Method for producing a magnetic sheet, magnetic sheet stack and electric machine

Abstract

The invention relates to a method for producing a magnetic sheet (2), comprising the following steps: - providing a first viscous mass (4), wherein this has auxiliary components (5) and functional components (6) and comprises, as functional components, iron particles (8) having at least 96 wt.% iron, - providing a second viscous mass (10), wherein this also has auxiliary components (5) and functional components (12) and comprises, as functional components (12), an iron-chromium-nickel alloy (14), - applying the first viscous mass (4) to a substrate surface (16) so that a first substructure (18) of the magnetic sheet (2) is formed, - applying the second viscous mass (10) to the substrate surface (16) so that a second substructure (20) of the magnetic sheet (2) is formed, - in such a way that both substructures (18, 20) have a planar extent on the substrate surface (16) exhibit,the height (22) of which is between 30 µm and 500 µm and the substructures (18, 20) each have an interface (26) at their edges (24) over this height (22) and the two substructures (18, 20) meet at least partially at their interfaces (26) and form a boundary line (28) there, wherein the first and the second substructure (18, 20) together form a magnetic sheet green body (30), - thermal removal of the auxiliary components from the magnetic sheet green body (30) and - sintering of the magnetic sheet green body (30) so that a magnetic sheet (2) is formed. The invention is characterized by the following features: - the iron particles (8) of the first viscous mass (4) contain between 0.1 wt % and 1 wt % carbon, - the functional components of the second viscous mass contain silicon particles (34), wherein the proportion of the silicon particles (34) is between 1 wt % and 1 wt % carbon. % and 4,5 wt. % of the functional components (12) of the second viscous mass (10) and - and that during sintering a decarburizing atmosphere prevails in a sintering chamber (32) so that the carbon is at least partially removed from the functional components (6) of the first viscous mass (4).

Description

[0001] The invention relates to a method for producing a magnetic sheet according to the preamble of claim 1, a stack of magnetic sheets according to claim 14 and an electrical machine according to claim 15.

[0002] The performance of electric machines, especially electric motors, is essentially determined by the maximum speed and the achievable torque. Therefore, it is desirable to design electric machines that can mechanically withstand the highest possible speeds. This applies particularly to the rotors of electric machines. Winded asynchronous machines can be used here, but so-called permanent magnet-free synchronous reluctance machines can also be employed. According to the current state of the art, synchronous reluctance machines (SRMs) are manufactured by stamping individual laminations and then bonding perforated magnetic lamination structures together.These state-of-the-art magnetic laminations feature a material with a homogeneous composition and microstructure, which must meet both the mechanical strength requirements at high speeds and the soft magnetic requirements of a magnetic lamination. Furthermore, such a single-component construction of magnetic laminations for rotors in reluctance machines results in lower torques, caused by magnetically conductive webs, which are essential for stability. This design also presents further constraints, as the web structure must be sufficiently wide to absorb the centripetal forces, which increase quadratically with speed, thereby also reducing noise generation.

[0003] Recently, it has become possible to produce two-component magnetic sheets using an additive manufacturing process. This process involves applying (usually printing) two viscous materials with different functional components to a substrate surface using a printing, slip, or spraying method. These viscous materials, which can be printing pastes or slips, for example, are applied to the substrate surface in such a selective manner that each forms a specific functional substructure. Firstly, magnetically advantageous materials are selected to form a substructure of the final magnetic sheet that is important for its magnetic properties. Secondly, a second substructure is applied to ensure the mechanical properties of the final magnetic sheet. These two substructures complement each other in such a way that, from a top view perspective, a two-component magnetic sheet is created.These two adjacent substructures are then subjected to a heat treatment process, in particular a sintering process, so that after sintering and densification of the magnetic sheet green body, which is composed of the two substructures, a magnetic sheet is produced. Such techniques are described, for example, in EP 4342672 A1, EP 3921928 B1, and EP 3788701 A1.

