CN100545960C - Magnetic core and application products using the magnetic core - Google Patents

Abstract

A magnetic core using a Fe-based amorphous alloy ribbon material, which simultaneously achieves miniaturization and noise reduction by realizing a high B _s , and an application product using the same. Provided is a magnetic core using an Fe-based amorphous alloy ribbon, wherein the saturation magnetic flux density (B _s ) of the Fe-based amorphous alloy ribbon is ≥ 1.60T, and wherein the core external magnetic field of 80A/m The ratio B ₈₀ /B _s of the magnetic flux density (B ₈₀ ) of the Fe-based amorphous alloy strip to the B _s of the strip is ≥ 0.90.

Description

Magnetic core and application products using the magnetic core

technical field

The present invention relates to a magnetic core using Fe-based amorphous alloy ribbon mainly for noise reduction, and can be used for applied products such as motors, transformers, choke coils, generators or sensors.

Background technique

As magnetic core materials for transformers, motors, choke coils, sensors, etc., Fe-based amorphous alloy ribbons have attracted attention due to their excellent soft magnetic properties, especially low iron loss in them. It has been used in virtually all kinds of cores, components and devices. Among Fe-based amorphous alloy ribbons, especially FeSiB-based amorphous alloy ribbon has been widely used because it shows relatively high saturation magnetic flux density _Bs and excellent thermal stability. However, the FeSiB-based amorphous alloy ribbon has problems in that: since the FeSiB-based amorphous alloy ribbon has a lower B _s than a silicon steel sheet, the magnetic core becomes large; and the magnetic core generates a high noise level. As for the method of increasing B _s in the Fe-based amorphous alloy strip, the following methods have been practiced: increasing the amount of Fe with magnetism; Deterioration of thermal stability; adding C; or adding C and P. JP-A-05-140703 discloses a method of increasing B _s by using a composition of FeSiBCSn, improving the formability of the amorphous state in the iron-rich region by adding Sn. On the other hand, JP-A-2002-285304 discloses a method of increasing B _s by using a composition of FeSiBCP, and greatly increasing Fe content by specifically adding P to a limited compositional range of Fe, Si, B, and C. method. With regard to the reduced magnetostriction necessary for reduced noise levels, the saturation magnetostriction of Fe-based amorphous alloy ribbons is approximately proportional to the square of B _s . Therefore, Fe-based amorphous alloy ribbons with high B _s and low magnetostriction have not been realized so far. For this reason, amorphous or nano-crystalline alloy ribbons with low B _s and low magnetostriction are used for magnetic cores that do not create noise problems and for applications using such cores.

[Patent Document 1]

JP-A-05-140703 ((0008) to (0010), and Figure 1)

[Patent Document 2]

JP-A-2002-285304 ((0010) to (0016), and Table 1)

Contents of the invention

problem to be solved

As mentioned above, magnetic cores made from conventional Fe-based amorphous alloy ribbons with high _Bs have high saturation magnetostriction and cause high noise levels. In other words, there is no such core that can satisfy high B _s and low noise level at the same time. For this reason, it is an object of the present invention to provide a magnetic core using Fe-based amorphous alloy strip material and an applied product using the same, which achieve both miniaturization _and Noise reduction.

way of solving the problem

In order to achieve miniaturization by achieving high B _s and noise reduction, the origin of the noise was investigated, and it was found that the squareness (squareness) of the Fe-based amorphous alloy ribbon is related to the The noise generated by strip cores is closely related; and by optimizing the composition of the alloy, the composition near the surface and the segregation in the alloy, and by improving the surface condition, the squareness can be further improved. As a result, it was found that a magnetic core producing an unprecedentedly low noise level can be formed from a Fe-based amorphous alloy strip material, and thus the present invention has been accomplished.

The magnetic core according to the present invention uses an Fe-based amorphous alloy strip, and is characterized in that the strip has a saturation magnetic flux density B _s of not less than 1.60T and a ratio B ₈₀ /B _s of not less than 0.90, so The ratio B ₈₀ /B _s is the ratio of the magnetic flux density B ₈₀ to B _s generated in an external magnetic field of 80 A/m applied to the magnetic core.

