Method for producing a CoFe alloy

Abstract

Method for producing a CoFe alloy, comprising: Providing a melt consisting of 35 wt% ≤ Co ≤ 55 wt%, 0 wt% ≤ V ≤ 3 wt%, 0 wt% ≤ Ni ≤ 2 wt%, 0 wt% ≤ Nb ≤ 0.50 wt%, 0 wt% ≤ Zr + Ta ≤ 1.5 wt%, 0 wt% ≤ Cr ≤ 3 wt%, 0 wt% ≤ Si ≤ 3 wt%, 0 wt% ≤ Al ≤ 1 wt%, 0 wt% ≤ Mn ≤ 1 wt%, 0 wt% ≤ B ≤ 0.25 wt%, 0 wt% ≤ C ≤ 0.1 wt%, balance Fe, and up to 1 wt% impurities, wherein the impurities are one or more of the may contain group O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W Pouring the molten metal under vacuum and subsequent solidification into a cast block, Hot rolling of the cast ingot into a slab and then into a hot-rolled strip with a thickness D1, followed by quenching of the strip from a temperature above 700°C to a temperature below 200°C, Cold rolling of the hot-rolled strip to an intermediate strip with a thickness D2, Intermediate annealing of the intermediate strip in a continuous process at a temperature above 700°C, wherein the intermediate strip is cooled at a temperature above 700°C to a temperature below 200°C in a gaseous medium, Cold rolling of the heat-treated intermediate strip with a metallically bright surface to a strip with a thickness D3, wherein the degree of cold forming is (D2-D3) / D2 ≤ 80%.

Description

[0001] The invention relates to a method for producing a CoFe alloy.

[0002] Soft magnetic cobalt-iron alloys (CoFe) with a Co content of 49% are used due to their high saturation polarization. A typical CoFe alloy has a composition of 49 wt% Fe, 49 wt% Co, and 2 wt% V, and may also contain additions of Ni, Nb, Zr, Ta, or B. With such a composition, a saturation polarization of approximately 2.3 T is achieved, along with a sufficiently high electrical resistance of 0.4 µΩm.

[0003] Such alloys are used, for example, as highly saturated flux guides or in electrical machines. In generator and motor applications, stators or rotors are typically manufactured in the form of laminated stacks. The material is used in strip thicknesses ranging from 0.50 mm down to very thin dimensions of 0.050 mm.

[0004] To achieve its magnetic properties, the material undergoes a heat treatment also known as magnetic annealing. This heat treatment takes place above the recrystallization temperature and below the α / γ phase transition, typically in the range of 700°C to 900°C. Subsequent cooling results in the establishment of an ordered structure, i.e., the formation of a B2 superstructure.

[0005] Unlike iron-silicon (FeSi) electrical steel sheets, CoFe strip is typically not offered pre-annealed. Annealed strip is soft due to a recrystallized microstructure and simultaneously brittle due to the ordered structure, making it difficult to stamp. Furthermore, cutting or stamping processes lead to a significant deterioration of the magnetic properties. Therefore, CoFe sheets always undergo final annealing after forming, either on sheets, individual laminations, or finished stacks.

[0006] However, the magnetic final annealing and the associated alignment also result in a change in the sheet's dimensions. This increase in length ranges from 0.03% to 0.20%.

[0007] Knowing the growth pattern allows for isotropic growth to be compensated for within certain limits by adjusting the allowance of the stamping tool, and / or the sheets or sheet stacks can be reworked, as disclosed, for example, in WO 2007 / 009 442 A2 A2. Such processes are associated with higher costs and, depending on the geometry, are not always practical.

[0008] Documents US 6 146 474 A, US 3 065 118 A, WO 02 / 055 749 A1 and US 3 634 072 A each disclose FeCo alloys.

[0009] The task is therefore to specify a method for producing a CoFe alloy that exhibits reduced growth after magnetic final annealing.