[0004] The problem with these two-component magnetic sheets lies in the fact that the functional components of the respective viscous mass, which are generally inorganic metallic particles, exhibit different shrinkage rates during the sintering process. This leads to stresses at the interfaces between the substructures right from the start of shrinkage and can result, for example, in warping of the magnetic sheet. Such stresses during the manufacturing process, as well as thermally induced (alternating) stresses during rotor operation, in turn reduce the fatigue strength of the magnetic sheet or stack of sheets and the rotor of the electric machine. This, in turn, leads to limitations in the rotational speed and / or lifespan of the rotor in the electric machine. This, in turn, results in a lower maximum power output of the electric machine.

[0005] The invention is therefore based on the objective of providing a method for manufacturing a magnetic sheet, wherein the magnetic sheet has both better mechanical and better magnetic properties compared to the prior art, and enables the provision of an electric machine that ensures higher rotational speeds with better magnetic properties compared to the prior art.

[0006] The solution to the problem consists of a method with the features of claim 1, as well as a stack of magnetic sheets according to claim 14 and an electrical machine according to claim 15.

[0007] The process for manufacturing a magnetic sheet comprises the following steps: Providing a first viscous mass, wherein this has auxiliary components and functional components and comprises as functional components iron particles having at least 96% iron; providing a second viscous mass, wherein this also has auxiliary components and functional components and comprises as functional components iron-chromium-nickel alloy;Applying the first viscous mass to a substrate surface to form a first substructure of the magnetic sheet; applying a second viscous mass to the substrate surface to form a second substructure of the magnetic sheet, such that both substructures have a planar extent on the substrate surface with heights of 30 µm and 500 µm, respectively, and each substructure has an interface at its edges over this height, and the two substructures meet at least partially at their interfaces and form a boundary line there, wherein the first and second substructures together form a magnetic sheet green body; thermally removing the auxiliary components from the magnetic sheet green body and sintering the magnetic sheet green body to create a magnetic sheet structure.

[0008] The invention is characterized by the fact that The iron particles of the first viscous mass contain between 0.1 wt.% and 1 wt.% carbon, the functional components of the second viscous mass contain silicon particles, wherein the proportion of silicon particles is between 1 wt.% and 4.5 wt.% of the functional components of the viscous mass, and that during sintering a decarburizing atmosphere prevails in a sintering chamber, so that the carbon is at least partially removed from the functional component of the first viscous mass.

[0009] The described process differs from the prior art in three main features. First, the iron particles in the initial viscous mass, which forms the magnetically relevant substructure of the subsequent magnetic sheet, contain carbon. This means that a low-alloy (≤ 4%) iron-carbon steel can be used as a functional component. During sintering in a decarburizing atmosphere, this carbon is removed from the material derived from the initial viscous mass, resulting in a steel with a very high iron content and large crystallites, and thus also with very good soft magnetic properties. This steel, sintered in this way, significantly exceeds the soft magnetic properties of iron-silicon alloys otherwise used for magnetic sheets.Simultaneously, silicon particles are added to the functional components of the second viscous mass, which forms the basis for the mechanically load-bearing substructure of the magnetic sheet. During the sintering process, these silicon particles diffuse into the particles of the iron-chromium-nickel alloy, which constitute the main functional components of the second viscous mass. This diffusion of silicon particles into the particles of the iron-chromium-nickel alloy causes the austenitic structure of the iron-chromium-nickel alloy to form or be maintained in the reducing atmosphere during sintering, i.e., the decarburization atmosphere. This allows the second substructure to fulfill its function as a mechanically stabilizing substructure of the magnetic sheet by means of an austenitic steel (resulting from the aforementioned iron-chromium-nickel alloy).

[0010] These three characteristic features result in the formation of a highly magnetically active material from the initial viscous mass, which is made from a conventional low-alloy carbon steel, while simultaneously preserving the austenitic structure of the supporting high-alloy steel. This is particularly advantageous because the low-alloy iron-carbon steel has approximately the same compression temperature as the high-alloy austenitic steel. Consequently, during the so-called co-sintering of two different steels, the warping between the individual substructures or within the entire magnetic sheet is significantly reduced, thus reducing the mechanical and thermal stresses within the magnetic sheet.This in turn leads to a higher load-bearing capacity of the magnetic sheet produced in this way and the resulting stack of magnetic sheets and of a rotor formed from the stack of magnetic sheets for an electric machine, in particular for a reluctance motor.