Magnetic cores made using Fe-based amorphous alloy strips with suitable rectangularity show a magnetic flux density of 1.4T at a frequency of 50Hz and an iron loss W _14/50 not higher than 0.28W/kg. In addition, when the magnetic flux density is 1.4T, the frequency is 50Hz and the average magnetic path length is Lmm, it can provide 20×log[(L ² ×10 ^-9 +2×10 ^-5 )/(2×10 ^-6 )]dB or less unprecedented low noise level products. The average magnetic path length "L" mm refers to the circumference length in the middle of the core thickness. For example, when the magnetic core has a preferably annular shape and the average diameter ((outer diameter+inner diameter)/2) is R, the length L becomes ΠR (L=ΠR). The above expression for the noise level shows a boundary between the present invention and the comparative example in an approximate expression when the relationship between the average magnetic path length and the noise level of the present invention and the comparative example is measured.

The Fe-based amorphous alloy strip used in the magnetic core preferably uses a high Bs material having a composition of the formula T _a Si _b B _c C _d (where T represents Fe, or, or Fe and At least one element in Co and Ni, the amount of at least one element in the Co and Ni is no more than 10% relative to Fe), in the formula, in atomic %, the subscript satisfies the expression: 76≤ a<84%, 0<b≤12%, 8≤c≤18%, and 0.01≤d≤3%, and the composition contains unavoidable impurities. The tape to be used has a thickness of 5 μm to 100 μm. When it has a thickness of not more than 5 µm, the Fe-based amorphous alloy ribbon is difficult to produce, and uniform properties cannot be obtained because surface conditions greatly affect the properties. When it has a thickness exceeding 100 μm, it tends to suffer from surface crystallization and deteriorate in properties.

The Fe-based amorphous alloy ribbon used in the magnetic core exhibiting higher B _s and high rectangularity preferably has a composition in which, in atomic %, the amount of Fe is 81 ≤ a ≤ 83; The amount is 0<b≦5; the amount of B is 10≦c≦18; and the amount of C is 0.2≦d≦3. An alloy having such a composition within the foregoing composition range has particularly high squareness. The strip material having the above composition exhibited a ratio B ₈₀ /B _s of not less than 0.93, which is the magnetic flux density B ₈₀ relative to B generated in an external magnetic field _of 80 A/m applied to the magnetic core _. ratio of _s .

The reason for the limitation of the above composition will be described below. Hereinafter, only units described as "%" represent atomic percent.

When the Fe content "a" is less than 76%, the amorphous alloy strip does not obtain sufficient B _s for the core material, and thus the size of the magnetic core increases, which is not preferable. On the other hand, when the Fe content "a" is not less than 84%, the amorphous alloy strip shows low thermal stability and cannot be stably produced. In order to obtain a high B _s , the value "a" is preferably not less than 81% but not more than 83%. Depending on the desired magnetic properties, no more than 10% of the Fe content may be substituted by at least one of Co and Ni.

The element Si contributes to the ability of the alloy to form an amorphous state. In order to increase B _s , the Si content "b" does not exceed 12%. In order to obtain high B _s , it is preferably not more than 5%.

The B (boron) content "c" most notably contributes to the ability of the alloy to form an amorphous state. When the boron content "c" is less than 8%, the thermal stability of the amorphous alloy strip decreases, but even if the boron content "c" exceeds 18%, the ability to form an amorphous state does not increase any more. In order to maintain the thermal stability of the amorphous material with high B _s , the boron content "c" is preferably not less than 10%.

The element C (carbon) has the effect of increasing the rectangularity of the material and B _s to miniaturize the magnetic core and reduce noise. When the carbon content "d" is less than 0.01%, this effect does not show. When it exceeds 3%, the amorphous alloy becomes brittle, and thermal stability decreases, so that it becomes difficult to be manufactured as a magnetic core, which is not preferable. In order for the amorphous alloy to have high B _s and high rectangularity, the carbon content "d" is preferably not less than 0.2%, and further preferably not less than 0.5%.

