Non-oriented Fe-Si Research Articles

Magnetostrictive strain monitoring in Non-Oriented Si-Fe steels using a SAW resonator sensor

The aim of this study is to introduce a new technique for characterizing the magnetostrictive behavior of non-oriented ferromagnetic steel sheets using miniaturized wireless surface acoustic wave sensors (SAW). Unlike conventional optical and electromechanical techniques, this type of sensor offers advantages such as on-board capability, high-temperature resistance (up to 400 °C), and the ability to be connected remotely. The final objective is to monitor magnetic stresses in electrical machines, aligning with the requirements of Industry 4.0 and predictive maintenance. The focus of the present study is the measurement of magnetostriction in ferromagnetic steel sheets, employing a wireless surface acoustic wave resonator operating within the 433 MHz ISM band, under various mechanical fixation configurations. To ensure the accuracy and reliability of SAW measurements, a commercial strain gauge is employed as a reference sensor. Measurements are conducted at different excitation frequencies to explore the phenomenon comprehensively.

Skin Effect and Losses in Soft Magnetic Sheets: From Low Inductions to Magnetic Saturation

High frequencies are ubiquitous in present-day power applications: most electrical equipment, like rotating machines, are supplied by Pulse Width Modulation (PWM) switching inverters, often working at tens or hundreds of kilohertz. PWM is responsible of minor cycles along the major hysteresis loop of the magnetic core, lasting a few microseconds. Such minor loops can cause deep skin effect, even if the thinnest today available laminations (0.1 - 0.2 mm thick sheets) are used. Common mode currents in the megahertz range, flowing from the electrical machine windings to the machine chassis through capacitive effects, can engender strong electromagnetic disturbances and bearing damages. A correct prediction of high frequency phenomena is necessary, for example, for the accurate calculation of common mode filters, requiring a magnetic model of the laminated cores suited to high frequencies and low induction values and the ensuing dramatic skin effect. For power conversion applications, such as embedded planar transformers, the mandatory reduction of volume and cross-sectional area of the core, often made of high-permeability grain-oriented (HGO) sheets, imposes the increase of the conversion frequency from a few hundred hertz to several kilohertz and high peak induction values. The skin effect in this case is affected by the non-linear saturable magnetic response of the material and its treatment requires non-trivial experimental methods and modeling approaches. In this work, we discuss physically based modeling of magnetization process and energy loss in magnetic sheets at high frequencies. We focus first on the low induction regimes occurring in thin non-oriented (NO) Fe-Si laminations. We consider then the case of high inductions, as encountered in power conversion devices using NO, HGO, and Fe-Co alloys, where non-linear models, possibly validated by magneto-optical observations of the domain wall dynamics, are developed and implemented.

An Improved Cross-Yoke SST for Accurate 1-D and 2-D Magnetic Testing of Fe-Si Sheets

Single-sheet testers (SSTs) with asymmetrical yokes were developed for convenient measurement of 1-D and 2-D magnetic properties of Fe-Si sheets. An inherent drawback of such SSTs is that the magnetic properties in the central region of the specimen are affected by the planar eddy currents induced in the specimen plane facing the pole faces of the yokes, where the magnetic flux enters the specimen in the normal direction. Most relevant studies reported in the literature use large symmetrical double yokes to mitigate the influence of planar eddy currents on the magnetic properties. However, such configuration significantly increases the system complexity. This article proposes a compact cross-yoke SST with the novel arm-slotted specimen and the integrated 2-D B-H sensor to minimize the influence of the planar eddy currents and simplify the structure of the SST. The magnetic properties of non-oriented (NO) Fe-Si sheets of 50JN470 under 1-D and 2-D magnetizations are measured and analyzed. The experimental results from the proposed cross-yoke SST show the agreement with those measured by using the international standard SST.

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.