[0011] The combination of the characterizing features of the invention thus enables the use of iron-based materials for a magnetic sheet consisting of two material phases, whereby the sintering density (especially already at the beginning of the sintering, definition see below) of the two iron-based materials is adapted to each other by the powder mixture and by the corresponding decarburizing gas flow during the sintering process, while their properties differ after sintering - functionally optimized.

[0012] The terms used here are defined as follows: A viscous mass is, depending on its viscosity, a high-viscosity printing paste, a low-viscosity slurry, or a spray paste, which contains auxiliary components such as binders, in particular organic binders and liquefiers, organic solvents, or water. Furthermore, the viscous mass contains the aforementioned functional components, which, in both the first and second viscous masses described, are essentially particles of an iron-based alloy. Depending on the composition, and particularly in the second viscous mass, other functional particles, especially the silicon particles described, are also added to these particles. In advantageous embodiments of the invention, nickel particles are also added to the functional components of the second viscous mass, which will be discussed later.

[0013] The term "application of the viscous material" means that the viscous material is applied to a substrate surface using a suitable method. Stencil printing, or a subcategory of stencil printing namely screen printing, has proven particularly advantageous. Such a method allows the corresponding substructure to be represented with very high precision and well-defined edges. The aforementioned substructure, each formed by a viscous material, and the two substructures (in principle, several viscous materials can be used, and additional functional substructures can be formed if necessary) constitute the overall structure of the subsequent magnetic sheet. The moment both substructures are represented by the viscous materials, it is referred to as a magnetic sheet green body.The magnetic sheet green body comprises all components of the viscous mass, namely the auxiliary components and the functional components. The magnetic sheet green body is generally first dried, causing the liquefiers of the auxiliary components, such as water or organic solvents, to evaporate. At this stage, it is referred to as a dried green body. Subsequently, the additional auxiliary components, binders, especially organic binders, are thermally removed from the green body, particularly through decomposition. In this state, it is referred to as a debound green body or debound magnetic sheet green body.

[0014] The debound magnetic sheet green body is then subjected to a sintering process, whereby sintering is understood as an essentially diffusion-controlled densification of the individual functional particles at elevated temperature. Liquid phases can also be present, at least partially, during a sintering process. The sintering process dissolves pores between the individual functional particles of the former viscous mass by forming so-called sinter necks between the particles, which are thereby brought closer together, resulting in so-called sinter shrinkage and densification. The advantage of the present invention, as described, lies precisely in the fact that the densification temperature, i.e., the temperature at which measurable sinter shrinkage occurs, is very close for both functional components. The densification temperature is therefore the temperature on a dilatometer curve at which the constant length (or...)volume) of the powder body ends and a non-linear compaction of the material occurs.

[0015] The previously described substructures, formed by the two viscous masses in the green magnetic sheet, abut each other at interfaces according to the design of the final magnetic sheet. Each individual substructure has a planar extent and ideally includes a perpendicular edge at its margins, with a height of between 30 µm and 500 µm as described. It should be noted that this represents an idealized state; in actual manufacturing, this is not a 90° edge, and overlaps of the individual material substructures may occur at the interfaces between the two substructures due to positioning inaccuracies. Nevertheless, despite the material overlaps and the resulting potential zones of two different materials, we refer to an idealized interface where the two substructures meet.In a top view of the layout of the magnetic sheet green body or the subsequent sheet stack, this meeting of the two substructures can be observed via a boundary line. In a cross-section, this is referred to as an interface.

[0016] In an advantageous embodiment of the invention, the functional components of the second viscous mass comprise particles consisting of an iron-chromium-nickel alloy and having the following composition: - Chrome 14 to 16 wt.% - Nickel 2 to 18 wt.% - Molybdenum 0.5 to 2 wt.% - Carbon < 0.25 wt.% - Iron Rest.

[0017] In addition, there are unavoidable impurities.