When not more than 10% of the Fe content is substituted by one or two elements of Ni and Co, B _s increases, which contributes to the miniaturization of the magnetic core. However, since the raw material of this element is expensive, it is impractical for an amorphous alloy to contain more than 10% of this element. The element Mn can show an effect of increasing B _s even when added in a small amount. When not less than 0.5 atomic % of Mn is added, B _s decreases. Therefore, the amount of Mn is preferably not less than 0.1%, but not more than 0.3%.

In addition, the amorphous alloy may contain one or more elements of Cr, Mo, Zr, Hf, and Nb in an amount of 0.01 to 5%, and may contain S as an unavoidable impurity in an amount of not more than 0.5%. , P, Sn, Cu, Al and Ti at least one element.

A method for increasing the rectangularity will be specifically described. Figure 1 shows the relationship between the noise level and the value B ₈₀ for a toroidal core with an average core diameter of 30mm at 1.4T and 50Hz. As the B ₈₀ value increases, the value of the magnetic flux density at which noise starts to occur (at or above the background noise level) shifts to the higher magnetic flux density side. To increase the B ₈₀ of the core, it is important to increase the B _s of the strip, as well as increase the squareness of the core. The squareness of the core can be improved by annealing the core in a magnetic field while controlling the annealing temperature and annealing time. The magnetic field is a DC magnetic field or an AC magnetic field with an intensity not lower than 200A/m, and is applied to the magnetic core parallel to the longitudinal direction of the strip (in the circumferential direction of the magnetic core). The magnetic core is heated to 250 to 450° C. at an average heating rate of 0.3 to 600° C./minute, and maintained at this temperature for not less than 0.05 hours. It is then cooled at an average cooling rate of 0.3 to 600°C/min. It is preferably heated at a heating rate of 1 to 20°C/minute and kept at 270 to 370°C for not less than 0.5 hours. The atmosphere is preferably an atmosphere of an inert gas such as _N2 and Ar, but may be an atmosphere of air. In addition, the same effect can be obtained by two-step heat treatment or long-term heat treatment at a low temperature not higher than 250°C. When the core has a large size and thus a large heat capacity, it can be heat treated in the following manner: temporarily hold the core at a temperature lower than the target holding temperature; then heat it to the target temperature; keep it at this temperature; and cool it down. Any of DC, AC, and repetitive pulse current magnetic fields can be used for the applied magnetic field. The strength of the magnetic field applied to the core is only sufficient to saturate the core magnetically, and is usually not lower than 80 A/m in terms of effective value. It is preferably not lower than 400A/m, and particularly preferably not lower than 800A/m. Heat treatment makes the core have low noise. The heat treatment is preferably performed in an atmosphere of an inert gas usually having a dew point of not higher than -30°C. Further preferable is heat treatment in an inert gas atmosphere having a dew point of not lower than -60°C because more preferable effects are obtained due to smaller distribution.

In order to further improve the rectangularity, preference is given to using Fe-based amorphous alloy strips with carbon segregation layers which exhibit peaks in the region 2 to 20 nm deep from the free surface and/or the rolled surface. A magnetic core using Fe-based amorphous alloy ribbon exhibits a ratio B ₈₀ /B _s of not less than 0.95 in an external magnetic field of 80 _A / _m applied to the magnetic core The ratio of the magnetic flux density B ₈₀ to the saturation magnetic flux density B _s of the Fe-based amorphous alloy strip.

