Effects of warm rolling reduction on the microstructure, texture and magnetic properties of Fe-6.5 wt% Si steel
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As the core materials with excellent soft magnetic properties, Fe–6.5 wt% Si steel was fabricated by using the warm rolling process due to its extremely limited ductility and formability at room temperature. In this work, the effects of warm rolling reduction varying from 50% to 85% on the microstructure, texture, and magnetic properties of sheets were explored. The microstructure and texture evolution at the various processing steps were investigated in detail using optical microscopy, electron backscatter diffraction, and transmission electron microscopy. The results demonstrate that the finer recrystallization grains are accompanied with an increasing warm rolling reduction, and the final annealed sheets are characterized by strong a-fiber and c-fiber textures. Accordingly, on the whole, as the increase of warm rolling reductions, the values of magnetic induction (B8, B50) in the final annealed sheets increase sharply up to a maximum value and then decrease to a certain value, and the values of iron loss (P15/50, P10/400) increase monotonically.
I. INTRODUCTION
Compared with common silicon steel, Fe–6.5 wt% Si steel has exhibited higher magnetic induction and lower iron loss characteristics due to very large electrical resistivity and the smaller eddy current loss.1 As a kind of nonoriented electrical steel with excellent soft magnetic properties,2 it is widely used in high frequency fields, such as the choke coil, high-frequency transformer, highfrequency motor as well as magnetic shield.3 However, extremely poor formability at room temperature makes it very difficult to produce Fe–6.5 wt% Si sheets by using the conventional cold rolling processes,4 so its manufacture and application are severely restricted. In recent years, various relevant techniques avoiding the brittleness of Fe–6.5 wt% Si steel have been invented, such as electrochemical reduction,5 physical chemical vapour deposition,6 spray forming, etc. But using the methods above can bring a longer production cycle and a high production cost. Therefore based on the traditional rolling techniques, developing the warm rolling method is urgent. Presently, a number of studies about recrystallization behaviors and ordered phases of high silicon electrical steel with initial equiaxed or columnar grains have been carried out. T. Ros-Yañez et al.7 studied a thermomechanical route about recrystallisation process and texture in hot rolled sheet for the production of high silicon steel. Jung et al.8 pointed out that the ordered phases of Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.179 J. Mater. Res., Vol. 31, No. 12, Jun 28, 2016
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Fe–6.5 wt% Si steel had important effect on the iron loss of alloy through changing the cooling rate. But little work has been performed on warm rolling reduction causing the changes of microstructure and texture of Fe–6.5 wt% Si steel. In previous work, we reported that ordered phases and microhardness
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