[0010] According to the invention, in one embodiment, a method for producing a CoFe alloy is provided, comprising the following: First, a melt consisting essentially of 35 wt.% ≤ Co ≤ 55 wt.%, 0 wt.% ≤ V ≤ 3 wt.% .-%, 0 wt.% ≤ Ni ≤ 2 wt.%, 0 wt.% ≤ Nb ≤ 0.50 wt.%, 0 wt.% ≤ Zr + Ta ≤ 1.5 wt.%, 0 wt.% ≤ Cr ≤ 3 wt.%, 0 wt.% ≤ Si ≤ 3 wt.%, 0 wt.% ≤ Al ≤ 1 wt.%, 0 wt.% ≤ Mn ≤ 1 wt.%, 0 wt.% ≤ B ≤ 0.25 wt.%, 0 wt.% ≤ C ≤ 0.1 wt.%, balance Fe and up to 1 wt.% impurities provided, wherein the impurities may include one or more of the group O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W. The molten metal is poured under vacuum and then solidified into a cast ingot. The cast ingot is then hot-rolled into a slab and subsequently into a hot-rolled strip with a thickness of D1. The hot-rolled strip is then quenched from a temperature above 700°C to a temperature below 200°C.The hot-rolled strip is cold-rolled to an intermediate strip with a thickness of D2. This intermediate strip is continuously annealed at a temperature above 700°C and cooled in a gaseous medium at a temperature above 700°C to below 200°C. The heat-treated intermediate strip is then cold-rolled to a strip with a thickness of D3, resulting in a bright metallic surface. The degree of cold working (D2-D3) / D2 is ≤ 80%, preferably ≤ 60%.

[0011] After intermediate annealing of the cold-rolled intermediate strip in a continuous process, no quenching or pickling is performed, so the heat-treated intermediate strip has a metallically bright surface. This heat-treated intermediate strip is then further processed by another cold rolling step with this metallically bright surface. This simplifies the manufacturing process. Furthermore, the degree of cold deformation in the final cold rolling step is limited, which allows the resulting strip, after a final magnetic anneal (i.e., after heat treatment at a temperature between 700°C and 900°C), to exhibit a longitudinal length growth dI / I0 of less than 0.08%, preferably 0.06%, and / or a transverse length growth dI / I0 of less than 0.08%, preferably 0.06%. Here, I0 denotes the initial length before final annealing, dl the absolute length change after final annealing, and dI / I0 the relative length change with respect to the initial length.

[0012] It was found that a key factor influencing the magnitude of this growth is the degree of cold working (KV): the higher the cold working of the material, the more pronounced the length growth after final annealing. By using an intermediate annealing step, the degree of cold working in the final step can be reduced, so that after magnetic final annealing, the strip exhibits reduced length growth.

[0013] The thickness of the strip achieved by hot rolling and / or cold rolling, as well as the thickness of the strip after intermediate annealing, can be defined more precisely. For example, the strip can have a thickness D1 of 1.0 mm ≤ D1 ≤ 2.5 mm after hot rolling, a thickness D2 of 0.1 mm ≤ D2 ≤ 1.0 mm before intermediate annealing, and / or a thickness D3 of 0.05 mm ≤ D3 ≤ 0.5 mm after the second cold rolling.

[0014] In one embodiment, the thickness of the hot-rolled strip is reduced from D1 to D2 by means of cold rolling, and / or the thickness of the intermediate strip is reduced from D2 to D3 by means of cold rolling. No further intermediate annealing is therefore carried out.

[0015] The conditions for intermediate annealing in the continuous process are selected such that the strip can be cold-rolled after intermediate annealing. In one embodiment, after intermediate annealing, the strip exhibits a microstructure in which a ferritically recrystallized portion has a mean grain size of less than 10 µm and / or a ferritically recrystallized portion has no grains larger than 10 µm. This microstructure can be produced, for example, by a temperature of 800°C to 900°C.

[0016] In one embodiment, the intermediate strip exhibits a bending stress of at least 20 in a flexural fatigue test after intermediate annealing. The flexural fatigue test can be used to determine the cold formability of the strip.

