Papers by Keyword: Electrical Steel

Abstract: The texture evolution in the surface and center layer of hot rolled electrical steel containing initial columnar grains with their <100> nearly along ND, RD and TD of sheets were determined by EBSD technique. The transition from Goss to Brass or Copper orientation in surface was analyzed. The difference in texture of center layers in these samples was compared. In particular, orientation evolutions within grains and at grain boundaries of different types of orientations were explored. The results are discussed in terms of the special alignments of grain boundaries among columnar grains.

Abstract: Magnetic properties of electrical steels such as magnetization behavior and electrical losses are mainly related to chemical composition, crystallographic orientation and microstructure. By now, several models have been proposed to empirically correlate magnetic properties and affecting parameters. A quantitative model based on physical understanding of the interaction between the magnetic field variables (e.g. domain structure) and local microstructural variables (e.g. grain orientation and misorientation, grain boundary plane inclination) is still missing. To obtain a better understanding of the interaction between grain boundaries and domain walls, the magnitude of free pole density at grain boundaries was taken into account. Experimental results from 3-dimentional EBSD experiments were employed to measure the grain boundary orientation for several samples with different chemical composition and grain size. The free pole density was calculated using the relative misorientation between adjacent grains, and was included in a model together with grain size, magnetocrystalline anisotropy energy and silicon equivalent. By comparison with the experimental results of the magnetic induction measured at low, medium and high magnetic fields, is shown that the magnetization behavior can be more accurately predicted when the above mentioned phenomena are taken into account.

Abstract: The core loss and magnetic induction of electrical steels are dependent on the microstructure and texture of the material, which are produced by the thermo-mechanical processing. After a conventional rolling process, crystal orientations of the α-(//RD) and γ-(//ND) fibers are strongly present in the final texture. These fibers have a drastically negative effect on the magnetic properties of electrical steels. By applying asymmetric rolling, significant shear strains could be introduced across the thickness of the sheet and thus a deformation texture with more magnetically favorable components is expected. In this study, an electrical steel of 1.23 wt.% Si was subjected to asymmetric warm rolling in a rolling mill with different roll diameters. The evolutions of both deformed and annealed textures were investigated. The texture evolution during asymmetric warm rolling was analyzed by crystal plasticity simulations using the ALAMEL model. A good fit between measured and calculated textures was obtained. The annealing texture could be understood in terms of an oriented nucleation model that selects crystal orientations with a lower than average stored energy of plastic deformation.

Abstract: Magnetic Non Destructive Testing (MNDT) methods are a tool not limited in the detection of cracks and defects, like traditional NDT methods for ferrous structures, but they have shown a potential for the monitoring of the structure and crack prevention. MNDT techniques include surface Magnetic Barkhausen Noise measurements (MBN) yielding localized information about the surface stresses and magnetization processes in the vicinity of the measurement; the use of Magnetostrictive Delay Lines (MDL) for the measurement of surface stresses; the Magneto Acoustic Emission (MAE), revealing information about the magnetic domain wall propagation and indirectly about the underlying structure’s role in the magnetization process of the material; magnetic major and minor loop (B-H) bulk measurements which yield information on the macroscopic magnetic properties of the material such as, the coercivity, H_c, the remanence, B_r, or the permeability, µ. Results show that changes in these properties are definite signs of non-uniformly distributed stresses along the material and reveal a definitive dependence of the various magnetization reversal mechanisms such as domain wall propagation and domain rotation on the microstructure of the material, eg, the domain wall structure, the effect of dislocations, the grain size, built-in stresses. However, the quantitative mapping of the MNDT results to the microstructure and from there to the possibility of crack generation and propagation is still a very attractive but open question. Modeling at the atomic level involving Ising Models, at the microscopic level using micromagnetic calculations and at the macroscopic level employing the Preisach formalism, has so far provided useful insight. The use of modeling in order to not only explain experimental results but in forecasting is expected to greatly enhance the position of the MNDT techniques in industrial NDT.