Usually, carbon is not actively added, since carbon addition creates a carbon segregation layer on the surface of the strip, which causes embrittlement and thermal instability of the strip, and increases iron losses at high magnetic flux densities. The effect of adding carbon and the carbon distribution behavior on the surface has been studied, and it has been found that by controlling the ratio of carbon content to Si content and the surface state, the position of the carbon segregation layer and the peak position of the segregation layer can be controlled at predetermined Within the range, an amorphous alloy with high rectangularity, low brittleness and high thermal stability can be obtained. The formed carbon segregation layer causes structural relaxation near the surface at low temperature, which has a great influence on stress relaxation. When stress relaxation is high, high squareness is obtained, and noise level and iron loss are reduced in high magnetic flux density. In order for the carbon segregation layer to exhibit an effect, it is important to set such that the carbon segregation layer is at a predetermined portion and that the peak value is within a predetermined range. When the surface of the amorphous alloy strip has large roughness due to air pockets or the like, the thickness of the oxide layer becomes uneven, and thus the position and thickness in the depth direction of the carbon segregation layer become uneven. Therefore, structural relaxation becomes uneven, and locally brittle parts are generated. In addition, since the inhomogeneity of the surface reduces its cooling rate, crystallization is promoted at the surface of the nearby carbon segregation layer, thereby reducing the squareness. Therefore, it is important to control the surface roughness and form the peak position of the carbon segregation layer in a uniform depth region of 2 to 20 nm from the surface. As for the method, it is effective to blow CO ₂ , He or Ar gas onto the roll, or blow Co gas to combust the roll during pouring of the alloy to reduce the roughness. It was found that controlling the oxygen concentration near the outlet of the nozzle tip to not more than about 10% greatly improved the surface roughness and controlled the peak position of the carbon segregation layer to within 2 to 20 nm deep. In order to control the oxygen concentration in the atmospheric air at the outlet of the nozzle tip not to exceed 10%, as shown in FIG. 2, it is effective to blow the gas onto the roller portion on the rear side of the outlet. If the gas directly hits the paddle that flows out of the molten alloy, the gas will affect the shape of the paddle, causing the thickness of the alloy strip to be uneven; or the gas is wrapped in the alloy strip and on the surface of the alloy strip Inhomogeneity is created, which increases the surface roughness, which shifts the position of the carbon segregation layer to the inside. Gases sometimes cause further edge defects. For this reason, it is preferable to blow the injection gas onto the roller 2 so that the injection gas may not have an influence on the gate. It is preferable to adjust the angle between the roll surface and the gas-blowing nozzle (gas-blowing nozzle) 6, the distance between the roll surface and the exhaust nozzle, and the air pressure so that the air pressure near the surface of the roll located at the exhaust nozzle may not be higher than 0.20MPa, and while the oxygen concentration of the exhaust nozzle may not exceed 10%, the Fe-based amorphous alloy is cast. Thus, the surface roughness can be controlled to not exceed 0.6 μm, and the peak position of the carbon segregation layer can be controlled within a region between 2 and 20 nm from the surface of the alloy strip. When the air pressure near the roll surface of the exhaust nozzle is not lower than 0.20 MPa, the gas exerts an influence on the gate, thereby shifting the peak position of the carbon segregation layer more than 20 nm inward. When the width of the amorphous alloy ribbon becomes large, the oxygen concentration tends to be distributed in the width direction, which makes the surface roughness uneven. Therefore, near the edge where the oxygen concentration tends to be high, it is important to adjust the oxygen concentration to not exceed 10%. The thus controlled oxygen concentration of not more than 10% at the exhaust nozzle significantly reduces surface roughness and makes the position and thickness of the carbon segregation layer approximately uniform. It improves stress relaxation and squareness; reduces noise and iron loss of magnetic cores using the Fe-based amorphous alloy ribbon and parts containing the magnetic cores; and suppresses surface crystallization and embrittlement. Therefore, it can sufficiently obtain the effect of adding carbon.

The effect can be further enhanced by controlling the surface state, and also controlling the Si content to a certain level or lower relative to the carbon content. Although dependent on the carbon content, this effect can also be enhanced by reducing the value of b/d relative to a fixed carbon content. Figure 3 shows the relationship between the degree of stress relaxation and the maximum deformation with respect to carbon content and Si content. As a result of having used 82 atomic % of Fe (Fe _{82 Six} B _18-xy C _y ), when the composition satisfies b≤5×d ^1/3 , the alloy shows a stress of not less than 90% (region I) Slack. The reason is considered to be that, for a fixed carbon content, the peak value of the carbon segregation layer increases by decreasing the Si content. In other words, the peak value, and thus the stress relaxation, can be controlled by varying the Si content relative to the carbon content. When the carbon content "d" is not less than 3%, the amorphous alloy shows a maximum deformation of not more than 0.020 (region II), and causes a problem of thermal stability. The carbon content "d" controlled to not exceed 3% forms such a composition that a high degree of stress relaxation and a high saturation magnetic flux density are obtained, and squareness can be improved and noise can be reduced. It further suppresses embrittlement, surface crystallization and lowering of thermal stability which occur when a large amount of carbon is added.

