Electrical Steel Strip, Use of an Electrical Steel Strip and Method for Producing an Electrical Steel Strip

Abstract

The invention relates to an electrical strip with at least one functional layer at least partially consisting of a ferromagnetic material, with at least one additional layer at least partially consisting of a non-magnetisable material. The at least one additional layer and the at least one functional layer are bonded to one another by an adhesive bond with atomic diffusion and/or in that at least one functional layer has a thickness in the range from 2 to 100 ?m, preferably from 2 to 60 ?m. The invention also relates to a use of such an electrical strip as an iron core and to a method of manufacturing an electrical strip. The invention solves the object of providing an electrical strip and a method for producing an electrical strip which improves the disadvantages described for the prior art and, in particular, increases the efficiency of energy conversion in an application as an inductive component.

Claims

1-17. (canceled)

18. An electrical strip, with at least one functional layer at least partially consisting of a ferromagnetic material and with at least one additional layer at least partially consisting of a non-magnetisable material, wherein the at least one additional layer and the at least one functional layer are connected to each other, wherein at least one functional layer has a thickness in the range from 2 to 100 ?m, preferably from 2 to 60 ?m. wherein that the at least one additional layer and the at least one functional layer are bonded to one another by an adhesive bond with atomic diffusion.

19. The electrical strip according to claim 18, wherein the at least one additional layer has a thickness in the range from 2 to 100 ?m, preferably from 2 to 60 ?m.

20. The electrical strip according to claim 18, wherein the at least one additional layer consists at least partially, preferably completely, of a metallic material.

21. The electrical strip according to claim 18, wherein the at least one additional layer has copper (Cu), preferably a copper content with a mass fraction in the range from 1 to 15%.

22. The electrical strip according to claim 18, wherein the at least one additional layer has aluminium (Al), preferably an aluminium content with a mass fraction in the range from 1 to 15%, in particular in the range from 3 to 15%.

23. The electrical strip according to claim 18, wherein the at least one additional layer has a specific thermal conductivity at least equal to, preferably greater than, the specific thermal conductivity of the at least one functional layer.

24. The electrical strip according to claim 18, wherein the at least one additional layer consists at least partially, preferably completely, of an austenitic alloy or an austenitic steel.

25. The electrical strip according to claim 18, wherein the at least one additional layer consists at least partially, preferably completely, of a non-metallic material, preferably a carbon (C)-containing material, particularly preferably graphene or graphite.

26. The electrical strip according to claim 18, wherein at least two functional layers have different ferromagnetic materials and/or when several additional layers are used, at least two additional layers have different non-magnetisable materials.

27. The electrical strip according to claim 18, wherein the material properties vary in the at least one functional layer and/or in the at least one additional layer.

28. An arrangement of electrical strips, in particular electrical sheets, claim 18, wherein at least two electrical strips are arranged in a stack and a separating layer is provided between at least two electrical strips.

29. An iron core, comprising the electrical strip according to claim 18.

30. A method of manufacturing an electrical strip, in particular an electrical sheet claim 18, in which at least one functional layer is provided, wherein the at least one functional layer at least partially, preferably completely, consisting of a ferromagnetic material, in which at least one additional layer is provided, wherein the at least one additional layer at least partially, preferably completely, consisting of a non-magnetisable material, in which the at least one functional layer and the at least one additional layer are arranged adjacent to one another, in which an adhesive bond with atomic diffusion is created between the at least one functional layer and the at least one additional layer by applying pressure, and in which at least one functional layer has a thickness in the range from 2 to 100 ?m, preferably from 2 to 60 ?m.

31. The method according to claim 30, in which at least one of the at least one functional layer and/or at least one of the at least one additional layer are heat-treated.

32. The method according to claim 30, in which the at least one functional layer and the at least one additional layer are joined together by means of cold roll cladding or by means of hot cladding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Further features and advantages of the invention will be apparent from the following description of examples of embodiments, reference being made to the accompanying drawing.

[0113] In the drawing show

[0114] FIG. 1a-d Various embodiments of an electrical strip according to the invention in the form of an electrical sheet,

[0115] FIG. 2a-b Steps of an embodiment example of the method according to the invention for manufacturing an electrical strip in the form of an electrical sheet in schematic representation,

[0116] FIG. 3a-b Results of tests on various electrical strips in the form of electrical sheets and

[0117] FIG. 4a-b Hysteresis measurements on various electrical strips in the form of electrical sheets.

DESCRIPTION OF THE INVENTION

[0118] In the following description of the various embodiments according to the invention, components and elements with the same function and the same mode of operation are given the same reference signs, even if the components and elements may differ in dimension or shape in the various embodiments.

[0119] The embodiments relate to electrical sheets, which are described as examples of electrical strips.

[0120] FIG. 1a to FIG. 1d first show various embodiments of an electric sheet 2 according to the invention.

