EP2697399A1

EP2697399A1 - Alloy, magnet core and process for producing a strip made of an alloy

Info

Publication number: EP2697399A1
Application number: EP12720963.3A
Authority: EP
Inventors: Giselher Herzer; Christian Polak; Viktoria BUDINSKY
Original assignee: Vacuumschmelze GmbH and Co KG
Current assignee: Vacuumschmelze GmbH and Co KG
Priority date: 2011-04-15
Filing date: 2012-04-05
Publication date: 2014-02-19
Anticipated expiration: 2032-04-05
Also published as: EP2697399B1; KR101911569B1; JP2014516386A; DE102011002114A1; CN103502481A; KR20140014188A; DE102011002114A9; WO2012140550A1; JP6040429B2; CN103502481B

Abstract

Provision is made of an alloy consisting of Fe_{100-a-b-c-d-x-y-z}Cu_aNb_bM_cT_dSi_xB_yZ_z and up to 1 atom% impurities, where M is one or more of the elements Mo, Ta or Zr, T is one or more of the elements V, Mn, Cr, Co or Ni and Z is one or more of the elements C, P or Ge, and 0 atom% ≤ a < 1.5 atom%, 0 atom% ≤ b < 2 atom%, 0 atom% ≤ (b+c) < 2 atom%, 0 atom% ≤ d < 5 atom%, 10 atom% < x < 18 atom%, 5 atom% < y < 11 atom% and 0 atom% ≤ z < 2 atom%. The alloy is in the form of a strip and has a nanocrystalline microstructure, in which at least 50% by volume of the grains have a mean size of smaller than 100 nm, a hysteresis loop with a central linear part, a remanence ratio, J_r/J_s, < 0.1, and a ratio of coercive field strength, H_c, to anisotropy field strength, H_a, < 10%.

Description

description

Alloy, magnetic core and method of making an alloy strip

The present invention relates to an alloy, in particular a soft magnetic alloy suitable for use as a magnetic core, a magnetic core and a method for producing an alloy strip.

Nanocrystalline alloys based on a composition Feioo-a- _b -cdxy- _z Cu _a Nb _b M _c T _d Si _x B _y Z _z can be used as a magnetic core for different applications. The US 7,583,173 discloses a wound magnetic core which is used, inter alia, with a current transformer of (Fei_ _a Ni _a) _ioo-x-y _ _z _ _a _ _b _c CUxSiyBz baM 'M'_'γ, wherein a <0 , 3, 0.6 <x <1.5, 10 <y <17, 5 <z <14, 2 <α <6, β <7, γ <8, Μ 'at least one of the elements V, Cr, AI and Zn and M "are at least one of C, Ge, P, Ga, Sb, In and Be.

EP 0 271 657 A2 also discloses alloys with a summary on this basis.

These alloys, also in the form of tapes, can be used as the magnetic core in various components, such as power transformers, current transformers and storage chokes.

In applications for magnetic cores, the lowest possible production costs are generally desirable. However, the cost reduction should have as little or no effect on the operation of the magnetic core. In some applications of magnetic cores, further reduction of the size and weight of the magnetic core is desirable so that the size and weight of the component itself can be further reduced. At the same time, however, no increase in the manufacturing cost of the magnetic core is desired.

The object is therefore to provide an alloy which is suitable for use as a magnetic core, which can be produced more cheaply. Another object is to select the alloys so that the size and / or weight of the magnetic core can be reduced compared to a conventional magnetic core.

This is solved by the subject matters of the independent claims. Further developments are the subject of the respective dependent claims. According to the invention, an alloy is specified which

from Fei _oo -a- _b -cdxy- _z Cu _a Nb _b M _c T _d Si _x B _y Z _z, and up to 1 atom% is impurities. M is one or more of Mo, Ta or Zr, T is one or more of V, Mn, Cr, Co or Ni, Z is one or more of C, P or Ge and 0 at% <a <1.5 Atom%, 0 atom% <b <2 atom%, 0 atom% <(b + c) <2

Atom%, 0 atom% <d <5 atom%, 10 atom% <x <18 atom%, 5 atom% <y <11 atom% and 0 atom% z <2 atom%. The alloy is further formed in the form of a band and has a nanocrystalline structure in which at least 50% by volume of the grains have an average size of less than 100 nm. The alloy also has a hysteresis loop with a central linear part, a remanence ratio, J _T / J _S , <0.1, and a ratio of coercive field strength, H _c , to anisotropic field strength, H _a , <10%.

The alloy thus has a composition with a niobium content of less than 2 atomic percent. This has the advantage that the raw material costs are lower compared to a composition with a higher niobium content, since niobium is a relatively expensive element. Further, the lower limit of the silicon content and the upper limit of the boron content of the alloy are determined so that the alloy can be made in the form of a strip under tension in a continuous furnace, thereby achieving the above-mentioned magnetic properties. Thus, despite the lower niobium content, with this fabrication process, the alloy may also exhibit the desired soft magnetic properties for magnetic core applications.

The shape as a band not only makes it possible to manufacture the alloy under tension in a continuous furnace, but also to manufacture a magnetic core having any number of windings. Consequently, the size and magnetic properties of the magnetic core can be easily adjusted by appropriate selection of the windings to the application. Due to the nanocrystalline structure with a particle size of less than 100 nm in at least 50% by volume of the alloy, a low saturation magnetostriction is achieved at high saturation polarization. Due to the heat treatment under tensile stress, a suitable magnetic alloy selection results in a magnetic hysteresis loop with a central linear part, a remanence ratio of less than 0.1 and a coercive field strength of less than 10% of the anisotropy field. Linked to this are low re-magnetization losses and a permeability which is independent of the applied magnetic field or the bias in the linear, central part of the hysteresis loop and which is desired in magnetic cores for applications such as current transformers, power transmitters and storage chokes.

Here, the central part of the hysteresis loop is defined as the part of the hysteresis loop that lies between the anisotropy field strength points that characterize the transition to saturation. A linear part of this central part of the hysteresis loop is defined herein by a nonlinearity factor NL of less than 3%, the nonlinearity factor being calculated as follows: NL (in%) = 100 (δJ _to + EJ _ab ) / (2J _s ) (1)

In this case, 5J _on or 5J _ab denote the standard deviation of the magnetization from a compensation straight line by the rising or rising branch of the hysteresis loop between magnetization values of + 75% of the saturation polarization J _s .