[0017] Intermediate annealing in a continuous process can be carried out at a speed of 1 m / min to 10 m / min, and the residence time of the strip in the heating zone of the continuous furnace, at a temperature of 700°C to 1100°C, preferably 800°C to 1000°C, can range from 30 seconds to 5 minutes. Intermediate annealing of the intermediate strip in a continuous process can be performed at a temperature of 800°C to 900°C or 1000°C to 1100°C. Depending on the length of the heating zone of the continuous furnace, the parameters annealing temperature and strip speed can be adjusted to achieve the properties described here.

[0018] After intermediate annealing, the strip can essentially exhibit a deformation microstructure or a mixed microstructure with components of a former γ-phase in a matrix of an α-phase. A deformation microstructure can be achieved, for example, at a temperature of 800°C to 900°C. A mixed microstructure with components of a former γ-phase in a matrix of an α-phase can be achieved at a temperature of 1000°C to 1100°C.

[0019] Intermediate annealing can be carried out under an inert gas or a dry hydrogen-containing atmosphere with a dew point below -30°C. After continuous intermediate annealing, the intermediate strip is cooled to a temperature below 200°C in a gaseous medium such as an inert gas or a dry hydrogen-containing atmosphere. However, the intermediate strip is not quenched, for example, in water.

[0020] In an alternative method not pertaining to the claimed invention, the degree of deformation during hot rolling is adjusted so that the degree of deformation during cold rolling remains below a predetermined limit, thus keeping the linear growth after magnetic final annealing low. This method for producing a CoFe alloy comprises the following. A melt consisting essentially of 35 wt.% ≤ Co ≤ 55 wt.%, 0 wt.% ≤ V ≤ 3 wt.%, 0 wt.% ≤ Ni ≤ 2 wt.%, 0 wt.% ≤ Nb ≤ 0.50 wt.%, 0 wt.% ≤ Zr + Ta ≤ 1.5 wt.%, 0 wt.% ≤ Cr ≤ 3 wt.%, 0 wt.% ≤ Si ≤ 3 wt.%, 0 wt.% ≤ Al ≤ 1 wt.%, 0 wt.% ≤ Mn ≤ 1 wt.%, 0 wt.% ≤ B ≤ 0.25 wt.%, 0 wt.% ≤ C ≤ 0.1 wt.%, balance Fe, and up to 1 wt.% impurities is provided, wherein the impurities constitute one or It may contain several elements from the groups O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W. The molten metal is poured under vacuum and then solidified into a cast block.The cast ingot is hot-rolled into a slab and then into a strip with a thickness D1, where 1 mm ≤ D1 < 2 mm. The strip is then quenched from a temperature above 700°C to a temperature below 200°C. The strip is then cold-rolled, reducing its thickness from D1 to D2, with a cold-working degree (D1-D2) / D1 ≤ 80%, preferably ≤ 60%.

[0021] In this process, the degree of deformation during hot rolling, and thus the thickness D1 of the strip after hot rolling and before cold rolling, is adjusted so that the desired final thickness D2 can be achieved with a degree of deformation of less than 80%, preferably less than 60%. Typically, compared to a conventional commercial process, the degree of deformation during hot rolling is increased and the degree of deformation during cold rolling is reduced accordingly.

[0022] In one embodiment, the final thickness D2 ≤ 0.05 mm ≤ D2 ≤ 0.5 mm. The heat treatment of the strip can take place under a dry, hydrogen-containing atmosphere.

[0023] Both alternative methods can further include forming at least one sheet from the strip. The sheet can be punched from the strip. A large number of sheets can be joined together to form a laminated core. The strip, sheet, or laminated core can also be heat-treated at a temperature between 700°C and 900°C, i.e., a final magnetic annealing can be performed. This heat treatment takes place above the recrystallization temperature and below the α / γ phase transition temperature, usually in the range of 700°C to 900°C. Upon subsequent cooling, ordering occurs, i.e., a B2 superstructure forms, and the desired magnetic properties, for example, a saturation polarization of approximately 2.3 T and an electrical resistivity of 0.4 µΩm, are achieved.