[0121] FIG. 1a shows, in the form of a section of a micrograph, a structure of an electrical sheet 2 having several functional layers 4 made of a ferromagnetic material and additional layers 8 arranged one above the other, the functional layers 4 and the additional layers 8 each being arranged in alternating sequence.

[0122] The functional layers 4 are made of ferromagnetic hot-rolled steel of grade DD11 (1.0332). The grain structure of the ferromagnetic material of the functional layers 4 is characterised by grain sizes of less than 100 ?m, with many of the grain sizes being in the range of 20 to 50 ?m.

[0123] In this example, the additional layers 8 are designed as continuous layers and separate the functional layers 4 from each other. The non-magnetisable material of the additional layers 8 is copper (Cu).

[0124] An electric sheet 2 with functional layers 4 of approximately constant thickness (layer thickness) d.sub.1i is shown, where i indicates the respective functional layer 4 and runs from 1 to n, with n the total number of functional layers 4 present. Here, d.sub.11=d.sub.12=d.sub.13= . . . =d.sub.1n, the thicknesses are approximately constant, but vary over the width of the representation due to the manufacturing process.

[0125] Alternatively, the functional layers 4 can be formed with thicknesses d.sub.1i, for which applies d.sub.11?d.sub.12?d.sub.13? . . . +d.sub.1n, which thus have different thicknesses d.sub.1i. Also, only some of the functional layers 4 can have different thicknesses d.sub.1i and other functional layers 4 can have approximately constant thicknesses d.sub.1i. The same applies to the thicknesses d.sub.2i of the additional layers 8.

[0126] As can be seen from the scale in FIG. 1a, layer thicknesses d.sub.1i and d.sub.2i of significantly less than 100 ?m, in particular less than 60 ?m, are achieved throughout.

[0127] FIG. 1b also shows, by means of a section of a micrograph, a structure of an electrical sheet 2 also having several functional layers 4 and additional layers 8 arranged one above the other, the functional layers 4 and the additional layers 8 each being arranged in alternating sequence. The functional layers 4 again consist of the steel DD11. In this example, the additional layers 8 are formed as non-continuous layers, so that contact between the functional layers 4 is possible. In particular, an irregular shape of the additional layers 8 and the functional layers 4 is clearly visible in this example. Here the additional layers 8 have the non-magnetisable material aluminium (Al). The structure of the ferromagnetic material is particularly fine-grained, the thickness of the functional layers 4 is less than 25 ?m and the additional layers have a thickness of a few ?m.

[0128] FIGS. 1c and 1d also show, in the form of a section of a micrograph, the structure of electrical sheets 2 having several functional layers 4 and additional layers 8 arranged one above the other, the functional layers 4 and the additional layers 8 each being arranged in alternating sequence. The functional layers 4 again consist of the steel DD11. In this example, the additional layers 8 are designed as particularly thin and partially discontinuous layers, so that contact between the functional layers 4 is also possible here at some points. The presence of an inhomogeneous material of the functional layers 4 is also clearly visible here, whereby the different shades of grey in individual functional layers 4 indicate a varying composition of the ferromagnetic material.

[0129] The thickness of the functional layers 4 is less than 75 ?m on average. In the examples shown in FIGS. 1c and 1d, the non-magnetisable material of the additional layers 8 is austenitic steel. It is also possible that the additional layers 8 appear as discontinuous layers on the micrograph due to their very small thickness of less than 10 ?m and below at the selected resolution, but they still allow intact isolation of the functional layers 4 from each other.

[0130] The functional layers 4 and additional layers 8 of the embodiments of an electric sheet 2 shown in FIG. 1a-d are bonded to each other by an adhesive bond with atomic diffusion. In particular, FIG. 1b shows an interdiffusion of the different materials of the functional and additional layers 4, 8 with each other on a microscopic level.

[0131] In FIGS. 2a and 2b, steps of an embodiment example of the method according to the invention for manufacturing an electrical sheet 2 are shown in schematic representation.

[0132] FIG. 2a first shows the process sequence with a cold-roll plating device 18, in which an electrical strip 2 to be produced is manufactured by various process steps. This can be, for example, an electrical sheet 2 according to the embodiments shown in FIG. 1a-d.

[0133] In a first method step 20, the bonding partners are first pretreated; the pretreatment of the material of the additional layer 8 is shown here. In this first method step 20, a pre-cleaning 20a is carried out, including a degreasing of the surfaces, as well as an activation 20b, in which the surfaces are mechanically torn open. In the example shown, the material fed from above and below and used for the functional layers 4 is not activated. However, this can be provided additionally, depending on the material selected for the functional layers 4.

