Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO electrical steel

doi:10.1016/j.jmmm.2016.05.049

Journal of Magnetism and Magnetic Materials

Volume 417, 1 November 2016, Pages 42-48

https://doi.org/10.1016/j.jmmm.2016.05.049 Get rights and content

Highlights

•
A detailed look at magnetic anisotropy of FeSi NGO electrical steel.
•
Study of magnetic behavior under elastic as well as plastic tensile stresses.
•
Correlation of magnetic behavior with microscopic deformation mechanisms.
•
Discussion of detrimental and beneficial effects of external stresses.
•
Loss separation at different polarizations and frequencies under increasing stress.

Abstract

The magnetic properties of non-grain-oriented (NGO) electrical steels are highly susceptible to mechanical stresses, i.e., residual, external or thermal ones. For rotating electrical machines, mechanical stresses are inevitable and originate from different sources, e.g., material processing, machine manufacturing and operating conditions. The efficiency and specific losses are largely altered by different mechanical stress states. In this paper the effect of tensile stresses and plastic deformations on the magnetic properties of a 2.9 wt% Si electrical steel are studied. Particular attention is paid to the effect of magnetic anisotropy, i.e., the influence of the direction of applied mechanical stress with respect to the rolling direction. Due to mechanical stress, the induced anisotropy has to be evaluated as it is related to the stress-dependent magnetostriction constant and the grain alignment.

Graphical abstract

Introduction

Isotropic magnetic properties are expedient for non-grain-oriented (NGO) electrical steels. Low losses and improved magnetizability in any spatial direction characterize best suited materials. The tailored magnetic properties of the raw material are affected decisively by mechanical stresses of diverse origin. In particular, mechanical stresses induced during material processing, i.e., sheet metal blanking, stacking or shrinking, alter the magnetic properties of the core detrimentally. For improvement of rotating electrical machines in terms of energy efficiency and operation characteristics, the interdependence of mechanical stresses and magnetic properties deterioration needs to be investigated and understood. The detrimental effect of mechanical stresses on iron-loss and magnetizability requires, in particular, an in-depth study.

The final product of the conventionally used, fully finished material, has a fixed microstructure, magneto-crystalline texture and specific magnetic properties which have been adjusted through hot band annealing, cold rolling and final annealing of thin steel strip. However, material processing, such as shear cutting, stacking, welding or final assembly affects the magnetic properties drastically [1], [2]. Various research papers elaborate the severe effect of different cutting techniques, e.g., ${CO}_{2}$ laser, Nd:YAG laser, electrical discharge machining (EDM), water-jet or shear cutting [3], [4], [5]. According to [6] the dominant effect for the deterioration of magnetic properties are residual stresses induced by mechanical processing. When constructing the machine, stresses are inevitable and therefore need to be accounted for. In order to not only to characterize the effect of specific processes on a certain material, the general effects on the material need to be studied to find general correlations and enable understanding of all mechanical processing.

This paper particularly focuses on the effect of plastic deformation on the magnetic properties of a high silicon electrical steel and the differentiation regarding the effect of elastic tensile stresses. When studying non-grain-oriented (NGO) electrical steels, it is crucial to consider different spatial directions because in rotating electrical machines a homogeneous and isotropic magnetic field in all rotation directions is necessary to ensure consistent behavior at all times, in every planar direction. Therefore, each experiment is performed in rolling direction (RD) as well as transversal direction (TD) to enable a comparison and to ensure comprehensible considerations.

Section snippets

Experimental procedure

The investigated material is a commercially available fully finished and isolated grade, classified as M270-50A, with 2.9 wt% silicon content and 0.5 mm sheet thickness. Experiments on elastic tensile stresses are performed on a 100 mm by 600 mm single sheet tester (SST) equipped with a tensile and compression unit. The test bench is incorporated into a computer-aided setup according to the international standard IEC 60404-3 and the non-grain-oriented (NGO) electrical steel sample is characterized

Results and discussion

This section is divided into two parts. At first, the results of the metrological characterization under tensile mechanical loading, i.e., elastic and plastic deformations, are introduced. Both the change of hysteresis loop shapes and, by way of example, the variation of the required magnetic field to reach 1.0 T at 100 Hz as well as the corresponding coercive field in RD and TD are discussed. In the second part, the measured data is processed in order to divide the iron losses into static and

Conclusions

The optimization of non-grain-oriented (NGO) in regard to its application in rotating electrical machines, requires comprehensive considerations of spatial variations of magnetic properties in the sheet plane and careful awareness of occurring anisotropic effects. Extensive study on the stress related changes of electromagnetic properties in non-grain-oriented (NGO) electrical steels is thereby, necessary. The presented results of the studied non-grain-oriented (NGO) electrical steel enable

Acknowledgment

The work of N. Leuning and S. Steentjes is supported by the DFG and performed in the research group project “FOR 1897 - Low-Loss Electrical Steel for Energy-Efficient Electrical Drives” and as part of the DFG research project “Improved modeling and characterization of ferromagnetic materials and their losses”. M. Schulte and W. Bleck would like to thank company C.D. Wälzholz for their support and the material staging.

