ELECTRICAL SHEET, USE OF ELECTRICAL SHEET AND METHOD FOR MANUFACTURING ELECTRICAL SHEET

Description

[0001] The invention relates to electrical steel strip with at least one functional layer consisting at least partially of a ferromagnetic material and with at least one additional layer consisting at least partially of a non-magnetizable material. The invention also relates to the use of an electrical steel strip and a method for producing an electrical steel strip.

[0002] Electrical sheets and strips are widely used in all types of electrical systems, for example for energy generation in generators, in energy transmission and distribution in transformers, in energy utilization in motors and other electrical machines, and in other applications in the field of electrical engineering.

[0003] Electrical steel strip is primarily used as inductive components such as magnetic cores in electrical machines or in transformers. Electrical steel strip is generally understood to be rolled strip made of a magnetic material, for example, iron-silicon alloys. After a multi-stage manufacturing process, which includes, for example, steel production, hot-rolled or cold-rolled strip treatment, and, if necessary, heat treatment and strip coating, as well as skin-passing and straightening (stretch-bend leveling) of the strip in the finishing lines, the electrical steel strip is cut lengthwise into required widths and processed into electrical sheets, i.e., individual parts of electrical steel strip, by punching, etching, erosion, wire erosion, cutting, waterjet cutting, or laser cutting.

[0004] In further processing steps, the electrical sheets are then layered, packaged, and fixed into electromagnetic components, particularly laminations. These electromagnetic components are used in electrical systems such as generators, transformers, electric motors, and other magnetic applications as magnetic cores in the form of stators, rotors, transformers, and other magnetic cores in relays, switches, contactors, choke coils, ignition coils, electricity meters, and controllable deflection magnets.

[0005] Numerous characteristics, such as its geometric, mechanical-technological, and other material properties, are of great importance for the targeted use of electrical steel in relevant application areas. However, its behavior in an electromagnetic field is particularly important for the function of the respective component. Electrical steel is generally made of so-called soft magnetic materials, i.e., materials that are particularly easily magnetized in an external magnetic field and thus optimally utilize energy when used in electrical systems.

[0006] The magnetizability of a material is determined by the material-dependent absolute permeability µ Between the magnetic field strength acting on a magnetic material H and the magnetic material by H The relationship applies to the magnetic flux density generated B = µH. In empty space B = µ0 H , where µ 0 is the so-called magnetic field constant. The dimensionless quantity µ r = µ / µ 0 , which is called the permeability number or relative permeability, characterizes the magnetic behavior of a material. Ferromagnetic materials are those materials for which the following applies: µ r » 1, which amplify the external magnetic field within the material. Ferromagnetic materials are primarily important for the construction of electrical machines due to their field-enhancing effect.

[0007] The magnetizability of a ferromagnetic material is determined by the curve B vs. H described. A changing magnetic field strength Hleads to movements and growth processes of the magnetic domains, i.e. microscopic areas in a ferromagnetic material, within which the individual atomic or molecular magnetic particles are oriented in the same way, within the interior of the ferromagnetic material. Due to these processes occurring within the magnetic material, increasing magnetic field strength H a course of B vs. H, which differs from that observed with decreasing magnetic field strength. This deviation is called hysteresis.

[0008] The types of electrical steel strip are determined by the characteristic curve B vs. H determined, whereby the ascending branch of the characteristic curve, the course of B with increasing magnetic field strength H , with the descending branch of the characteristic curve, the course of BAs the magnetic field strength decreases, the magnetic field closes at its endpoints to form a hysteresis loop. The area of ​​the hysteresis loop describes the energy required to remagnetize the magnetic material.

[0009] When the external magnetic field is switched off H a certain value of the magnetic polarization remains J the portion of the flux density caused by the magnetic material B This value is called magnetic remanence B r. The width of the hysteresis is determined by the coercive field strength H c, the field strength required to reduce the flux density to zero. During magnetization reversal, the material passes through a closed hysteresis loop, the area of ​​which represents the amount of energy (heat) released to the environment per material volume per magnetization reversal cycle.

[0010] The magnetic behavior of a component in an electrical system therefore significantly influences its efficiency and thus its energy consumption. Increased efficiency and thus improved energy conversion can be achieved through application-specific optimization, particularly with regard to the magnetic properties of the electrical steel, and in particular with regard to core loss. Core loss or iron loss is the heat loss in the magnetic material that occurs in alternating magnetic fields due to the change in magnetization. The change in magnetization can be caused by alternating currents or by the movement of the magnetic field or the component made of magnetic material. For example, the rotor of a DC motor is also subject to an alternating magnetic field.

[0011] Electrical steel is currently manufactured in thicknesses ranging predominantly from 1 mm to 0.5 mm, and sometimes even down to 0.1 mm. For applications in electrical engineering where the magnetic flux is not restricted to a specific direction, electrical steel with properties that are as isotropic as possible is used. For such a non-grain-oriented (NO) electrical steel, a polycrystalline microstructure with grain sizes between 20 µm and 200 µm represents the ideal structure. For applications requiring particularly low core loss and particularly high demands on permeability or polarization, an electrical steel with a uniform orientation of the crystallographic texture, known as grain-oriented (KO) electrical steel, is typically used.

[0012] When it comes to magnetization losses, a distinction is essentially made between eddy current losses and hysteresis losses. Hysteresis losses describe the work required to shift the magnetic domains during magnetization reversal of a magnetic material. This loss is proportional to the area of ​​the hysteresis loop passed through by the material. B vs. H - course and is described by P hyst = ( k H 4 H C B max f ) / ρ, where k H describes the form factor, which depends on the geometry of the material and the influences of the stress during processing (e.g. punching, bending, drawing). H c is the coercive field strength, B max is the amplitude of the magnetic induction in the material, f the magnetic reversal frequency and ρ the material density of the material.

[0013] When an electrically conductive body is exposed to a changing magnetic field, an electrical voltage is induced, which in turn causes an electric current. The heat losses caused by this current are called eddy current losses and are calculated according to P wirbel = k wirbel ( B max fπ ) 2< calculated, with the material-dependent size k wirbel = κd 2< / ( 6ρ ), also called eddy current loss factor, where κ the specific conductivity (electrical conductivity) of the material, d is the thickness of the electrical sheet and ρ is the material density of the electrical sheet material.

[0014] The magnetic properties, and in particular the core reversal losses, of electrical steel sheets are therefore largely determined by material-specific parameters and the thickness of the sheet. Iron cores made of solid material are hardly usable due to high eddy current losses; in addition, the core heats up due to eddy currents with increasing frequency. To avoid this and to reduce core reversal losses, iron cores for electrical machines are designed as laminated, i.e., stacked and insulated, cores in stacks or as wound cut-core cores.

[0015] To effectively suppress the formation of eddy currents, the laminations of electrical steel sheets are coated with an insulating layer, such as varnish. The thickness of such insulating layers is in the range of a few µm; typically, the individual sheets are coated on each side with a 1-2 µm thick layer of insulating varnish and exhibit a certain roughness. When the electrical steel sheets are stacked and connected, the stack consists primarily of electrical steel sheets, but also varnish and air inclusions. The entire volume of the stack, also called the package, is therefore not completely filled with the magnetic material.

[0016] Eddy current losses also decrease with decreasing thicknesses of the electrical steel sheet. However, the production of thin electrical steel strip places increased demands on the manufacturing process. It should also be noted that the ratio between the magnetizable material of the electrical steel sheet and the non-magnetizable material of the coating becomes unfavorable with very thin electrical steel sheets: the more paint there is on the electrical steel sheet surface relative to its thickness, the less iron is contained in a laminated core of a given height. This ratio worsens the thinner the electrical steel sheet is; the ratio of sheet to paint thickness becomes increasingly smaller, and beyond a certain point, the positive effect of using particularly thin electrical steel sheets diminishes.