This alloy is therefore particularly suitable for a magnetic core having a reduced size and a smaller weight with lower raw material costs and at the same time the desired soft magnetic properties for use as a magnetic core.

In one embodiment, the remanence ratio of the alloy is less than 0.05. The hysteresis loop of the alloy is thus even more linear or flat. In a further embodiment, the ratio of coercive strength to anisotropic field strength is less than 5%. Also is In this embodiment, the hysteresis loop even more linear, so that the Ummagnetisierungsverluste are even lower. In one embodiment, the alloy further has a permeability μ of 40 to 3000 or 80 to 1500. In another embodiment, the alloy has a permeability between about 200 and 9000. In these and other examples, the permeability is determined primarily by the choice of tensile stress in the heat treatment. The tensile stress can be up to about 800 MPa without the band breaking. Thus, with a given composition, it is possible to cover a band having a permeability within the entire permeability range from μ = 40 to about μ = 10000. Especially linear loops result in the range of low permeabilities, ie approximately μ = 40 to 3000.

Such relatively low permeabilities are advantageous for current transformers, power transmitters, storage chokes, and other applications where the magnetic core should not be ferromagnetic saturated so that the inductance does not suffer losses when high electrical currents flow through windings around the magnetic core. Suitable permeability ranges result from the specific requirements of the respective application. Suitable ranges are 1500 to 3000, 200 to 1500 and 50 to 200. Thus, for example, a permeability μ of about 1500 to about 3000 is advantageous for DC-tolerant current transformers, while for power transmitters a permeability range of about 200 to 1500 and for storage chokes rather a permeability range from about 50 to 200 is particularly suitable. The lower the permeability, the higher the electrical currents through the windings of the magnetic core can be without saturating the material. Likewise, with the same permeability, these currents can be higher, the higher the saturation polarization, J _s , of the material. On the other hand, the inductance of the magnetic core increases with the permeability and the size. To build magnetic cores with simultaneously high inductance and high current tolerance, it is therefore advantageous to use alloys with a higher saturation polarization. In one embodiment, for example, by reducing the niobium content, the saturation polarization of J _s = 1.21 T is increased to J _s = 1.34 T, ie, by more than 10%. This can ultimately be exploited without sacrificing the size and weight of the core to reduce.

The alloy may have a saturation magnetostriction of less than 5 ppm in magnitude. Alloys with a saturation magnetostriction below these limits have particularly good soft magnetic properties even with internal stress, especially when the permeability is not significantly greater than 500. For higher permeabilities it is advantageous to select alloys with smaller values of saturation magnetostriction.

The alloy may also have a saturation magnetostriction of less than 2 ppm, preferably less than 1 ppm. Alloys with a saturation magnetostriction below these limits have particularly good soft-magnetic properties, even with internal stress, in particular if the permeability μ is greater than 500 or greater than 1000. In one embodiment, the alloy is niobium-free, ie, b = 0. This embodiment has the advantage that the raw material costs are even further reduced since the element niobium is completely omitted.

In another embodiment, the alloy is copper-free, i. a = 0. In another embodiment, the alloy is niobium and copper free, i. a = 0 and b = 0. In further embodiments, the alloy comprises niobium and / or copper, where 0 <a <0.5 and 0 <b <0.5.

In further embodiments, the silicon content and / or the boron content is further defined such that the alloy has 14 atom% <x <17 atom% and / or 5.5 atom% <y <8 atom%.

As already mentioned above, the alloy has the shape of a band. This band may have a thickness of 10 μπι to 50 μπι. This thickness makes it possible to wind a magnetic core with a large number of windings, which at the same time has a small outer diameter.

In a further exemplary embodiment, at least 70 vol-% of the grains have a mean size of less than 50 nm. This allows a further increase in the magnetic properties.

The alloy is heat-treated in the form of a ribbon under tension to produce the desired magnetic properties. The alloy, ie the finished heat-treated strip, is thus also characterized by a structure which originated by this manufacturing process. In one embodiment, the crystallites have an average size of about 20-25 nm and a remanent elongation in the tape longitudinal direction between about 0.02% and 0.5%, which is proportional to the tensile stress applied during the heat treatment. For example, a heat treatment under a tensile stress of 100 MPa results in an elongation of about 0.1%.

The crystalline grains may have an elongation of at least 0.02% in a preferred direction.

An alloy magnetic core according to any one of the above embodiments is also given. The magnetic core may be in the form of a wound tape, wherein to form the magnetic core, depending on the application, the tape may be wound in a plane or as a solenoid about an axis.

The band of the magnetic core may be coated with an insulating layer to electrically insulate the windings of the magnetic core from each other. The layer may be, for example, a polymer layer or a ceramic layer. The tape may be coated with the insulating layer before and / or after winding into a magnetic core.

As already mentioned, the magnetic core according to one of the preceding embodiments can be used in various components. A power transformer, a current transformer and a storage choke with a magnetic core according to one of these exemplary embodiments are also specified. A method for producing a tape is also disclosed, comprising: providing an amorphous alloy tape having a composition consisting of

Fei _oo -a- _b -cdxy- _z Cu _a Nb _b M _c T _d Si _x B _y Z _z, and up to 1 atom% is impurities gen, where M is one or more of the elements Mo, Ta, or Zr, a T or more of the elements V, Mn, Cr, Co or Ni and Z, one or more of the elements C, P or Ge and 0 atom% <a <1.5 atom%, 0 atom% <b <2 atom%, 0 atom % <(b + c) <2 atom%, 0 atom% <d <5 atom%, 10 atom% <x <18 atom%, 5 atom% <y <11 atom% and 0 atom% <z <2 atom % is. This

Tape is heat treated under tension in a continuous oven at a temperature T _a , where 450 ° C <Ta <750 ° C. This composition can be prepared with a heat treatment between 450 ° C and 750 ° C under tension with suitable magnetic properties for use as a magnetic core. The heat treatment results in the formation of a nanocrystalline microstructure in which at least 50% by volume of the grains have an average size smaller than 100 nm. In particular, this composition with less than 2 atomic percent of niobium can be made by this method to have a hysteresis loop with a central linear part, a remanence ratio, J _r / J _s , <0.1, and a coercive-field strength, H _c , to anisotropic field strength, H _a , <10%.

