Thin soft magnetic alloy strip

Abstract: In the production by the single-roll technique of a thin amorphous strip as the matrix for the manufacture of a thin Co-based amorphous alloy strip or a thin Fe-based microcrystalline alloy strip, the conditions for the production are controlled to those specified by the invention. The production conditions thus controlled concern the atmosphere and the pressure to be used for ejecting a molten metal onto a rotating cooling member, the shape of a nozzle, the distance between the nozzle and the rotary cooling member, the material for the rotary cooling member and peripheral speed of the rotary cooling member, etc. The individual numerical values of these conditions are severally important. The thin strips thus obtained are in an extremely small thickness and in a wholesome state destitute of pinholes and other similar defects. In the thin Co-based amorphous alloy strip, the extreme decrease of thickness to below 4.8 µm notably enhances the soft magnetic properties such as permeability and core loss in the high frequency range. In the thin Fe-based microcrystalline alloy strip, the extreme decrease of thickness not more than 10 µm permits improvement of resistance to embrittlement in addition to the improvement in the soft magnetic properties.

Description: THIN SOFT MAGNETIC ALLOY STRIP Method for production of very thin soft magnetic alloy strip, very thin soft magnetic alloy strip by use of the method, magnetic core by use of the method, electronic apparatus including the magnetic core, and apparatus for production of thin soft magnetic alloy strip This invention relates to a method for the production of a very thin soft magnetic alloy strip suitable for use in a noise filter, a saturable reactor, a miniature inductance element for abating spike noise, main transformer, choke coil, a zero-phase current transformer, a magnetic head, etc., namely the devices which are expected to exhibit high levels of permeability at high frequencies, a very thin soft magnetic alloy strip by the use of the method, and an apparatus for the production of a soft magnetic alloy strip. In recent years, the trend of electronic equipments and devices toward reduction in size and weight and enhancement of performance has been urging magnetic parts serving as important functional parts to embody highly advanced improvements. The magnetic materials to be used in such magnetic parts, as a natural consequence, are urged to possess outstanding magnetic properties. Particularly, materials of high permeability are effective in numerous magnetic parts such as current sensors in zero-phase current transformers and noise filters, for example. In the case of a noise filter, for example, a switching power source is widely used as a stabilizing power source for electronic equipments and devices. In the switching power source, adoption of a measure for the abatement of noise constitutes itself an important task. The high-frequency noise including a switching frequency as its basic frequency and the noise of the MHz range issuing from a load such as, for example the logic circuit of a personal computer pose a problem. For the abatement of the conducted noise of this kind, therefore, a common mode choke coil has found acceptance for use as a noise filter. When this filter is inserted in a power source line, the magnitude of the noise output voltage relative to the noise input voltage has such bearing on the permeability of a magnetic core that the noise output voltage decreases in proportion as the permeability increases. Further, the filter is required to function effectively not only in the low frequency range but equally in the high frequency range exceeding 1 MHz. For this reason, the frequency characteristic of the permeability is required to be favorable as well. In recent years, the switching power source of the kind incorporating a magnetic amplifier has been finding widespread utility. The main component in the magnetic amplifier is a saturable reactor and is claimed to require a magnetic core material excelling in the angular magnetization characteristic. The aforementioned trend of recent electronic machines and devices toward reduction in size and weight and enhancement of quality performance has been strongly urging switching power sources to attain generous reduction in size and weight. For the realization of the reduction in size and weight, there has been