[0017] Therefore, due to market requirements, electrical steel is manufactured in various thicknesses and then further processed into electrical steel sheets. Layering the electrical steel laminations into cores requires very tight tolerances regarding sheet or strip thickness, particularly for large core heights. Non-grain-oriented electrical steel is primarily produced in thicknesses of 0.50 mm and 0.65 mm, but 0.35 mm and 1.00 mm are also common. Grain-oriented electrical steel is commonly produced in strip thicknesses of 0.35 mm, 0.30 mm, 0.27 mm, and 0.23 mm. Electrical steel with a nominal thickness of 0.1 mm is also known.

[0018] Another important method for reducing core loss is the use of adapted alloys. For example, core loss can be reduced by adding silicon to the alloy, as increasing silicon content increases the specific electrical resistance of the magnetic material and thus reduces conductivity. However, since increasing silicon content impairs the cold formability of the electrical steel strip, and commercially available electrical steel strip is usually cold-rolled, this results in increased demands on the manufacturing and processing processes. Therefore, a silicon content of 3.5% by mass is generally not exceeded.

[0019] Other suitable measures for improving the material properties of electrical steel sheets, in addition to reducing sheet thickness and using adapted alloys, include the adjustment of favorable microstructure properties, particularly with regard to grain size and texture. However, this adjustment usually has a negative impact on the mechanical properties and thus the processability of the electrical steel sheets.

[0020] WO 2018 / 157946 A1 discloses a composite material with two grain-oriented electrical steel layers with layer thicknesses of 50 to 1500 µm, which is produced by coating one electrical steel layer with a polymeric agent and subsequently laminating two electrical steel layers.

[0021] WO 2018 / 019602 A1 describes a steel strip for producing a non-grain-oriented electrical steel sheet with an insulation layer, which has a final thickness of at least 100 µm.

[0022] According to US 3,682,606 A, an aluminum-steel composite material is described for the construction of lightweight vehicle structures or their armor.

[0023] EP 3 127 647 A1 describes the production of a metal laminate material of different materials by joining two sheets M1 and M2 by roll pressure bonding

[0024] DE 10 2018 102422 describes the use of a composite material for shielding against electric and magnetic fields.

[0025] Therefore, the present invention is based on the technical problem of providing an electrical steel strip of the type mentioned at the outset and a method for producing an electrical steel strip which improves the disadvantages described for the prior art and in particular increases the efficiency of energy conversion when used as an inductive component.

[0026] The above-mentioned technical problem is solved according to the invention according to a first teaching in an electrical steel strip with at least one functional layer at least partially, preferably completely, consisting of a ferromagnetic material and with at least one additional layer at least partially, preferably completely, consisting of a non-magnetizable material, and wherein at least one functional layer has a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm, in that the at least one additional layer is connected to one another by an adhesive bond with atomic diffusion.

[0027] In the following, an electrical strip is understood to mean, for example, an electrical strip with at least two layers, or an electrical sheet cut from this electrical strip with at least two layers. An electrical strip can therefore also represent an electrical sheet. Due to their ferromagnetic properties, electrical strips or sheets of the specified type are used as inductive components in electrical machines or in transformers.

[0028] In principle, the properties of the electrical steel strip described below are already achieved with the small number of layers mentioned. For example, two functional layers with an additional layer arranged between them are preferred. Furthermore, three to ten functional layers can be provided, each with nine additional layers arranged between them. As described further below, two functional layers can also be adjacent to each other, separated from further functional layers by additional layers.

[0029] Also preferred is an electrical steel strip comprising a plurality of functional layers and additional layers, which are arranged adjacent to one another, preferably alternating. Typically, 10 to 100 functional layers with a corresponding number of additional layers can be present in a stack. However, the number of layers is generally not limited, as long as production is possible.

[0030] Within the scope of the invention, it was recognized that by bonding the at least one functional layer and the at least one additional layer together by adhesive bonding with atomic diffusion, an electrical steel strip with improved material properties, in particular with improved magnetic properties, can be provided. Such a bond can reduce internal stresses at the junction of the bonding partners involved and thus within the electrical steel strip or sheet.

[0031] In this context, a bond formed by adhesive bonding with atomic diffusion is understood to be a bond between two bonding partners in which a transition layer forms as a bonding zone through atomic diffusion of the bonding partners' materials, across which a continuous adaptation of the material properties takes place. Adhesive bonding with atomic diffusion thus arises through the formation of the transition layer between the layers.

[0032] In the transition layer, the atoms of the bonding partners are gradually intermixed, and the formation of a bond occurs through exchange processes (diffusion) in the transition layer, also called the bonding zone. This transition layer reduces internal stresses. The extent of the transition zone depends on the bonding partners used, particularly the diffusion properties of the materials involved.

[0033] To characterize the adhesion bonding with atomic diffusion, i.e., the bonding zone of the adhesion bond in the transition layer, and its properties, various methods can be used. These methods include optical light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), secondary ion mass spectrometry (SIMS), and microhardness profile analysis.

[0034] Such a composite can be referred to, for example, as a clad composite. Preferably, the two bonding partners are metallic materials, and the clad composite represents a metallic connection between the two bonding partners or clad partners. However, bonds between metallic materials and non-metallic materials, such as carbon-containing materials, or between non-metallic bonding partners, such as plastics, are also possible. The bonding partners of the composite are typically arranged in layers adjacent to one another. The bonding partners in the clad composite can be connected by clad-bonding. For this purpose, the clad bond can be performed by cold-rolling or hot-plating.

[0035] The bonding partners can alternatively be connected by welding metal packages, particularly diffusion welding or electric welding, or by stacking and partial welding. Furthermore, production by sintering or hot isostatic pressing (HIP) is possible.

[0036] According to the invention, the at least one functional layer consists at least partially, preferably entirely, of a ferromagnetic material, in particular of iron, nickel, cobalt, other ferromagnetic materials, their alloys, or a plating of two or more of these materials. Even with fundamentally paramagnetic materials such as copper, it is known that ferromagnetic properties can be induced by appropriate processing of the metal. In this case, such a material is also suitable for the production of the functional layer.

[0037] The aim, and in this respect, is to form the functional layer as a continuous layer in order to achieve the properties of the functional layer as best as possible. However, the functional layer can also be formed as a discontinuous layer, since the continuity of the layer cannot be fully guaranteed during production. On the other hand, depending on the materials used, the production of a functional layer formed as a discontinuous layer can also be aimed for, so that the material of the additional layer at least partially penetrates the material of the functional layer. In this way, other properties of the composite such as conductivity or durability can be improved. The material of the functional layer can also contain other, non-ferromagnetic components and inclusions.

[0038] Likewise, the at least one additional layer consisting at least partially, preferably entirely, of a non-magnetizable material is understood to mean a layer that is designed as a continuous layer or as a discontinuous layer. Here, too, a continuous layer is desired and preferred in order to best achieve the properties of the additional layer. The at least one additional layer can also contain other materials in addition to a non-magnetizable material. In particular, open or closed pores, for example air pores, can be present both in the at least one functional layer and in the at least one additional layer.

[0039] The at least one additional layer can itself consist of one layer or of at least two layers. Preferably, the at least one additional layer is a clad material or a multilayer composite material. Particularly preferably, the at least one additional layer comprises a mica layer or a graphene layer on a metal layer made of copper or aluminum. A fiber composite material, a ceramic material, or a phyllosilicate (mica) can also be used as the material of the at least one additional layer, which in particular allows electrical insulation to be introduced into the composite of the electrical steel strip or electrical sheet.

[0040] In particular, the provision of such at least one additional layer can also advantageously influence the material properties, such as the magnetic properties, of the electrical steel strip if the additional layer is designed as a discontinuous additional layer. A discontinuous additional layer enables contact between the functional layers arranged on both sides of the at least one additional layer.