[0134] Furthermore, the layers 4, 8 to be joined are cold-rolled together, whereby a significant reduction in thickness is achieved. The joining of an additional layer 8 of the material with two functional layers 4 of the material is shown here. The rolls shown in 20c exert a pressure on the layers 4, 8 to be joined, which brings the layers 4, 8 into intimate contact with each other at the atomic level.

[0135] It is also possible that the pre-treatment steps shown in method step 20, pre-cleaning and activation, are carried out additionally or only for the material of the functional layers 4, and the material of the additional layers 8, depending on the material selected, is not pretreated before the layers 4, 8 are joined. Thus, a method can also be provided in which, for the method step 20 shown in FIG. 2a, the material of the functional layers 4 takes the place of the material of the additional layers 8 and the pre-treatment is carried out on a functional layer 4 of the material before bonding with additional layers 8 of the material.

[0136] FIG. 2b shows an enlarged section of the formation of an electrical strip 2 by adhesive bonding 12 with atomic diffusion 14. This adhesive bonding 12 of the materials of the respective functional layer 4 and additional layer 8 to be joined is already initiated in the first method step 20. For some material combinations, this adhesive bond 12 is already sufficient for an electrical strip 2.

[0137] According to FIG. 2a, a further method step 22 involves adhesion annealing, also known as diffusion annealing, in which further rearrangement processes 14 are activated or reinforced at the atomic level by means of heat treatment and layers 4, 8 that are still incompletely adhering can be converted into a bond. For some material combinations, however, the adhesion generated during plating is already sufficient, so that adhesion annealing can be dispensed with. This is because a diffusion bond is already generated during cladding, regardless of whether cold or hot rolling was used,

[0138] After the adhesion annealing, a further rolling of the electrical strip 2 takes place in a next step 24, during which it is rolled almost to final thickness. In addition, a further heat treatment, also called bell annealing, to adjust the strength and structural properties of the electrical sheet 2 can take place in a subsequent step 26. The method steps 24 and 26 can be carried out several times, especially for very thin final dimensions. However, a single rolling/annealing cycle 24, 26 may also be sufficient, especially for thicker final dimensions.

[0139] FIG. 2a shows a further method step 28, skin-pass rolling, which denotes finish rolling with a low degree of deformation, in which any stretching of the yield point that may occur in the soft-annealed state can be removed from the composite material 32. In this step 28, targeted surface finishes of the electrical sheet 2 can be set simultaneously by rolling with different roll roughnesses. The last method step 30 shown here is slitting, in which the composite material 32 is slit to its final width.

[0140] FIGS. 3a and 3b show results of tests in the form of tables on various electrical sheets, wherein embodiments of an electrical sheet 2 according to the invention are compared with reference sheets from the prior art, wherein the reference sheets R1 and R2 are made of the steel DD11. The reference sheet R1 is heat-treated at approx. 670? C. after production and the reference sheet R2 is heat-treated at approx. 1000? C. after production.

[0141] In the table in FIG. 3a, the material parameters electrical conductivity K, material density p and the respective composition of the electrical sheets, from which the material parameters are calculated as an arithmetic mean over the individual layers, are first given for the embodiments of electrical sheets E1, E2, austenite1 and austenite2 according to the invention and for the reference R1.

[0142] While the reference consists of a single functional layer with a sheet thickness of 0.5 mm, the electrical sheets E1, E2, Austenit1 and Austenit2 each consist of 16 layers: eight additional layers each 10 ?m thick and eight functional layers each 53 ?m thick. The electrical sheet designated E1 has a structure and composition as shown in FIG. 1a, the electrical sheets E2, Austenit1 and Austenit2 correspond to FIGS. 1b, 1c and 1d respectively.

[0143] All listed electrical sheets have a total thickness or sheet thickness of 0.5 mm, as indicated in column 5.

[0144] The functional layers are made of DD11 steelas describedto ensure comparability with references R1 and R2.

[0145] Furthermore, the table in FIG. 3a serves to illustrate the reduced eddy current losses by means of the embodiments of an electrical sheet 2 according to the invention. In column 6 of the table in FIG. 3a, the eddy current loss factor k.sub.eddie=*d.sup.2/(6*?) calculated for the respective electrical sheets 2 is indicated, which according to P.sub.eddie=K.sub.eddie (B.sub.maxf?).sup.2 indicates the material-specific eddy current loss. In particular, by column 7 of the table, which indicates the reduction in eddy current loss of the electrical sheets E1, E2, austenite1 and austenite 2 achieved compared to the reference R1, it is clear that these latter electrical sheets can reduce eddy current losses significantly, by 90% on average. This reduction can be attributed in particular to the low thickness of the individual functional layers of less than 60 ?m each.