[0018] The described alloy has, or can have, a relatively high nickel content. Since even small amounts of carbon provide significant austenite stabilization (Ni equivalent), a high nickel content in the alloy must be selected to maintain the austenitic structure under the decarburizing atmosphere during sintering. A particularly advantageous steel for this purpose, designated 434L (1.4113), which comprises such an iron-chromium-nickel alloy, provides an excellent starting point for the functional components of the second viscous mass. Nickel can be added to such a steel, a 434L steel, even before powder production, resulting in a nickel content of up to 18%.

[0019] In a further advantageous embodiment, the described steel or a similar alloy is used, and nickel particles, containing essentially pure nickel, are additionally added to the functional components of the second viscous mass. In this way, the nickel can be alloyed into the base steel alloy in situ, i.e., during the sintering process, and the nickel content can be advantageously added for austenite formation. This is because nickel exhibits similar properties to silicon and supports its effect on austenite formation.

[0020] In another advantageous embodiment, the functional components of the first viscous mass comprise particles made of an iron-chromium-manganese alloy composed as follows: - Chrome 0.5 to 1.5 wt.% - Manganese 0.5 to 1.5 wt.% - Carbon 0.05 to 0.25 wt.% - Iron rest - as well as unavoidable impurities

[0021] This is an advantageous low-alloy chromium-manganese steel alloyed with carbon. Typically, this composition includes a so-called 20MnCr5 alloy. This material also exists in small particles and forms at least some of the functional components of the first mass. It has been found that this low-alloy 20MnCr5 steel, or a comparable alloy as described above, exhibits excellent magnetic properties when the carbon is carburized, properties that closely approach the soft magnetic properties of pure iron.The further, complementary advantage of this material is that, as already mentioned, the compression temperature of this material is very close to that of an ice-chromium-manganese alloy and enables a so-called co-sintering of the two materials without causing high mechanical stresses between the individual areas (substructures) in the respective shrinkage range.

[0022] Furthermore, it has been found that—as has long been known for the sintering of pure iron—phosphorus doping of the functional components of the first viscous mass, such as the aforementioned chromium-manganese alloy or the material 20MnCr5, but also of other advantageous low-alloy steels with at least 96% iron, is beneficial. The addition of phosphorus stabilizes the soft magnetic ferritic alpha-iron phases by forming a liquid phase, with a doping content of < 3 wt%, and in particular < 1 wt%, achieving a particularly good effect. The resulting saturation polarization of the soft magnetic material in the magnetic sheet produced in this way is 1.95 T, i.e., this value is very close to that of pure iron and significantly higher than that of FeSi4,5 used in conventional single-phase magnetic sheets.Particularly preferred is the weight fraction of the phosphorus particles in the functional components of the first mass between 0.2 wt.% and 0.9 wt.%.

[0023] The previously mentioned decarburization atmosphere in the sintering chamber serves to remove carbon, particularly from the low-alloy steel introduced as a functional component of the initial mass, in order to achieve the desired soft magnetic properties. Hydrogen is especially suitable as a decarburization atmosphere for this purpose, as it methanizes (i.e., at least partially converts) the carbon contained in the steel to methane. It is advantageous and beneficial if the carbon content of the functional components of the initial mass is reduced to as close to 0 as possible during sintering, but at least to less than 0.1 wt%.

[0024] Furthermore, it is advantageous if the compression temperature of the functional components of the first and second masses lies in a range between 850°C and 1000°C. In particular, the compression temperatures of the two material phases should be as close as possible and preferably no more than 30°C to 50°C apart in order to ensure homogeneous sintering without mechanical distortion.

[0025] Another component of the invention is a stack of magnetic sheets with the features of claim 14, wherein this stack of magnetic sheets is produced from a plurality of stacked magnetic sheets manufactured according to a method according to one of claims 1 to 13.

[0026] Furthermore, an electric machine is part of the invention, comprising a stack of magnetic laminations according to claim 14 as a rotor. In particular, this is a so-called reluctance motor.

[0027] Further embodiments and features of the invention are explained in more detail with reference to the following drawings. These are purely schematic embodiments and do not represent a limitation of the scope of protection. Features with the same designation but in different embodiments are each provided with the same reference numerals.