High saturation magnetic induction and low magnetostriction of a novel ferritic Fe-Ti alloy compared to a non-oriented silicon steel

Non-oriented (NO) silicon steel is used in magnetic cores of electrical machines due to its good magnetic and electric properties, such as high electric resistivity, high permeability, low coercive field, and low power losses. However, the noise and vibration, caused by magnetostriction, may lead to early failure of the equipment. Since the stator core is submitted to compressive stresses due to the shrinking fitting, positive values of magnetostriction are not appropriate. Fe-Ti alloys have low negative magnetostriction values making them strong candidates for replacing Fe-Si alloys. In this work, Fe-3wt.%Ti alloy was cold rolled down to 0.3 mm of thickness and annealed for 48 h at 850 °C. Magnetization showed to be 7 kA/m (0.09 T) higher than Fe-Si, and the magnetostriction is lower than 1 ppm up to 1.5 T while for Fe-Si is higher than 1 ppm for <0.25 T. Microstructure and texture were evaluated to explain the magnetic properties. The magnetic properties of Fe-3wt.%Ti are better than commercial non-oriented Fe-Si and could be an alternative to improve the performance of electrical motors.

Experimental set up for magnetomechanical measurements with a closed flux path sample

AbstractIn this article, an experimental procedure is presented to handle magnetic measurements under uniaxial tensile stress reaching the plastic domain. The main advantage of the proposed procedure is that it does not require an additional magnetic core to close the magnetic flux path through the studied sample. The flux flows only in the sample, and no parasitic air gaps are introduced, thus avoiding the use of the H-coil to evaluate the magnetic field, which is often very sensitive and not easy to calibrate. A specimen of nonoriented FeSi (1.3%) sheet (M330-35A) is characterized under uniaxial tensile stress. To validate the proposed procedure, a comparison with the single sheet tester procedure is carried out. The results obtained by the two procedures are in good agreement. Moreover, to illustrate the possibilities offered by the proposed procedure, we confirm some results obtained in the literature. We show that the positive plastic strain leads to a significant degradation of magnetic behavior. An applied tensile stress on a virgin (unstrained) sample leads to a degradation of the magnetic behavior. However, on a pre-strained sample, an applied tensile stress results in reducing the deterioration caused by the plastic strain until a stress value called optimum is attained. Above this threshold, the magnetic behavior re-deteriorates progressively.

New Investigations in Play Static Hysteresis Model for Increased Accuracy and Robustness

This article presents an evolution of the inverse Play model to reconstruct static hysteresis from a flux density waveform input. It is to be combined with dynamic and 2-D or 3-D models to estimate the complete iron loss in electrical machines. In the first part of the article, the article shows the significant improvement in the original inverse Play model accuracy obtained by modifying the characterization measurement methodology, the subsequent discretization, and the identification method. Thereafter, a new version of the Play model, named “continuous,” is introduced, which allowed a significant gain in performance at the expense of greater computation time for the identification process. Both model versions have been validated through experimental comparison. All measurements, characterization, and validation have been done according to IEC60404-2 on two different test laboratories. The studied material is non-oriented SiFe M400-50A electrical steel.

Influence of mechanical and water-jet cutting on the dynamic magnetic properties of NO Fe-Si steels

Magnetization curve and energy losses have been analyzed in non-oriented (NO) Fe-Si alloys with variable thickness (0.20 mm–0.35 mm), cut at widths ranging between 5 mm and 60 mm, in order to assess the impact of cutting, either done by punching or water-jet techniques. Measurements were performed by means of a digitally controlled single strip tester, from dc up to 1.5 kHz, at peak polarization values Jp = 1.0 T and 1.5 T. The evolution of the magnetization curve and the structure-dependent hysteresis Wh and excess Wexc loss components have been assessed as a function of the strip width using a simple phenomenological model, by which the extension of the damaged area at the edges of the cut sheets is estimated. Such a model assumes a hyperbolic dependence of the measured polarization on the cut strip width. The limiting values of Wh and Wexc for the fully damaged and the pristine sheets are in this way estimated, showing that one can simply and affordably predict the magnetic behavior of NO Fe-Si steels subjected to cutting.