References (18)

A. Schoppa et al.
Influence of welding and sticking of laminations on the magnetic properties of non-oriented electrical steels
J. Magn. Magn. Mater.
(2003)
Y. Kurosaki et al.
Importance of punching and workability in non-oriented electrical steel sheets
J. Magn. Magn. Mater.
(2008)
M. Emura et al.
The influence of cutting technique on the magnetic properties of electrical steels
J. Magn. Magn. Mater.
(2003)
F.J.G. Landgraf et al.
Losses and permeability improvement by stress relieving fully processed electrical steels with previous small deformations
J. Magn. Magn. Mater.
(2002)
V.E. Iordache et al.
Magnetic behaviour versus tensile deformation mechanisms in a non-oriented Fe–(3 wt%)Si steel
Mater. Sci. Eng.: A
(2003)
V.E. Iordache et al.
Magnetic characterisation of elastically and plastically tensile strained non-oriented Fe–3.2%Si steel
J. Magn. Magn. Mater.
(2003)
J.M. Makar et al.
The effect of plastic deformation and residual stress on the permeability and magnetostriction of steels
J. Magn. Magn. Mater.
(2000)
R. Siebert et al.
Laser cutting and mechanical cutting of electrical steels and its effect on the magnetic properties
IEEE Trans. Magn.
(2014)
E. Araujo et al.
Dimensional effects on magnetic properties of Fe–Si steels due to laser and mechanical cutting
IEEE Trans. Magn.
(2010)

There are more references available in the full text version of this article.

Cited by (62)

