Rapidly quenched ribbon-form silicon-iron alloy with high silicon concentration

RAPIDLY Q U E N C H E D R I B B O N - F O R M S I L I C O N - I R O N ALLOY W I T H H I G H SILICON CONCENTRATION K. I. ARAI, N. TSUYA, K. O H M O R I Research Institute of Electrical Communication, Tohuku University, Sendai, Japan

H. S H I M A N A K A Research Laboratory, Kawasaki Steel Corporation, Chiba, Japan

and T. MIYAZAKI Hitach Metals Ltd, Kumagaya, Japan By rapid quenching techniques polycrystalline silicon-iron ribbons SixFel00_ x (3.8 < x < 9.3 in weight), 20-150/xm thick and 2-25 mm wide were prepared. After annealing, the grains about 200 ptm and a columnar structure with ll00] perpendicular to the ribbon plane were observed, in a Si~.sFe~a.5 ribbon, the coercive field was 80 mOe.

I. Introduction The silicon-iron alloy containing about 6.5 wt% silicon is well known to exhibit excellent magnetic properties such as low hysteresis loss and low magnetostriction [1]. On an industrial scale, it is very difficult to roll this alloy into a thin sheet because of its poor ductility [2]. We have already reported briefly the results of rapid quenching techniques for making ribbon-form silicon-iron [3, 4]. In this paper, we report in detail the results of the preparation of SixFel0o_ x (3.8 < x < 9.3 in weight) ribbons by rapid quenching techniques, as well as of the observation of the metallurgical structure and the magnetic properties of the ribbons. 2. Experiments Ribbon-form silicon-iron alloys SixFel00_ x (3.8 < x < 9.3 in weight) were made by roller quenching techniques [3, 4]. In these techniques, a molten alloy was ejected onto the surface of a single roll (single roller quenching) or between a pair of rapidly rotating rolls (double roller quenching) and cooled immediately into a long ribbon. The dc hysteresis loops were measured by means of a Cioffi recording fluxmeter (Toei Instrument Co. Ltd., TRF-IIIA) using straight ribbons about 6 cm in length. 3. Results and discussion The silicon-iron ribbons obtained showed silver white luster, and their size was 20-150 /tm in thickness, 2-25 mm in width and 5-10 m in length.

Microscopic examinations were made on 5i6.5Fe93.5 as prepared and on annealed ribbons etched for ten minutes in a solution of 5% nitric acid. In the as-prepared ribbon, the average grain size was about 10 /~m on the surface, and grew perpendicular to the surface. Fig. l a and b shows the structure of the surface and of the cross-section of the 20 ~m thick ribbon annealed at 1180°C for 30 min. When the annealing temperature and the annealing time were increased, the grains about 200 #m grew larger and became about 1 mm after annealing at 1250°C for 30 min. In order to determine the direction of the columnar structure perpendicular to the ribbon plane with grains extending through the entire thickness of the ribbon, we observed X-ray pole figures using C o - K a radiation. Fig. 2 shows the (200) pole figure of the Si6.3Fe93.7 ribbon annealed at 1160°C for 30 min. From this figure, it is found that the columnar structure is almost parallel to [100] axis of the crystal. The saturation magnetization of all ribbons was almost the same as that reported previously [5]. The soft magnetic properties of ribbons were degraded by stresses produced during the production process. Using as-prepared and annealed ribbons 20 #m thick and 2.5 mm wide, the coercive field H c was observed. The maximum amplitude of the static magnetic field in this experiment was 10 Oe, and the coercive field of as-prepared ribbons was about 2 Oe. The heat treatments were conducted at 1100-1240°C for 10-45 min in vacuum, and the most suitable annealing condition was determined to be 1200°C and 35 min. We applied this condition to all ribbons made by single roller quenching and obtained the composition dependence of the

Journal of Magnetism and Magnetic Materials 15-18 (1980) 1425-1426 ©North Holland

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coercive field as s h o w n in fig. 3. F r o m this figure, it is f o u n d that, by a n n e a l i n g the coercive field becomes more than one order smaller than that of as -prepared ribbons. Hc is lowered by increasing the silicon c o n c e n t r a t i o n , has a m i n i m u m of 80 m O e a b o u t the c o m p o s i t i o n 5i6.5Fe93.5 a n d then increases again. F o r r i b b o n s p r e p a r e d by d o u b l e roller quenching, a coercive field of 60 m O e was observed. The coercive field of a thin electrical sheet, 3% oriented silicon steel (GT01 0.025 J E M S t a n d a r d 1976) 25 ffm thick is k n o w n to be a b o u t 0.6 Oe. The relationship b e t w e e n the coercive field a n d the thickness of the sheet 5i65Fe935 investigated by Albert [6] gives the coercive field 0 . 5 0 e for 2 5 / z m thick sheet. These values are more than 6 times larger t h a n that of r i b b o n s o b t a i n e d in the present work.

References

Fig. 2. (200) pole figure of Si6.3Fe93.7 ribbon annealed at 1160°C for 30 roan.

[1] W. J. Carr Jr. and R. Smoluchovski, Phys. Rev. 83 (1951) 1236. 12] T. d. Yansen, Trans. Am. Inst. Elec. Eng. 34 (1915) 2601 [3] N. Tsuya and K. I. Arai, Solid State Phys. 13 (1978) 237. [4l N. Tsuya and K. I. Arai, Japan, J. Appl. Phys. 18 (1979) 207. [5] R. M. Bozorth, Ferromagnetism (Van Nostrand, Princeton, 1951) p. 77. [6] P. A. Albert, J. Appl. Phys. 29 (1958) 351.