expressed a desire to heighten the switching frequency as much as possible. In the circumstances, the magnetic core material as one of the component parts of the saturable reactor is strongly desired to suffer from as small loss in the high frequency range as possible. A proprietary product (by trademark designation) made of a Fe-Ni crystalline alloy and found utility to date is far short of fitting use in the high frequency range because it suffers from a notably increase of eddy-current loss in a high frequency range exceeding 20 kHz. The magnetic core material using an amorphous alloy capable of exhibiting a low core loss and a high angular shape ratio in the high frequency range is actually used only in a frequency range approximately in the range of 200 to 500 kHz because it entails an increased core loss in the MHz range. Generally, in the case of metallic materials, it has been known that the core loss can be curbed and the high-frequency characteristic improved by decreasing the plate thickness. Even in the case of amorphous alloys, the feasibility of decreasing the plate thickness is being studied. Thin amorphous alloy strips are generally manufactured by the liquid quenching method which resorts to the single roll technique. Under the conventional production condition, in the case of Co-based amorphous alloy, the thickness of 6 µm could be obtained by the single roll technique in vacuum [ J.Appl, Phys. 64 6050, etc. ]. However, it was thought that it was substantial impossible to make the thickness thinner than 5 µm. These thin strips contain relatively numerous pinholes because they entrain bubbles with themselves during the reduction of plate thickness and , therefore, pose problems on practicability as well as adaptability for higher frequency. For perfect realization of a switching frequency in the MHz range, the desirability of further decreasing the plate thickness has been finding enthusiastic recognition. However, it was thought that this desire could not be realized practically. Recently, a Fe-based microcrystalline alloy possessing a practically equal soft magnetic property as amorphous alloys has been reported [EPO Publication No. 0271657, Japanese patent Publication SHO 63(1988)-320,504, etc.]. This alloy is produced by causing a Fe-Si-B type alloy, for example, to incorporate therein Cu and one element selected from among Nb, W, Ta, Zr, Hf, Ti, Mo, etc., forming the resultant alloy tentatively as a thin strip similarly to any amorphous alloy, and thereafter heat-treating the thin amorphous strip in a temperature range exceeding the crystallizing temperature thereof thereby inducing formation of ultrafine crystalline grains. Even in the case of the Fe-based microcrystalline alloy of the nature described above, for the purpose of improving the high frequency property by decreasing the plate thickness thereby effecting crystallization of a thin strip of amorphous alloy, it is necessary that the thin amorphous strip should be produced in a fine state destitute of a pinhole. The existing manufacturing technique such as of the single-role principle, however, has never been successful in turning out a product fully conforming with the recent trend toward higher frequency. Further, since in the case of the Fe-based microcrystalline alloy microcrystalline grains are formed, the thin strip is brittle. Therefore, from quality point of view, it entails the important problem that it tends to sustain chipping and other similar defects during the process of manufacture as like core making. Likewise from this point of view, the desirability of further decreasing the thickness of the strip of amorphous alloy thereby improving the brittleness has been finding growing recognition. As described above, the magnetic material for various kinds of magnetic cores is expected to manifest high permeability and low core loss at varying levels of frequency up to the high frequency range (to MHz range). This requirement leads electronic machines and devices toward further improvement of efficiency and further reduction in size and weight and magnetic cores toward reduction of size and improvement of quality. An object of this invention, therefore, is to provide a method for the production of an extremely thin amorphous alloy strip which fulfills the magnetic properties mentioned above and maintains a fine state destitute of such defects as pinholes. Another object of this invention