Breaking the Orientation Pinning Limit Using an External Field
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wide range of technologically important properties in single-crystal and polycrystalline materials are controlled by grain growth, which has attracted significant attention in recent years. The growth of grains is accompanied by changes in grain size and texture.[1] It is well known that the magnetic properties of soft magnetic materials such as Fe-Si electrical steels are particularly dependent on grain growth and texture control.[2] Goss texture ({110} h001i) and cube texture ({100} h001i) in steel sheets are preferable for magnetic applications since the easy magnetization axis h001i is parallel to the rolling direction.[3] Considering the model of Ph and the linear relationship between core loss and the anisotropy parameter e when the grain size is held constant, a model of the hysteresis loss coefficient kh has been established to differentiate the effects of grain size and texture on hysteresis loss[4]:
MENGCHENG ZHOU, XIN BA, and XINFANG ZHAZNG are with the State Key Laboratory of Advanced Metallurgy, School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 18, 2019. Article published online February 5, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
kh ¼ kd þ ke ¼ a þ
b þ k1 ðe 0:199Þ; D
½1
where kh is divided into kd and ke. Here, kd and ke represent the effects of grain size and texture, respectively. Parameters a and b are constants, which can be obtained by nonlinear fitting of the values obtained to kd via Eq. [1]. D is the average grain size, e is the average anisotropy parameter, and k1 is the correction coefficient that is not related to e. The value of k1 can be obtained by calculating the hysteresis loss difference between two samples. Further, e is 0.199 for a random orientation distribution. Therefore, the hysteresis loss of electrical steel can be greatly reduced by increasing the grain size and optimizing the texture of the sheet.[5] However, preferential growth will change the original recrystallization texture in electrical steels. It is difficult to obtain a strong single-orientation texture in non-oriented electrical steels.[6] Although abnormal grain growth will enhance the Goss texture sharpness in oriented electrical steels, uniformity of grain size is possibly an important factor affecting core loss. This is because a wide spread leads not only to a localized non-uniform flux distribution and hence higher average losses, but also to a higher proportion of transverse flux and associated extra losses.[7] Meanwhile, the abnormal grain growth of Goss grains during secondary recrystallization can be interpreted in terms of an initial size advantage that these grains inherit from primary recrystallization.[8,9] Unfortunately, the initial size advantage and effective magnetic texture cannot be obtained at the same time via an annealing process considering the texture inhibition effect caused by the low mobility of small-angle grain boundaries, a phenomenon known as orien
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