The strip is heat treated in the pass. Consequently, the belt is pulled through the continuous furnace at a speed s. This speed s can be set so that a residence time of the belt in a temperature zone of the belt

Continuous furnace with the temperature within 5% of the T _a is between 2 seconds and 2 minutes. In this case, the time to heat the tape to the temperature T _{a is of a} comparable order of magnitude as the duration of the heat treatment itself. The same applies to the duration of the subsequent cooling. This residence time leads in this tempering temperature range to the desired structure and the desired magnetic properties.

In one embodiment, the tape is pulled through the continuous furnace under a tension of between 5 and 160 MPa. In a further embodiment, the band is pulled through the continuous furnace under a tensile stress of 20 MPa to 500 MPa. It is also possible to pull the strip through the kiln even with a higher tensile stress up to about 800 MPa without tearing it. This range of tensile stress is suitable for achieving the desired magnetic properties in the abovementioned compositions.

The value of the permeability μ achieved is inversely proportional to the tensile stress a _a applied during the heat treatment. In order to achieve a predetermined value of the relative permeability μ, during the heat treatment a tensile stress δ _{a is} required which corresponds to the relation σ ₃ ~ α / μ enough. In one embodiment, α has a value of ~ 48,000 MPa. In another embodiment, α has a value of, for example, α~36000 MPa. Thus, values in the range of ~ 30,000 MPa to α ~ 700,000 MPa can be used for the alloys according to the invention and the corresponding heat treatment process. The exact value depends on the composition, the tempering temperature and to some extent on the tempering time. The tensile stress that leads to the desired magnetic properties may therefore be dependent on the composition of the alloy and on the tempering temperature as well as the tempering time. In one embodiment, the μ for a bene vorgege- permeability tensile stress required a _a from the permeability is a UTest Testglühung out under a tension a _Te st according to the relation

σ ₃ ~ σ _ΤθΞ ίμτθ _Ξ ί / μ selected.

The desired magnetic properties may also be dependent on the tempering temperature T _a and consequently set by the selection of the tempering temperature. The temperature T _a <(T _x2 + 30 ° C) is selected for execution in an off depending on the niobium content B according to the relation (T _xi + 50 ° C) <T _a. In this case, T _xi and T _x2 correspond to the crystallization temperatures defined by the maximum of the heat of transformation, which are determined by means of thermal standard methods such as DSC (differential scanning calometry) at a heating rate of 10 K / min.

In a further embodiment, a desired value of the permeability or anisotropic field strength, as well as a permitted deviation range is predetermined. In order to achieve this value over the length of the belt, magnetic properties of the belt are continuously measured when leaving the continuous furnace. When deviations are detected from the allowed deviation ranges of the magnetic properties, the tension on the belt is adjusted accordingly to bring the measured values of the magnetic properties back within the allowable deviation ranges. This embodiment reduces the deviations of the magnetic properties over the length of the band, so that the magnetic properties within a magnetic core are more homogeneous and / or the magnetic properties of a plurality of magnetic cores made from a single band deviate less. Thus, the uniformity of the soft magnetic properties of the magnetic cores, especially in commercial production, can be improved.

Embodiments will now be explained in more detail with reference to the following examples, tables and drawings.

FIG. 1 shows a diagram of hysteresis loops of comparative examples of nanocrystalline Fe ₇₇ -xCui b _x Sii _5.5 B _s .5 with different niobium content after heat treatment in a magnetic field transverse to the strip direction. FIG. 2 shows a diagram of hysteresis loops of nanocrystalline Fe _{7 7} - _x Cui b _x Sii _5.5 B _s .5 after heat treatment under a tensile stress along the strip direction for different niobium contents, Figure 3 shows a diagram of the remanence ratio of nanocrystalline Fe _{7 7} _ _x Cui b _x Sii _5.5 B _s .5 after heat treatment in the magnetic field and after heat treatment Tensile stress as a function of Nb content, Figure 4 shows a diagram of the saturation polarization of

Fe ₇ 7-xCui b _x Sii5.5B _s . ₅ as a function of Nb content, FIG. 5 shows a diagram of saturation magnetostriction

A _s , anisotropy field H _ai coercive field strength H _c , remanence ratio J _r / J _s and nonlinearity factor NL of Fe ₇₅ . ₅ Cu _{1 1} . ₅ S i ₁₅ .5B5. ₅ after heat treatment under a tensile stress at different tempering temperatures, a graph of remanence ratio J _t / J _s and coercive field strength H _{c of} the alloy FewCuiSiis.sBe.s after heat treatment under a tensile stress is shown by Differential Scanning Calometry with a heating rate of 10 K / min measured crystallization behavior of the alloy FewCuiSiis.sBe.s and the definition of crystallization temperatures

Figure 8 shows the X-ray diffraction patterns for the alloy

Fe ₇₇ CuiS ii ₅ . ₅ B _s .5 in the amorphous initial state and after heat treatment under tension at various tempering temperatures corresponding to different crystallization stages.

FIG. 9 shows a diagram of permeability μ, anisotropy field Ha _/ coercive field strength H _c , remanence ratio

Jr / Js and non-linearity factor of nano- NL linem Fevs.sCuiNbi.sSiis.sBs.s after heat treatment under the specified tension o _a, Figure 10 shows the upper and lower optimum annealing temperature

Tai and T _a2 for different alloy compositions as a function of crystallization _temperatures T _xl and T _x2 .

FIG. 11 shows a diagram of coercive field strength H _c and

Remanence ratio J _T / J _{s of} the alloy Fe ₈ oSinB ₉ and a comparative composition Fe ₇₈ .5SiioBii. ₅ after a heat treatment under a tensile stress,

Figure 12 shows a graph of hysteresis loops of a LE Government Fe _8o SINB ₉ and a comparative composition

Fe ₇₈ .5SiioBii. ₅ after heat treatment under different tensile stresses, and

FIG. 13 shows a schematic view of a continuous furnace.