[0024] After this heat treatment of the strip, the growth dI / I0 in the longitudinal direction of the strip is less than 0.08% and / or in the transverse direction of the strip is less than 0.08% and / or the difference between the growth in the longitudinal direction and the growth in the transverse direction of the strip is less than 0.06%, preferably less than 0.04%. Here, I0 denotes the initial length before final annealing, dl the absolute change in length after final annealing, and dI / I0 the relative change in length with respect to the initial length.

[0025] In one embodiment, a semi-finished product is provided which comprises at least one metallic strip consisting essentially of 35 wt.% ≤ Co ≤ 55 wt.%, 0 wt.% ≤ V ≤ 3 wt.%, 0 wt.% ≤ Ni ≤ 2 wt.%, 0 wt.% ≤ Nb ≤ 0.50 wt.%, 0 wt.% ≤ Zr + Ta ≤ 1.5 wt.%, 0 wt.% ≤ Cr ≤ 3 wt.%, 0 wt.% ≤ Si ≤ 3 wt.%, 0 wt.% ≤ Al ≤ 1 wt.%, 0 wt.% ≤ Mn ≤ 1 wt.%, 0 wt.% ≤ B ≤ 0.25 wt.%, 0 wt.% ≤ C ≤ 0.1 wt.%, the remainder being Fe, and up to 1 wt.% The strip comprises impurities, wherein the impurities may include one or more of the group consisting of O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W. The strip has a thickness d, where 0.05 mm ≤ d ≤ 0.5 mm, a Vickers hardness greater than 300, an elongation at break of less than 5%, and, after heat treatment of the strip at a temperature between 700°C and 900°C, a growth dI / I0 in the longitudinal direction of the strip of less than 0.08%, preferably 0.06%, and / or in the transverse direction of the strip of less than 0.08%, preferably 0.06%.

[0026] This semi-finished product therefore exhibits mechanical properties typical of a cold-rolled state, namely an elongation at break of less than 5% and a Vickers hardness greater than 300. This semi-finished product can be further processed, for example, to form sheets from the strip and assemble the sheets into a laminated core, which is then heat-treated to adjust the magnetic properties. This heat treatment of the strip is called magnetic annealing, as it serves to adjust the magnetic properties, and can be carried out at a temperature between 700°C and 900°C.

[0027] The strip enables the production of sheet metal sections, which can then be subjected to a final annealing to achieve optimal magnetic properties, resulting in sufficiently high dimensional accuracy to eliminate the need for further geometric correction. The potential disadvantages of subsequent geometric correction, such as grinding, include a reduction in magnetic permeability at these points, the risk of eddy currents (since grinding processes can cause smearing of the laminations), and higher costs. This allows for the use of smaller air gaps in applications such as stators or rotors, leading to improved efficiency of the electric machine.

[0028] In one embodiment, the strip can have a smaller thickness, for example, 0.05 mm ≤ d ≤ 0.356 mm. Furthermore, the semi-finished product can comprise a plurality of sheets forming a sheet stack.

[0029] In one embodiment, after heat treatment of the strip at a temperature between 700 °C and 900 °C, the difference between the longitudinal growth and the transverse growth of the strip is less than 0.06%, preferably less than 0.04%.

[0030] The CoFe strip with significantly reduced growth has the further advantage that a stamping tool can be designed to be used for both other alloys such as SiFe and CoFe. Given the high cost of such a tool, this results in an economic advantage.

