Non-oriented Electrical Steel Sheets Research Articles

Development of Non-Oriented Electrical Steel Sheets for Energy Efficient Motor based on Ultra Low Sulfur Technology.

The effect of sulfur on the magnetic properties of non-oriented electrical steel sheets was studied. In an ultra low sulfur steel with annealing temperatures ranging from 850°C to 975°C, hysteresis loss is lower than that of a high sulfur steel. However, the hysteresis loss in the ultra low S steel increases with an increase in the final annealing temperature ranging from 975°C to 1050°C. This phenomenon is associated with the precipitation of AlN near the surface of the steel. The nitride forming reaction is accelerated with a decrease in S content. In the ultra low S non-oriented electrical steel sheets, the low core loss was obtained by the reduction of the surface nitriding and the high magnetic flux density was obtained by a reduction of Si and Al content. This steel shows; 1)low hysteresis loss, 2)high magnetic flux density, 3)excellent punching properties and 4)low production cost.

The effects of sulfur on magnetic properties of non-oriented electrical steel sheets

The effect of sulfur on the hysteresis loss of non-oriented electrical steel sheets was studied. The hysteresis loss in ultra-low S steel increases with an increase in the final annealing temperature ranging from 975°C to 1050°C. This phenomenon is associated with an increase in nitride precipitation as AlN near to the surface of the steel. The nitride forming reaction is accelerated by a decrease in S content.

The gas composition that causes oxide scale formation during the decarburisation of non-oriented electrical steel sheets

en

Effects of manganese and sulfur contents and slab reheating temperatures on the magnetic properties of non-oriented semi-processed electrical steel sheet

The effects of manganese and sulfur contents and slab reheating temperatures (SRTs) on the magnetic properties of non-oriented semi-processed electrical steel sheets were investigated. The core loss W15/50 of the steels increases with an increase of sulfur content in each steel with different manganese contents, while, the magnetic induction B50 hardly changed with an increase of the sulfur content at any manganese level. The SRTs affect the core loss in steels without hot band annealing, and in steels processed at an SRT of 1273 K showed the lowest core loss. Steels with higher sulfur content processed at an SRT of 1523 K showed deterioration of the core loss caused by the retardation of the grain growth at the recrystallization annealing by the fine MnS (ca.0.1 μm in diameter).

無方向性珪素鋼板の厚みによる磁区構造変化

The anomaly factor that is the ratio of the measured eddy current loss to the classical calculated value tends to increase steeply when the thickness of non-oriented Si-Fe electrical steel sheets is decreased. To investigate the behavior of the anomaly factor in relation to the sheets’ thickness, magnetic domain observation was performed, using the Kerr effect. The grains of a thinned sheet exhibit a stripe domain pattern. Grains exhibiting a stripe domain on the surface had a closure domain structure in a cross section of a sheet. It was found that a field applied in the sheet plane induced a magnetization component normal to the sheet plane, which may increase the anomaly factor of thin sheets.

Effect of Zirconium on the Magnetic Properties of Nonoriented Semiprocessed Electrical Steel Sheet

The effects of zirconium precipitates on the magnetic properties of nonoriented semiprocessed electrical steel sheets were investigated. Core loss of the test specimens declined for zirconium contents of 0.01 wt.%, whereas the magnetic induction did not change due to the addition of zirconium less than 0.133 wt.%. Precipitates and texture studies revealed that the zirconium precipitates had no effect on the grain coarsening at hot rolling and after final annealing after being cold rolled.

HRAES study of oxide scale formation by decarburization of non-oriented electrical steel sheets

The oxide growth during the decarburization process of non-oriented silicon steel sheets alloyed with 0.5 and 1 mass% of aluminium was studied using high-resolution auger electron spectroscopy (HRAES), the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The samples were annealed in a H 2–H 2O–N 2 gas mixture with different oxygen potential in the temperature range from 800 to 1050°C. We found that oxide scale was a mixture of FeO, Fe 3O 4 and SiO 2 and Fayalite (FeSi 2O 4). This oxide scale was porous. In the high Al alloyed sheets (2 mass% Si and 1 mass% Al) the oxide scale was a mixture of FeO, Fe 3O 4, and Al 2O 3 and also Hercynite (Fe Al 2O 4). In this case the oxide scale was compact. For thermodynamic calculations of Fayalite and Hercynite formation during the decarburization process the Gibbs energy minimization model (GPRO) was applied (Koroušić, Kovine zlitine tehnol 1994;28:609; Koroušić and Rosina, RadexRundsch 1994;1(2):523).

Effect of aluminum and nitrogen on the magnetic properties of non-oriented semi-processed electrical steel sheet

The effects of aluminum and nitrogen on the magnetic properties of non-oriented semi-processed electrical steel sheets were investigated. Test specimens with <0.0024 wt% AlN keeps lower core loss, while, the core loss of the specimens with >0.0024 wt% AlN and <0.1 aluminum is deteriorated by the ‘harmful AlN (<0.5 μm in size)’, which pinned down the grain boundaries at the grain growth process. The core loss of the test specimens with >0.0024 wt% AlN and >0.1 wt% aluminum is not deteriorated, due to the ‘harmless large AlN (>1.0 μm)’, which did not pin down the grain boundaries

Effects of Aluminum on Weldability of Nonoriented Electrical Steel Sheets.