[0028] This shows: Figure 1 is an exploded view of an electric machine, Figure 2 is a prior art magnetic sheet for a reluctance motor made from a single material phase, Figure 3 is a magnetic sheet green body and a magnetic sheet which are almost identical in their schematic representation, Figure 4 is an alternative magnetic sheet or magnetic sheet green body for Figure 3Figure 5 a-c a schematic sequence of the process for manufacturing a magnetic sheet and a magnetic sheet stack, Figure 6 a schematic illustration of a magnetic sheet stack for a rotor, Figure 7 a highly enlarged schematic representation as a cross-section through a magnetic sheet green body at a boundary line between a first and a second substructure, Figure 8 a dilatometer representation of compaction of different ferrous materials.

[0029] In Figure 1 An exploded view is given to illustrate the construction of an electric machine 54, which comprises a housing 50, a rotor 48, and a stator 52. The rotor 48 includes a laminated core 46, as is found, for example, in Figure 6 is shown, and a conventional sheet metal stack, which is not shown here, is formed by stacking a large number of magnetic sheets 2' on top of each other according to the prior art. Figure 2assembled. The magnetic sheet 2' according to Figure 2 It is a single-component material, consisting of a single iron-based material, for example an iron-silicon alloy, which is designed as a compromise in terms of both mechanical strength against centrifugal forces and mechanical properties, especially soft magnetic properties. The material in Figure 2 The magnetic sheet 2' shown is neither particularly strong nor particularly soft magnetic. Furthermore, it has continuous ribs that have a negative magnetic effect. Such a magnetic sheet 2' according to Figure 2 is suitable, for example, for a reluctance motor.

[0030] In an advantageous further development according to Figures 3 and 4 Magnetic sheet 2 and magnetic sheet green body 30 are shown, which have a two-component design (and in the Fig. 3 and 4(the chosen representation has the same contours and therefore leads to the identical image). Firstly, these magnetic sheet green bodies comprise 30 (the difference between magnetic sheet green body and magnetic sheet is discussed with regard to Figure 5 (discussed in more detail) two substructures. A first substructure 18 comprises a highly pure iron with particularly good soft magnetic properties. This iron material preferably contains more than 94% iron. Such a material is particularly well suited for soft magnetic repolarization and is especially advantageous for use in a reluctance motor. Since this soft magnetic iron material of the first substructure 18 does not have good mechanical strength, a second substructure 20 is produced, which preferably consists of a stainless steel, which in turn preferably has an austenitic microstructure. Both substructures 18, 20 border at least partially on interfaces 26 (compare Figure 7) abut each other and form a common interface 26, which is visible from above as the boundary line 28. The two magnetic sheets 2 or magnetic sheet green body 30 according to Figures 3 and 4 They differ only in the geometric structure of their substructures, which are adapted to different electrical machines.

[0031] Based on Figure 5 The process suitable for manufacturing such a two-component magnetic sheet 2 will be described in more detail. First, the following will be considered: Figure 5aA first viscous mass 4 and a second viscous mass 10 are successively applied to a substrate surface 16 using a stencil printing process via a printing frame 56 and a printing stencil 58 mounted therein. This is done using a stencil printing process with a squeegee 60. The two viscous masses 4 and 10 are printed onto a substrate surface 16 by means of the squeegee and appear in their printed image analogous to a magnetic sheet green body 30, as schematically shown in the Figures 3 and 4The stencil printing process, also known as screen printing when using an additional screen in the stencil, is a preferred method for applying the magnetic sheet green body 30 to the substrate surface 16. A similar structure can also be applied to a substrate surface 16 using a stencil and a slip casting or slip drawing process. Spraying or other additive application methods for viscous materials are also fundamentally suitable for producing the magnetic sheet green body 30.