[0031] Various CoFe alloys can be used. In other embodiments, the CoFe alloy has one of the following compositions: 35 to 55 wt.% Co, up to 2.5 wt.% V, balance Fe and up to 1 wt.% impurities, for example 49 wt.% Co, 49 wt.% Fe and 2 wt.% V, 45 wt.% ≤ Co ≤ 52 wt.%, 45 wt.% ≤ Fe ≤ 52 wt.%, 0.5 wt.% ≤ V ≤ 2.5 wt.% balance Fe and up to 1 wt.% impurities, 35 wt.% ≤ Co ≤ 55 wt.%, preferably 45 wt.% ≤ Co ≤ 52 wt.%, 0 wt.% ≤ Ni ≤ 0.5 wt.%, 0.5 wt.% ≤ V ≤ 2.5 wt.%, and up to 1 wt.% impurities, 35 wt.% ≤ Co ≤ 55 wt.%, 0 wt.% ≤ V ≤ 2.5 wt.%, 0 wt.% ≤ (Ta + 2Nb) ≤ 1 wt.%, 0 wt.% ≤ Zr ≤ 1.5 wt.%, 0 wt.% ≤ Ni ≤ 5 wt.%, 0 wt.% ≤ C ≤ 0.5 wt.%, 0 wt.% ≤ Cr ≤ 1 wt.%, 0 wt.% ≤ Mn ≤ 1 wt.%, 0 wt.% ≤ Si ≤ 1 wt.%, 0 wt.% ≤ Al ≤ 1 wt.%, 0 wt.% ≤ B ≤ 0.01 wt.%, balance Fe and up to 1 wt.% impurities, 47 wt.% ≤ Co ≤ 50 wt.%, 1 wt.% ≤ V ≤ 3 wt.%, 0 wt.% ≤ Ni ≤ 0.25 wt.%, 0 wt.% ≤ C ≤ 0.007 wt.%, 0 wt.% ≤ Mn ≤ 0.1 wt.%, 0 wt.% ≤ Si ≤ 0.1 wt.%, 0.07 wt.% ≤ Nb ≤ 0.125 wt.%, 0 wt.% ≤ Zr ≤ 0.5 wt.%, balance Fe and up to 1 wt.% impurities, or 49 wt.% ≤ Co ≤ 51 wt.%, 0.8 wt.% ≤ V ≤ 1.8 wt.%, 0 wt.% ≤ Ni ≤ 0.5 wt.%, balance Fe and up to 1 wt.% impurities.

[0032] CoFe-based alloys are available under the trade names VACOFLUX 50, VACOFLUX 48, VACODUR 49, VACODUR 50, VACODUR S Plus, Rotelloy, HIPERCO 50, Permendur, AFK and 1J22.

[0033] The impurities may include one or more of the group elements O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W.

[0034] Examples of implementation will now be explained in more detail using the drawings and the following examples. Fig. Figure 1 shows a graph of measured mean growth dI / I0 after a final annealing of strips that are cold-rolled to different thicknesses d. Fig. Figure 2 shows a graph of yield strength R p0,2 and tensile strength R m depending on the temperature of the continuous annealing process. Fig.Figure 3 shows optical images of the microstructure of three samples after intermediate annealing at different temperatures. Fig. Figure 4 shows magnetization curves B(H) after various intermediate annealing processes and a final annealing process. Fig. Figure 5 shows a graph of the measured change in length in the rolling direction versus the degree of cold forming for two different samples.

[0035] It has been shown that the length growth of a strip made from a CoFe alloy after final annealing can be reduced by limiting the degree of cold deformation.

[0036] Fig.Figure 1 shows a graph of the measured mean growth dI / I0 in % in the longitudinal direction after final annealing for the 50% CoFe alloys VACOFLUX 50 (49Fe-49Co-2V) and, as a comparison example, HIPERCO 50 (49Fe-49Co-2V). The samples examined had a thickness of 2 mm or greater after hot rolling and were cold-rolled to different final thicknesses, thus subjecting them to different degrees of cold forming. I0 denotes the initial length before final annealing, dl the absolute change in length after final annealing, and dI / I0 the relative change in length with respect to the initial length.

[0037] While hot-rolled material, i.e., with 0% cold working (KV), still exhibits a small length growth in the range of 0.03% to 0.05%, a strip with a thickness of 0.35 mm already shows a growth of over 0.10%. With even higher cold working, e.g., at a strip thickness of 0.10 mm, growth exceeding 0.20% occurs. This change in length growth is likely due to an increasingly pronounced texture. These results demonstrate that a key influencing factor on the magnitude of this growth is the degree of cold working: the higher the cold working of the material, the more pronounced the length growth becomes after final annealing.

