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Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Energy Materials".

Deadline for manuscript submissions: closed (10 October 2021) | Viewed by 13692

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Prof. Dr. Rudolf Kawalla

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Institute of Metal Forming (IMF), Technische Universitat Bergakademie Freiberg, Freiberg, Germany
Interests: rolling strategies; material processing; material characterization; metallurgical engineering; nonoriented electrical steels
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Dear Colleagues,

Energy demand is rising all over the world. Simultaneously, saving energy is a global challenge for environmental and climate protection. In this regard, one focus is improving nonoriented electrical steels, which have a significant influence on losses during energy conversion and, therefore, determine the efficiency of generators and electrical drives.

Research demands with regard to the optimization of electrical steel sheets result from the high complexity of the influencing factors that have to be taken into account. The mechanical and magnetic properties are influenced by the composition, microstructure, texture, and induced residual stresses of the selected material. Both, the material itself and the design concept of the machine, with the loads related to the specific application, have to be considered. During production and processing, the different interdependencies need to be understood in order to design a material for a defined application.

It is my pleasure to invite you to submit a manuscript for this Special Issue and contribute to the exciting field of the material research and development of nonoriented electrical steel. This Special Issue welcomes papers focused on, though not limited to, nonoriented electrical steel production, processing, and characterization.

Prof. Dr. Rudolf Kawalla
Guest Editor

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Keywords

nonoriented electrical steel
rolling strategies
annealing methods
nano-/micromechanics
simulation
crystallographic texture
shear cutting
residual stresses
magnetic anisotropy
magnetic properties

Published Papers (5 papers)

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Research

32 pages, 10924 KiB

Open AccessArticle

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

by Martin Heller, Anett Stöcker, Rudolf Kawalla, Nora Leuning, Kay Hameyer, Xuefei Wei, Gerhard Hirt, Lucas Böhm, Wolfram Volk and Sandra Korte-Kerzel

Materials 2022, 15(1), 32; https://doi.org/10.3390/ma15010032 - 21 Dec 2021

Cited by 6 | Viewed by 3268 | Correction

Abstract

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. Full article

(This article belongs to the Special Issue Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives)

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10 pages, 2696 KiB

Open AccessArticle

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

by Lucas Boehm, Christoph Hartmann, Ines Gilch, Anett Stoecker, Rudolf Kawalla, Xuefei Wei, Gerhard Hirt, Martin Heller, Sandra Korte-Kerzel, Nora Leuning, Kay Hameyer and Wolfram Volk

Materials 2021, 14(22), 7055; https://doi.org/10.3390/ma14227055 - 20 Nov 2021

Cited by 10 | Viewed by 2267

Abstract

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. Full article

(This article belongs to the Special Issue Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives)

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21 pages, 14448 KiB

Open AccessArticle

Influence of Process Parameters on Grain Size and Texture Evolution of Fe-3.2 wt.-% Si Non-Oriented Electrical Steels

by Xuefei Wei, Alexander Krämer, Gerhard Hirt, Anett Stöcker, Rudolf Kawalla, Martin Heller, Sandra Korte-Kerzel, Lucas Böhm, Wolfram Volk, Nora Leuning, Kay Hameyer and Johannes Lohmar

Materials 2021, 14(22), 6822; https://doi.org/10.3390/ma14226822 - 12 Nov 2021

Cited by 10 | Viewed by 2240

Abstract

The magnetic properties of non-oriented electrical steel, widely used in electric machines, are closely related to the grain size and texture of the material. How to control the evolution of grain size and texture through processing in order to improve the magnetic properties is the research focus of this article. Therefore, the complete process chain of a non-oriented electrical steel with 3.2 wt.-% Si was studied with regard to hot rolling, cold rolling, and final annealing on laboratory scale. Through a comprehensive analysis of the process chain, the influence of important process parameters on the grain size and texture evolution as well as the magnetic properties was determined. It was found that furnace cooling after the last hot rolling pass led to a fully recrystallized grain structure with the favorable ND-rotated-cube component, and a large portion of this component was retained in the thin strip after cold rolling, resulting in a texture with a low γ-fiber and a high ND-cube component after final annealing at moderate to high temperatures. These promising results on a laboratory scale can be regarded as an effective way to control the processing on an industrial scale, to finally tailor the magnetic properties of non-oriented electrical steel according to their final application. Full article