The Fe-based amorphous alloy strip can be impregnated or coated if desired. It can be used as wound and cut core or multi-layer core by impregnation in resins such as epoxy, acrylic or polyimide resins, or in combination with alloys. The magnetic core is usually used after being housed in a resin case or coated.

Advantages of the invention

As described above, by using a material with high B _s and increased B ₈₀ /B _s , it is possible to obtain a magnetic core that generates little noise, produces low iron loss, suppresses embrittlement, and is thermally stable Sexual regression. Furthermore, an alloy composition capable of effectively increasing B ₈₀ /B _s was found so that such a magnetic core having a value of B ₈₀ /B _s of not less than 0.93 and further preferable for noise reduction can be provided. In addition, it is possible to provide a magnetic core having a value B ₈₀ /B _s of not less than 0.95, and further preferably for noise reduction, by using such an amorphous alloy ribbon having a controlled The composition and surface state, as well as the controlled position and peak of the carbon segregation layer within a fixed range. By using such a magnetic core, it is possible to provide an applied product that generates little noise, generates low iron loss, suppresses embrittlement, and lowers thermal stability.

Best Mode for Carrying Out the Invention

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

(Example 1)

An amorphous alloy strip with a thickness of 23 to 25 μm and a width of 5 mm was prepared by the following steps: preparing 200 g of a master alloy with a composition of Fe ₈₂ Si ₂ B _13.9 C ₂ Mn _0.1 ; heating the master alloy to 1300° C. with high-frequency power, to melt it and prepare a molten alloy; and, spray the molten alloy onto a Cu—Be alloy roll rotating at 25 to 30 m/s. Install the nozzle for blowing CO gas at a position 10 _cm away from the exhaust nozzle of the Cu roll in the rear direction so that the nozzle for blowing _CO gas forms an angle of 45 degrees with respect to the surface of the roll. While adjusting the blowing pressure of _CO2 gas, and controlling the air pressure in the vicinity of the roll at the exhaust nozzle to 0 (unblown gas), 0.1 and 0.3 MPa, the amorphous alloy was cast. Then, it was found that the oxygen concentrations in the vicinity of the exhaust nozzle (within 3 cm from the position where the molten metal contacts the roll) were 20.5, 8.5 and 7.5%, respectively. From the measurement results, it can be confirmed that the amorphous alloy ribbon produced by controlling the air pressure in the vicinity of the roll at the exhaust nozzle to 0.1 MPa (8.5% oxygen near the exhaust nozzle) is 2 to 20 nm from the surface. Deep positions have peaks of carbon segregation layers. Amorphous alloy strips were cut to a width of 5 mm and three toroidal cores were prepared with inner/outer diameters of 20/25, 25/35 and 70/75 mm, respectively. Then, measure the properties. The amorphous alloy strip has a width of 5 mm and a thickness of 23 to 25 μm. Anneal the core. Specifically, they were heated to 300 to 370°C at a heating rate of 5°C/min, kept at this temperature for 1 hour, and then cooled in a furnace while, in an argon atmosphere, magnetically opposed in the circumferential direction of the core. A magnetic field of 1500 A/m is applied to the core. Properties are compared at the annealing temperature at which iron loss is minimized. Properties are shown in Table 1. B _s is measured by using a vibrating probe magnetometer (VSM) in which a magnetic field of 5 kOe is applied to the monolithic sample. The B ₈₀ of the toroidal core; the iron loss W _13/50 at a passing frequency of 50 Hz at 1.3 T; and the iron loss W _14/50 at a passing frequency of 50 Hz at a magnetic flux density of 1.4 T were measured. The noise level is measured in an anechoic chamber with a background noise level of 12 to 14 dB under conditions of passing 50 Hz, a magnetic flux density of 1.4 T. In the chamber, the microphone was placed 10 cm away from the toroidal core. Stress relaxation is determined by rolling a monolithic sample around a quartz ring; measuring the diameter in the initial stage (i.e., the diameter of the sample when it is rolled around the quartz ring); The value is defined as R ₀ ; the monolithic sample rolled up around the quartz ring is annealed; the diameter of the sample that has been removed from the quartz ring is measured, and this value is defined as R; and R ₀ /R× A value of 100. The surface roughness of the rolled surface is 0.30 to 0.50 μm. All the samples showed B ₈₀ /B _s not less than 0.95, which means rectangularity. The results show that the higher the value of rectangularity, the lower the value of noise level.