[0038] Consequently, these results show that, in principle, the change in length growth can be reduced by reducing the degree of cold working. In principle, the degree of cold working can be reduced by performing an intermediate annealing between two cold working steps, each with a smaller degree of cold working. However, due to the order imparted by an intermediate annealing, a CoFe alloy subsequently becomes brittle and no longer processable. Therefore, the brittleness is conventionally reversed by a subsequent quenching process. However, this quenching process is complex and associated with technical disadvantages and high costs. According to the invention, the reduction of the degree of cold working at a given final thickness is achieved by introducing an intermediate annealing or by reducing the hot-rolling thickness.

[0039] According to the invention, intermediate annealing is carried out in a continuous process such that the work hardening caused by rolling is reduced and, at the same time, a rollable microstructure is created despite embrittlement by avoiding coarse-grained ferrite. Furthermore, the strip is not quenched, for example in water or oil, or pickled after intermediate annealing, so that the strip is cold-rolled with a bright, metallic surface. Consequently, the process is simpler and more cost-effective.

[0040] After intermediate annealing, it is thus possible to carry out further cold forming up to the final thickness. In principle, such a process makes it possible to limit the degree of cold forming at a final thickness of 0.50 mm or less to such an extent that longitudinal growth is simultaneously significantly reduced. According to the invention, the cold forming should be a maximum of 80%, preferably up to 60%, as demonstrated by the following examples and test results. Table 1 Intermediate annealing at thickness Final thickness no additional costs 1.0 mm 0.5 mm 0.35 mm 0.20 mm 0.10 mm 0.35 mm 83 % 65 % (*) 30 % (*) - - - 0.20 mm 90 % 80 % (*) 60 % (*) 43 % (*) - - 0.10 mm 95 % 90 % 80 % (*) 71 % (*) 50 % (*) - 0.05 mm 98 % 95 % 90 % 86 % 75 % (*) 50 % (*)

[0041] Table 1 shows the degree of cold working as a function of final thickness and intermediate annealing. A hot rolling thickness of 2 mm was assumed. Conditions marked with (*) represent conditions according to the invention.

[0042] The material used was a strip of alloy VACODUR 49, with a composition of 48.6 wt% Co, 1.86 wt% V, 0.09 wt% Nb, C < 0.0070 wt%, balance Fe and impurities. The strip was hot-rolled to a thickness of 2 mm and then quenched in an ice-salt water bath at a temperature above 700°C. Subsequently, the strip could be cold-rolled to a thickness of 0.35 mm.

[0043] Intermediate annealing in a continuous furnace was tested on a 6 m long annealing zone. Temperatures of 850°C, 900°C, 950°C, 1000°C, and 1050°C were selected at a speed of 6 m / min. The annealing was carried out under dry hydrogen. The different temperatures for intermediate annealing in a continuous furnace are referred to below as variants 1 to 5.

[0044] Table 2 shows the measured mechanical properties of the continuously annealed strips of variants 1 to 5. Tensile specimens were taken along the rolling direction. Bending cycles were determined on strips (longitudinal / transverse to the rolling direction). A bending test at 900°C and 6 m / min transversely was not available.

[0045] Fig. Figure 2 shows a graph of yield strength R p0,2 and tensile strength R m The tensile test specimens are heated against the temperature T of the continuous annealing process at 6 m / min. The condition Ref. denotes the condition of a specimen without continuous annealing and thus a comparative condition.