Table 1 shows the nonlinearity factor NL for various

Nb contents of the alloy Fe _{7 7} _× Cui b _× Sii _5.5 B _s .5 after heat treatment in the magnetic field (comparative example) and after heat treatment under a mechanical tensile stress (method according to the invention),

Table 2 shows measured temperatures and crystallization temperatures T _a suitable occasion for annealing times of about 2s to 10s for different Nb contents of the alloy Fe ₇₇ _ _x _x CuiNb Sii5.5B _s .5,

Table 3 shows magnetic properties of an alloy

Fe _7S CuiNbi.5Sii3 _.5 B ₈ after heat treatment in the course at 610 ° C under a tensile stress of approx. 120 MPa as a function of the tempering time t _a , Table 4 shows magnetic properties of an alloy

Fe ₇₅ Cuo. ₅ b ₁ . ₅ Si ₁₅ .5B5. ₅ after heat treatment with the specified tensile stress o _a , Table 5 shows in the production state measured saturation polarization J _s , after heat treatment at different tempering temperatures T _a measured values of

Non-linearity NL, remanence ratio J _T / J _S , coercive field strength H _c , anisotropic field strength H _a and relative permeability μ of different alloy compositions,

Table 6 shows in the manufactured measured saturation polarization J _s, measured after heat treatment values of non-linearity NL, remanence J _T / J _S, Koerzi - tivfeidstärke H _c, anisotropy field H _a and relative permeability μ of various alloy compositions, and Table 7 shows the saturation magnetostriction A _s of different Alloy compositions measured in the state of manufacture and after heat treatment under tension at the specified tempering temperature T _a . FIG. 1 shows a diagram of hysteresis loops of nanocrystalline alloys in the form of a band.

The investigations were carried out by way of example on 6 mm and 10 mm wide and typically 17 μπι to 25 μπι thick metal bands. However, the inventive idea is not limited to these dimensions. The bands have a composition of Fe ₇ 7_ _x Cui _x Sii ₅ . ₅ B _s .5. The hysteresis loops are measured after heat treatment in the magnetic field, whereby a heat treatment of 0.5 h at 540 ° C in a magnetic field of H = 200 kA / m is performed transversely to the band direction. Figure 1 shows that with decreasing Nb content the hysteresis loops become non-linear. This nonlinear hysteresis loop is undesirable in some magnetic core applications because the core loss losses are increased.

Table 1 shows the nonlinearity factors NL of the hysteresis loops shown in Figs. 1 and 2 for various heat treatments and various Nb contents. In particular, Table 1 shows the nonlinearity factor of nanocrystalline Fe ₇₇ - _x Cui b _x Sii ₅ . ₅ B _s .5 after heat treatment in a magnetic field for 0.5 h at a temperature of 540 ° C and after a heat treatment under tensile stress of 100 MPa for 4s at 600 ° C for various Nb contents. Figure 3 shows a graph of remanence J _r / ^'J _s heat-treated samples as a function of the Nb content. In particular, Figure 3 shows the remanence ratio of nanocrystalline Fe ₇₇ _ _x _x CuiNb Sii. ₅ ₅ B _s . ₅ after heat treatment in a magnetic field of 0.5 h at temperatures of 480 ° C to 540 ° C and after heat treatment under tensile stress of 4 s at temperatures between 520 ° C and 700 ° C as a function of the Nb content.

For a heat treatment in the magnetic field, which is represented by open circular symbols in FIG. 3, particularly linear loops with a remanence ratio smaller than 0.1 and a non-linearity factor smaller than 3% are reliably achieved only for Nb contents greater than 2 at%. In contrast, For linear heat treatment, linear loops with a remanence ratio less than 0.1 and a nonlinearity factor less than 3% can be reliably achieved for Nb contents less than 2 at% and even for compositions without niobium.

From the results of Figs. 1 and 3, it can be seen that a minimum Nb content of preferably greater than 2 at% is required to produce a tape having suitable magnetoresin magnetic properties when the heat treatment is performed in a magnetic field ,

Tables 1 to 6 and Figures 2 to 12 show that linear loops with a small remanence ratio at

Compositions can be achieved with a niobium content of less than 2 atom%, when the heat treatment is carried out under a tensile stress in the tape longitudinal direction. These compositions have the advantage that raw material costs are reduced since niobium is a relatively expensive element.

FIG. 2 shows a diagram of hysteresis loops of bands after heat treatment in the course of an effective one

Tempering time of 4s at a temperature of 600 ° C and under a tensile stress of about 100 MPa.

As starting time in the run, the time is defined at which the band passes through the temperature zone at which the temperature within 5% corresponds to the tempering temperature given here. In this case, the time to heat the tape to the tempering temperature is comparable to the duration of the heat treatment itself. The same applies to the duration of the subsequent

Cooling .

FIG. 2 shows that for Nb contents of less than 2 at%, hysteresis loops with a central linear part and a small remanence ratio can be obtained. The composition with Nb 3at% is a comparative example and the compositions with Nb <2at% are examples according to the invention. The arrow shows by way of example the definition of the anisotropy field strength H _a .

FIG. 3 shows a graph of a remanence ratio comparison for such tension-tempered samples, shown in FIG. 3 with filled diamonds, and for magnetic field-annealed samples, shown with open circle symbols, as a function of Nb content. Alloys with Nb contents below 2 at% have a small remanence ratio of less than 0.05 only when heat-treated under tension. However, when these compositions are annealed under a magnetic field, the remanence ratio is significantly higher, so that these alloys are not suitable for some magnetic core applications. Even for the alloy Fe ₇₇ CuiSii _5.5 B _s .5, ie without addition of Nb, a substantially linear loop with a remanence ratio of less than 0.05 results when heat-treated under a tensile stress.

FIG. 4 shows a diagram of the saturation polarization of alloys with a composition of Fe _{7 7} - _x Cu _x b _x Sii _5.5 B _s .5 as a function of the Nb content. The alloys with reduced Nb content have a significantly increased saturation polarization. This can be beneficial in a corresponding weight and Reduced manufacturing costs of the magnetic core can be implemented. Thus, in addition to reduced raw material costs, a further advantage results since the device having the magnetic core can be made smaller.

FIG. 5 shows a plot of saturation magnetostriction λ _Ξ , anisotropy field H _a , coercive field strength H _c , remanence ratio J _r / J _s and nonlinearity factor NL of a composition Fe 75. ₅ Cu ₁ b ₁ . ₅ Si ₁₅ .5B5.5 after heat treatment of about 4 seconds duration under a tensile stress of about 50 MPa as a function of the tempering temperature. The anisotropy field H _a field corresponds to that in which the linear portion of the hysteresis loop passes into the saturation shown in FIG. 2 The tempering temperatures, between which the desired properties can be achieved, are in the range of about 535 ° C to 670 ° C, which is highlighted hatched in the figure. The hatched area shows the area in which linear loops with small saturation magnetostriction, high anisotropy field and small remanence ratio result. This is also the area in which the alloys have particularly linear loops. In the embodiment of Figure 5 thus is the most suitable tempering temperature between 535 ° C and 670 ° C.