[0032] The magnetic sheet green body 30 exhibits, as still in Figure 7As explained in more detail below, two different viscous masses are formed, both of which, in addition to the functional components 6, 12, also include auxiliary components 5. The auxiliary components 5, in turn, include liquefiers, for example water, but also organic solvents, and usually organic binders. Therefore, in a thermal process, the following must first be carried out according to... Figure 5b , left section, a so-called debinding process is carried out, which includes a drying step. For this purpose, the magnetic sheet green body 30 is placed in a debinding oven 62, whereby this in Figure 5b This is done schematically using a continuous oven via a conveyor belt 60. Basically, the following can be done in Figure 5bThe described partial steps can also be carried out in closed ovens in individual batches. The magnetic sheet green body 30 is first dried and then thermally debound from the organic binders, which are not described in detail here, by increasing the temperature. This leaves behind another body 30, now referred to as a debound magnetic sheet green body, which is subsequently subjected to a sintering process. The sintering process is shown on the right side of the Figure 5bThis illustrates the process, in which a decarburization atmosphere (not explicitly shown here) prevails within a sintering chamber 32. A reducing gas atmosphere is provided with the aid of hydrogen. However, a decarburization atmosphere can also include other oxidizing agents, such as oxygen, so that the gas components of the decarburization atmosphere remove the carbon from the steel particles of the magnetic sheet green body 30 to be sintered. Once the sintering process is complete and the now sintered magnetic sheets 2 leave the continuous furnace, they are, if necessary, mechanically post-processed and, as in Figure 5c As described schematically, a robot stacks the magnetic sheets 46 on top of each other. Such a magnetic sheet stack 46 is in Figure 6 shown. This is based on the magnetic sheet 2 according to Figure 4 .

[0033] In Figure 7Figure 1 shows a cross-section through a magnetic sheet green body 30, in which the individual components of the viscous mass are schematically illustrated after application to a substrate 38 or to a substrate surface 16. A distinction is made here between the first viscous mass 4 on the left side of the Figure 7 , which forms the first substructure 18. In contrast, on the right side of the Figure 7The second substructure 20, formed by the viscous mass, is shown. First, the first viscous mass and the first substructure 18 will be explained. These are functional components 6, which include, in particular, iron particles 8. The iron particles are a 20MnCr5 steel (d50 grain size of 10 µm, d90 grain size 80 µm), comprising iron, chromium, manganese, and carbon. The exact composition of this specific example is described in reaction equation 1. Furthermore, the viscous mass 4 also contains phosphorus particles 40 among the functional components 6. These particles are embedded between the iron-manganese-chromium particles and interact with them during sintering by diffusion. 20MnCr5 [Fe 0.9763 Cr 1.1 Mn 1.1 C 0.17 ] + 0.45P → (H2) □ Fe 0.9735 Mn 1.1 Cr 1.1 P0.45

[0034] Furthermore, the first viscous mass comprises auxiliary components 5, in particular organic solvents and binders, which are thermally removed from the substructure during the debonding process. The iron particles 8, which form the functional components 6 of the first mass 4, are a low-alloy chromium-manganese steel which, as shown, contains carbon. During the previously described sintering in the decarburizing atmosphere, the carbon is removed from this steel, resulting in a 97% pure iron material with a saturation polarization of 1.95, making it an excellent soft magnetic material for use in the reluctance motor, which can be repolarized very quickly at high rotational speeds.

[0035] On the right side of the cross-section in Figure 7The arrangement of the second substructure 20 with the second viscous mass 10 is shown. This mass comprises, as functional components 12, an iron-chromium-nickel alloy 14, as well as silicon particles 34, which are arranged between the iron-chromium-nickel particles 14. The iron-chromium-nickel alloy is a 434L steel, the composition of which is shown in Equation 2. Furthermore, the functional components 12 of the second mass 10 also include nickel particles 36, which are likewise arranged next to the iron-chromium-nickel particles 14. It has been found that a high nickel content, exceeding that of a conventional 434L steel, stabilizes the austenitic structure, which is desirable in this second substructure 20 and is responsible for the high mechanical strength of the magnetic sheet 2, even during decarburization.This stabilization is primarily ensured by the silicon particles that diffuse into these 434L steel particles during the sintering process. The additional alloying of nickel further enhances this behavior. Thus, starting with a 434L stainless steel powder, the austenitic phase is stabilized by increasing the nickel content. This introduces a non-magnetic, high-strength phase as a new alloy. Its composition ranges from that of 434L steels to that of 316L alloys. The final alloy is formed during heat treatment, i.e., during sintering, through the in-situ alloying of the powder mixture based on fine-grained 434L with fine nickel particles 36 and fine silicon particles 34 (d50 grain size of 1 µm, d90 grain size 10 µm). 434L [FeNi 0.0396 Cr 0.178 Mo 0.01 C 0.003 ...] + 12 Ni+ 1%Si --> [FeNi 0.1596 Cr 0.178 Mo 0.01 S i0.01 C<0.003...]. .