[0046] The mechanical properties of these 0.35 mm thick samples show that all continuously annealed variants (1-5) exhibit high elongation at break. Furthermore, the difference R is... m to p0,2 relatively large (>400 MPa), which indicates good plastic deformability. Table 2 variant Intermediate annealing in continuous operation Hardness HV10 E-modulus GPa R p0,2 MPa RmMPa R m -R p0,2 MPa A% #Bending change Sampling longitudinal / transverse reference rolled hard 342 214 1119 1194 75 1,6 >20 / 3-7 1 850°C, 6 m / min 337 243 868 1322 454 16,0 >20 / 15 2 900°C, 6 m / min 256 223 514 798 284 8,0 3 / nv 3 950°C, 6 m / min 233 219 459 865 406 10,6 2-7 / 2 4 1000°C, 6 m / min 247 197 492 1084 592 18,5 >20 / >20 5 1050°C, 6 m / min 266 224 576 1005 429 11,9 >20 / >20

[0047] Further evidence of the differing ductility is provided by the number of bending cycles in the bending cycle test. The conditions designated as variants 1, 4, and 5 show a high number of possible bending cycles in both directions.

[0048] A metallographic examination shows that the different variants have very different microstructures, which can be divided into three groups.

[0049] In variant 1, intermediate annealing at low temperatures leads only to incomplete recrystallization. The microstructure shown here was achieved at a temperature of 850°C as an example.

[0050] In variants 2 and 3, intermediate annealing at 900°C and 950°C respectively leads to a ferritically recrystallized, coarse-grained microstructure.

[0051] In variants 4 and 5, intermediate annealing in the two-phase region α / γ leads to a mixed microstructure with portions of the former γ-phase in an α-matrix. The microstructure shown here was achieved as an example at a temperature of 1000°C.

[0052] Fig. Figure 3 shows optical images of the microstructures of three samples after intermediate annealing at different temperatures. Variant 1 was heat-treated at 850°C at 6 m / min and exhibits good rollability (N > 20), a deformation microstructure, and incipient recrystallization. Variant 3 was heat-treated at 950°C at 6 m / min and exhibits poor rollability (N = 2–7) and ferritic recrystallization. Variant 4 was heat-treated at 1000°C at 6 m / min and shows good rollability (N > 20), a non-uniform ferrite, and a mixed microstructure with portions of the former γ-phase in an α-matrix.

[0053] Table 3 shows the influence of additional cold working on the mechanical properties of continuously annealed VACODUR 49. All annealed strips were rolled on a commercial 20-roll mill. Significant hardening of the material is already evident after the first pass, indicating that the material is in an ordered state. Table 3 variant Continuous annealing Band thickness Hardness HV E-modulus GPa R p0,2 MPa RmMPa A% reference rolled hard 0,35 342 214 1119 1194 1,6 1 850°C 6 m / min 0,35 337 243 868 1322 16,0 0,27 461 210 1541 1570 0,6 0,20 443 214 1505 1549 0,6 0,10 424 215 1399 1470 0,8 2 900°C 6 m / min 0,35 256 223 514 798 8,0 0,33 414 213 1189 1269 4,8 4 1000°C 6 m / min 0,35 247 197 492 1084 18,5 0,10 368 200 1157 1217 0,6

[0054] The strips manufactured according to variants 1, 4, and 5 could be rolled to a thickness of 0.10 mm. In contrast, variants 2 and 3 exhibited significant brittleness and were sensitive to tension. Therefore, the material of variant 2 could not be rolled, and the material of variant 3 could only be rolled to a limited extent.

[0055] Surprisingly, the experiments revealed that it is possible to roll a CoFe strip after continuous annealing, provided that the formation of a coarse-grained microstructure is avoided.

[0056] The length growth after further heat treatment to adjust the magnetic properties at a temperature between 700°C and 900°C, i.e. after a final annealing, is investigated.

