Texture Of Non-oriented Electrical Steel Research Articles

Effect of pre-recovery annealing on recrystallisation behaviour of strip-cast non-oriented electrical steel

In order to improve the {100} recrystallisation texture of non-oriented electrical steel, a pre-recovery annealing process was proposed to regulate recrystallisation behaviour of {100} grains by altering the structure and stored energy of deformed microstructure. Pre-annealing was conducted at 500°C for 0–90 min. The microstructural and textural evolution was carried out by optical microscopy, electron backscattered diffraction and X-ray diffraction analysis. The results indicate that the pre-recovery annealing promotes the formation of large {100} recrystallised grains. With the prolongation of pre-annealing time, the {100} recrystallisation texture expands from Cube to the vicinity of {001}<130>-{001}<110>, and the volume fraction gradually increases. In addition, the changes of recrystallised microstructure are discussed on the basis of strain-induced boundary migration.

Deformation heterogeneity and its effect on the recrystallisation texture of non-oriented electrical steel

ABSTRACT Non-oriented electrical steel (NOES) is the most commonly used material for the manufacturing of soft magnetic cores for electric motors. The magnetic properties of the steel lamination, which have a significant effect on the energy efficiency of electric motors, are highly dependent on the microstructure and crystallographic texture of the steel. The final microstructure and texture of the NOES are closely related to the thermomechanical processing history of the material, especially the deformed microstructure and texture before final annealing. This is because both nucleation and grain growth during recrystallisation are determined by the microstructure/substructure and texture of the material after cold deformation. During cold rolling, the plastic deformation does not occur in a homogeneous manner in metals, which usually leads to heterogeneous deformation substructures, including shear bands, deformation bands, transition bands, etc., which play a crucial role in determining the final microstructure and texture. In this paper, the formation of deformation heterogeneity during cold rolling of NOES and its effect on the subsequent recrystallisation are investigated using electron backscatter diffraction (EBSD) techniques. The relationships between the deformation substructures and the recrystallisation texture are discussed.

Mechanical properties and crystallographic texture of non-oriented electrical steel processed by repetitive bending under tension

Improving the magnetic properties of non-oriented electrical steel (NOES) through the optimization of crystallographic texture has been an on-going research activity for decades. However, using traditional rolling and annealing procedures, the obtained final textures were usually very similar, i.e., exhibiting the {111} (γ) and <110> (α) fibres, which were not the desired {001} texture (θ-fibre) for optimal magnetic quality. In the current work, a 1.8 wt% Si NOES was processed using a new sheet metal deformation method, i.e., repetitive bending under tension (R-BUT), also known as continuous bending under tension (C-BUT), to modify the texture of the electrical steel. The hot-rolled and annealed NOES plates were repeatedly bent and unbent when they were pulled under tension. The deformed plates were then heat treated at different temperatures for various times. Neutron diffraction and electron backscatter diffraction (EBSD) characterisation of the macro- and micro-textures proved that the R-BUT process significantly reduced the undesired {111} texture while promoting the {001} texture. The cube texture, which rarely formed after conventional rolling and annealing, was also seen in the R-BUT samples after annealing. It was shown that, the shear plastic deformation (induced by R-BUT) played a significant role in promoting the desired textures. In addition, the results indicated that the NOES processed by R-BUT could be deformed beyond its common formability limit, which may provide a method to address the poor workability challenge of high silicon electrical steels.