Effect of mechanical stress on magnetization and magnetostriction strain behavior of non-oriented Si-Fe steels at different directions and under pseudo-DC conditions

Effect of mechanical stress on magnetization and magnetostriction strain behavior of non-oriented Si-Fe steels at different directions and under pseudo-DC conditions

Energy Losses in Soft Magnetic Materials Under Symmetric and Asymmetric Induction Waveforms

Magnetic losses under triangular symmetric and asymmetric induction waveforms have been measured over a broad range of frequencies and predicted starting from standard results obtained with sinusoidal induction. Nonoriented Fe-Si and Fe-Co sheets, nanocrystalline Finemet–type ribbons, and Mn-Zn ferrites have been investigated up to f = 1 MHz and duty cycles ranging between 0.5 and 0.1. The intrinsic shortcomings of the popular approach to loss calculation of inductive components in power electronics, based on the empirical Steinmetz equation and its numerous modified versions, are overcome by generalized application of the statistical theory of losses and the related concept of loss separation. While showing that this concept applies both to ferrites and metallic alloys and extracting the hysteresis (quasi-static), excess, and classical loss components, we relate in a simple way the magnetic energy losses under symmetric triangular induction (square wave voltage) and sinusoidal induction. The loss behavior under asymmetric triangular induction is retrieved from the symmetric one, by averaging the energy losses pertaining to the two different semiperiods. Good comparison with the experimentally measured energy loss versus frequency behavior is demonstrated in all materials.

An analysis of power losses in nanocrystalline and thin-gauge non-oriented SiFe materials for application to high-speed electrical machines

In this paper, the potential of thin sheet SiFe NO20 and nanocrystalline materials for the realization of the magnetic circuit of high-speed machines is analyzed in a complete procedure. Firstly, intrinsic properties of materials are precisely characterized. Next, the original and a modified model of Bertotti are applied for the modeling of power losses. These models are then used to predict losses in a simplified test bench which simulates the magnetic core of a real machine. FEM simulations in Altair FLUX 2D and experimental measurements are respectively carried out and results obtained show a good agreement leading to the confirmation of the potential of materials and the validation of the realized procedure.

Magnetic Loss Versus Frequency in Non-Oriented Steel Sheets and Its Prediction: Minor Loops, PWM, and the Limits of the Analytical Approach

The pulsewidth modulation (PWM) technique is commonly used to supply modern high-speed electrical machines. The fundamental frequency is typically in the kilohertz range, with switching frequencies of several tens of kilohertz, as determined by the new SiC- or GaAs-based power transistors modules. Switching introduces minor loops in the major hysteresis cycle, with durations of the order of $100~\mu \text{s}$ or lower, with the resulting magnetization dynamics influenced by strong skin effect. However, since these minor loops have relatively small amplitude, their constitutive equation may be described by an equivalent permeability (real or complex), depending on the mean slope of the minor loop and its static energy loss. By retrieving this permeability, the classical loss is straightforwardly calculated by analytical solution of Maxwell's equations. In this paper, we measure and calculate, according to the quasi-linear approximation for the minor loops, the magnetic energy losses of 0.194 mm thick non-oriented Fe–Si 3.2% sheets subjected to PWM induction waveform. Minor loop peak amplitudes ranging between 50 mT and 0.2 T and frequencies up to 10 kHz are investigated. The results are consistent with the proposed model, to within 5%.

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.

Influence of Thermal Processing in High Magnetic Field on Soft Magnetic Properties and Crystallographic Texture of Non-Oriented Fe-Si Steels

Influence of Thermal Processing in High Magnetic Field on Soft Magnetic Properties and Crystallographic Texture of Non-Oriented Fe-Si Steels

Evolution of microstructure at hot band annealing of ferritic FeSi steels

The magnetic properties of the finally fabricated nonoriented FeSi steels critically depend on the microstructure and on the occurring crystallographic texture. The fabrication route comprises hot rolling, coiling and cooling, hot band annealing before cold rolling (optional), cold rolling and the final thermal treatment. As well known there is an interplay between the microstructure and texture during the various processing steps. For that reason, it is of interest to know more on the evolution of the microstructure at hot band annealing of hot band prepared in different ways. In this paper we will summarize our recent results on the evolution of microstructure during thermal annealing of hot band: thermal treatment following immediately the last pass of hot rolling or a hot band annealing as a separate processing step before cold rolling.