[0041] Alternatively, the at least one additional layer is preferably formed as a continuous layer, so that contact between the functional layers arranged on both sides of the at least one additional layer is prevented. Both by providing at least one continuous additional layer and by providing at least one discontinuous additional layer, the material properties, and in particular the magnetic properties, of an electrical steel strip can be particularly effectively influenced. In particular, the remagnetization losses of the electrical steel strip can be reduced.

[0042] The material of at least one functional layer can comprise an iron-silicon alloy. Such alloys have proven to be advantageous materials, particularly with regard to core losses, for electrical steel strips and, in particular, for electrical steel sheets. The functional layer can have a grain-oriented or non-grain-oriented microstructure. In addition, the material of at least one functional layer can also comprise other iron (Fe) alloys as well as alloys of cobalt (Co), aluminum (Al), and / or nickel (Ni).

[0043] When manufacturing the functional layers, the preferred approach is to generate as many large grains as possible, preferably up to grain sizes equal to the layer thickness. Furthermore, depending on the material of the additional layer, the diffusion of elements and their integration into the crystal lattice of the functional layer material is possible.

[0044] By means of the composite described above, an electrical steel strip can be provided, in particular, comprising functional layers and / or additional layers made of different materials, preferably comprising functional layers made of different ferromagnetic materials and additional layers made of different non-magnetizable materials. The different materials can, in particular, have different material properties, for example, different properties regarding electrical conductivity or thermal conductivity, as well as material density. This allows for a targeted selection of the material properties, which, with advantageous selection and combination, can, in particular, improve the magnetic properties of the electrical steel strip.

[0045] Within the scope of the invention, it was particularly recognized that the composite according to the invention, by means of adhesive bonding with atomic diffusion, can reduce the magnetic reversal losses, in particular the hysteresis and eddy current losses. Preferably, the introduction of additional layers which are responsible for the eddy current losses, given by P wirbel = κd 2 6 ρ B max fπ 2 , and for the hysteresis losses, given by P hyst = ( k H 4 H C B max f ) / ρ , of an electrical steel important material-specific parameters, in particular ρ and κ , so that the core losses are reduced overall. A reduction in core losses, particularly both hysteresis and eddy current losses, was observed at frequencies ranging from 1 kHz to 10 kHz. The possible frequency range depends on the specific material of the functional layer and / or the additional layer.

[0046] A reduction in hysteresis losses could be achieved in particular by reducing the area of ​​the hysteresis loop of the B vs. H - the course of the composite according to the invention with at least one functional layer and with at least one additional layer compared to measurements of a comparably thick electrical steel sheet without additional layers. Furthermore, the composite can influence the coercive field strength through atomic adhesion bonding with atomic diffusion. Regarding the reduction of eddy current losses, a reduction of the eddy current loss factor was observed. k wirbel = kd 2< / (6 ρ ) can be observed.

[0047] Furthermore, by providing at least one additional layer made of a non-magnetizable material, other material properties of the electrical steel can be specifically influenced in addition to the magnetic properties. For example, it is possible to achieve a weight reduction of the electrical steel by using at least one additional layer with a material density ρ lower than the material density ρ of the functional layer material. A weight reduction of the electrical steel advantageously leads to a further improvement in the energy efficiency of an electrical steel, particularly when used as electrical steel in moving components.

[0048] In addition, the thermal conductivity of the electrical steel strip can be specifically influenced by providing at least one additional layer. For example, the material used for the at least one additional layer can have a higher thermal conductivity than the material used for the at least one functional layer. In this way, the thermal conductivity of the electrical steel strip can be improved, enabling operation at higher thermal loads compared to an electrical steel strip without at least one additional layer.

[0049] Furthermore, the composite according to the invention allows a reduction in the thickness of the magnetically active functional layers of the electrical steel strip by means of adhesive bonding with atomic diffusion. Due to the quadratic dependence of the eddy current loss factor on the thickness d of the individual functional layers of the electrical steel strip, this is particularly advantageous for achieving lower remagnetization losses.

[0050] The above-mentioned technical problem is solved according to a second teaching in an electrical strip with at least one functional layer at least partially, preferably completely, consisting of a ferromagnetic material and with at least one additional layer at least partially, preferably completely, consisting of a non-magnetizable material, wherein the at least one additional layer and the at least one functional layer are connected to one another, in that the at least one functional layer has a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm.

[0051] In principle, the properties of the electrical steel strip described below are also achieved even with the small number of layers mentioned. However, an electrical steel strip consisting of a plurality of functional layers and additional layers, preferably arranged adjacent to one another in alternating fashion, is preferred. Typically, there can be 5 to 100 functional layers with a corresponding number of additional layers in a stack. However, the number of layers is generally not limited, as long as production is feasible.

[0052] It has been recognized that by using such an electrical steel strip with at least one functional layer with a thickness in the range of 2 to 100 µm, preferably 2 to 60 µm, the magnetic reversal losses can be significantly reduced. In particular, the thicknesses of the functional layers mentioned above achieve a significant reduction in eddy current losses: the eddy current loss factor k vortex = κ * d 2< / ( 6* ρ ) depends quadratically on the thickness of the individual functional layer d. By providing at least one functional layer partially, preferably entirely, composed of a magnetizable material with the specified thicknesses and at least one additional layer of non-magnetizable material, the thickness of the respective functional layers of the electrical steel strip that contribute to eddy current losses is reduced. However, the total thickness of the functional layers can then essentially correspond to conventional electrical steel sheets. Thus, the described electrical steel sheets can exhibit the same magnetic effect as an inductive component as conventional electrical steel sheets, but with lower energy losses. This is because the eddy current loss factor and thus the eddy current loss can be significantly reduced. This enables particularly efficient energy conversion.

[0053] Furthermore, it was recognized that by providing at least one functional layer with the aforementioned thicknesses, the coercive field strengths can be influenced and hysteresis losses reduced. In particular, providing at least one functional layer with the aforementioned low thicknesses, while maintaining a fixed overall thickness of the electrical steel strip, enables separation of the magnetically active layers, thus spatially limiting the propagation of eddy currents.

[0054] In the above-described electrical steel strip according to the second teaching of the invention, the at least one additional layer and the at least one functional layer are preferably bonded to one another by an adhesive bond with atomic diffusion. In this way, an electrical steel strip can be provided that combines the advantages attributable to the bonding by an adhesive bond with atomic diffusion and to the aforementioned low thicknesses of the at least one functional layer. This advantageously leads to a particularly significant reduction in core losses. The described bond also makes it possible to achieve, in particular, improved material properties in addition to the magnetic properties. For example, a reduction in internal stresses and increased adhesive strength between the individual layers are achieved through the adhesive bond.

[0055] In a further embodiment of the electrical steel strip, the at least one additional layer has a thickness in a range from 2 µm to 100 µm, preferably in a range from 2 to 60 µm. By introducing at least one, preferably several, additional layers of such a small thickness, the material properties of the composite material can be specifically influenced. In particular, the provision of the described at least one additional layer or several additional layers allows the diffusion of the material of the functional layers through an additional layer. If the additional layer comprises, for example, an electrically insulating material, the electrical insulation of the functional layers from one another can be eliminated if the material of the functional layers diffuses through an additional layer. The thermal conduction between the layers can also be improved by this diffusion.

[0056] The aim when designing the functional layers and additional layers is for them to form continuous layers. However, the magnetic properties can also be improved by using at least one additional layer that is not designed as a continuous layer, or several such additional layers, and in particular the magnetic reversal losses, especially the hysteresis and eddy current losses, can be reduced compared to conventional electrical steel strips. Furthermore, it can be deliberately achieved that the functional layers are in contact with one another, for example by electrical contact. This can have a further positive influence on the electromagnetic properties of the electrical steel strip, especially with specific geometries of the components manufactured from it, and especially in applications where a composite material with variable thicknesses and good electrical conductivity is required.