[0036] For example, a base material 434L of GKN Höganäs steel (d50 grain size 10 µm, d90 grain size 80 µm), atomized using the EIGA process, was used with manually added nickel (d50 grain size 10 µm, d90 grain size 80 µm). This resulted in average mechanical properties such as yield strengths of approximately 170 MPa and tensile strengths around 400 MPa. By adding 1% to 4% fine silicon, yield strengths exceeding 300 MPa and tensile strengths exceeding 500 MPa are achieved after sintering in H₂.

[0037] The addition of fine-grained silicon as a pure substance (purity within the range of metallurgically produced silicon with impurities) causes the formation of solid FeSe x (x = 1 to 4 wt.%) due to the high diffusion coefficient of silicon in iron; on the other hand, this leads to a strengthening of liquid-phase-assisted sintering, so that densification is supported, grain growth is stimulated, and porosity is reduced.

[0038] In Figure 8A so-called dilatometer curve is shown, depicting the change in length of samples made of a specific material as a function of temperature in degrees Celsius. The legend describes the so-called 20MnCr5 material, which exhibits similar compaction behavior to a modified 434L material with varying silicon content and an increased nickel content. All four materials shown have a compaction temperature (λ) that lies between 900°C and 1000°C. The compaction temperature (λ) of the 434L material can be altered by adding silicon. However, it is particularly noteworthy that the iron 20MnCr5 material has a compaction temperature (λ) of approximately 950°C, which is very close to that of the 434L material.Unlike pure iron, which has a compression temperature 44 between 600°C and 800°C, the compression temperatures 44 of the material of the first substructure 18 and the material of the second substructure 20 are very close to each other, thus reducing thermal stresses that arise due to this compression of the material during the sintering process. The compression of both substructures 18 and 20 occurs at the same time during the sintering process due to the similar compression temperatures, allowing their changes in expansion to synchronize.

[0039] In summary, the advantage of the present design is that a two-component magnetic sheet can be produced. The magnetically active phase can be a conventional low-alloy steel, such as 20MnCr5 with carbon, which has a similar densification temperature to an austenitic high-strength steel like 434L. Silicon particles stabilize the austenitic structure of the 434L steel, and this structure is retained even after decarburization. However, decarburization during the sintering process is necessary to remove the carbon from the low-alloy steel and thus provide the soft magnetic properties of this otherwise not very suitable soft magnetic material. Reference symbol list

[0040] 2 Magnetic sheet 4 First viscous mass 5 Auxiliary component 6 Functional components 1st mass 8 Iron particles 10 Second viscous mass 1 12 Functional components 2nd mass 14 Iron-chromium-nickel alloy 16 Substrate surface 18 First substructure 20 Second substructure 22 Height of substructure 24 Edges of substructures 26 Interface 28 Boundary line 30 Magnetic sheet green body 32 Sintering chamber 34 Silicon particles 36 Nickel particles 38 Substrate 40 Phosphor particles 42 Sintering temperature 44 Compaction temperature 46 Magnetic sheet stack 48 Rotor 50 Housing 52 Stator 54 Electric machine 56 Printing frame 58 Stencil 60 Doctor blade 62 Debinding furnace 64 Robot arm 66 Conveyor belt Temperature ΔLength change

