Si Steel Sheet Research Articles

Development of High Si Steel Sheet Contributes to the Downsizing and High Efficiency of Electrical Equipment

1．はじめに

Thin Fe–Si–Al alloy sheet fabricated by Al gradient diffusion through PVD for excellent high-frequency magnetic properties

In recent years, research on environmentally friendly methods to reduce energy loss of high-frequency transformers has gained momentum. In this study, an Fe–Si–Al alloy sheet with excellent magnetic properties at high frequencies was fabricated by an environment-friendly method involving Al diffusion through physical vapor deposition for high-frequency transformer applications. To improve the magnetic properties of the alloy, the effects of Al diffusion patterns and frequency on the magnetic properties of the Fe–Si alloy sheet were theoretically and experimentally investigated. Up to 12-µm-thick Al was deposited via physical sputtering on a 0.2-mm Fe–Si alloy sheet, which was subsequently annealed for 10–90 min under 10−4 Torr without changing the grain size and texture or forming an intermetallic phase. At 50 Hz, the eddy current loss reached a minimum, when the Al diffusion into the surface and interior was uniform with a deviation of approximately 10 %. In contrast, the high-frequency (above 400 Hz) eddy current loss was minimized, when more than 70 % of the total Al was concentrated on the surface to a depth of 1/4 area. Tension effect occurred owing to the difference between the thermal expansion coefficients of the surface Al-diffused part and the that in the interior. This tension effect minimized the eddy current loss by reducing the domain width. The core loss of our specimen at 20 kHz (8.36 W/kg) was approximately 15 % superior to that of a commercial Si steel sheet of the same thickness. These results indicate the potential of the proposed method in high-frequency transformer eco-technology.

Insight into internal oxidation mechanism of hot rolled Si–Mn added high strength steel: Pure iron layer formation

In order to reveal special morphology formation mechanism of surface continuous Fe layer, through the vacuum sealing heat treatment experiment, the scale transformation process and the mechanism of oxygen pressure reduction in the coiling process of hot rolled steel are obtained. After discussion, it is considered that the surface pure Fe produced by heat treatment under the condition of vacuum sealing of C–Mn–Si steel sheet is due to the internal oxidation of Mn and Si in the substrate and decarburization reaction, and finally lead to the decomposition of oxide scale, resulting in the special structure of surface pure Fe, intermediate oxide scale and internal oxidation.

Effect of Y on Recrystallization Behavior in Non-Oriented 4.5 wt% Si Steel Sheets.

4.5 wt% Si steel sheets with four different yttrium (Y) contents (0, 0.006, 0.012 and 0.016 wt%) were fabricated by hot rolling, normalizing, warm rolling and a final annealing process. Y addition greatly weakened the γ -fiber (〈111〉//ND) texture and enhanced the {001} 〈130〉 and {114} 〈481〉 texture components, and the magnetic properties were improved related to the effects of Y on the recrystallized grain nucleation. Y segregation at the grain boundaries inhibited the nucleation of {111} oriented grains at grain boundaries, which was beneficial to the nucleation and growth of other oriented grains elsewhere. At the same rolling reduction, Y2O2S inclusion caused more stress concentration than Al2O3 inclusion. Y2O2S in deformed grains with low energy storage provided more preferential nucleation sites for {001} 〈130〉 and {114} 〈481〉 grains. Strong {001} 〈130〉 and {114} 〈481〉 recrystallization textures due to the high mobility were obtained in samples containing 0.012 wt% Y.