(This article belongs to the Special Issue Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives)

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33 pages, 7134 KiB

Open AccessArticle

Integrated Process Simulation of Non-Oriented Electrical Steel

by Anett Stöcker, Max Weiner, Grzegorz Korpała, Ulrich Prahl, Xuefei Wei, Johannes Lohmar, Gerhard Hirt, Martin Heller, Sandra Korte-Kerzel, Lucas Böhm, Wolfram Volk, Nora Leuning, Kay Hameyer and Rudolf Kawalla

Materials 2021, 14(21), 6659; https://doi.org/10.3390/ma14216659 - 4 Nov 2021

Cited by 8 | Viewed by 2400

Abstract

A tailor-made microstructure, especially regarding grain size and texture, improves the magnetic properties of non-oriented electrical steels. One way to adjust the microstructure is to control the production and processing in great detail. Simulation and modeling approaches can help to evaluate the impact of different process parameters and finally select them appropriately. We present individual model approaches for hot rolling, cold rolling, annealing and shear cutting and aim to connect the models to account for the complex interrelationships between the process steps. A layer model combined with a microstructure model describes the grain size evolution during hot rolling. The crystal plasticity finite-element method (CPFEM) predicts the cold-rolling texture. Grain size and texture evolution during annealing is captured by the level-set method and the heat treatment model GraGLeS2D+. The impact of different grain sizes across the sheet thickness on residual stress state is evaluated by the surface model. All models take heterogeneous microstructures across the sheet thickness into account. Furthermore, a relationship is established between process and material parameters and magnetic properties. The basic mathematical principles of the models are explained and demonstrated using laboratory experiments on a non-oriented electrical steel with

3.16

wt.% Si as an example. Full article

(This article belongs to the Special Issue Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives)

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19 pages, 32441 KiB

Open AccessArticle

Material Design for Low-Loss Non-Oriented Electrical Steel for Energy Efficient Drives

by Nora Leuning, Markus Jaeger, Benedikt Schauerte, Anett Stöcker, Rudolf Kawalla, Xuefei Wei, Gerhard Hirt, Martin Heller, Sandra Korte-Kerzel, Lucas Böhm, Wolfram Volk and Kay Hameyer

Materials 2021, 14(21), 6588; https://doi.org/10.3390/ma14216588 - 2 Nov 2021

Cited by 23 | Viewed by 2434

Abstract

Due to the nonlinear material behavior and contradicting application requirements, the selection of a specific electrical steel grade for a highly efficient electrical machine during its design stage is challenging. With sufficient knowledge of the correlations between material and magnetic properties and capable material models, a material design for specific requirements can be enabled. In this work, the correlations between magnetization behavior, iron loss and the most relevant material parameters for non-oriented electrical steels, i.e., alloying, sheet thickness and grain size, are studied on laboratory-produced iron-based electrical steels of 2.4 and 3.2 wt % silicon. Different final thicknesses and grain sizes for both alloys are obtained by different production parameters to produce a total of 21 final material states, which are characterized by state-of-the-art material characterization methods. The magnetic properties are measured on a single sheet tester, quantified up to 5 kHz and used to parametrize the semi-physical IEM loss model. From the loss parameters, a tailor-made material, marked by its thickness and grain size is deduced. The influence of different steel grades and the chance of tailor-made material design is discussed in the context of an exemplary e-mobility application by performing finite-element electrical machine simulations and post-processing on four of the twenty-one materials and the tailor-made material. It is shown that thicker materials can lead to fewer iron losses if the alloying and grain size are adapted and that the three studied parameters are in fact levers for material design where resources can be saved by a targeted optimization. Full article

(This article belongs to the Special Issue Low-Loss Nonoriented Electrical Steel Sheet for Energy-Efficient Electrical Drives)

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