[0057] According to a further embodiment of the electrical steel strip, the at least one additional layer consists at least partially, preferably entirely, of a metallic material. By using a metallic, but non-magnetizable material for the material of the at least one additional layer, a particularly strong metallic adhesive bond with atomic diffusion can be achieved. This leads to increased durability of the electrical steel strip and thus to a longer service life. Overall, a particularly resource-efficient electrical steel strip is specified. Since metals predominantly exhibit good electrical conductivity and good thermal conductivity, the electrical conductivity and / or thermal conductivity of the electrical steel strip can also be increased, depending on the metallic materials used.

[0058] In a further embodiment, the at least one additional layer comprises copper (Cu), preferably with a copper content in the range of 1 to 15% by mass. Copper is characterized by its high thermal conductivity, thus providing an electrical steel strip with improved thermal conductivity.

[0059] In a further embodiment of the electrical steel strip, the at least one additional layer comprises aluminum (Al), preferably an aluminum content with a mass fraction in the range of 1 to 15%, in particular in the range of 3 to 15%. Aluminum also has high thermal conductivity, so that an electrical steel strip with improved thermal conductivity is also specified in this way.

[0060] An electrical steel strip with improved thermal conductivity allows for improved heat dissipation, for example, the heat generated by induction-based eddy currents. Overall, the heat generated in the electrical steel strip due to core reversal losses can be dissipated more efficiently. Heat can also be better distributed within the electrical component in which the electrical steel strip is used as electrical sheet. Since heat losses increase with increasing speed of an electrical machine and increasing frequency, the electrical steel strip or the electrical sheet made from it can be used particularly advantageously for applications requiring high frequency and speed.

[0061] Furthermore, the provision of at least one additional layer containing aluminum is advantageous because aluminum has a low material density compared to other metallic materials. Thus, the provision of at least one additional layer containing aluminum results in a weight reduction of the electrical steel strip. A weight reduction enables greater flexibility in the application of the electrical steel strip or sheet in electrical and electronic components. This is particularly advantageous for the use of electrical steel strip in moving electrical or electronic elements, as it saves energy required to move these elements.

[0062] In another embodiment of the electrical steel strip, the at least one additional layer comprises zirconium (Zr). Zirconium is characterized not only by high thermal conductivity but also by good corrosion resistance. This increases both the durability and thermal conductivity of the electrical steel strip. Furthermore, the relatively soft and flexible nature of zirconium makes processing the at least one additional layer and / or the electrical steel strip easier and thus more efficient, for example, by rolling, forging, and hammering.

[0063] Furthermore, the at least one additional layer can have a specific thermal conductivity at least equal to, and preferably greater than, the specific thermal conductivity of the at least one functional layer. This results in an overall improved thermal conductivity of the electrical steel strip, resulting in the previously described advantages.

[0064] In a further embodiment, the at least one additional layer consists at least partially, preferably entirely, of an austenitic alloy or an austenitic steel, referred to as austenite for short. By providing at least one additional layer of austenite, a reduction in the magnetic reversal losses, in particular the hysteresis and eddy current losses, can be achieved. By providing at least one additional layer of this paramagnetic material, two functional layers of an electrical steel strip, between which the additional layer is arranged, can be magnetically separated from one another, i.e., insulated. This leads, in particular, to a reduction in the eddy currents caused by electromagnetic induction.

[0065] Furthermore, the provision of at least one additional layer of austenite is advantageous because austenite has advantageous mechanical properties, such as high formability, and is therefore easy to process. This simplifies the production of electrical steel and offers increased flexibility for applications. Austenitic steels and alloys also exhibit high resistance to aggressive environmental conditions, particularly corrosion. This can increase the durability of electrical steel and extend its service life.

[0066] In particular, it has proven advantageous to provide at least one additional layer of austenite which has been subjected to a heat treatment at a temperature in the range of 650 to 1000°C, preferably 670°C or 1000°C.

[0067] In a further embodiment, the at least one additional layer consists at least partially, preferably entirely, of Damascus steel, also called damask steel. The use of damask steel allows the combination of different steels with different advantages in one material. For example, the at least one additional layer can thus consist of a material that is both flexible and has excellent edge retention. This is advantageous for the processing and subsequent application of the electrical steel.

[0068] Furthermore, the at least one additional layer can be made at least partially, preferably entirely, of a non-metallic material, preferably a carbon (C)-containing material, particularly preferably graphene or graphite. Non-metallic materials generally have very low to negligible electrical conductivity, making such materials well-suited as at least one additional layer for insulating the at least one functional layer. The provision of non-metallic materials can also positively influence other material properties of the electrical steel strip.

[0069] Due to the inherent high thermal conductivity of graphene or graphite, one embodiment provides an electrical steel strip with improved thermal conductivity, so that heat generated, for example, by loss processes in the electrical steel strip can be dissipated more quickly. Furthermore, graphene or graphite is a very flexible, pliable, transparent, and extremely tensile material, thus improving the mechanical properties and, in particular, the processability of the composite material comprising at least one functional layer and at least one additional layer.

[0070] In a further embodiment, at least two functional layers comprise different ferromagnetic materials and / or at least two additional layers comprise different non-magnetizable materials. This makes it possible to provide an electrical steel strip that offers high flexibility in the combination of different materials and thus improved optimization options for different applications. For example, it is possible to provide higher proportions of certain alloying elements in the outermost layers of the electrical steel strip, which, for example, contribute to improved corrosion resistance of the outer layers.

[0071] Furthermore, it is preferred that the material properties in the at least one functional layer and / or in the at least one additional layer vary. Thus, different ferromagnetic properties or different electrical or thermal conductivities can be set and achieved in the surface of the layers. For this purpose, different materials are arranged in sections in one of the layers before joining, which are then bonded to one another after joining, in particular after plating. Thus, for example, a stator can be produced for a specific electric motor design in which high thermal conductivity is provided inside the motor with at least one additional layer containing copper for dissipating the resulting heat energy and at least one additional layer containing aluminum outside the motor for weight reduction.

[0072] The proportions of alloying elements with different diffusion properties can also be varied within the layers, for example, in different additional layers and / or in different functional layers. With external heat input that gradually diminishes as the material enters the interior, it is possible to achieve uniform thermal diffusion across the entire thickness of the electrical steel strip. Alloying elements that act as diffusion barriers can also be incorporated into individual layers. This allows for a targeted influence on the electrical properties in different areas of the electrical steel strip, particularly during its production.

[0073] Preferably, different regions of the three-dimensional structure of the electrical steel strip have different material properties, in particular different magnetic properties. This enables the production of a pattern of electrically conductive and / or magnetically connected regions within an electrical steel strip. Furthermore, the introduction of alloying elements is possible to specifically influence the microstructure, for example, to bind impurities at grain boundaries. In this way, the magnetic reversal losses of the electrical steel strip can be further reduced by using purer materials, in particular purer functional layers. In particular, by providing anisotropic microstructures, different material properties can be achieved in a direction parallel to the layer plane and in a plane orthogonal to the layer plane.

[0074] Furthermore, when using multiple functional layers, it is possible for at least two functional layers or multiple functional layers to have different thicknesses. Likewise, when using multiple additional layers, these additional layers can have different thicknesses. This allows for an electrical steel strip with high geometric flexibility for targeted adaptation to the available installation space in the respective application. This allows for particularly fine-tuning of optimized material properties of the electrical steel strip.

[0075] According to a further preferred embodiment for solving the above-mentioned technical problem, an arrangement of electrical strips, in particular of electrical sheets, is specified, wherein at least two electrical strips are arranged in a stack and wherein a separating layer, in particular a lacquer layer, is provided between at least two electrical strips and wherein the electrical strips are designed according to one of the preceding embodiments.

[0076] Such an arrangement or stack is also called a lamination stack and can be used, for example, as part of the stators and / or rotors of an electric motor. Due to the improved properties of the individual electrical steel strips, particularly with regard to core losses, the power transmission via the lamination stack can be improved by conducting and amplifying magnetic fields. The separating layer serves to insulate the individual electrical steel strips from each other and further optimizes the efficiency of the lamination stack by reducing core losses.