Effect of antimony addition and asymmetric cold rolling on the texture and magnetic properties of a 1.2% Si steel

This paper investigates the effect of antimony on the microstructure, texture, and magnetic properties of a 1.2 wt% Si steel sheet produced by asymmetric cold rolling. First, the specimens were cast with three different antimony percentages, and after homogenization and hot rolling, they were subjected to an intermediate annealing treatment at 1150 °C for 30 min. The sheet thickness was then reduced to 1 mm using an asymmetric cold rolling process with 80% thickness reduction and finally, the final annealing treatment was performed at 1000 °C for 3 min. The results indicated that increasing antimony improved the texture parameter by increasing the intensity of the θ-fiber. Antimony also accelerated the formation and density of shear bands. Additionally, Cube components nucleated predominantly in shear bands, enhancing the desired texture in the microstructure. Texture evolution affected the magnetic properties of the specimens such that the sample containing 0.026 wt% Sb exhibiting the lowest coercivity and remanence compared to the sample devoid of antimony. It seems that asymmetric rolling has a good interaction with antimony to improve the magnetic properties of low silicon steels.

Role of subsurface Goss-oriented grains in abnormal grain growth in Fe-3% Si steel

In this study, the differences in the crystallographic orientation, grain size, and grain boundary characteristic distribution along the sheet thickness in Si steel sheets were investigated in order to evaluate preferential sites for the abnormal grain growth of Goss-oriented grains. The grains having exact Goss orientation in the subsurface region of the primary recrystallized Si steel sheets had larger grain size, higher fraction, and higher frequencies of HEGBs and Σ9 GBs, which are claimed to be beneficial to the occurrence of the abnormal grain growth than the grains in the central region. On the other hand, the grains having deviated Goss orientation in the central region had larger grain size and higher Σ9 GBs than the grains having same orientation in the subsurface region. Therefore, it is considered that the high Goss selectivity is peculiar to the position of the nuclei and the beneficial conditions for the abnormal grain growth of exact Goss-orientated grains in the subsurface region.

Effects of yttrium on the microstructure, texture, and magnetic properties of non-oriented 6.5 wt% Si steel sheets by a rolling process

Non-oriented 6.5 wt% Si steel thin sheets with three different yttrium (Y) contents (0, 0.012, and 0.03 wt%) were prepared by hot rolling, warm rolling, intermediate annealing, cold rolling and final annealing processes. The effects of the Y content on the microstructure, texture, and magnetic properties of cold-rolled 6.5 wt% Si steel sheets were studied by optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and electron backscattered diffraction. The results showed that the sample with 0.012 wt% Y had the lowest volume fraction of inclusions, and Y played a role in purifying steel. The final average grain size of sheets decreased upon increasing the Y content. As the Y content increased, the {100} texture continuously weakened, and the overall intensity of the η (〈100〉//RD) texture increased first and then decreased, while the intensity of the detrimental γ (〈111〉//ND) texture decreased first and then increased. Adding an appropriate amount of Y optimized the recrystallization texture by promoting the occurrence of shear bands, which provided more nucleation sites for η - fiber oriented grains. When the Y content was 0.012 wt%, the magnetic induction B 50 reached the maximum (1.64655 T) due to the enhanced η texture and weakened γ texture. The sample with 0.012 wt% Y showed the lowest core loss at high frequencies (>5 kHz) because of the favorable grain size. The addition of excess Y increased the number of inclusions and increased γ -fiber oriented grain nucleation, which deteriorated the magnetic properties of non-oriented 6.5 wt%Si steel.

Goss Texture Evolution in a Grain-Oriented Fe-6.5wt%Si Steel Processed by Strip-Casting

Fe-6.5wt%Si steel is an excellent soft magnetic material due to the near-zero magnetostriction and low core losses. In this study, a 0.3 mm-thick grain-oriented 6.5wt%Si steel sheet was produced by a novel strip casting and two-stage rolling. The microstructure and texture evolution were investigated with a special emphasis on the nucleation and growth of Goss grains. The thin normalized strip was composed of large columnar grains and small equiaxed grains. During intermediate annealing, Goss grains nucleated in the shear bands of the deformed <111>//ND grains, and the deformed {111}<112> grains provided most of the nucleation sites. After primary annealing, the Goss grains distributed across the entire thickness, which was different from the conventional rolling route. The fraction of high-angle boundaries (20°-45°) surrounding the Goss grains was apparently higher than those of the matrix grains, which promoted the abnormal growth of the Goss grains during secondary recrystallization.