is to provide an extremely thin amorphous alloy strip which is capable of manifesting high permeability and low core loss in varying levels of frequency up to the high frequency range (to MHz range). Yet another object of this invention is to provide a thin amorphous alloy strip which is capable of manifesting high permeability and low core loss in varying levels of frequency up to the high frequency range (to MHz range) and which exhibits enhanced resistance to embrittlement. Still another object of this invention is to provide an apparatus for the production of a thin soft magnetic alloy strip, which apparatus is capable of producing an extremely thin amorphous alloy strip which fulfills the magnetic properties mentioned above and maintains a fine state destitute of such defects as pinholes. The present invention is defined by claims 1, and 8. A method of manufacturing a chill block melt spinning process for manufacturing an amorphous alloy ribbon is disclosed in IEEE Trans. Mag. MAG -25 (1979) 1393-1397. J. Appl. Phys. 55 (1984) IIA 1787-1789 discloses another amorphous alloy ribbon of 13-80 µm thickness. A known alloy based on Co, Fe and B is disclosed in Chem. Abs. 92 (1980) no. 68684 f. J. Appl. Phys. 64 (1988) 6050-6051 describes Co-based amorphous alloy ribbons with a thickness of 6-10 µm. This application describes a method for production of a thin soft magnetic alloy strip, comprising the steps of ejecting a molten alloy through a nozzle onto the surface of a rotating cooling member and rapidly quenching the ejected molten alloy thereby producing a thin amorphous alloy strip, which method is characterized by wholly fulfilling the following conditions. Specifically, the conditions are as follows: (1) A reduced pressure of not higher than 10⁻⁴ Torr * should be used for the atmosphere in which the molten alloy infected through the nozzle travels until it impinges on the rotating cooling member. (2) The rotary cooling member should be formed of a Fe-based alloy or a Cu-based alloy. (3) The nozzle should be provided with an orifice of a rectangular cross section, the short side of which lying parallelly to the circumferential direction of the rotary cooling member should possess a length in the range of 0.07 to 0.13 mm. (4) The distance between the nozzle and the rotary cooling member should be in the range of 0.05 to 0.20mm. (5) The pressure to be used for ejecting the molten alloy onto the rotary cooling member should be in the range of 0.015 to 0.025 kg/cm². (6) The peripheral speed of the rotary cooling member should be in the range of 20 to 50 m/sec. By the adoption of the method for production described above, it is made possible to provide a thin Co-based amorphous alloy strip possessing a thickness of less than 4.8 µm and consequently conforming with the trend toward higher frequency. The Co-based amorphous alloy to be used in this invention is essentially represented by the following general formula: (Co 1-a A a ) 100-b X b [wherein A stands for at least one element selected from the class consisting of Fe, Ni, Cr, Mo, V, Nb, Ta, Ti, Zr, Hf, Mn, Cu, and the platinum-group elements, X for at least one element selected from the class consisting of Si, B, P, and C, and a and b for numbers satisfying the following formulas, 0 ≦ a ≦ 0.5 (providing that 0 ≦ a ≦ 0.3 is satisfied where Fe and Ni are excluded as A), 10 at % ≦ b ≦ 35 at %]. In accordance with a method of this invention for the production of a very thin soft magnetic alloy strip, a thin Co-based amorphous alloy strip possessing a thickness of less than 4.8 µm. Since these alloy strips exhibit excellent soft magnetic properties such as permeability and core loss in the high frequency range, they can be offered as magnetic materials for use in a noise filer, a saturable reactor, a miniature inductance element for the abatement of spike noise, main transformer, choke coil, a zero-phase current transformer, a magnetic head, etc. which invariably demand excellent soft magnetic properties to be exhibited in the high frequency range. Fig. 1 is a diagram illustrating in model a typical construction of the apparatus for the production a thin soft magnetic alloy strip used in one embodiment of the present invention, Fig. 2 is a diagram illustrating the shape of a nozzle for the apparatus from a bottom end view, Fig. 3 is a diagram illustrating the nozzle and the cooling roll, Fig. 4 is a graph showing the