[0077] The technical problem outlined above is also solved according to a further teaching of the invention by using an electrical steel strip, in particular an electrical sheet, as an iron core, wherein the electrical steel strip is designed according to one of the previously explained examples and variants. In particular, the electrical sheet is used as the iron core of an electromagnet, in particular in a transformer or in an electric motor, or for relays, switches, contactors, choke coils, ignition coils, electricity meters, and controllable deflection magnets.

[0078] An iron core, also called a magnetic core, is a component from which, together with electrical conductors and mechanical parts, an electrical or electronic component, also called an inductor, can be manufactured. Iron cores made of electrical steel sheets are characterized primarily by their scalable sizes and are used in a wide variety of applications, from small matchbox-sized power transformers to transformers and electric motors and power plant generators.

[0079] The use of an electrical steel strip according to one of the previously explained examples and variants as an iron core enables great flexibility with regard to the size of the electrical or electronic component while simultaneously optimizing energy conversion. In particular, by using at least one functional layer with the aforementioned low thicknesses, the thickness of the electrical steel strip can be flexibly designed and, in particular, reduced. Furthermore, it has been recognized that by using an electrical steel strip according to one of the previously explained examples and variants as an iron core, the remagnetization losses, in particular the hysteresis and eddy current losses, of the iron core can be reduced.By constructing the electrical steel strip as a composite material having the previously described at least one functional layer and the previously described at least one additional layer, the eddy currents caused by electromagnetic induction are spatially limited to the at least one functional layer, so that eddy current losses can be reduced.

[0080] The use of multiple electrical strips, which can be arranged one above the other in a stack, for example, as the iron core is also particularly advantageous. The multiple electrical strips in the stack can be bonded or otherwise connected to one another by means of a separating layer, in particular a lacquer layer.

[0081] An electrical steel strip characterized by the bond described above through adhesion formation with atomic diffusion allows the targeted modification of material properties that significantly influence the design parameters of an iron core. For example, the weight of the iron core can be reduced by providing at least one additional layer with a lower material density compared to the at least one functional layer. Furthermore, through targeted material selection of the at least one additional layer and the described bond, an electrical steel strip and thus an iron core with improved thermal conductivity can be realized. This is particularly advantageous at high power densities, which can quickly lead to overheating of the iron core. Thus, the use of the described electrical steel strip also enables operation of the electrical or electronic component at higher temperatures.Overall, energy conversion can be made more efficient by using the described electrical steel strip as an iron core.

[0082] The described electrical steel strip is advantageous for use as an iron core, as a magnetic core for low-frequency (mains frequency down to a few kHz) applications, and for high and very high power applications up to the megawatt range. In particular, the previously described electrical steel strip can be used advantageously as an iron core for stators or in transformers, as well as for electrical machines in general. By selecting the appropriate materials, other properties of an iron core, such as tensile strength, can also be influenced.

[0083] The technical problem outlined above is also solved according to the invention by a method for producing an electrical steel strip, in which at least one functional layer is provided, wherein the at least one functional layer consists at least partially, preferably completely, of a ferromagnetic material, in which at least one additional layer is provided, wherein the at least one additional layer consists at least partially, preferably completely, of a non-magnetizable material, in which the at least one functional layer and the at least one additional layer are arranged adjacent to one another, in particular one above the other, and in which an adhesive bond with atomic diffusion is produced 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 is brought to a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm.

[0084] The process enables a customized composite structure from layers of different materials as well as a variation in the layer thicknesses of the individual layers with high adhesive strength between the layers. In particular, the at least one functional layer and the at least one additional layer are bonded together to form a composite material. Overall, this enables a targeted adaptation of the properties of the electrical steel strip to a variety of applications. In particular, the targeted material selection of the layers can positively influence the magnetic properties of the electrical steel strip and reduce remagnetization losses, particularly advantageously eddy current and hysteresis losses. Furthermore, the selection of materials with different thermal expansion can positively influence the interaction between the layers and the resulting stresses.For example, by compensating for the thermal expansion between the layers, the overall thermal expansion of the electrical steel strip can be reduced. This allows for an optimized design of the component, such as the motor, in which the electrical steel strip is used as electrical sheet.

[0085] In this process, a different material is used for the at least one functional layer than for the at least one additional layer. This produces a composite material with properties that lie between the extreme values ​​of the material-specific properties of the bonding partners. The above-mentioned process also allows for varying the layer thicknesses of the individual layers, allowing the desired properties of the electrical steel strip to be further influenced in a targeted manner.

[0086] Preferably, the at least one functional layer consists at least partially, preferably entirely, of a ferromagnetic material, in particular of one of the above-mentioned ferromagnetic materials. Further preferably, the at least one additional layer consists at least partially, preferably entirely, of a non-magnetizable material, in particular of one of the above-mentioned materials. Other material combinations, for example, metallic materials or carbon-containing materials, in particular graphene, are also possible.

[0087] The process also enables the production of an electrical steel strip with multiple functional layers and multiple additional layers, with the functional layers and additional layers preferably being arranged in an alternating sequence. For example, it is possible to produce a composite material with insulating additional layers. Preferably, an adhesive bond with atomic diffusion is created between each additional layer and each functional layer by applying pressure.

[0088] Alternatively, several functional layers or several additional layers can be arranged adjacent to one another, so that by using layers of uniform thickness, the thickness of a layer consisting of similar layers can be varied. For example, by arranging several functional layers one above the other, a functional layer layer with a variable thickness that represents a multiple of the thickness of a single functional layer can be created. Arranging several additional layers one above the other can also enhance the insulating effect of the functional layers adjacent to the additional layer layer.

[0089] In the above-mentioned process, the bonding partners, in this case the at least one functional layer and the at least one additional layer, are arranged adjacent to one another and brought into close contact, in particular within atomic distances. The superimposition of the layers can be preceded by a cleaning process in which the contacting surfaces are freed of, for example, absorbed gases, oxide layers, or contaminants such as oil residues.

[0090] The cleaning process, and in particular the removal of oxide layers, increases the bonding capacity of the surfaces of the bonding partners. The oxide layers and, in general, the surface layers of the bonding partners can also be broken down or roughened by further processes, such as forming, to increase surface reactivity. Other processes such as rolling or stretching are also used to strengthen near-surface areas of the bonding partners and create highly active surfaces.

[0091] By applying pressure, the surfaces to be joined are brought into close contact over a large area. This pressure can also be applied in conjunction with other processes, such as a forming process. The bond formed by the adhesive bond between the bonding partners is formed by mixing via atomic diffusion, whereby a transition layer is formed through which a continuous adaptation of the material properties takes place. It is also possible to introduce further energy in the form of heat, which can enhance atomic diffusion. However, an adhesive bond with atomic diffusion can also be created without the additional introduction of heat. The introduction of pressure, for example by pressing the bonding partners together, and the introduction of further energy, for example in the form of heat, can occur simultaneously or at different times.

[0092] The introduction of additional energy can also influence the expansion of the transition layer, although this generally depends on the respective materials of the bonding partners. Enlarging the expansion zone and increasing atomic diffusion can be used specifically to influence the material properties of the electrical steel strip. For example, enlarging the expansion zone and increasing atomic diffusion leads to greater mixing of the composite material, which can promote increased electrical conductivity and / or thermal conductivity and increased dimensional stability of the electrical steel strip.

[0093] In addition, the microstructure of the composite material can be specifically influenced by the introduction of energy and heat. For example, recrystallization of the materials, for example, of the at least one functional layer and / or the at least one additional layer, can occur. The degree of hardening of the materials, for example, of the at least one functional layer and / or the at least one additional layer, can also be influenced.