Effects of Ce on DO3-Ordered Phase, Coincident Site Lattice Grain Boundary and Plastic Deformation of Fe-6.9 Wt.%Si Alloy

Fe-6.9 wt.%Si steel sheets with different Ce doping were prepared by warm rolling and annealing. Fe-6.9 wt.%Si alloys’ poor plasticity was mainly caused by the large amount of highly brittle DO3-ordered structure, and the significant improvement in their plastic deformation ability was found after adding rare earth Ce. The results reveal that the solid drag effect of Ce on the enhancement of dislocation slip reduces the difference of energy between antiphase boundaries and matrix and affects diffusion of Fe and Si atoms in DO3-ordered structure, hindering the nucleation and growth of DO3-ordered phases. λ-fiber textures are transformed into stable γ-fiber textures related to more frequency of ∑CSL boundaries because of an increment on Ce addition. The transgranular and intragranular cracks form in non-Ce-doped alloy with coarse DO3-ordered phases, and the ductile fracture zone characterized with some dimples occurs on the surface of 0.024 wt.% Ce-doped alloy, which indicates that the plastic deformation ability of Fe-6.9 wt.%Si alloy is significantly improved by rare earth Ce doping.

Implementation and Identification of Preisach Parameters: Comparison Between Genetic Algorithm, Particle Swarm Optimization, and Levenberg–Marquardt Algorithm

Electromagnetic simulations of devices with soft materials and the study of the influence of cutting edge deformations/stresses on the degradation of magnetic performances require the identification of hysteresis parameters. Hence, computationally efficient implementation and identification of the hysteresis model is needed to obtain a solution with high accuracy within a reasonable time. Many studies on hysteresis identification have been reported, but few compare different methods to identify the optimal one. In the present study, we focus on the Preisach hysteresis model combined with the Lorentz modified distribution function to describe the magnetic behavior of a fully processed nonoriented Fe–3wt% Si steel sheet under static excitation. Three different identification techniques are implemented and evaluated: particle swarm optimization (PSO), genetic algorithms (GAs), and nonlinear least-squares approximation based on the Levenberg–Marquardt (LM) method. We evaluate each approach with regard to the accuracy, central processing unit computation time, and repeatability of the results. All the techniques perform well in this high-nonlinearity problem. The root-mean-square error is < 3%. However, the implementation of the GA is more complex than the PSO and LM methods. The optimized parameters are obtained in a few minutes in the case of the LM method, but a few hours are required for both the other techniques. Therefore, the LM method is the most suitable technique for the identification of Preisach hysteresis.

Analysis of {100} Texture Formation in Vacuum Annealed Electrical Steel Based on Elastic Anisotropy and Surface Energy Anisotropy

In the present work, columnar grains with strong {100}&lt;0vw&gt; texture in the surface layer are obtained by controlling cold rolling reduction and vacuum annealing with α → γ → α transformation in a Fe–3%Si steel sheet containing Mn and C. The formation of the {100}&lt;0vw&gt; texture during vacuum annealing is related to cold rolling reduction. The {100}&lt;0uv&gt; seeds are retained during a low cold rolling reduction and recrystallization process. The annealed {100}&lt;001&gt; and {100}&lt;012&gt; originate mainly from the nucleation of recrystallization in deformed microstructures. The {100}&lt;011&gt; texture, that is, formed during vacuum annealing originates from the deformed {100}&lt;011&gt;. The development of sharp {100} texture is caused by α → γ → α transformation during vacuum annealing. In the process of γ to α transformation, the values of elastic strain energy for α grains with different orientations on the surface are estimated. By combining the surface energies of various crystallographic planes, it is reasonable to conclude that the elastic strain energy anisotropy plays a significant role in the formation of a sharp {100}&lt;0vw&gt; texture during γ → α transformation. The {100}&lt;0vw&gt; grains prefer to grow in the surface layer columnar grains by minimizing elastic strain energy during γ → α transformation.