The effects aluminum has on the weldability of nonoriented electrical steel sheets as related to blowholes and welding bead width was studied. The addition of aluminum to steel sheets decreased the numbers of blowholes and widened the welding bead width in Gas Tungsten Arc Welding. The following effect of aluminum in steel sheets on welding blowholes was observed. The organic components in the inorganic-organic coating applied on steel sheets gasified due to welding heat and CO gas was generated. The gas dissolved in weld pool and CO gas became dissolving C and O. Aluminum acted as a deoxidizer and decreased dissolving oxygen. CO gas which generated at solidification of the weld pool was decreased. As a result, the addition of aluminum in steel decreased blowholes. The effect of aluminum in steel sheets had on welding bead width was as follows. Oxygen has been known to make the shape of welding bead deep and narrow. In the case of welding after consumer annealing, oxide film formed on the cut surface during consumer annealing. Aluminum deoxidized the dissolved oxygen which penetrated from the oxide film into the weld pool at the time of welding. As a result, the addition of aluminum in steel made the shape of welding bead shallow and wide. The driving force of convection in the weld pool of nonoriented electrical steel sheets was the surface tension because the penetration changed by the presence of oxide film on the surface in Al-free specimens even in laser welding in which electromagnetic force did not work.

Computationally efficient rate dependent hysteresis model

A fast dynamic hysteresis model is constructed based on the classical Preisach model and a differential equation which delays its input with respect to the actual value to encompass dynamic effects such as eddy currents and domain wall displacement. It is applied to describe the magnetic behaviour of both grain oriented and nonoriented electrical steel sheets. The results of numerical simulations are compared to experiment and power loss prediction is performed.

Analysis and prevention of edge cracking phenomenon during hot rolling of non-oriented electrical steel sheets

In this study, a microstructural investigation was conducted on the edge cracking phenomenon in non-oriented electrical steel sheets during hot rolling. Particular emphasis was placed on the role of iron oxides and ferrite grain shape in the edge cracking. Detailed microstructural analyses of the sheets showed that highly elongated, fine grains were predominantly found in the edge region which did not recrystallize. The hardness of this region was higher than that of the central region composed of equiaxed grains where dynamic recrystallization occurred. Various oxides were observed in this edge region, and initiated intergranular or cleavage cracks when the edge regions were impacted by side guide rolls. These oxides were identified to be Si- and Mn-containing iron oxides which might have formed during continuous casting or hot rolling. In addition to edge cracks, line scabs were found in a linear mode parallel to the rolling direction on the surface of the edge-cracked region, probably due to the exposure to an oxidation atmosphere. Thus, in order to prevent the edge cracking, the minimization of iron oxides and highly elongated grains in the edge region and the careful control of the spacing between steel sheets and side guide rolls were suggested.

Nonoriented electrical steel sheet with low iron loss for high-efficiency motor cores

A new material was studied for high-efficiency motor cores that need higher magnetic flux density, lower iron loss, and lower mechanical hardness. Excessively high Si content tends to decrease magnetic flux density of nonoriented electrical steel sheets. The composite addition of rare-earth metals (REM) and Al into molten steel was found to make inclusions coarse and remarkably improve grain growth during stress relief annealing, which resulted in decreased iron loss. A new nonoriented electrical steel sheet (50RMA350) with Si, Al, and REM has been successfully developed to give a higher efficiency to inverter drive model motors than a conventional material.

加工性に優れた無方向性電磁鋼板の磁気特性と被削性

Influence of S (Sulfur) content on the iron loss deterioration by punching operation and the machinability of non-oriented electrical steel sheets was investigated. The iron loss deterioration of the higher S steels (0.020-0.025 mass% S) by punching fine pieces is less than that of the lower one (0.005 mass% S), as a result of inhibiting plastic strain effectively near punching edge in the higher's ones. Moreover, cutting tool wear and cutting burr of the higher S steel is less than that of the lower's one. It is concluded that non-oriented electrical steels containing higher S show good performance for applying to small size motors, which can be required to be higher energy efficiency and higher productivity.

Effect of Oxide Shape on Magnetic Properties of Semiprocessed Nonoriented Electrical Steel Sheets.

The effect of oxide shape on magnetic properties of semiprocessed nonoriented electrical steel sheets produced by single reduction cold rolling process was studied. When oxides in steel sheets were elongated inclusions which were prescribed as B type by JIS, the oxides inhibited grain growth during consumer annealing and average grain size became small. As a result, core loss was bad. When oxides were spherical inclusions which were prescribed as C type by JIS, the oxides did not inhibit grain growth and average grain size became large. As a result, core loss was good. Oxide composition affected the shape remarkably. The degree of elongation of oxides had much to do with the viscosity during hot rolling. The viscosity of oxides containing less MnO and much SiO2 was high, and the degree of elongation was small. Consequently, these oxides became spherical C type inclusions.