Recrystallization behaviour and texture of non-oriented electrical steels

Five numbers of Si steels with different alloying elements, viz., 1.35% Si, 2.2% Si, 1.48% Si with 0.11% Sn, 1.44% Si with 0.05% Sb and, 1.52% Si with 0.11% P (all are in wt%), were made in laboratory. Hot bands of 2.2% Si and 1.52% Si with 0.11% P showed recovered grains of very coarse elongated ferrite while that of 1.35% Si steel showed fine ferrite grain of both elongated and fine equiaxed type similar to that of remaining two steels. Grain boundary misorientation and recrystallization study of hot bands before and after annealing indicated nearly complete recrystallization of 1.35% Si and partial recrystallization of Sn and Sb added steels containing low Si. In the case of 2.2% Si and 1.52% Si with 0.11% P steels, the recovered grains were observed mostly containing substructures. The retardation to recrystallization in these two steels has been attributed to the elemental effect of P and high Si. The no-recrystallization temperature (Tnr) of only these two steels were noticed at ≤ 1000 °C. The ϕ2 = 45° and ϕ2 = 90° ODF sections of hot bands indicated that all experimental steels except 1.35% Si steel show magnetically favourable texture components of θ fiber (<001>//ND) and η fiber (<001>//RD) components. The beneficial θ fiber components were also further noticed in cold rolled and final annealed 2.2% Si, 1.44% Si with 0.05% Sb and, 1.52% Si with 0.11% P steels. The presence of the magnetically favourable texture in these steels probably resulted in reduced core loss of these steels while the highest core loss was noticed in 1.35% Si steel. The mechanical properties of final processed steels were also found to be suitable for cold forming and stamping operation during their electrical applications.

Texture Evolution of a Non-oriented Electrical Steel Cold Rolled at Directions Different from the Hot Rolling Direction

With the objective of optimizing the crystallographic texture of non-oriented electrical steel, i.e., reducing the 〈111〉//ND and 〈110〉//RD fibers and promoting the 〈001〉//ND texture, a new rolling scheme was proposed and tested, in which the cold rolling direction (CRD) was intentionally inclined at an angle to the hot rolling direction (HRD) in order to change the orientation flow paths during cold rolling and alter the final texture of the annealed sheets. A non-oriented electrical steel containing 0.88 wt pct Si was hot rolled using conventional routes and annealed, and a number of rectangular plates were cut from the hot band with the longitudinal directions inclined at various angles, i.e., 0, 15, 30, 45, 60, 75, and 90 deg, to the HRD. These plates were then cold rolled along the longitudinal directions with a thickness reduction of 72 pct. The cold-rolled samples were annealed, temper rolled and annealed again (final annealing). The texture evolution during hot rolling, hot band annealing, cold rolling, and final annealing was characterized by electron backscatter diffraction and X-ray diffraction techniques. By changing the CRD with respect to the HRD, the initial texture and the orientation flow paths were altered, which resulted in apparent differences in the textures as compared to conventional cold rolling. After temper rolling and final annealing, the recrystallization textures consisted of mainly a 〈001〉//ND fiber and there was almost no 〈111〉//ND fiber. The sample cold rolled at an angle of 60 deg to the HRD had the strongest texture (intensity almost 2× of conventional rolling) with a maximum at the cube {001}〈100〉 orientation—a magnetically favorable orientation for non-oriented electrical steels.

Effects of Sn Addition on Core Loss and Texture of Non-Oriented Electrical Steels

The effects of Sn addition on core loss and texture of non-oriented electrical steels were investigated. Experiments revealed that the core loss of non-oriented electrical steels could be obviously decreased and the intensity of {111} texture and {112} texture of final annealed specimens could be markedly reduced by Sn addition. The reasons for reducing core loss and the intensity of unfavorable texture were analyzed.

Modelling magnetic polarisation J50 by different methods

Two different methods for modelling the angular behaviour of magnetic polarisation at 5000 A/m ( J 50) of electrical steels were evaluated and compared. Both methods are based upon crystallographic texture data. The texture of non-oriented electrical steels with silicon content ranging from 0.11 to 3%Si was determined by X-ray diffraction. In the first method, J 50 was correlated to the calculated value of the average anisotropy energy in each direction, using texture data. In the second method, the first three coefficients of the spherical harmonic series of the ODF and two experimental points were used to estimate the angular variation of J 50. The first method allows the estimation of J 50 for samples with different textures and Si contents using only the texture data, with no need of magnetic measurement, and this is advantageous, because texture data can be acquired with less than 2 g of material. The second method may give better adjust in some situations but besides the texture data, it requests magnetic measurements in at least two directions, for example, rolling and transverse directions.