Abstract: Results of an experimental study of electrical steel annealed at 500, 600, 700 °C and subsequently cooled via quenching or air, are presented. The samples have been characterized with respect to their magnetic properties using Magnetic Barkhausen Noise (MBN) and major and minor loop (B-H) measurements. MBN increases slightly with the annealing temperature especially in the quenched samples. The B-H loops suggest that the prevalent magnetization reversal mechanism in the air cooled samples is domain wall propagation, while in the quenched samples non 180^o domain rotation seems to be significant approaching the high induction region. Scanning Electron Microscopy studies show a more homogeneous texture after annealing which in the case of the quenched samples is accompanied by not fully formed grain boundaries and orientation along he easy axis

Abstract: The effect of pressures on microstructure and properties of as-deposited high silicon electrical steel by EB-PVD during hot pressing was studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the phase composition and morphology; the density and electrical resistivity were measured using the bottle method and four-probing method, respectively. It was found that the density increased from 7.25×10³ kg/m³ to 7.5 ×10³ kg/m³, while the electrical resistivity decreased from 85µΩ•cm to 75µΩ•cm with the increase of the pressure from 30 MPa to 60 MPa.

Abstract: A possibility to reduce core loss in non-oriented (NO) electrical steel by applying magnetic coating has been investigated. This technique involves electroless plating of magnetic coating onto the surface of electrical steel. The material system was NiCoP coatings with different thicknesses (1, 5, and 10 􀁐m) deposited onto the surface of commercially available Fe-3%Si NO electrical steel. Characterization of deposited NiCoP coating was carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectrometer. The deposited Ni-Co-P coatings were amorphous/nanocrystalline and composed of 56-59% Ni, 32-35% Co and 8-10% P by mass. Effect of coatings on core loss of the electrical steel was determined using a single sheet test. A core loss reduction was achieved with the NiCoP coating with a thickness of 1 􀁐m magnetized at a magnetic flux density of 0.3T.

Abstract: In order to improve the magnetic properties of electrical steels, it may be desirable to increase the Si and/or Al content of the steel. A possible and alternative route to realize this is through the application of an Al-Si-rich coating on the steel substrate using a hot dipping process, followed by a diffusion annealing treatment. Previously, a series of compositions were used for dipping, namely: pure Al, Al + 10wt% Si (hypo-eutectic composition) and Al + 25wt% Si (hypereutectic composition). After these dipping experiments, and the subsequent evaluation of the coating and its formed intermetallic phases, the use of a hypo-eutectic Al-Si-bath was recommended for further investigation, because of certain advantages: i.e. hypo-eutectic concentrations allow lower dipping temperatures and reduce the formation of ordered Fe-Si-structures that cause brittleness in the coating and substrate. The present work reports on the results obtained on materials that were hot dipped in a hypo-eutectic Al-Si bath. An Al + 1wt%Si bath was used to coat electrical steel substrates with different silicon contents with dipping times, varying between 0 to 20 seconds, after a preheating of the samples to a temperature of 700°C. A thorough characterization of the formed intermetallics was made by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). Three different compounds were identified as Fe2Al5, FeAl3 and a nearly pure Al phase.

Abstract: Although plenty of research has already been carried out on the issue of texture control in non-oriented electrical steels, there is not yet a universally applied industrial process to obtain an optimized {001} fibre texture. Among the various laboratory processes that have been studied so far, cross rolling seems to be one of the most promising approaches. For evident reasons cross-rolling cannot be implemented on a conventional continuous rolling line of an industrial plant. In the present study a potential interesting alternative is presented which may deliver a similar texture evolution as the cross rolling process, but can be applied in a continuous line of hot and cold rolling operations followed by recrystallization annealing. By applying severe rolling reductions a very strong rotated cube texture is obtained very much similar to the one that is observed after cross rolling. After annealing, the rotated cube texture changes to a {h11}<1/h,21> fibre texture with a maximum on the {311}<136> component which implies the potential to develop a {001} fibre texture after further processing. It is argued that the appearance of the {311}<136> recrystallization texture component can be attributed to oriented nucleation in the vicinity of grain boundaries between slightly misoriented rotated cube grains.

Abstract: Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.