Influence of uniaxial tensile strain on magnetization behavior of Fe-9wt%Ni steel
2024, Journal of Materials Research and Technology
This study investigated the effects of uniaxial tensile strain on the magnetization process of an Fe-9wt%Ni (9Ni) alloy to increase understanding of its magnetic behavior. As the applied strain was increased from 0 to 14 %, the magnetization curve changed remarkably, particularly under a high-intensity magnetic field, and magnetic flux density, relative permeability, remanence, and coercive force degraded significantly, especially at strains greater than the upper yield point. Increase in tensile strain caused increase in hysteresis losses, primarily because strain induced crystal defects, which affected the rearrangement of magnetic domains. Increased dislocation density was the primary contributor to the observed deterioration in magnetic properties; changes in texture and phase had little influence. This finding indicates that strain-induced deformation strongly affects the magnetic behavior of 9Ni alloys; this insight will be useful in research aimed at mitigating welding defects such as arc blow, that are attributed to the magnetization of Ni steel.
Magnetic shielding mechanism and structure design of composites at low frequency: A review
2023, Journal of Magnetism and Magnetic Materials
The ultra-low magnetic field environment is essential for the research of fundamental physics and further application of biomedicine and space exploration etc. The single material structure is hard to meet the increasing demand for better shielding performances, whereas the composite shows great potential in addressing this problem. However, the state of art summary about magnetic shielding of composites, especially at low frequencies is insufficient. This review first introduces the magnetic shielding mechanism and the theoretical model of the shielding factor. The calculation method of permeability and the importance of accurate hysteresis properties characterization of magnetic composites are systematically discussed. Subsequently, the current status of magnetic shielding investigation on composite structures including stacked, coating, and foam forms is generalized. Emerging strategies for composite materials to further enhance shielding performances using the synergistic effect of structural and material properties are described. Finally, the challenges faced by composite materials in structural design and mechanism exploration of magnetic shielding are presented, providing a fresh perspective for its development.
Stress annealing effects on magnetic properties of grain oriented electrical steel under compressive stress
2022, Journal of Magnetism and Magnetic Materials
There is a strict relation between Gross National Product and electric energy consumption; consequently, the improvement of electrical machines efficiency is highly desired. Regarding power transformers, power loss of magnetic core sheets increases due to compressive stresses appearing during its operation, decreasing power transformer performance. In this article, the effects of tensile stress annealing on power loss of grain oriented electrical steel under compressive stress are evaluated. To do that, the power loss of two uncoated sheets was measured before and after tensile stress annealing for several magnetic inductions (0.7, 1.0, 1.3, 1.5, and 1.7 T) and compressive stress (0, 2, 4, 6, 8, and 10 MPa). This thermomechanical procedure was performed at 500°C, 40 MPa for 10–20 min. Although the tensile stress annealing performance depends on crystallographic texture, a power loss reduction occurs for both samples when compressive stresses were higher than 6 MPa, regardless of magnetic induction. In summary, tensile stress annealing could reduce the deleterious effects of compressive stress on power loss, making commercial grain oriented electrical steel more magnetic uniform and improving power transformer efficiency.
Quantitative characterisation and modelling of the effect of cut edge damage on the magnetic properties in NGO electrical steel
2022, Journal of Magnetism and Magnetic Materials
Citation Excerpt :
The residual stress (both tensile and compressive elastic stresses are present) acts on the plastically deformed cut edge region and extends into the non-plastically deformed region; the total width affected by the residual elastic stress is reported to be 300–500 µm, compared to the plastic strain affected region of 220 µm. Both tensile and compressive stresses deteriorate the magnetic properties, with compressive stress being more detrimental [58]. An average elastic residual stress over the region that is also plastically deformed has been estimated to be −133 MPa by integrating the compressive stress distribution in [18] and averaging over the plastic deformation width of 250 µm.
The cut edges of electrical steel NGO laminations in electric motors experience mechanically induced plastic deformation and residual elastic stress, which deteriorate the magnetic performance of the material. This deterioration is accounted for empirically in electric machine modelling tools by introducing a ‘build factor’ on the iron losses. Currently, a wide range of cut edge deteriorated widths have been reported in the literature, depending on the method used for characterisation, the material and the cutting method. In this paper, cut edge plastic damage characterisation was carried out using EBSD kernel average misorientation (KAM) maps and nano-indentation to quantify the magnitude and width of the plastic damage at the cut edge for a stamped tooth of a segmented stator and a guillotined single sheet tester (SST) sample. The relationship between the EBSD KAM and nano-hardness values and plastic strain was found using tensile samples tested to varying applied strain levels. Therefore, the plastic strain gradient with respect to distance from the cut edge was determined. It was found that both EBSD and nano-indentation gave similar predictions of effective plastic strain values and damage width: up to 1.45–1.50 at stamped cut edge over 180 µm width and up to 1.35–1.4 at guillotine cut edge over 250 µm width. The relationships between the magnetic performance and elastic stress, plastic strain, and plastic strain with elastic stress were determined using single sheet tester (SST) measurements. In addition, SST 3D FEA models of the cut edge sample were built using COMSOL Multi-Physics software considering a single layer for plastic damage only and two layers for plastic damage + elastic stress and elastic stress. The modelling results for the guillotine cut edge SST samples were compared to measured data. It was found that to obtain accurate cut edge magnetic property deterioration for NGO electrical steel laminations both the plastic strain and residual elastic stress cut edge effects need to be included. In the cut edge model, a first layer width of 250 µm with magnetic properties for an effective plastic strain of 1.17 under residual compressive elastic stress of −133 MPa and a second layer width of 220 µm with magnetic properties for residual compressive elastic stress of −119 MPa give excellent results for hysteretic BH curves and specific iron loss evaluation.
Experimental characterization of the effect of uniaxial stress on magnetization and iron losses of electrical steel sheets cut by punching process
2022, Journal of Magnetism and Magnetic Materials
Citation Excerpt :
On the other hand, low tensile stress improves the magnetization and reduces the iron losses, while high tensile stress shows similar effect to the compressive stress along the applied direction. It was reported in [22,23,30] that the effect of stress on the magnetization and iron losses exhibits quantitative differences for the rolling direction (RD) and transverse direction (TD), which can be attributed to anisotropic behavior of the material as a result of its crystallographic texture [37]. All these selected literature studies in [21–36] present highly relevant results showing how the stress affects the electrical steel sheets.
The effect of uniaxial stress on iron losses of M400-50A grade non-oriented electrical steel sheets cut by punching process is experimentally studied. Samples cut along the rolling and transverse directions and having different number of cutting edges are used for this purpose. Measurements are carried out in the range of 10–100 Hz frequency of sinusoidal excitations at different magnetization levels under varying uniaxial stress by using a single sheet tester. The iron losses are obtained from the measurements and comparative analyses are made for different cases. The study shows that the effect of stress on the iron losses of the punched samples varies depending on the degradation level that the samples have after the cutting process. By considering this varying effect, when the combined effect of stress and punching is analyzed, it is observed that the iron losses increased up to 55.2% under compressive stress. It is also observed that the increase in the losses due to the effect of cutting can be recovered by applying tensile stress.
Effect of dislocation pattern on the magnetic domain structure of pure polycrystalline Ni
2022, Journal of Materials Research and Technology
We investigated the influence of discrete dislocation, dislocation cell, and cell block on the magnetic domain structure in deformed polycrystalline Ni. Discrete dislocation and dislocation cell structure manifested a short-range effect on the local domain structure. By contrast, dislocation cell block structure significantly changed the magnetic domain by generating 180° domain walls. Our observations indicated that the change of magnetic property as a function of plastic deformation should be discontinuous. However, in macroscale, the coercivity and hysteresis loss monotonically increased as increasing flow stress increases. The discrepancy between the phenomena at different scales is attributed to the crystallographic orientation change in plastic deformation.

View all citing articles on Scopus

View full text

Effect of elastic and plastic tensile mechanical loading on the magnetic properties of NGO electrical steel

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusions

Acknowledgment

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Mater. Sci. Eng.: A

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Laser cutting and mechanical cutting of electrical steels and its effect on the magnetic properties

IEEE Trans. Magn.

Dimensional effects on magnetic properties of Fe–Si steels due to laser and mechanical cutting

IEEE Trans. Magn.