Balancing Magnetic and Mechanical Properties of Non-oriented Electrical Steel: Correlation Between Microstructure and Properties

doi:10.1007/s40195-024-01757-2

Abstract

Abstract:

High performance e-motors require a continuous enhancement of physical and mechanical properties for non-oriented electrical steel (NOES). However, the optimization of mechanical and magnetic properties simultaneously during NOES processing is extremely challenging where both properties directly influenced by alloy grain size, crystallographic texture, and dislocation density. In the current investigation, recrystallization annealing cycles were employed to modify the microstructure with the aim of balance magnetic and mechanical properties of NOES concurrently. The results showed that with increasing annealing temperatures, the degree of recrystallization and grain size increased, while the dislocation density reduced considerably at the early stage of recrystallization. Meanwhile, the values of texture parameter $A_{{{\text{overall}}}}^{*}$ (which is a function of overall individual grain orientations and their alignments with easy magnetization directions) were increased. It was evident that the magnetic properties were significantly improved, however the alloy strength was reduced with increasing annealing temperatures. Here, the correlation between magnetic properties as well as alloy strength on grain size, texture, and dislocation density were determined. From crystallographic texture intensity and measured properties quantitative analyses it was concluded that grain size was the predominant factor in balancing the mechanical and magnetic properties of the studied steel. Furthermore, the optimal comprehensive properties (both magnetic and mechanical) were achieved by annealing at 800 °C, which yielded a magnetic induction B₅₀₀₀ of 1.616 T, a high-frequency iron loss P_1.0/400 of 22.43 W/kg, and a yield strength of 527 MPa.

Key words: High strength non-oriented silicon steel, Microstructure, Texture, Magnetic properties, Mechanical properties

Zhaoyang Cheng, Jing Liu, Chunlei Yu, Bolin Zhong, Shenglin Chen, Bing Fu, Soran Birosca. Balancing Magnetic and Mechanical Properties of Non-oriented Electrical Steel: Correlation Between Microstructure and Properties[J]. Acta Metallurgica Sinica (English Letters), 2024, 37(12): 2136-2149.

Figures/Tables 16

Fig. 1 Microstructures of the NOES sheets annealed at different temperatures: a 650 °C, b 700 °C, c 750 °C, d 800 °C, e 850 °C

Fig. 2 GND of the NOES sheets annealed at different temperatures: a 650 °C, b 700 °C, c 750 °C, d 800 °C, e 850 °C

Fig. 3 TEM images showing dislocations in the specimens annealed at different temperatures: a, b 650 °C, c, d 700 °C. b and d showing the enlarged view of the regions demarcated in a and c, respectively

Fig. 4 XRD profiles of the annealed sheets: a complete spectra, b schematic illustration of the FWHM for the (200) peak of the sheet annealed at 650 °C as an example

Table 1 Values of $\varepsilon$ and the dislocation density of different specimens

Annealing temperature (°C)	650	700	750	800	850
$\varepsilon$	1.04 × 10⁻³	2.06 × 10⁻⁴	5.02 × 10⁻⁵	3.75 × 10⁻⁵	2.83 × 10⁻⁵
Dislocation density (mm⁻²)	2.50 × 10⁸	9.91 × 10⁶	5.90 × 10⁵	3.29 × 10⁵	1.88 × 10⁵

Fig. 5 Texture (φ2 = 45° ODF section) of the NOES sheets annealed at various annealing temperatures: a 650 °C, b 700 °C, c 750 °C, d 800 °C, e 850 °C; f the typical texture components in φ2 = 45° ODF section

Fig. 6 Volume fractions of different texture components in the NOES sheets annealed at various annealing temperatures

Fig. 7 Magnetic properties of the sheets annealed at various annealing temperatures

Fig. 8 Mechanical properties of the sheets annealed at various annealing temperatures: a stress-strain curves, b yield stress and tensile stress

Fig. 9 Schematic illustration of the texture parameter $A_{\theta } \left( g \right)$ defined as the minimum angle between the magnetization vector (${\boldsymbol{M}}$) and the crystal easy magnetization axes [100], [010], and [001]. α1 is the minimum angle in this example (α1 < α2 < α3), and $A_{\theta } \left( g \right)$ would be equal to α1

Table 2 Values of $A^{*}$-parameter of different texture components (Data obtained from Ref. [31])

Texture components	{100}	{110}	{111}	Random
A* (°)	22.50	35.60	38.68	31.88

Table 3 Values of $A_{{{\text{overall}}}}^{*}$ of the sheets annealed at different temperatures

Annealing temperature (°C)	650	700	750	800	850
$A_{{{\text{overall}}}}^{*}$(°)	29.48	30.38	30.39	30.67	31.35

Fig. 10 a–e Inverse pole figures of the sheets annealed at various annealing temperatures, f the values of $A^{*}$-parameter of different texture components, and g the theoretical value of $B_{5000}$ as a function of $A_{{{\text{overall}}}}^{*}$ and $\overline{d}$ for the annealed sheets together with the experimental results

Fig. 11 Contribution of various strengthening mechanisms to the yield strength in the steels annealed at different temperatures

Fig. 12 Schematic diagram for the balance of magnetic and mechanical properties of NOES via recrystallization annealing

Fig. 13 Value of δ at different annealing temperatures: a $P_{1.5/50}$, b $P_{1.0/400}$

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