These temperature limits are largely independent of the magnitude of the tensile stress. However, they depend on the duration of the heat treatment and the Nb content. For example, they decrease with decreasing Nb content or with longer lasting heat. mebehandlung, as shown in Figure 6 and Table 2.

FIG. 6 shows the tempering behavior of a niobium-free alloy variant in which the optimum tempering temperatures are in the range of approximately 500 ° C. to 570 ° C., ie significantly lower than the composition of FIG. 5. In particular, FIG. 6 shows a graph of the remanence ratio J _t / J _s and the coercive field strength H _{c of} the alloy FewCuiSii _s .sbs. S after heat treatment for 4 seconds at T _a = 613 ° C. under a tensile stress of approximately 50 MPa. The optimum tempering temperatures according to the invention here are in the range of about 500 ° C to 570 ° C. Here, as schematically indicated by the inset, a flat linear hysteresis loop with a remanence ratio of less than 0.1 results.

FIG. 7 shows the crystallization behavior measured by means of differential scanning calometry (DSC) at a heating rate of 10 K / min using the example of the alloy Fe ₇₇ CuiSii _5.5 B _s .5. One recognizes two crystallization _stages which are characterized by the crystallization _temperatures T _xl and T _x2 . The temperature range limited by T _xl and T _x2 in the DSC measurement corresponds to the range of optimum tempering temperatures corresponding to FIG. 6 for the alloy between 500 ° C. and 570 ° C.

FIG. 8 shows the X-ray diffraction diagrams for the alloy Fe ₇₇ CuiSii _5.5 B _s .5 in the amorphous initial state and after heat treatment under tension at different tempering temperatures in accordance with the different crystallization _stages defined by T _xi and T _x2 . In particular, FIG. 8 shows the X-ray diffraction pattern after a heat treatment under tension for 4s at 515 ° C, ie in the starting area, where magnetic properties according to the invention are achieved, and at 680 ° C, ie in the unfavorable starting area where no linear hysteresis loops with a small remanence ratio can be achieved more.

From the analysis of the diffraction maxima, it follows that at tempering temperatures where linear hysteresis loops with a small remanence ratio result, essentially only cubic Fe-Si crystallites form, which are embedded in an amorphous minority matrix, as the crystalline phase. In the case of

Alloy Fe ₇ 7CuiSii ₅ .5B ₆ .5, the average size of these crystallites is approximately in the range 38-44 nm. Performing an analogous analysis with the alloy composition Fe75.5Cu1 1.5Si15.5B6.5 by so obtained at the appropriate optimal occasion - Temperatures a mean crystallite size in the range 20-25 nm.

In the second stage of crystallization, boride phases crystallize out of the amorphous residual matrix, which unfavorably influence the magnetic properties and lead to a non-linear loop with a high remanence ratio and high coercive strength.

In Table 2 are further examples, as well as additional data in the form of the differential scanning calorimetry (DSC) at 10K / min measured crystallization temperatures T _x i, which corresponds to the crystallization of bcc-FeSi, and T _x2 , which corresponds to the crystallization of borides, shown. The suitable tempering temperature is approximately between T _xi and T _x2 and leads to a structure of nanocrystalline grains with a mean grain size less than 50 nm, which in an amorphous Embedded matrix, and the desired magnetic properties.

However, T _xi and T _x2 and the tempering temperatures T _a depend on the heating rate and the duration of the heat treatment. Therefore, with a heat treatment time of less than 10 seconds, the optimum tempering temperatures at higher temperatures than the measured by differential scanning calorimetry (DSC) at 10K / min crystallization temperatures T _xi and T _x2 of Table 2. Accordingly, for longer tempering times, for example, 10 min up to 60 minutes, the optimum tempering temperatures T _a typically 50 ° C to 100 ° C lower than the values of T _a listed in Table 2 for a heat treatment time of a few seconds.

Correspondingly, the tempering temperatures T _a may be adjusted according to the composition and duration of the heat treatment according to the teaching of FIG. 5 and based on the crystallization temperatures measured in the DSC according to Table 2.

Table 3 shows the influence of tempering time using the alloy composition Fe _7S Cui bi.5Sii3 _.5 B ₈ as an example. For tempering times in the range of a few seconds to a few minutes, hardly any significant influence on the resulting magnetic properties is shown. This applies as long as the tempering temperature T _{a is} between the limit temperatures discussed with reference to Table 2. The latter are in the present embodiment T _xl = 489 ° C and T _x2 = 630 ° C from the DSC measurement at

10 K / min or T _al = 540 ° C and T _a2 = 640 ° C for a heat treatment of 4 s duration. The tempering temperature in the present embodiment is T _a = 610 ° C and thus lies between the lower and upper values of both definitions of limit temperatures. The crystallization temperatures measured at a heating rate of 10 K / min correspond approximately to the optimum starting range for an isothermal heat treatment lasting a few minutes.

FIG. 9 shows the dependence of the permeability, the anisotropy field, the coercive field strength, the remanence ratio and the nonlinearity factor on the tensile stress applied during the heat treatment. In particular, FIG. 9 shows a diagram of the permeability, the anisotropy field, the coercive field strength, the remanence ratio and the nonlinearity factor of nanocrystalline

Fe ₇₅ . ₅ Cu ₁ b ₁ . ₅ Si ₁₅ . ₅ B ₅ .5 after heat treatment for 4 seconds at 613 ° C below the specified tension o _a . In all cases, this gave a remanence ratio of typically less than J _r / ^' J _s <0.04 and a nonlinearity factor less than 2%.