[0094] The process described above can be understood, for example, as plating, although in English usage, the term "cladding" can primarily be used to describe such a process. The process described above primarily creates a metallic bond between two bonding partners. An adhesive bond with atomic diffusion between metallic materials and non-metallic materials, such as carbon-containing materials, or between non-metallic materials can also be created.

[0095] According to a preferred embodiment of the method, at least one of the at least one functional layer and / or at least one of the at least one additional layer is heat-treated. Heat treatment can be used to specifically influence material properties, in particular the microstructure. Individual or multiple layers can be heat-treated separately before joining, or multiple layers can be heat-treated together during or after joining.

[0096] Heat treatment of individual layers prior to joining offers the possibility of specifically influencing the material properties of only some of the multiple layers of an electrical steel strip, for example, the outermost layers. This allows the microstructure and the resulting electromagnetic properties of individual layers to be specifically modified. For example, heat treatment can lead to increased grain growth or the formation of precipitates of individual elements, especially alloying elements.

[0097] Heat treatment of multiple layers during bonding can enhance atomic diffusion between the layers and thus increase the bond strength of the layers to be bonded. Heat treatment after bonding can further adjust the material properties, particularly the microstructure, and can also further increase the bond strength.

[0098] In a further preferred embodiment of the method, the at least one functional layer and the at least one additional layer are joined together by cold roll bonding. This makes it possible to separate the forming and diffusion processes during the production of an electrical steel strip.

[0099] A composite can also be further processed by cold roll cladding in the same way as a homogeneous material can be further processed by cold rolling.

[0100] During the cold-roll cladding process, the bonding partners, in this case, for example, the at least one functional layer and the at least one additional layer, can first be pretreated. Here, the materials to be plated are degreased and activated shortly before the cladding process, typically by matting with steel wire brushes. For some materials, activation may not be necessary. In the next step, the layers to be joined are cold-rolled together, which can result in a significant reduction in thickness combined with a considerable elongation of the material combination.

[0101] Before and / or during cold roll cladding, it can be advantageous if at least one of the layers is heated, with a temperature of 50 to 500°C being preferred. Preheating can also be carried out by indirect material heating by heating the system in which the cold roll cladding is carried out. Preheating is not the same as hot roll cladding, as temperatures close to the melting point are selected here. The heating temperature improves the reactivity of the layer surfaces, allowing the layers to bond more effectively. The temperatures subsequently generated during cold rolling due to stretching of the material and surface cracking are then, for example, in the range of up to 400°C. During cold rolling, additional heating can also be provided at temperatures below the recrystallization temperature of the rolled stock.

[0102] By applying high pressure during rolling, new, highly active surfaces can be created between the layers to be joined under the absence of air, allowing them to be brought into close contact with one another. Adhesive forces, mechanical clamping, and the beginning of bonding at certain points can achieve initial adhesion between the layers to be joined.

[0103] Directly following the plating process, adhesion annealing or diffusion annealing can be performed. Heat treatment activates or enhances rearrangement processes at the atomic level, allowing incompletely bonded layers to be converted into a composite. However, for some material combinations, the adhesion generated during plating is already sufficient, making adhesion annealing unnecessary. Heat treatment can optimize the process parameters to prevent or minimize the formation of intermetallic layers. In addition, recrystallization of materials that may have been severely strain-hardened by the plating process can occur. This restores the material's forming potential, which is necessary for further processing.

[0104] In a subsequent step, the composite material can be rolled almost to its final thickness. A further heat treatment can also be performed to adjust the strength and microstructure properties of the electrical steel strip. For very thin final dimensions, it may be necessary to perform multiple rolling and / or annealing cycles due to the high overall deformation. On the other hand, especially for thicker final dimensions, it is also possible to directly plate to the final thickness, omitting a subsequent rolling process.

[0105] Subsequently, skin-pass rolling, a finish rolling process with a low degree of deformation, can be performed, as can a stretch-bend leveling process, in which the material composite can be subjected to any yield point elongation that may occur in the annealed state. Different roll roughnesses can simultaneously achieve specific surface finishes – from rough to bright, or even isotropic or structured, e.g., by laser structuring (etching) of the surfaces or indirectly by laser structuring (etching) of the rolls used. Skin-pass cutting can also be omitted, especially if specific surface finishes are not important.

[0106] Furthermore, particularly as a final process step, longitudinal cutting can be provided, in which the material is cut lengthwise to the final width and / or trimmed at the edges.

[0107] According to an alternative embodiment of the method, the at least one functional layer and the at least one additional layer are bonded together by hot-roll cladding. During hot-roll cladding, the layers are bonded during a hot-rolling process at temperatures above the recrystallization threshold. For this purpose, the layers to be bonded are typically assembled into a stack prior to rolling and hot-rolled as a complete unit. The bond can occur simultaneously through diffusion processes, which require a specific temperature for activation.

[0108] According to another alternative embodiment of the method, the at least one functional layer and the at least one additional layer are bonded together by explosive plating. By manufacturing by explosive plating, no thermal energy is introduced during the plating process, thereby preventing the formation of brittle intermetallic phases.

[0109] Regardless of the specific embodiment of the process described above, the electrical steel strip is typically in the form of a strip after joining. The strip-shaped electrical steel strip can be further processed after carrying out the process according to the invention, particularly after plating, for example, formed, cut, and joined. Due to its good adhesive properties, it is possible to form the electrical steel strip like a homogeneous material. Forming processes typically used include rolling, bending, deep drawing or stretch drawing, hydroforming, or roll forming.

[0110] Furthermore, mechanical separation, such as cutting or punching, can be provided. Thermal separation processes and laser processing are also possible. Furthermore, chemical etching, wire EDM, or waterjet cutting can be used. These processes advantageously do not increase, or only insignificantly increase, the k-form factor when calculating the core losses. The provision of additional layers, in particular comprising non-magnetizable materials, preferably materials containing aluminum, can also offer advantages with regard to material properties influenced by the separation process. For example, by providing additional layers comprising corrosion-resistant materials, for example materials containing aluminum or other reactive alloying elements, corrosion can be delayed, particularly at the cut edges of an electrical steel sheet.

[0111] Individual electrical steel strips can be joined to form a package, a process generally referred to as packaging. A package consisting at least partially, preferably entirely, of at least one electrical steel strip according to the invention allows for virtually unchanged further processing in known, standardized processes, thus eliminating the need to adapt any further process steps that may follow the process according to the invention.

[0112] A single-step process known as punch-packing, in which the electrical steel strip is punched out, placed on a stack and joined to the stack, can also be provided.

[0113] Further features and advantages of the invention will become apparent from the following description of embodiments, with reference to the accompanying drawings.

[0114] In the drawing show Fig. 1a-d various embodiments of an electrical steel strip according to the invention in the form of an electrical steel sheet, Fig. 2a-b steps of an embodiment of the method according to the invention for producing an electrical steel strip in the form of an electrical steel sheet in a schematic representation, Fig. 3a-b results of tests on various electrical steel strips in the form of electrical steel sheets and Fig. 4a-b hysteresis measurements on various electrical steel strips in the form of electrical steel sheets.

[0115] 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 provided with the same reference numerals, even if the components and elements in the various embodiments may have differences in their dimensions or shape.

[0116] The embodiments relate to electrical sheets, which are described as examples of electrical strips.

[0117] The Fig. 1a bis Fig. 1d first show various embodiments of an electrical steel sheet 2 according to the invention.

[0118] In Fig. 1a In the form of a section of a micrograph, a structure of an electrical sheet 2 is shown comprising several functional layers 4 made of a ferromagnetic material and additional layers 8 arranged one above the other, wherein the functional layers 4 and the additional layers 8 are each arranged in an alternating sequence.

[0119] Functional layers 4 are made of ferromagnetic hot-rolled steel of grade DD11 (1.0332). The grain structure of the ferromagnetic material of functional layers 4 is characterized by grain sizes of less than 100 µm, with many of the grain sizes in the range of 20 to 50 µm.