Characteristics of Adhesive Coating Non-oriented Electrical Steel Sheet Cores

Magnetic and mechanical characteristics of adhesive coating non-oriented electrical steel sheet cores were measured in the conditions of motor, comparing with those of welded cores. The deteriorations of iron losses and exciting currents by adhesion are less than those by welding. The noise levels and vibrating levels of adhesive coating cores are about 10dB lower than welded cores. The results of modal analysis of adhesive coating core and welded one support the results of noise and vibration tests. The heat conductivities of adhesive coating cores in lamination direction are higher.

Effect of skin-pass rolling direction on magnetic properties of semiprocessed nonoriented electrical steel sheets

Effect of skin-pass rolling direction on magnetic properties and directionality in semiprocessed nonoriented electrical steel sheets produced by skin-pass rolling process was studied. Skin-pass rolling direction affects greatly magnetic properties and directionality. By the control of skin-pass rolling direction, the value of B/sub 50/ in the required directions such as 0/spl deg/, 90/spl deg/ and circumferential direction can be adjusted and the value of B/sub 50/ is higher than that of the usual skin-pass rolling direction of 0/spl deg/. The textures of the steel sheets developed after batch annealing varied with the skin-pass rolling directions and this result indicates that the residual strain energy by skin-pass rolling varies with skin-pass rolling directions.

Magnetic properties of high-permeability thin gauge non-oriented electrical steel sheets

Magnetic properties of high permeability thinner gauge non-oriented electrical steel sheets are investigated from the viewpoint of applications in the audio frequency range. The steel sheets 0.75 mass% Si - 0, 3 mass% Al (0.20, 0.35 and 0.5 mm in thickness) were prepared, including the hot-band annealing prior to the cold-rolling for the purpose of controlling the texture. The stress-relief annealing was carried out before the characterization. The flux density at applied field of 5000 A/m is 1.76 T for 0.2 mm-thick sheet. The decrease of the thickness from 0.5 mm to 0.2 mm results in the 67% reduction of the core loss measured at the flux density of 1.0 T and the frequency of 1 kHz. The core losses measured at 1.0 T, 400 Hz and 1.0 T, 1 kHz are 15.7 W/kg and 57.9 W/kg. The RMS exciting force of the developed sheet (0.2 mm in thickness) at 1.6 T, 400 Hz was about one-fourth as large as that of a conventional 3 mass% Si steel sheets. Their results would indicate that such high permeability thin gauge steel sheet could be utilized in the audio frequency application, in particular, in the motor cores of the electric vehicles.

電磁鋼板における磁気特性の温度依存性

The magnetic properties of 0.15-3%Si non-oriented electrical steel sheets were measured at temperatures ranging from 4 K to 200°C. Except for the 3%Si sheet, all the sheets were more easily magnetized at higher temperatures. The hysteresis losses increased at lower temperatures, but the changes were less than those due to the crystalline grain size. The eddy current loss can be estimated as WRTeρRT/ρT,where WRTe, ρRT, and ρT are the eddy current loss at room temperature and the electric resistivities at room temperature and T°C, respectively. The magnetic properties of a 6.5%Si steel sheet were also measured at the same temperatures.The 6.5%Si steel was the easiest to magnetize at room temperature. The change in the eddy current loss with temperature was proportional to those of resistivities,but the hysteresis loss increased very markedly at lower temperatures, because of the large change in magnetostriction.

Effects of vanadium on magnetic properties of semi-processed non-oriented electrical steel sheets

The effects of titanium inclusions on magnetic properties of non-oriented electrical steel sheets were investigated. The magnetic induction and core loss of test specimens deteriorated as the titanium content increased. Electron microscopic study revealed that the deterioration was classified into two types: one was caused in the steels containing 0.016 wt% titanium by numerous (Fe, Ti)P precipitates in both grains and grain boundaries.

Texture of primary recrystallization on nonoriented electrical steel sheet with phase transformation

The magnetic properties of nonoriented (NO) electrical steel sheet are commonly improved if the texture of their products possesses “cube texture” (e.g., {100 〈0vw〉, “goss texture”) (i.e., ¹10〈011〉, and less ²22 texture). Industrially “cube type” has not been obtained, but “goss texture” has been. In a greater or lesser degree, {222} texture exists. To improve “goss texture” and reduce ²22 texture, the grain size of the material prior to cold rolling should be larger. When the grain size before cold rolling is larger, during primary recrystallization, “goss texture” is enriched, ²22 texture is decreased, and the grain grows so easily that higher induction and lower core loss can be obtained. This does not depend on the presence of phase transformation. In case of NO steel with phase transformation, heat treatment before cold rolling has been done below the austenite transition temperature (Acin1) in order to prevent the fine grain size caused by α → γ(+α) → α transformation. By using material that was heated over Acin1 and cooled with changing cooling rates, this study describes (a) the relationship between textures before cold rolling and the texture of the final product, and (b) the development of the magnetic properties.