Table 4 shows another example of the dependence of the permeability, the anisotropy field, the coercive field strength, the remanence ratio and the nonlinearity factor on the tensile stress applied during the heat treatment. In particular, the table shows the permeability, the anisotropy field, the coercive field strength, the remanence ratio and the nonlinearity factor of nanocrystalline

Fe ₇ sCuo. ₅ Nb ₁ . ₅ Si ₁₅ . ₅ B ₅ .5 after heat treatment for 4 seconds at 605 ° C below the specified tension o _a . In all cases, this resulted in a remanence ratio of typically less than J _T / J _s <0.1 and a nonlinearity factor of less than 3%. FIG. 9 and Table 4 show that the anisotropic field strength H _a and the permeability μ can be adjusted in _a targeted manner by adjusting the tension o _a . In order to achieve a predetermined value of the anisotropic field strength H _a or permeability μ in the heat treatment, a tensile stress o _a ~ a μ ₀ Η ₃ / ιΤ _Ξ or o _a ~ α / μ is required, where μ ₀ = (4π 10 ^"7 A denotes a material parameter which may depend primarily on the alloy composition but also on the tempering temperature and the tempering time Typical values are in the range ~ 30,000 MPa to ~ ~ 70000 MPa For the example in FIG. 9, a value of ~ 48,000 MPa and for the example in Table 3 a value of α -36,000 MPa.

The exemplary embodiments in FIG. 9 and Table 3 further make it clear that the smaller the set permeability, the more linear loops can be achieved. Thus, for permeabilities less than approximately μ = 3000, especially linear loops with a nonlinearity of less than 2% and a remanence ratio J _r / J _s <0.05 result.

The bands of the preceding embodiments comprise an alloy having the composition

Feioo-a- _b -c _d -x- _y - _z Cu _a Nb _b M _c T _d Si _x B _y Z _z, wherein

Cu 0 <a <1.5,

Nb 0 <b <2,

M is one or more of Mo, Ta, or Zr with 0 ^ b + c <2,

T is one or more of the elements V, Mn, Cr, Co or Ni with 0 <d <5, Si 10 <x <18

B 5 <y <11

Z is one or more of the elements C, P or Ge with 0 ^ z <2, wherein the alloy can have up to 1 atom% of impurities. Typical impurities are C, P, S, Ti, Mn, Cr, Mo, Ni, and Ta.

The composition can exert an influence on the magnetic properties in certain heat treatments. In order to achieve the desired magnetic properties in a composition, the heat treatment and in particular the tensile stress can be adjusted. Table 5 shows examples of the alloy, which were approximately 4 seconds heat-treated under a tension of 50 MPa at an optimum for the respective composition tempering temperature T _A, and a Comparative Example having a composition with a niobium content of above 2 atomic%. The remaining examples, numbered 1 to 10, represent compositions according to the invention having an Nb content of less than 2 at%. FIG. 10 additionally shows the optimum tempering temperatures and the crystallization temperatures of alloy examples 1 to 10. In particular, FIG. 10 shows the lower and upper optimum Tempering temperature T _al and T _a2 for a tempering time of 4 s as a function of the crystallization temperatures T _xl and T _x2 measured in the DSC at 10 K / min.

These examples show that for alloys according to the invention the composition can be varied within certain limits. Within the previously indicated limits (1) instead of Nb further elements such as Mo, Ta and / or Zr (2) instead of iron other transition metals such as V, Mn, Cr, Co and or Ni or (3) elements such as C, P and / or Ge can be added without the properties change significantly. To substantiate this, the alloy composition was used as another embodiment

FS ₇₁ . 5C02. 5N10. sCro .5V0. 5 n0. 2Cu0.7Nb0. 5 O0. 5 a0. ₄ Si ₁₅ . ₅ B _s . ₅ Co.2 produced in 20 μπι tape thickness and 10 mm bandwidth. The alloy has a saturation polarization of J _s = 1.25 T and responds to heat treatment under tensile stress similar to, for example, alloy examples 2-5 from Table 3. Thus, with a heat treatment of about 4 s at 600 ° C., a tensile stress of 50 MPa a nonlinearity factor of 0.4%, a remanence ratio J _T / J _s = 0.01, a coercive field strength of H _c = 6 A / m, an anisotropy field of H _a = 855 A / m and a permeability value of μ = 1160.

It can be seen from Table 5 that desirable magnetic properties result even without addition of Cu.

Table 6 therefore shows other examples of alloys in which the Cu content was varied systematically and a heat treatment of about 7 seconds duration was carried out at 600 ° C under a tensile stress of about 15 MPa. Specifically, in Table 6, the element Fe was gradually replaced by Cu, with the remaining alloying components remaining unchanged. Table 6 shows no significant influence of the Cu content on the magnetic properties for Cu contents below 1.5at%. However, the addition of Cu promotes the Embrittlement tendency of the strips during production. In particular, alloys with Cu contents greater than 1.5at% (such as, for example, alloy no. 15 from Table 6) already exhibit a strong embrittlement in the production state, so that a 20 μm thick band of the alloy Fe 74.5 Cu 2 1.5 Si 15.5 B 6.5 in a Bending diameter of about 1 mm can break.

Such a brittle belt can not be caught or wound up directly during the casting process due to the high production line speeds (25-30 m / s) after leaving the cooling roller or only with great difficulty during the casting process. This makes the tape production uneconomical. Also, such break even at the beginning of brittle bands in the heat treatment to an increased extent, especially before they enter the zone of elevated temperature. With such a break, the heat treatment process is interrupted and the tape must be threaded through the oven again.

On the other hand, alloys with a Cu content of less than 1.5at% can be bent to a bending diameter of twice the strip thickness, ie typically less than 0.06 mm, without breaking. This allows the tape to be rewound directly during casting. Furthermore, the heat treatment of such initially ductile bands is much easier. Alloys with a Cu content of less than 1.5 at% become embrittled only after the heat treatment, but only after they have left the furnace and are cooled again. The probability of a ligament tear during the heat treatment is thus significantly lower. Also, in most cases, belt transport through the oven can continue despite demolition. All in all, ductile tapes can thus be produced more easily and thus more economically, as well as heat-treated at first. The compositions shown in Tables 5 and 6 are nominal compositions in at% which coincide, within an accuracy of typically +0.5 at%, with the concentrations of the individual elements found in the chemical analysis.

The silicon content and the boron content also exert an influence on the magnetic properties of this type of nanocrystalline alloy with a niobium content of less than 2 atomic% when it is produced under tensile stress.