frequency characteristic of the initial permeability of a thin Co-based amorphous alloy strip produced in one embodiment of this invention, as compared with that of the conventional outertype, Fig. 5 is a graph showing core loss and the plate thickness of a thin Co-based amorphous alloy strip produced in another embodiment of this invention as the functions of frequency. Now, the present invention will be described more specifically below with reference to working examples. Now, the first aspect of this invention, namely the method for the production of an extremely thin soft magnetic alloy strip will be described in detail below. Fig. 1 is a diagram illustrating the construction of an apparatus for the production of a thin soft magnetic alloy strip embodying the method of this invention for the production of a thin soft magnetic alloy strip. With reference to this diagram, a vacuum chamber 10 is provided with a gas supply system 12 and a discharge system 14. Inside this vacuum chamber 10, a single-roll mechanism 40 consisting mainly of a cooling roll 20 capable of being cooled to a prescribed temperature and controlled to a prescribed peripheral speed and a raw material melting container 30. In the lower part of the raw material melting container 30 is disposed a nozzle 32 which opens in the direction of a peripheral surface 22 of the cooling roll 20. The shape of the orifice of this nozzle 32 is rectangular as illustrated in Fig. 2. The short side of the rectangular cross section of the orifice falls parallelly to the circumferential direction of the cooling roll 20. The long side a and the short side b of the orifice of the nozzle 32 are to be set in accordance with the particular raw material to be used. As showed in Fig. 3, the nozzle 32 are set so the appropriate distance c between the nozzle 32 and the peripheral surface 22 of the working roll 20 can be formed. This distance c can be varied depending on the particular raw material to be used. The angle of ejection onto the cooling roll 20 is not limited to 90°. An induction heating coil 34 is disposed on the outer periphery of the raw material melting container 30 and is used for melting the raw material to be introduced. The molten raw material is ejected through the nozzle 32 onto the peripheral surface 22 of the cooling roll 20. In producing an extremely thin Co-based amorphous alloy strip by the use of the apparatus for the production of a thin soft magnetic alloy strip constructed as described above, the raw material for a Co-based alloy composition represented by the aforementioned general formula: (Co 1-a A a ) 100-b X b is first introduced into the raw material melting container 30 and melted therein. In the composition of the formula (I) mentioned above, A represents an element which is effective in enhancing the thermal stability and improving the magnetic properties. When A is selected from among Mn, Fe, Ni, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Cu, and the platinum-group elements, any value of a exceeding 0.3 is practically undesirable because this excess of the value goes to lower the Curie point. When A is Fe or Ni, any value of a exceeding 0.5 prevents the magnetic properties from being improved. X represents an element essential for the produced thin alloy strip to assume an amorphous texture. When the content of this element is less than 10 atomic % or not less than 35 atomic %, this assumption of the amorphous phase becomes difficult. Where the thin alloy strip is expected to possess particularly satisfactory high frequency properties so as to fit utility in a saturable reactor, a noise filter, main transformer, choke coil, or a magnetic head, for example, it is desirable to use a raw material of an alloy composition represented by the following general formula: (Co 1-m-n L m M n ) 100-o (Si 1-p B p )₀ [wherein L stands for at least one element selected from the class consisting of Fe and Mn, M for at least on element selected from the class consisting of Ti, V, Cr, Ni, Cu, Zr, Nb, Mo, Hf, Ta, W and the platinum-group elements, and m, n, o, and p for numbers satisfying the following formulas, 0.03 ≦ m ≦ 0.15, 0 ≦ n ≦ 0.10, 20 at % ≦ o ≦ 35 at %, and 0.2 ≦ p ≦ 1.0]. Particularly the use of at least one element selected from among Cr, Mo, and W as M in the composition of the formula (IV) is effective in decreasing the thickness of the strip to extremity. Then, the vacuum chamber 10 is evacuated