotary speed of 60 000 r/min. The preliminary performance tests with this prototype motor showed that after 1 h of uninterrupted operation, the temperature of a motor housing did not exceed 60 °C. It was also found that the operating efficiency of the PMBLDC motor incorporating a stator with half-open slots, made from an amorphous material, was almost 90% over a wide range of torques (from 40 to 140 mN $\cdot \text{m}$ ).