The examples from Tables 3 to 6 have the following desired combination of properties, ie, a central part linear magnetization loop with a remanence ratio J _r / J _s <0.1 and a small coercive field strength H _c which typically only a few percent of the anisotropic field strength H _a is. Figures 11 and 12 compare the magnetic properties of the compositions Fe ₈₀ SiB ₉ and Fevs. s i ioBn. s. FIG. 11 shows a diagram of the course of coercive field strength H _c and remanence ratio J _r / ^' J _{s of} both alloys after heat treatment under a tensile stress of about 50 MPa as a function of tempering temperature T _a . The coercive field strength H _c and the remanence ratio J _r / J _{s of} the alloy Fe ₈₀ S 11B ₉ according to the invention are represented by filled circle symbols and the comparative composition Fe ₇₈ . ₅ SiioBii.5 shown by open triangular symbols, after a heat treatment of 4 seconds duration at the tempering temperature T _a under a tensile stress of about 50 MPa. FIG. 12 shows a diagram of hysteresis loops of the two alloys after heat treatment for 4 s at about 565 ° C. under tensile stresses of 50 MPa (dashed line) or 220 MPa (solid line). The hysteresis loop of the alloy according to the invention Fe ₈ OSinB ₉ is on the left and that of the comparative composition Fe ₇ 8.5 SiioBii. ₅ is shown on the right.

Although the alloys shown in FIGS. 11 and 12 differ only slightly in their chemical composition, so great differences in the magnetic properties of both alloys result.

Thus, the inventive composition Fe _8o SINB ₉ after heat treatment between about 530 ° C and 570 ° C, a linear magnetization loop with a small remanence J _r / J _s <0.1 and a low coercive field strength onto which is clearly below 100 A / m and finally only a few percent of the anisotropic field strength H _a . By contrast, the composition Fevs.siioBn.s has a high remanence ratio throughout the entire heat treatment range.

Even the lowest values of the remanence ratio, which are achieved at tempering temperatures between 540 ° C and 570 ° C, are still around J _r / J _s ~ 0.5 (see Fig. 11). Furthermore, at these lowest values of J _r / J _s, an unfavorably high coercive field strength of approximately H _c ~ 800 - 1000 A / m results. As a result, the central part of the magnetization loop loses linearity, and the strong splitting of the hysteresis loop leads to disadvantageous high remagnetization losses (compare FIG. 12). These embodiments show that in alloy compositions having a Si content of more than 10 at% and a B content of less than 11 at% after heat treatment under tensile stress, a flat, substantially linear hysteresis loop with a remanence ratio J _T / J _s <0.1 and a low coercive field strength, which is well below 100 A / m and not more than 10% of the Anisotropiefeldes. With a lower silicon content and a higher boron content than these limits, the desired magnetic properties are not achieved in this tensile stress treatment.

The upper limit of the Si content and the lower limit of the boron content are also examined. While the alloy composition Fe75Cuo.5Nb1.5Si17.5B5.5 (see alloy no. 5 of Table 5) was produced as an amorphous, ductile band easily and had to heat treatment desirable properties, the alloy composition Fe had ₇ 5Cuo.5 bi.5Sii ₈ B ₅ after heat treatment only borderline magnetic _properties and the alloy composition Fe ₇₅ Cu _o.5 bi _.5 Sii _8.5 B _4.5 could no longer be prepared as a ductile amorphous band.

These embodiments show that for alloy compositions having a Si content of less than 18 at% and a B content of more than 5 at% after heat treatment

Tensile stress, a flat, largely linear hysteresis loop with a remanence ratio J _r / ^' J _s <0.1 and a low coercive field strength results, which is well below 100 A / m and not more than 10% of Anisotropiefeldes. At a silicon content higher than 18 at% and a boron content lower than 5at%, the desired magnetic properties in this tensile heat treatment are not reaches or can no longer produce an amorphous and ductile band.

Table 7 shows the saturation magnetostriction _constant λ _{Ξ of} various alloy compositions measured in the state of manufacture and after 4s heat treatment under a tension of 50 MPa at the indicated tempering temperature T _a . In particular, an annealing temperature was chosen, which is distant from the maximum annealing temperature T _a2 not more than 50 ° C, as this particularly small for a given composition values of the magnetostriction are obtained (see Figure 5) which will ultimately be determined by the alloy composition. The effect of the Si content of the alloy is shown. In addition to FIG. 5, Table 7 demonstrates that, after heat treatment under tensile stress, a significant reduction in the saturation magnetostriction results, which can lead to reproducible magnetic properties. In particular, little or no influence of mechanical stresses on the hysteresis loop results with small magnetostriction. Such mechanical stresses can occur when the heat-treated strip is wound into a magnetic core or when the magnetic core is embedded in a trough or in a plastics material or subsequently provided with turns of wire for further protection. From this it is possible to derive particularly advantageous compositions, namely those with a small magnetostriction.

As evidenced by the examples of Table 7, particularly advantageous magnetostriction values of less than 5 ppm can be achieved if the Si content is greater than 13 at% and the heat treatment temperature is not more than 50 ° C is below the upper limit T _{a2 of} the optimal starting range. Even smaller values of the saturation magnetostriction, which are smaller than 2 ppm in absolute value, can be achieved if the Si content is greater than 14 at% and less than 18 at%, and the heat treatment temperature is not more than 50 ° C. below the upper limit T _{a2 of} the optimum tempering range lies. Even smaller values of the saturation magnetostriction, whose absolute value is less than 1 ppm, can be achieved when the Si content is greater than 15 at% and and the heat treatment temperature is not more than 50 ° C. below the upper limit T _{a2 of} the optimum tempering range.

A small amount of magnetostriction is the more important the higher the permeability. For example, alloys with a permeability greater than 500 or greater than 1000 have a comparatively low dependence on mechanical stresses if the saturation magnetostriction is less than 2 ppm or less than 1 ppm. The alloy may also have a saturation magnetostriction of less than 5 ppm in magnitude. Alloys with a saturation magnetostriction below these limits still have good soft magnetic properties even at internal stress, when the permeability is less than 500.