to a reduced pressure of not higher than 10⁻⁴ Torr. The molten alloy composition is subsequently ejected under a pressure in the range of 0.015 to 0.025 kg/cm² through the nozzle onto the peripheral surface 22 of the cooling roll 20 operated at a controlled peripheral speed in the range of 20 to 50 m/sec, to rapidly quench the molten alloy and obtain a thin Co-based amorphous alloy strip 40. The upper limit, 10⁻⁴ Torr, fixed for the pressure to be used for the atmosphere in which the molten metal is ejected is critical because the thin amorphous alloy strip 40 containing only very few pinholes and measuring less than 4.8 µm in thickness is not easily produced when the pressure is lower vacuum (worse) than 10⁻⁴ Torr. If the peripheral speed of the cooling roll 20 is less than 20 m/sec, the thin strip measuring less than 4.8 µm in thickness is obtained with difficulty. If the peripheral speed exceeds 50 m/sec, the possibility of the thin strip being broken during the course of production is increased and the production of the thin strip cannot be continued. Particularly where the thin strip measuring not less than 5 mm in width is to be produced, the peripheral speed is desired to be in the range of 20 to 40 m/sec, preferably 20 to 35 m/sec. If the pressure for the ejection of the molten metal is less than 0.015 kg/cm², it often happens that the ejection itself fails to occur. Conversely, if the pressure exceeds 0.025 kg/cm², the thin strip measuring less than 4.8 µm in thickness is produced only with difficulty. The cooling roll 20 to be used herein is formed of a Fe-based alloy, preferably a Cr-containing Fe-based alloy such as, for example, tool steel. By the use of this cooling roll 20, the produced thin strip acquires improved surface smoothness and it is made possible to produce an extremely thin strip of fine state. The long side a of the rectangular cross section of the orifice of the nozzle 32 functions to determine the width of the produced thin strip and has no specific restriction except for the requirement that they should measure not less than 2 mm. The short side b is an important factor for determining the thickness of the thin strip and is set in the range of 0.07 to 0.13 mm. If the short side b is less than 0.07 mm, the molten metal is ejected only with extreme difficulty. Conversely, if the short side b exceeds 0.13 mm, the thin strip measuring less than 4.8 µm in thickness cannot be produced. Preferably, the short side b is in the range of 0.08 to 0.12 mm. Then, the distance c between the leading end of the nozzle 32 and the cooling roll 20 is set in the range of 0.05 to 0.20 mm. the reason for this range is that the thin strip is not easily obtained with desirable surface quality if this distance c is less than 0.05 mm and the thin strip measuring less than 4.8 µm is not obtained easily if this distance exceeds 0.20 mm. By rapidly quenching the molten metal while fulfilling the conditions mentioned above, the thin Co-based amorphous alloy strip 40 measuring less than 4.8 µm can be obtained. The thin Co-based amorphous alloy strip obtained as described above is coiled or superposed one ply over another to form a magnetic core, subjected to a heat treatment performed for the relief of strain at a temperature below the crystallizing temperature to the Curie point, and then cooled. The cooling speed is required to fall in the range between 0.5°C/min and the speed of quenching in water, preferably in the range of 1 to 50°C/min. Thereafter, the cooled core may be given an additional heat treatment or in the presence of a magnetic field (in the direction of the axis of the thin strip, the direction of the width, the direction of the plate thickness, or the rotary magnetic field) as occasion demands. The atmosphere in which this heat treatment is performed is not critical. An inert gas such as N₂ or Ar, a vacuum, a reducing atmosphere such as of H₂, or the ambient air may be used. The reason for setting the limit of less than 4.8 µm for the thickness of the thin Co-based amorphous alloy strip is that the thin strip exhibits particularly desirable magnetic properties in the high frequency range of MHz, for example. Now, typical examples of the manufacture of the thin Co-based amorphous alloy strip will be described below. Example 1: An alloy composition represented by the formula, [(Co 0.95 Fe 0.05 ) 0.95 Mo 0.05 ]₇₅(Si 0.5 B 0.5 )₂₅, was prepared and placed