Numerical simulation of shrink‐fit motor using gradient Si steel

AbstractA gradient Si steel sheet shows low iron loss in the high‐frequency range and lower iron loss deterioration under compressive stresses, therefore, it is suitable for use as the core material of high‐speed motors, which have seen considerable downsizing in recent years. By performing shearing and shrink‐fitting, the advantages of gradient Si steel as a motor material are investigated in this study. In both shearing and compressive stress experiments, gradient Si steel showed lower iron loss compared to conventional nonoriented electrical steel (0.2 mm thick). By numerical simulation, the efficiencies of the shrink‐fitted motors using gradient Si steel and 3% Si steel were calculated. The motor using the gradient Si steel showed significantly higher efficiency than that using the 3% Si steel. Moreover, even under city driving conditions, gradient Si steel showed good efficiency, because of lower iron loss deterioration. Therefore, gradient Si steel can be used for a wide variety of motors in addition to high‐frequency devices.

Goss Texture Formation by Asymmetric Rolling in Steel Sheet

The Goss texture, or {110}&lt;001&gt;, shows soft magnetic property due to the &lt;100&gt;. Therefore, it is one of the most important texture in Si steels. The Goss texture is one of the shear deformation texture in steel which has bcc structure. During the asymmetric rolling, shear deformation is imposed on steel sheets. To obtain the Goss texture, the carbon and Si steel sheets were asymmetrically rolled by 50-85% reduction in thickness at room temperature and at 770 °C. The asymmetric rolling of steel sheets gave rise to the well-developed Goss texture to them.

Investigation of the magnetic properties of Si-gradient steel sheet by comparison with 6.5%Si steel sheet

In this study, we investigated the magnetic properties of Si-gradient steel sheet produced by CVD (chemical vapor deposition) siliconizing process, comparing with 6.5% Si steel sheet. The Si-gradient steel sheet having silicon concentration gradient in the thickness direction, has larger hysteresis loss and smaller eddy current loss than the 6.5% Si steel sheet. In such a loss configuration, the iron loss of the Si-gradient steel sheet becomes lower than that of the 6.5% Si steel sheet at high frequencies. The experiment suggests that tensile stress is formed at the surface layer and compressive stress is formed at the inner layer in the Si gradient steel sheet. The magnetic anisotropy is induced by the internal stress and it is considered to affect the magnetization behavior of the Si-gradient steel sheet. The small eddy current loss of Si-gradient steel sheet can be explained as an effect of magnetic flux concentration on the surface layer.

Identification of Preisach hysteresis model parameters using genetic algorithms

Preisach model is widely used to characterize ferromagnetic material’s hysteresis. Thus, it is necessary to identify its parameters in order to complete magnetic hysteresis modeling successfully. In this paper, a stochastic identification method, Genetic algorithm, is implemented. The procedure consists of the minimization of the error between measurements and program results. Obtained results are compared with the classical nonlinear least square identification method and experimental hysteresis of a fully-process non oriented Fe-3 wt%Si steel sheet.

Numerical determination of Jiles-Atherton hysteresis parameters: Magnetic behavior under mechanical deformation

Magnetic properties of ferromagnetic materials are sensitive to mechanical deformation, temperature stress and frequency of excitation. This paper deals with the characterization of the behavior of ferromagnetic materials under plastic deformation. Our work attempts to take into account the plastic deformation in the analytical Jiles-Atherton model through its parameters: their variations with the mechanical deformation are deduced from an identification using genetic algorithm approach for each state of deformation. Sensitive parameters to the solicitation are extended to plastic deformation. Finally, simulation results are compared to experimental data of a fully process non oriented Fe-3wt%Si steel sheet. The mean square error is less than 5% for each case which confirms the good agreement between simulated and measured hysteresis curves.