Numerical Modeling of Excess Loss in SiFe Sheet Considering Pinning Effect

Compared with grain-oriented SiFe sheets, the domain structure of nonoriented (NO) SiFe sheets is very different, and the magnetization processes of NO SiFe sheets are much less investigated. Thus, the excess loss of NO SiFe sheets is less well-known. In this paper, we propose a numerical method to estimate the excess loss in NO SiFe sheets, considering the pinning and skin effects. We apply an initial magnetic field distribution that reflects the pinning effect in our nonlinear eddy current finite element analysis model, which reflects the skin effect of the magnetic flux. Thus, the pinning effect can be coupled with the skin effect in the proposed numerical method. The hysteresis loss and eddy current loss calculated from the flux and eddy current distributions are directly obtained from the proposed analysis method. Thus, excess loss is included in both the hysteresis and the eddy current loss calculations. We first apply the proposed method to two different grades of NO SiFe sheets. The calculated iron losses in one sheet are compared at various frequencies with the measured losses from catalogue data, and less than 2% deviation can be achieved. Finally, we apply the proposed method to the loss calculation for the iron core of a reactor.

Alternating and Rotational Losses Up to Magnetic Saturation in Non-Oriented Steel Sheets

A three-phase magnetizer has been developed, by which non-oriented Fe-Si steel sheets can be characterized under alternating and rotational flux up to a polarization value $J_{p}\approx 0.98~J_{s}$ , where $J_{s}$ is the saturation magnetization. The loss measurements, performed in the frequency range 2 Hz–1 kHz, require the combination of field-metric and thermometric methods, besides fine control of the induction wave-shape/loci under the required demanding exciting conditions. By exploiting the loss separation concept, it is observed that under rotational flux, both the hysteresis and excess loss components monotonically decrease with $J_{p}$ , to disappear at saturation. The measured losses then become equal to the calculated classical losses. This could actually be predicted, because of the expected disappearance of the domain walls under saturating rotational field, but it has never been previously verified by the experiments.

Deformation Structure and Recrystallization of Ferritic FeSi Steels

The magnetic properties of finally fabricated nonoriented FeSi electrical steels depend critically on microstructure and crystallographic texture components. The resulting microstructure and texture are influenced along the whole processing route of Fe–Si steels: hot rolling, coiling and cooling, hot band annealing before cold rolling (optional), cold rolling, and final thermal treatment. There is an interplay of microstructure and texture between the various processing steps, which is not investigated in any detail. Especially for ferritic FeSi steels are no specific investigations on the influence of microstructure and texture of cold‐rolled material on their evolution at final annealing. In this paper, authors summarize the recent experimental results on the evolution of microstructure and texture at final annealing for cold‐rolled material of ferritic FeSi steels with 2.4 and 3 wt% Si. The evolution of microstructure and texture is analyzed by metallographic studies and EBSD. Special attention is paid to the through‐thickness dependence of microstructure and texture, which is caused by the strain gradients as well as thermal gradients at processing. The obtained experimental results altogether demonstrate clearly the effect of different misoriented substructures after cold rolling due to nonuniform strain on recrystallization behavior for the ferritic FeSi steels.

Loss Decomposition in Non-Oriented Steel Sheets: The Role of the Classical Losses

—The concept of loss separation based on the Statistical Theory of Losses (STL) provides complete and accurate description of the frequency dependence of the energy losses in non-oriented soft magnetic sheets under the assumption of uniform magnetization reversal through the sheet cross-section. This assumption, implying a simple standard formulation for the classical loss component, has been recently challenged in the literature, in favor of a non-uniform reversal mechanism, expected to prevail in highly non-linear materials, where saturation magnetization wavefronts are deemed to symmetrically propagate across the sheet thickness (Saturation Wave Model, SWM). Different conclusions regarding the dynamic loss analysis and its decomposition into the classical and excess loss components correspondingly emerge. In this paper we discuss detailed investigations on the broadband energy loss versus frequency behavior in different non-oriented Fe-Si and low-carbon steel sheets. The experiments can be fully and consistently described by the STL. This occurs, in particular, for high-induction values and near-squared hysteresis loops, a predictable condition for adopting the SWM, which fails instead to account for the experiments.

Impact of Material on the Iron Losses of a Reactor With an Air Gap

The iron losses of a reactor with an air gap are investigated and compared for three different magnetic materials, namely, grain-oriented material (GO230), high performance non-oriented Fe-Si metal (super E ST125), and nanocrystalline soft magnetic material (FINEMET FT-3M). The iron losses of the reactor are measured by the experiments for different voltage supply frequencies and amplitudes. The measured data are compared with the material iron losses that are calculated from the manufacturer’s material datasheets. It is concluded that the air gap is responsible for a large part of the increase between the reactor and material iron losses and that the FT-3M has sensibly higher building factor compared with the other materials.