Herein, a simple and efficient method is proposed for fabricating Fe81Ga19 alloy thin sheets with a high magnetostriction coefficient. Sharp Goss texture ({110}) was successfully produced in the sheets by rapid secondary recrystallization induced by nanosized NbC particles at low temperatures. Numerous NbC precipitates (size ~90 nm) were obtained after hot rolling, intermediate annealing, and primary recrystallization annealing. The relatively higher quantity of nanosized NbC precipitates with 0.22 mol% resulted in finer and uniform grains (~10 μm) through thickness after primary recrystallization annealing. There was a slow coarsening of the NbC precipitates, from 104 nm to 130 nm, as the temperature rose from 850 °C to 900 °C in a pure nitrogen atmosphere, as well as a primary recrystallization textured by strong γ fibers with a peak at {111} favoring the development of secondary recrystallization of Goss texture at a temperature of 850 °C. Matching of the appropriate inhibitor characteristics and primary recrystallization texture guaranteed rapid secondary recrystallization at temperatures lower than 950 °C. A high magnetostriction coefficient of 304 ppm was achieved for the Fe81Ga19 sheet after rapid secondary recrystallization.
Matrix microstructure and texture controlling is an important way to optimize Goss ({110}) abnormal grain growth (AGG) in high magnetic induction grain-oriented silicon (Hi-B) steel during primary recrystallization. In the present work, a matrix with homogeneous grain size and favorable texture components was obtained through two-stage normalized annealing followed by primary recrystallization. Furthermore, secondary recrystallization was performed for sharp Goss orientation by slow heating and purified annealing. It was found that plenty of island grains, which occurred and disappeared gradually, accompanied the process of AGG. Through analyzing the evolution of microstructure and texture, we realized that the formation of island grains was related to the large-size grains in matrix, and the elimination of that was attributed to the special grain boundaries which satisfied both coincident site lattice (CSL) and high-energy (HE) models. It was essential to control grain size and favorable orientations in matrix comprehensively for the high-efficient abnormal growing of sharp Goss orientation, through which excellent magnetic properties could be obtained simultaneously.
29 August 2022 in Journal of Magnetism and Magnetic Materials
Orientation rotation at grain boundary regions associated with neighboring orientations in Fe-3.0 wt.% Si non-oriented silicon steel has been investigated by crystal plastic simulation. Rotation tendency relative to a certain target orientation is evaluated by deviation angle variation. Taking ideal λ (//ND, normal direction) as the target orientation, the deviation angle of scattered {001} <uv0> orientations at grain boundary regions affected by neighboring orientations during rolling is calculated and verified by experimental measurements. The rotation tendency and rotation velocity field at grain boundary regions are significantly changed by neighboring orientations. According to the neighbor affected orientation rotation, the initial texture can be precisely designed to control the deformation texture at grain boundary regions.
Secondary recrystallization Goss texture was efficiently achieved in rolled, binary Fe81Ga19 alloy sheets without the traditional dependence on inhibitors and the surface energy effect. The development of abnormal grain growth (AGG) of Goss grains was analyzed by quasi-situ electron backscatter diffraction (EBSD). The special primary recrystallization texture with strong {112}–{111} and weak Goss texture provides the inherent pinning effect for normal grain growth by a large number of low angle grain boundaries (45°) according to the calculation of misorientation angle distribution. The evolution of grain orientation and grain boundary characteristic indicates that the higher fraction of high energy grain boundaries (20–45°) around primary Goss grains supplies a relative advantage in grain boundary mobility from 950 °C to 1000 °C. The secondary recrystallization in binary Fe81Ga19 alloy is realized in terms of the controllable grain boundary mobility difference between Goss and matrix grains, coupled with the orientation and misorientation angle distribution of adjacent matrix grains.
As a critical factor for the magnetic properties of grain-oriented silicon steel, the orientation accuracy of shear bands is closely related to the matrix orientation deviation from {111}. This work investigates the orientation rotation of shear bands in {111} matrices with various types of deviation during cold rolling, using a visco-plastic self-consistent model that incorporates a two-dimensional inclined angle of the shear band dependent on matrix orientation. When the matrix orientation deviates from {111} along φ1, φ2, or both axes, the φ1 deviation of the shear band decreases, and the φ2 deviation is larger than φ1. Compared with a uniaxially deviated {111} matrix, a biaxially deviated matrix along φ1 and φ2 axes produces a higher shear band deviation from Goss due to the increased φ2 deviation. This suggests that improving the orientation accuracy of the shear band is necessary to decrease the matrix deviation from {111} in the φ1 and especially φ2 axes.