Claims

1. A method for producing a magnetic sheet (2) comprising the following steps: - providing a first viscous mass (4) comprising auxiliary components (5) and functional components (6), and comprising as functional components iron particles (8) having at least 96 wt.% iron content, - providing a second viscous mass (10) comprising also auxiliary components (5) and functional components (12), and comprising as functional components (12) an iron-chromium-nickel alloy (14), - applying the first viscous mass (4) to a substrate surface (16) such that a first substructure (18) of the magnetic sheet (2) is formed, - applying the second viscous mass (10) to the substrate surface (16) such that a second substructure (20) of the magnetic sheet (2) is formed, - in such a way that both substructures (18, 20) form a planar extent on the substrate surface (16) exhibit,whose height (22) is between 30 µm and 500 µm and the substructures (18, 20) each have an interface (26) at their edges (24) over this height (22) and the two substructures (18, 20) meet at least partially at their interfaces (26) and form a boundary line (28) there, wherein the first and the second substructure (18, 20) together form a magnetic sheet green body (30) - thermal removal of the auxiliary components from the magnetic sheet green body (30) and - sintering of the magnetic sheet green body (30) so that a magnetic sheet (2) is formed, , characterized by the fact that- the iron particles (8) of the first viscous mass (4) contain between 0.1 wt % and 1 wt % carbon, - the functional components of the second viscous mass contain silicon particles (34), wherein the proportion of silicon particles (34) is between 1 wt % and 4.5 wt % of the functional components (12) of the second viscous mass (10), and - that during sintering a decarburizing atmosphere prevails in a sintering chamber (32), so that the carbon is at least partially removed from the functional components (6) of the first viscous mass (4).

2. Method according to claim 1, characterized by the fact that the second viscous mass (10) comprises particles (14) with an iron-chromium-nickel alloy composed as follows: - Chrome 14 - 18 wt. % - Nickel 2 - 18 wt. % - Molybdenum 0.5 - 2 wt. % - Carbon less than 0.25 wt. % - Iron Rest.

3. Method according to one of claims 1 or 2, characterized by the fact that the particles (14) iron-chromium-nickel alloy is a 434L steel.

4. Method according to any one of the preceding claims, characterized by the fact thatthe functional components (12) of the second viscous mass (10) nickel particles (36) are added.

5. Method according to any one of the preceding claims, characterized by the fact that the first viscous mass (4) comprises particles (8) with an iron-chromium-manganese alloy composed as follows: - Chrome 0.5 - 1.5 wt. % - Manganese 0.5 - 1.5 wt. % - Carbon 0.05 - 0.25 wt. % - Iron rest 6. Method according to claim 5, characterized by the fact that the functional components (6) of the first viscous mass (4) comprise particles (8) made of a 20MnCr5 material.

7. Method according to any one of the preceding claims, characterized by the fact that the functional components (6) of the first viscous mass (4) contain phosphorus particles (40).

8. Method according to claim 7, characterized by the fact that the weight fraction of the phosphorus particles (40) is between 0.2 and 0.9 wt. %.

9. Method according to any one of the preceding claims, characterized by the fact that Hydrogen is supplied to the decarburization atmosphere in the sintering chamber (32).

10. Method according to any one of the preceding claims, characterized by the fact that the viscous masses (4, 10) are applied to the substrate surface (16) using a stencil printing process.

11. Method according to any of the preceding claims, characterized by the fact that the carbon content in a soft magnetic area of ​​the magnetic sheet (2), which is formed from the functional components (6) of the first viscous mass (4), is reduced to less than 0.1 wt.% during sintering.

12. Method according to any one of the preceding claims, characterized by the fact that the sintering of the magnetic sheet (2) is carried out at a maximum sintering temperature (42) which is between 1250°C and 1400°C.

13. Method according to any one of the preceding claims, characterized by the fact thata compression temperature (44) of the functional components (6) of the first viscous mass (4) and the compression temperature (44) of the functional components (12) of the second viscous mass (10) is in a range between 850 °C and 1000 °C.

14. Stack of magnetic sheets, composed of a plurality of stacked magnetic sheets (2) produced according to a method according to any one of claims 1 to 13.

15. Electric machine comprising a stack of magnetic laminations (46) according to claim 14 as rotor (48).

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