in a raw material melting container and melted therein. The nozzle used herein had a rectangular orifice measuring 10.3 mm x 0.10 mm (a x b) and the distance c between the nozzle and the cooling roll was 0.1 mm. The cooling roll was made of Fe. Then, the vacuum chamber was evacuated to 5 x 10⁻⁵ Torr and the molten alloy composition was ejected under pressure of 0.02 kg/cm² through the nozzle onto the peripheral surface of the cooling roll operated at a controlled peripheral speed of 33 m/sec, to superquench the molten metal and produce a thin Co-based amorphous strip. Thus, a long thin amorphous strip possessing satisfactory surface quality and measuring 4.7 µm in thickness and 10 mm in width was obtained. The long very thin Co-based amorphous strip thus obtained was coiled, then subjected to the optimum heat treatment at a temperature of not higher than the crystallizing temperature, and tested for the frequency characteristic of initial permeability and for the high-frequency core loss. Fig. 4 shows the frequency characteristic of initial permeability in an excited magnetic field of 2 mOe. For comparison, the results obtained similarly of a thin Co-based amorphous alloy strip using the same composition and measuring 15 µm in thickness are also shown in the diagram. It is clearly noted from the diagram that the effect of the plate thickness conspicuously manifested when the permeability exceeded 100 kHz. The thin Co-based amorphous alloy strip 4.7 µm in thickness produced in the present example exhibited higher degrees of permeability at 1 MHz and 10 MHz than the thin strip produced for comparison, indicating that the thin strip of this invention exhibits highly satisfactory permeability even in the high frequency range. The core loss of the thin strip of this example at 1 MHz under the condition of 1 kG of excited magnetic amplitude was about one half of that of the strip of a plate thickness of 15 µm. The rectangular ratio of the thin strip was almost 100% at a frequency above 500 kHz, indicating that this thin strip was useful in a saturable reactor, for example. Example 2: Thin Co-based amorphous alloy strips were produced by following the procedure of Example 1, excepting varying alloy compositions indicated in Table 1 were used as starting materials and varying conditions of manufacture similarly indicated in Table 1 were used. Comparative experiments indicated in the same table produced thin strips of the same compositions as those of the example, with some or other of the manufacturing conditions of this invention deviated from the respective ranges specified by this invention. It is clearly noted from Table 1 that an extremely thin Co-based amorphous alloy strip measuring less than 4.8 µm in thickness and possessing a fine state devoid of a pinhole could not be obtained when any one of the conditions of manufacture deviated from the relevant range specified by this invention. Example 3: Thin strips were produced by following the procedure of Example 1, excepting an alloy composition represented by the formula, [(Co 0.95 Fe 0.05 ) 0.95 Cr 0.05 ]₇₅(Si 0.5 B 0.5 )₂₅ , was used instead and the conditions of manufacture were varied from those of Example 1. Consequently, thin Co-based amorphous alloy strips measuring variously in the range of 3.0 to 10.2 µm in thickness. The thin strips had a fixed width of 5 mm. Then, the thin amorphous alloy strips thus obtained were insulated with MgO, wound in the form of a toroidal core 12 mm in outermost diameter and 8 mm in inner diameter, annealed at a temperature not exceeding the crystallizing temperature and exceeding the curie point, and then cooled at a cooling speed of 3°C/min, to produce magnetic cores. The magnetic cores thus obtained were tested for core loss at varying frequencies between 1 MHz and 5 MHz by the use of a magnetic property evaluating apparatus. The results were as shown in Fig. 5 During the test, the magnetic flux density was fixed at 1 KG. It is clearly noted from the diagram that the core loss decreased in proportion as the plate thickness decreased and that in the magnetic flux density of 1 kG the core loss value of the plate thickness of less than 4.8 µm in f=2MHz is smaller than the value in f=500kHz [3(w/cc)], comparing with 20 µm Co-based amorphous alloy which is used practically at present time. It is indicated that these thin strips were highly advantageous for use in the high frequency range.