(comparative example 1)

Under conditions similar to the case of Example 1, by subjecting the core to 320°C in a non-magnetic field; at 250°C in a non-magnetic field; and at 320°C in a magnetic field applied in a direction perpendicular to the circumferential direction The samples were prepared by annealing such that a different B ₈₀ /B _s in the range of less than 0.90 could be obtained for each sample. Properties are shown in Table 2. At 1.4T, the noise level increases from the low magnetic flux density region and increases to 24dB, 28dB and 35dB with the decrease of B ₈₀ /B _s . All samples showed B ₈₀ /B _s less than 0.90, which means rectangularity. It was confirmed that the magnetic core showed a value of noise level higher than 20×log[(L ² ×10 ^-9 +2×10 ^-5 )/(2×10 ^-6 )]dB specified in the present invention .

(Example 2)

200 g of master alloys with the composition shown in Table 3 were prepared, and then by steps similar to those in Example 1, an amorphous alloy strip with a width of 5 mm was prepared and the inner diameter/outer diameter was measured to be 25/35 mm properties of the toroidal core. Properties are shown in Table 3. By using GD-OES (Glow Discharge Optical Emission Spectrometer) manufactured by Horiba, Ltd., elements were quantitatively analyzed to measure the position of the carbon segregation layer from the rolling surface in the depth direction. As a result, a portion having a higher carbon concentration than the uniform concentration in the inside is regarded as a carbon segregation layer, and the position where the concentration is highest and the concentration value are read as the position of the carbon segregation layer and the value of the carbon peak. It is understood that the noise level is highly correlated with B ₈₀ and noise can be reduced by increasing B _s and squareness, and it is further understood that the addition of carbon is effective for improving squareness and reducing noise.

(Example 2-2)

Amorphous alloy ribbons having the compositions shown in Table 4 were prepared in a similar manner to the case of Example 1, and properties of toroidal cores with inner/outer diameters of 25/35 mm were measured. Properties are shown in Table 4. The addition of 4% carbon increases the iron loss of the amorphous alloy strip due to the increase in coercive force, and may cause problems in the manufacturing step due to the brittleness of the amorphous alloy strip. The addition of 0.7 atomic % of Mn reduces B _s , reduces squareness, increases coercive force and increases iron loss. Large additions of both carbon and Mn also increase the noise level.

(reference example 1)

Among the amorphous alloy strips prepared in Example 1, samples cast at an air pressure of 0 and 0.30 MPa in the vicinity of the roll surface at the exhaust nozzle were used to prepare a ring magnetic core with an inner diameter/outer diameter of 25/35 mm , and measure properties. Properties are shown in Table 5. Sample No. 33 is a sample prepared under an air pressure of 0 MPa (20.5% oxygen by concentration), and Sample No. 34 is a sample prepared under an air pressure of 0.3 MPa. The surface roughnesses of these two samples on the rolled surface were 0.64 to 0.70 μm and 0.63 to 0.82 μm, respectively. The peak position of the carbon segregation layer of the sample was out of range, and all values showing squareness, iron loss, and noise level were deteriorated. 4 and 5 show the results of elemental analysis in the depth direction from the rolled surface of samples 2 and 33.

(Example 3)

The above-mentioned toroidal core of Sample 2 and cores having an inner diameter/outer diameter of 90/120 mm were subjected to primary and secondary winding with metal wires, and properties were measured. As a result, both samples showed a 3% increase in B ₈₀ /B _s and a 3 to 5 dB decrease in noise level. Therefore, it can be confirmed that this magnetic core is expected to be used as a magnetic core for transformers, motors and electric reactors.