Evolution of microstructure and texture in grain-oriented 6.5%Si steel processed by strip-casting

Grain-oriented 6.5%Si steel was produced by strip-casting, followed hot rolling, cold rolling, primary annealing and secondary annealing. Microstructural and textural evolution was studied with particular focus on the effect of solidified microstructure on the ultimate microstructure and texture. The study indicated that solidified microstructure of the as-cast strip was determined by melt superheat. The relatively low melt superheat resulted in fine equiaxed grains with random texture, whereas large melt superheat led to coarse grains with moderate λ-fiber texture. After cold rolling, the fine-grained steel showed narrow pancake grain structure in comparison to the coarse-grained steel, which was similar to the microstructure of the initial as-cast strip. After primary annealing, fine equiaxed microstructure with favorable {111}⟨112⟩ texture was obtained in the fine-grained steel. While inhomogeneous microstructure with strong α-fiber and moderate γ-fiber texture was obtained in the coarse-grained steel. The desirable microstructure and texture in the fine-grained steel led to abnormal grain growth with B8=1.65T after secondary annealing. By comparison, normal grain growth occurred in the coarse-grained sample with B8=1.37T. Another observation was high frequency core losses of grain-oriented 6.5%Si steel sheet with adequate secondary grains was significantly lower than non-oriented 6.5%Si steel and grain-oriented 3.0%Si steel. The study suggests that the strip-casting is a suitable route to fabricate grain-oriented 6.5%Si steel, and the initial fine grain size with random texture is preferred to obtain adequate abnormal grain growth.

Effect of Compressive Stress on Iron Loss of Gradient Si Steel Sheet

SUMMARYA gradient Si steel sheet, which has high Si content in the surface layer and low Si content in the center of the thickness, shows extremely low iron loss in the high‐frequency range. In this paper, the magnetic properties of gradient Si steel sheets under compressive stress were investigated. In a 3.5% Si steel sheet, the iron loss under compressive stress increases with increase in compressive stress. On the other hand, a gradient Si steel sheet shows extremely low iron loss under compressive stress. This decrease is due to the residual tensile stress in the surface layer of the gradient Si steel sheet. To evaluate the effect of core materials on the iron loss of the motor, we fabricated interior permanent magnet motors using 3% Si steel, 6.5% Si steel, and gradient Si steel sheets. In the motor using a 3% Si steel sheet, the motor loss increases after the heat shrinking. On the other hand, in the motors using 6.5% Si steel and gradient Si steel sheets, the motor loss shows little change after the heat shrinking.

Texture control of 3.04%-Si electrical steel sheets by local laser melting and directional solidification

〈100〉 axes of the rod-shaped grains of laser irradiated cold-rolled 3.04%-Si steel sheets are parallel to either solidification direction or normal direction of the steel sheet. The portion of desirable textures was enhanced by controlling of atmosphere and the direction of heat flow. The area fraction of the texture, which has 〈100〉 axis parallel to normal direction of the steel sheet, in the laser-affected steel sheets in air and argon atmosphere increased up to 23.4% and 26.3%, respectively, compared to a conventionally annealed steel sheet (8.2%).

Inhomogeneous Distributions of Sub-Grains and Precipitates in Strip-Cast 3wt% Si Steel Sheet

A Fe-3wt% Si strip was produced using a vertical type twin-roll casting process. Sub-grains with an inhomogeneous distribution through the thickness direction were firstly observed in the as-cast strip. It was found that the surface layer was characterized by columnar grains containing lineage sub-grains, the subsurface layer was dominated by numerous polygonal sub-grains inside columnar grains or fine equiaxed grains, and the center layer was composed of coarse equiaxed grains without sub-grains. In addition, the sub-grain boundaries provided additional nucleation sites for precipitates and the nanoscale MnS particles were successfully obtained. Moreover, the average size of MnS precipitates in the surface layer was smaller than that in the subsurface layer. The inhomogeneous distributions of sub-grains and precipitates can be attributed to the large temperature gradient through the thickness direction during the strip casting process.