Claims: A thin Co-based soft magnetic alloy strip being formed of an alloy essentially consisting of Co, at least one element selected from the group consisting of Fe, Ni, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr. Hf, Cu and the platinum-group elements, and at least one element selected from the group consisting of Si, B, P and C, is characterised by the fact that said strip has a plate thickness of less than 4.8 µm. A thin Co-based soft magnetic alloy strip according to claim 1, wherein said alloy has a composition substantially represented by the general formula (Co 1-a A a ) 100-b X b , wherein A is at least one element selected from the group consisting of Fe, Ni, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Cu and the platinum-group elements, X is at least one element selected from the group consisting of Si, B, P and C, a is a number satisfying 0 ≦ a ≦ 0.5, and b is an atomic % satisfying 10 ≦ b ≦ 35. A thin soft Co-based soft magnetic alloy strip according to claim 2, wherein A is at least one element selected from the group consisting of Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Cu and the platinum-group elements, a is a number satisfying 0 ≦ a ≦ 0.3. A thin Co-based soft magnetic alloy strip according to claim 1, wherein said alloy has a composition substantially represented by the general formula (Co 1-m L m M n ) 100-o (Si 1-p B p ) o , wherein L is at least one element selected from the group consisting of Fe and Mn, M is at least one member selected from the group consisting of Ti, V, Cr, Mi, Cu, Zr, Nb, Mo, Hf, Ta, W and platinum-group elements, m is a number satisfying 0.03 ≦ m ≦ 0.14, n is a number satisfying 0 ≦ n ≦ 0.10, p is a number satisfying 0.2 ≦ p ≦ 1.0, and o is an atomic % satisfying 20 ≦ o ≦ 35. A thin Co-based soft magnetic alloy strip according to claim 4, wherein M is at least one member selected from the group consisting of Cr, Mo and W. A magnetic core comprising a thin Co-based soft magnetic alloy strip according to any one of claims 1 to 5, said magnetic core being formed by coiling the thin Co-based soft magnetic alloy strip. An electromagnetic apparatus, comprising a magnetic part including a magnetic core according to claim 6 and electric parts. A method for the production of a thin Co-based soft magnetic alloy strip by ejecting a molten alloy through a nozzle onto the surface of a rotating cooling member thereby rapidly quenching the ejected molten alloy, characterised in that said rotary cooling member is formed of a Fe-based alloy or a Cu-based alloy, said nozzle is provided with an orifice of a rectangular cross section, the short side of which falling parallelly to the periferal direction of said rotary cooling member is set in the range of 0.07 to 0.13 mm, the distance between said nozzle and said rotary cooling member is set in the range of 0.05 to 0.20 mm, said rotary cooling member is operated at a peripheral speed in the range of 20 to 50 m/sec and, at the same time, said molten alloy is ejected under a ejecting pressure of 0.015 to 0.025 kg/cm² through said nozzle onto the surface of said rotating cooling member in a atmosphere of reduced pressure of not higher than 1.33 x 10⁻⁴ mbar (1 x 10⁻⁴ Torr) to form said thin alloy strip with a thickness of less than 4.8 µm. A method according to claim 8, wherein said thin Co-based soft magnetic alloy strip has an alloy composition substantially represented by the general formula (Co 1-a A a ) 100-b X b , wherein A is at least one element selected from the group consisting of Fe, Ni, Mn, Cr, Mo, W, V, Nb, Ta, Ti, Zr, Hf, Cu and the platinum-group elements, X is at least one element selected from the group consisting of Si, B, P and C, a is a number satisfying 0 ≦ a ≦ 0.5, and b is an atomic % satisfying 10 ≦ b ≦ 35. A method according to claim 8, wherein said thin Co-based soft magnetic alloy strip has an alloy composition substantially represented by the general formula (Co 1-m-n L m M n ) 100-o (Si 1-p B p ) o , wherein L is at least one element selected from the group consisting of Fe and Mn, M is at least one member selected from the group consisting of Ti, V, Cr, Ni. Cu, Zr, Nb. Mo, Hf, Ta, W and platinum-group elements, m is a number satisfying 0.03 ≦ m ≦ 0.14, n is a number satisfying 0 ≦ n ≦ 0.10, p is a number satisfying 0.2 ≦ p ≦ 1.0. and o is an atomic % satisfying 20 ≦ o ≦ 35. A method for producing a magnetic core comprising a thin Co-based soft magnetic alloy strip produced by the method according to claim 10, characterized by that the alloy strip is coiled to form a coil and thereafter subjected to a heat treatment at a temperature not higher than the crystallizing temperature and not lower than the Curie point of said alloy.

Inventors: SAWA TAKAO, YAGI MASAAKI, SAWA, TAKAO, YAGI, MASAAKI
Applicants: TOSHIBA KK, YAGI MASAAKI, KABUSHIKI KAISHA TOSHIBA, YAGI, MASAAKI
Application year: 1989
Main classification: H01F1
IPC codes: B22D11, H01F1, H01F41