Industrial applicability

The present invention provides a magnetic core with high rectangularity, high magnetic flux density, low noise level and low iron loss by controlling heat treatment, surface roughness, amount of added carbon, and ratio of Si content to carbon content. An application product using the magnetic core is also provided. This core can be used as a core for transformers, motors and choke coils.

Brief description of the drawings

Figure 1 is a graph showing the magnetic flux density B ₈₀ in the magnetic core when an external magnetic field 80A/m is applied to the magnetic core and that produced by a toroidal core with an average core diameter of 30mm when the magnetic flux density is 1.4T and the frequency is 50Hz A plot of the relationship between noise levels;

2 is a schematic diagram of a position where gas is blown during casting, wherein reference numeral 2 denotes a roll; reference numeral 6 denotes a blowing nozzle; reference numeral 4 denotes molten metal; and reference numeral 8 denotes oxygen concentration and air pressure the measuring point;

3 is a graph showing the relationship between the degree of stress relaxation and the strain at fracture when the _{concentrations} of carbon and Si are varied in _{Fe82SixB18 -xyCy ,} where the region "I" shows where the degree of stress relaxation becomes insignificant. A compositional region of less than 90%, while a region "II" shows a compositional region in which the fracture strain becomes not more than 0.020;

Figure 4 shows the results of analysis of the rolled surface of sample 2; and

FIG. 5 shows the results of analyzing the rolled surface of sample 33.

Claims (7)

1. A magnetic core made of Fe-based amorphous alloy strip, wherein said Fe-based amorphous alloy strip has a composition represented by the formula T _a Si _b B _c C _d and contains unavoidable impurities, wherein T represents Fe, or Fe and at least one element of Co and Ni , the amount of at least one element among Co and Ni is not more than 10% relative to Fe, wherein the subscript satisfies the expression: 81≤a≤83, 0<b≤5, 10≤c ≤18 and 0.2≤d≤3, wherein said Fe-based amorphous alloy strip has a carbon concentration distribution peak in the segregated layer within a range between 2nm and 20nm deep from the strip surface, Wherein said Fe-based amorphous alloy strip has a saturation magnetic flux density B _s of not less than 1.60T and a ratio B ₈₀ /B _s of not less than 0.90, said ratio B ₈₀ /B _s being 80A/m The ratio of the magnetic flux density B ₈₀ generated when an external magnetic field is applied to the magnetic core relative to the saturation magnetic flux density B _s of the Fe-based amorphous alloy strip. 2. The magnetic core according to claim 1, wherein when the magnetic flux density is 1.4T and the frequency is 50Hz, the iron loss W _14/50 is not higher than 0.28W/kg. 3. The magnetic core according to claim 1, wherein when the magnetic flux density is 1.4T, the frequency is 50Hz and the average magnetic path length is L mm, the noise level is 20×log[(L ² ×10 ⁻⁹ +2× 10 ^-5 )/(2×10 ^-6 )] dB or less. 4. The magnetic core according to claim 1, wherein said Fe-based amorphous alloy strip exhibits a ratio B ₈₀ /B _s of not less than 0.93, said ratio B ₈₀ /B _s being 80 A/m The ratio of the magnetic flux density B ₈₀ generated when an external magnetic field is applied to the magnetic core relative to the saturation magnetic flux density B _s of the Fe-based amorphous alloy strip. 5. The magnetic core of claim 1, wherein the tape has a surface roughness of no more than 0.60 μm. 6. The magnetic core according to claim 1, wherein said Fe-based amorphous alloy strip exhibits a ratio B ₈₀ /B _s not lower than 0.95, said ratio B ₈₀ /B _s being when 80A/ The ratio of the magnetic flux density B ₈₀ generated when an external magnetic field of m is applied to the magnetic core relative to the saturation magnetic flux density B _s of the Fe-based amorphous alloy strip. 7. An application product selected from a motor, a transformer, a choke coil, a generator or a sensor, the application product comprising the magnetic core according to any one of claims 1 to 6.

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