[0120] In this example, the additional layers 8 are formed as continuous layers and separate the functional layers 4 from each other. The non-magnetizable material of the additional layers 8 comprises copper (Cu).

[0121] In the present case, an electrical steel sheet 2 with functional layers 4 of approximately constant thickness (layer thickness) d 1i where i indicates the respective functional layer 4 and runs from 1 to n, with n being the total number of functional layers 4. Here, therefore, d 11 = d 12 = d 13 =...= d 1n , The thicknesses are approximately constant, but vary across the width of the display due to manufacturing reasons.

[0122] Alternatively, the functional layers 4 can be made with thicknesses d 1i , for which applies d 11 ≠ d 12 ≠ d 13 ≠...≠ d 1n , which therefore have different thicknesses d 1i Only some of the functional layers 4 can have different thicknesses d 1i and other functional layers 4 approximately constant thicknesses d 1i . The same applies to the thick d 2i the additional layers 8.

[0123] As can be seen from the scale in Fig. 1a can be seen, layer thicknesses d 1i and d 2i consistently well below 100 µm, especially less than 60 µm.

[0124] In Fig. 1b is also shown using a section of a micrograph of a structure of an electrical steel sheet 2, likewise comprising a plurality of functional layers 4 and additional layers 8 arranged one above the other, wherein the functional layers 4 and the additional layers 8 are each arranged in an alternating sequence. The functional layers 4 are again made of DD11 steel. In this example, the additional layers 8 are designed as discontinuous 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 comprise the non-magnetizable material aluminum (Al). The microstructure of the ferromagnetic material is particularly fine-grained, the thickness of the functional layers 4 is less than 25 µm and the additional layers have a thickness of just a few µm.

[0125] Fig. 1c and 1dalso show, in the form of a section of a micrograph, the structure of electrical steel sheets 2 comprising a plurality of functional layers 4 and additional layers 8 arranged one above the other, wherein the functional layers 4 and the additional layers 8 are each arranged in an alternating sequence. The functional layers 4 are again made of DD11 steel. In this example, the additional layers 8 are designed as particularly thin and partially discontinuous layers, so that here too, contact between the functional layers 4 is possible in some places. Here, too, the presence of an inhomogeneous material in the functional layers 4 is clearly visible, wherein the different shades of gray in individual functional layers 4 indicate a varying composition of the ferromagnetic material.

[0126] The thickness of the functional layers 4 is on average less than 75 µm. In the Fig. 1c and 1dIn the examples shown, the non-magnetizable material of the additional layers 8 comprises an austenitic steel (austenite). 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 µm and below at the selected resolution, but they nevertheless enable intact isolation of the functional layers 4 from one another.

[0127] The Fig. 1a-d The functional layers 4 and additional layers 8 of the exemplary embodiments of an electrical steel sheet 2 shown are connected to one another by an adhesive bond with atomic diffusion. In particular in Fig. 1b At the microscopic level, an interdiffusion of the different materials of the functional and additional layers 4, 8 can be seen.

[0128] In Fig. 2a and 2bSteps of an embodiment of the method according to the invention for producing an electrical steel sheet 2 are shown in a schematic representation.

[0129] Fig. 2a shows the process sequence with a cold roll cladding device 18, in which an electrical steel strip 2 is produced through various process steps. This can, for example, be an electrical steel sheet 2 according to the Fig.1a-d shown embodiments.

[0130] In a first process step 20, the bonding partners are pretreated; in this case, the pretreatment of the material of the additional layer 8 is shown. In this first process step 20, a pre-cleaning step 20a, including degreasing the surfaces, and an activation step 20b, in which the surfaces are mechanically torn open, are performed. In the example shown, the material supplied 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.

[0131] Next, the layers 4, 8 to be joined are cold-rolled together, resulting in a significant reduction in thickness. This example shows the joining of an additional layer 8 of the material with two functional layers 4 of the material. The rollers shown in Figure 20c exert pressure on the layers 4, 8 to be joined, bringing the layers 4, 8 into intimate contact with each other at the atomic level.

[0132] It can also be provided that the steps shown in process step 20 within the scope of pretreatment, i.e. 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 selected material, is not pretreated before joining the layers 4, 8. Thus, a process can also be provided in which Fig. 2a In the process step 20 shown, the material of the functional layers 4 replaces the material of the additional layers 8 and the pretreatment is carried out on a functional layer 4 of the material before joining with additional layers 8 of the material.

[0133] Fig. 2b shows an enlarged section of the formation of an electrical steel strip 2 by adhesive bonding 12 with atomic diffusion 14. This adhesive bond 12 of the materials of the respective functional layer 4 and additional layer 8 to be joined is already initiated in the first process step 20. For some material combinations, this adhesive bond 12 is already sufficient for an electrical steel strip 2.

[0134] In this case, according to Fig. 2a In a further process step 22, adhesion annealing, also called diffusion annealing, takes place, in which further rearrangement processes 14 are activated or enhanced at the atomic level by means of heat treatment, and still incompletely bonded layers 4, 8 can be converted into a composite. However, for some material combinations, the adhesion generated during cladding is already sufficient, so that adhesion annealing can be dispensed with. This is because, regardless of whether cold or hot rolling was used, diffusion bonding is already generated during cladding.

[0135] After adhesion annealing, the electrical steel strip 2 is rolled again in a next step 24, during which it is rolled almost to its final thickness. In addition, a further heat treatment, also called batch annealing, can be performed in a subsequent step 26 to adjust the strength and structural properties of the electrical steel sheet 2. Process steps 24 and 26 can be performed multiple times, especially for very thin final dimensions. However, a single rolling / annealing cycle 24, 26 may also be sufficient, especially for thicker final dimensions.

[0136] In Fig. 2a A further process step 28, skin-pass rolling, is shown. This refers to a finish rolling process with a low degree of deformation, in which any yield point elongation that may occur in the soft-annealed state can be removed from the material composite 32. In this step 28, specific surface finishes of the electrical steel sheet 2 can be achieved simultaneously by rolling with different roll roughnesses. Furthermore, the final process step 30 shown here is slitting, in which the material composite 32 is slitted longitudinally to its final width.

[0137] In Fig. 3a and 3bThe results of tests on various electrical steel sheets are shown in tables, comparing embodiments of an electrical steel sheet 2 according to the invention with reference sheets from the prior art, wherein the reference sheets R1 and R2 are made of DD11 steel. The reference sheet R1 is heat-treated at approximately 670 °C after production, and the reference sheet R2 is heat-treated at approximately 1000 °C after production.

[0138] In the table in Fig. 3a For the embodiments of electrical steel sheets E1, E2, Austenit1 and Austenit2 according to the invention as well as for the reference R1, the material parameters electrical conductivity κ , material density ρ and the respective composition of the electrical sheets, from which the material parameters are calculated as an arithmetic mean over the individual layers.

[0139] While the reference sheet 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 µm thick, and eight functional layers, each 53 µm thick. The electrical sheet designated E1 has a structure and composition according to Fig. 1a The electrical sheets E2, Austenit1 and Austenit2 correspond to the Figuren 1b , 1c and 1d All listed electrical sheets have a total thickness or sheet thickness of 0.5 mm, as specified in column 5.

[0140] The functional layers are made of steel DD11, as described, to ensure comparability with the references R1 and R2.

[0141] The table also serves in Fig. 3a the illustration of the reduced eddy current losses by means of the embodiments of an electrical steel sheet according to the invention 2. In column 6 of the table in Fig. 3a is the eddy current loss factor calculated for the respective electrical sheets 2 k vortex = κ * d 2< / ( 6* ρ ) specified, which according to P wirbel = k vortex ( B max fπ ) 2< indicates the material-specific eddy current loss. In particular, column 7 of the table, which shows the reduction in eddy current loss achieved for the E1, E2, Austenit1, and Austenit2 electrical steel sheets compared to reference R1, clearly demonstrates that these latter electrical steel sheets can significantly reduce eddy current losses, by an average of 90%. This reduction can be attributed in particular to the small thickness of the individual functional layers, each less than 60 µm.