[0146] The table in FIG. 3b compares the hysteresis losses achieved with embodiments of an electrical sheet according to the invention, E1, E2, austenite1 and austenite2, with the hysteresis losses achieved with electrical sheets made of the reference materials R1 and R2. The table compares the material-specific quantities material density p, the measured coercivity H.sub.c and the hysteresis loss measured at frequencies of 1 kHz and 10 kHz of the respective electrical sheets.

[0147] Columns 7 and 8 of the table show the reduction in hysteresis loss achieved by means of the electrical sheets E1, E2, Austenit1 and Austenit2 with respect to the reference R1 at a frequency of 1 kHz and with respect to the reference R2 at 10 kHz. For each of the electrical sheets E1, E2, Austenite1 and Austenite2 a reduction in hysteresis loss is obtained. At a frequency of 1 kHz a reduction of at least 14% up to 34% can be achieved, at a frequency of 10 kHz a reduction of 1% up to 43%.

[0148] To reduce the hysteresis losses, it is advantageous according to P.sub.hyst=(k.sub.H4H.sub.CB.sub.maxf)/? it is advantageous to reduce the coercivity H.sub.c and to increase the material density p. In the present experiments, it was found that by using an electrical sheet 2 according to the invention with layers connected by adhesive bonding 12 with atomic diffusion 14 and by providing the additional layers 8 according to the invention, the hysteresis losses can be reduced on the one hand by a reduced coercive field strength H.sub.c, shown here for E2, austenite1 and austenite 2. In addition, even with an increased coercive field strength H.sub.c, shown here at E1, compared to the reference value, the hysteresis loss can be significantly reduced, whereby this reduction is not solely due to the increase in the arithmetic mean of the material density p.

[0149] By means of an electrical sheet 2 according to the invention with functional layers 4 and additional layers 8 connected by adhesive bonding 12 with atomic diffusion 14 and by providing the additional layers 8 according to the invention for separating the individual functional layers 4 with a small thickness of the functional layers 4 according to the invention, an effect can also be achieved by which the hysteresis losses due to structural processes in the interior of the composite material are reduced. For example, the energy required for the changed alignment of internal elementary structures, the magnetic domains, is reduced. This effect can be seen as an increase in the increased material density that is effective in the electromagnetically relevant remagnetisation effects.

[0150] FIGS. 4a and 4b show hysteresis measurements on various electrical sheets, whereby FIG. 4a compares the hysteresis loops 34 and 36 measured with embodiments E1 and E2 of an electrical sheet 2 according to the invention as explained above with the hysteresis loops 38 and 40 measured for the single-layer reference sheets R3 and R4 made of steel DD11. The reference sheet R3 has been heat treated at approx. 600? C. and the reference sheet R4 is mill-hard and has not been heat treated. Both reference sheets also have a sheet thickness of 0.5 mm.

[0151] In FIG. 4b, the hysteresis loops 42 and 44 measured with austenite1 and austenite2 embodiments of an electrical sheet 2 according to the invention as explained above are compared with the hysteresis loop 46 measured for the reference sheet R1 explained above.

[0152] All hysteresis loops 34, 36, 38, 40, 42, 44 and 46 shown in FIGS. 4a and 4b were measured at a frequency of 1 kHz.

[0153] The hysteresis loss is proportional to the area of the respective hysteresis loop traversed, so that it can be seen from the figures that a lower hysteresis loss was measured in the respective graphs for the embodiments of an electrical sheet E1, E2, austenite1 and austenite2 according to the invention compared to the referenced electrical sheets R1, R3 and R4.

[0154] In particular, the hysteresis loss measured for E2 with a value of P.sub.hyst=1647 W/kg can be significantly reduced compared to all other measured values. The measured hysteresis losses for E1 P.sub.hyst=2280 W/kg, for austenite1 P.sub.hyst=2121 W/kg and for austenite2 P.sub.hyst=2131 W/kg are also below the measured values for the reference materials R1 P.sub.hyst=2556 W/kg, R3 P.sub.hyst=2436 W/kg and R4 P.sub.hyst=2732 W/kg.

[0155] All the measurements shown make it clear that a reduction in both hysteresis and eddy current losses is achieved with electrical sheets 2 according to the embodiments of the invention described above. Overall, when using electrical sheets 2 according to the invention in electromagnetic components, the core losses are significantly reduced by targeted material selection of the materials of the functional layers 4 and additional layers 8 on the one hand, and by targeted material design on the other hand, in particular by reducing the thicknesses of the functional layers 4. This enables an optimised energy conversion of electromagnetic components and allows a more flexible design of the same, in particular through variably combinable layer thicknesses and variable material selection.

[0156] The absolute values of the hysteresis curves shown in FIGS. 4a and 4b are to be understood as examples. If a steel with different ferromagnetic properties is used for the reference materials and the functional layers of the electrical sheets according to the invention, other absolute magnetisation values may result, but the relative course of the hysteresis curves and the improvements explained occur in the same way with other steels.