The value of the saturation magnetostriction may still slightly depend on the tensile stress o _a applied during the heat treatment. For example, the result is alloy

Fe75. ₅ Cu ₁ Nb ₁ . ₅ Si ₁₅ .5B5. ₅ for a heat treatment of 4s at 610 ° C, depending on the initial tensile stress: λ _Ξ ~ 1 ppm at o _a ~ 50 MPa, λ _Ξ ~ 0.7 ppm at o _a ~ 260 MPa and λ _Ξ ~ 0.3 ppm at o _a ~ 500 MPa This corresponds to a small decrease the magnetostriction of Δλ _Ξ ~ -0.15 ppm / 100 MPa. The other alloy compositions show similar behavior. FIG. 13 shows a schematic view of a device 1 which is suitable for producing the alloy with a composition according to one of the preceding embodiments in the form of a band. The apparatus 1 has a continuous furnace 2 with a temperature zone 3, this temperature zone being set so that the temperature in the furnace in this zone is within 5 ° C. of the tempering temperature T _a . The device 1 further comprises a coil 4, on which the amorphous alloy 5 is wound, and a take-up spool 6, on which the heat-treated belt 7 is received. The tape is drawn at a speed s from the spool 4, through the continuous oven 2 to the take-up spool 6. In this case, the belt 7 is in the direction of the device 9 to the device 10 under a tensile stress σ. ₃ The apparatus 1 further comprises an apparatus 8 for continuously measuring the magnetic properties of the belt 6 after it has been heat treated and drawn out of the continuous furnace 2. In the area of this device 8, the belt 7 is no longer under tension. The measured magnetic properties can be used to set the tension under which the belt 7 is pulled through the continuous furnace 2. This is schematically illustrated by the arrows 9 and 10 in FIG. By measuring the magnetic properties and continuously adjusting the tensile stress, the uniformity of the magnetic properties over the length of the ribbon can be improved.

Claims

alloy, the

consists of Feioo- _a - _b - _c - _d - _x - _y - _z Cu _a Nb _b M _c T _d Si _x B _y Z _z and up to 1 atom% impurities, where M is one or more of the elements Mo, Ta or Zr, T is one or more of the elements V, Mn, Cr, Co or Ni and Z is one or more of the elements C, P or Ge and 0 atom% <a <1.5 atom%, 0 atom% <b <2 Atom%, 0 Atom% < (b+c) < 2 Atom%, 0 Atom% < d < 5 Atom%, 10 Atom% < x < 18 Atom%, 5 Atom% < y < 11 Atom% and 0 Atom% < z < 2 atom%,

is designed in the form of a band,

a nanocrystalline structure in which at least 50% by volume of the grains have an average size of less than 100 nm,

a hysteresis loop with a central linear part,

a remanence ratio, J _r /J _s , < 0.1, and

a ratio of coercive field strength, H _c , to anisotropy field strength, H _a , <10%.

The alloy of claim 1, wherein the remanence ratio, Jr/Js is <0.05.

Alloy according to claim 1 or claim 2, wherein the ratio of coercive field strength to anisotropy field strength is <5%.

Alloy according to one of claims 1 to 3, further having a permeability μ between 40 and 3000.

5. Alloy according to one of claims 1 to 4, further having a saturation magnetostriction of less than 2 ppm, preferably less than 1 ppm.

6 Alloy according to one of claims 1 to 5, which has a permeability of less than 500 and a saturation magnetostriction of less than 5 ppm.

7. Alloy according to one of claims 1 to 6, where b <0.5.

8. Alloy according to one of claims 1 to 7, where a is <0.5.

9. Alloy according to one of claims 1 to 8, wherein 14 atomic%

< x < 17 atom% and 5.5 atom% < y < 8 atom%.

10. Alloy according to one of claims 1 to 9, wherein the strip has a thickness of 10 μπι to 50 μπι.

11. Alloy according to one of claims 1 to 10, wherein at least 70% of the grains have an average size of less than 50 nm.

12. Alloy according to one of claims 1 to 11, wherein the

Crystalline grains have an elongation of at least 0.02% in a preferred direction.

13. Magnetic core made of an alloy according to one of claims 1 to 12.

4. Magnetic core according to claim 13, which has the shape of a wound tape.

5. Magnetic core according to claim 13 or claim 14, wherein the tape is coated with an insulating layer.

6. DC-tolerant current transformer made of a magnetic core according to one of claims 13 to 15, which has a permeability between 1500 and 3000

7. Power transmitter made of a magnetic core according to one of claims 13 to 15, which has a permeability between 200 and 1500.

8. Storage choke made of a magnetic core according to one of claims 13 to 15, which has a permeability between 50 and 200.

9. Method for producing a band comprising:

Providing an amorphous alloy ribbon having a composition consisting of

Fei _oo -a- _b -cdxy- _z Cu _a Nb _b M _c T _d Si _x B _y Z _z and up to 1 atom% impurities, where M is one or more of the elements Mo, Ta or Zr, T is one or more of the elements V, Mn, Cr, Co or Ni and Z one or more of the elements C, P or Ge and 0 atom% <a <1.5 atom%, 0 atom% <b <2 atom%, 0 atom % < (b+c) < 2 atom%, 0 atom% < d < 5 atom%, 10 atom% < x < 18 atom%, 5 atom% < y < 11 atom% and 0 atom% z < 2 Atom% is, Heat treatment of the strip under tension in a continuous furnace at a temperature T _a , where 450 ° C < Ta ^ 750 ° C.

0. The method according to claim 19, wherein the strip is pulled through the continuous furnace at a speed s, so that a residence time of the strip in a temperature zone of the continuous furnace with the temperature T _a is between 2 seconds and 2 minutes.

1. The method according to claim 19 or claim 20, wherein the strip is pulled through the continuous furnace under a tensile stress of 5 MPa to 800 MPa.

2. The method according to any one of claims 19 to 21, wherein the tensile stress a _a depends on the composition according to the ratio σ ₃ ~ a _Te st is, where μ is the desired permeability and _Τ β _Ξ ί is the permeability that results from a test voltage a _Test .

3. The method according to any one of claims 19 to 22, wherein the temperature T _a is selected depending on the niobium content b according to the ratio (T _xl + 50 ° C) < T _a < (T _x2 + 30 ° C).

4. The method according to any one of claims 19 to 23, wherein

a desired value of permeability or anisotropy field, a maximum value of a remanence ratio, J _r /J _s , of less than 0.1, and a maximum value of a ratio of coercive field strength to anisotropy field strength, H _c /H _a , of less than 10% and a permissible deviation range for each of these values can be predetermined, magnetic properties of the strip are continuously measured as it leaves the continuous furnace, and

If deviations from the permitted deviation ranges of the magnetic properties are detected, the tension on the band is adjusted accordingly in order to bring the measured values of the magnetic properties back within the permitted deviation ranges.