[0142] In the table in Fig. 3b The hysteresis losses achieved with embodiments of an inventive electrical steel sheet, E1, E2, Austenite1 and Austenite2, are compared with the hysteresis losses achieved with electrical steel sheets made of the reference materials R1 and R2. The table compares the material-specific parameters material density ρ, the measured coercive field strength H c and the hysteresis loss of the respective electrical sheets measured at frequencies of 1 kHz and 10 kHz.

[0143] Columns 7 and 8 of the table show the reduction in hysteresis loss achieved using the E1, E2, Austenit1, and Austenit2 electrical steel sheets relative to reference R1 at a frequency of 1 kHz and relative to reference R2 at 10 kHz. A reduction in hysteresis losses is achieved for each of the E1, E2, Austenit1, and Austenit2 electrical steel sheets. At a frequency of 1 kHz, a reduction of at least 14% up to 34% can be achieved, and at a frequency of 10 kHz, a reduction of 1% up to 43%.

[0144] To reduce hysteresis losses, P hyst = ( k H 4 H C B max f ) / ρ a reduction in coercive field strength H c and increasing the material density ρ is advantageous.

[0145] In the present experiments it was found that by means of an electrical steel 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 on the one hand by a reduced coercive field strength H c , shown here for E2, Austenite1 and Austenite2, the hysteresis losses can be reduced. In addition, even with an increased coercive field strength compared to the reference value H c , shown here at E1, the hysteresis loss can be significantly reduced, whereby this reduction is not only due to the increase in the arithmetic mean of the material density ρ.

[0146] By using an inventive electrical steel sheet 2 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 to separate the individual functional layers 4 with a thin thickness of the functional layers 4 according to the invention, an effect can be achieved by which the hysteresis losses due to structural processes within 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 viewed as an increase in the increased material density that effectively contributes to the electromagnetically relevant remagnetization effects.

[0147] In the Fig. 4a and 4b Hysteresis measurements on various electrical steel sheets are shown, where Fig. 4a The hysteresis loops 34 and 36 measured with the above-explained embodiments E1 and E2 of an inventive electrical steel sheet 2 are compared with the hysteresis loops 38 and 40 measured for the single-layer reference sheets R3 and R4 made of DD11 steel. Reference sheet R3 was heat-treated at approximately 600 °C, and reference sheet R4 is as-rolled and not heat-treated. Both reference sheets also have a sheet thickness of 0.5 mm.

[0148] In Fig. 4b the hysteresis loops 42 and 44 measured with the above-explained embodiments Austenite1 and Austenite2 of an electrical steel sheet 2 according to the invention are compared with the hysteresis loop 46 measured for the above-explained reference sheet R1.

[0149] All in the Fig. 4a and 4b The hysteresis loops 34, 36, 38, 40, 42, 44 and 46 shown were measured at a frequency of 1 kHz.

[0150] The hysteresis loss is proportional to the area of ​​the hysteresis loop passed through in each case, so that it can be seen from the figures that, in comparison to the referenced reference sheets R1, R3 and R4, a lower hysteresis loss was measured in the respective graphs for the embodiments of an electrical steel sheet according to the invention E1, E2, Austenit1 and Austenit2 in each case compared to the referenced electrical steel sheets.

[0151] In particular, the hysteresis loss measured for E2 can be calculated with a value of P hyst = 1647 W / kg compared to all other measured values. The measured hysteresis losses for E1 P hyst = 2280 W / kg, for austenite1 P hyst = 2121 W / kg and for austenite2 P hyst = 2131 W / kg are below the measured values ​​for the reference materials R1 P hyst = 2556 W / kg, R3 P hyst = 2436 W / kg and R4 P hyst = 2732 W / kg.

[0152] All measurements shown demonstrate that a reduction in both hysteresis and eddy current losses is achieved with electrical steel sheets 2 according to the inventive embodiments described above. Overall, the core losses are significantly reduced when using electrical steel sheets 2 according to the invention in electromagnetic components through targeted material selection of the materials for the functional layers 4 and additional layers 8, on the one hand, and through targeted material design, in particular by reducing the thicknesses of the functional layers 4, on the other. This enables optimized energy conversion of electromagnetic components and permits more flexible design, in particular through variably combinable layer thicknesses and variable material selection.

[0153] The Fig. 4a and 4bThe absolute values ​​of the hysteresis curves shown 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 steel sheets according to the invention, different absolute magnetization values ​​may result; however, the relative shape of the hysteresis curves and the improvements explained occur in the same way with other steels.

Claims

1. Electrical strip, - with at least one functional layer (4) at least partially consisting of a ferromagnetic material and - with at least one additional layer (8) at least partially consisting of a non-magnetisable material, - wherein the at least one additional layer (8) and the at least one functional layer (4) are connected to each other, - wherein at least one functional layer (4) has a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm, characterised in - that the at least one functional layer (4) and the at least one additional layer (8) are bonded to each other by an adhesive bond (12) with atomic diffusion (14).

2. Electrical strip according to claim 1, characterised in that the at least one additional layer (8) has a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm.

3. Electrical strip according to claim 1 or 2, characterised in that the at least one additional layer (8) consists at least partially, preferably completely, of a metallic material.

4. Electrical strip according to any one of claims 1 to 3, characterised in that the at least one additional layer (8) has copper (Cu), preferably a copper content with a mass fraction in the range from 1 to 15%.

5. Electrical strip according to any one of claims 1 to 4, characterised in that the at least one additional layer (8) 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%.

6. Electrical strip according to any one of claims 1 to 5, characterised in that the at least one additional layer (8) has a specific thermal conductivity at least equal to, preferably greater than, the specific thermal conductivity of the at least one functional layer (4).

7. Electrical strip according to any one of claims 1 to 6, characterised in that the at least one additional layer (8) consists at least partially, preferably completely, of an austenitic alloy or an austenitic steel.

8. Electrical strip according to any one of claims 1 to 7, characterised in that the at least one additional layer (8) consists at least partially, preferably completely, of a non-metallic material, preferably a carbon (C)-containing material, particularly preferably graphene or graphite.

9. Electrical strip according to any one of claims 1 to 8, characterised in - that at least two functional layers (4) have different ferromagnetic materials and / or - that, when several additional layers (8) are used, at least two additional layers (8) have different non-magnetisable materials.

10. Electrical strip according to any one of claims 1 to 9, characterised in that the material properties vary in the at least one functional layer and / or in the at least one additional layer.

11. Arrangement of electrical strips, in particular electrical sheets, according to one of claims 1 to 10, characterised in - that at least two electrical strips are arranged in a stack and - that a separating layer is provided between at least two electrical strips.

12. Use of an electrical strip according to any one of claims 1 to 10 as an iron core.

13. Method of manufacturing an electrical strip, in particular an electrical strip according to any one of claims 1 to 10, - in which at least one functional layer (4) is provided, - wherein the at least one functional layer (4) consists at least partially, preferentially completely, of a ferromagnetic material, - in which at least one additional layer (8) is provided, - wherein the at least one additional layer (8) consists at least partially, preferentially completely, of a non-magnetisable material, - in which the at least one functional layer (8) and the at least one additional layer (8) are arranged adjacent to one another, - in which an adhesive bond (12) with atomic diffusion (14) is created between the at least one functional layer (4) and the at least one additional layer (8) by applying pressure, and - in which at least one functional layer (4) has a thickness in the range from 2 to 100 µm, preferably from 2 to 60 µm.

14. Method according to claim 13, in which at least one of the at least one functional layer (4) and / or at least one of the at least one additional layer (8) are heat-treated.

15. Method according to claim 13 or 14, in which the at least one functional layer (4) and the at least one additional layer (8) are joined together by means of cold roll cladding or by means of hot cladding.