[0057] Table 4 shows the length growth (measured in the longitudinal direction) after magnetic final annealing of VACODUR 49, hot-rolled thickness 2 mm. Both variants, i.e., variants 1 and 4, therefore exhibit significantly reduced growth at lower strip thicknesses. Table 4 Reference: no intermediate annealing Variant 1: Intermediate annealing at 0.35 mm at 850°C 6 m / min Variant 4: Intermediate annealing at 0.35 mm at 1000°C, 6 m / min Final thickness KV dI / I0 KV dI / I0 KV dI / I0 0.35 mm 83 % 0,129 % 0 % 0,035 % 0 % 0,032 % 0.20 mm 90 % 0,145 % 43 % 0,055 % 43 % 0,037 % 0.10 mm 95 % 0,195 % 71 % 0,054 % 71 % 0,000 % 0.055 mm - - - - 84 % 0,159 %

[0058] The resulting strip was characterized with respect to its length growth at an intermediate thickness of 0.25 mm and at various final thicknesses of 0.20 mm and 0.10 mm. Measurements were taken on individual strips 165 mm long, the length of which was precisely measured before and after final annealing (6 hours at 880°C under H₂). The change in length dl can be determined from the difference in the measured lengths. Relating this change to the initial length I₀ yields the relative length growth dI / I₀. The measurements listed in Table 4 were always performed longitudinally, i.e., the growth was determined along the rolling direction.

[0059] For the conventionally manufactured reference material, i.e., without intermediate annealing, the length growth at a thickness of 0.35 mm is already 0.129%. With increasing cold working, the growth rises to 0.195% at a thickness of 0.10 mm.

[0060] In contrast, variant 1 according to the invention exhibits a significantly reduced change in length at a final thickness of 0.10 mm. For example, after magnetic final annealing, an average longitudinal growth dI / I0 of 0.054% was measured on the strip at 0.10 mm.

[0061] The band of variant 4 also showed reduced growth. A mean longitudinal growth dI / I0 of 0.000% was measured, with individual values ​​ranging from +0.013% to -0.010%.

[0062] If the cold working after intermediate annealing becomes too high, the growth increases significantly again. In embodiment variant 4 (intermediate annealing at 1000°C, 6 m / min at 0.35 mm), a final thickness of 0.055 mm is obtained, meaning that at 84% cold working, there is already a very pronounced longitudinal growth dI / I0 of 0.159%.

[0063] The anisotropy of growth, i.e., the difference between longitudinal and transverse growth of the band, is investigated.

[0064] Table 5 shows the longitudinal growth of VACODUR 49 samples after an additional final annealing of 6 h at 880°C, measured on tensile specimens or longitudinal strips 165 mm × 20 mm. The roll-hard state, 0.10 mm, was measured on a comparable VACOFLUX 48 sample, also after a final annealing of 6 h at 880°C. Table 5 Growth after additional final annealing (6h 880°C) variant Continuous annealing Final thickness along across |longitudinal - transverse| reference no intermediate annealing 0.35 mm 0.10 mm 0,129 %0,210 % 0,106 %0,110 % 0,023 %0,100 % 1 850°C, 6 m / min 0.35 mm 0.10 mm 0,035 %0,054 % 0,051 %0,052 % 0,016 %0,002 % 4 1000°C, 6 m / min 0.35 mm 0.10 mm 0,032 %0,000 % 0,058 %0,056 % 0,026 %0,056 %

[0065] Variant 1 in Table 5 demonstrates the advantageous property that growth in the longitudinal and transverse directions is almost identical. The difference in growth between the longitudinal and transverse directions, |longitudinal - transverse|, is only 0.002% at a strip thickness of 0.10 mm. This makes it possible to maintain correspondingly symmetrical stamping tools. Stamped round parts remain round after final annealing.

[0066] Variant 4 in Table 5 still exhibits slight anisotropy, but also shows a significantly lower increase in length in magnitude. The difference between the longitudinal and transverse directions (longitudinal - transverse) is considerably smaller at approximately 0.06% of the initial length than the difference observed in conventionally manufactured tape, which is approximately 0.10%.

[0067] Magnetically, both variants exhibit properties at final thickness that correspond to those obtained with the starting material at a thickness of 0.35 mm without continuous annealing. The following figure shows the new curves after magnetic final annealing for various strip thicknesses.

[0068] Fig. Figure 4 shows magnetization curves and the influence of further cold working on the new B(H) curve of continuously annealed strip (850°C, 1050°C; 6 m / min each). The measurements were carried out on stamped rings after a final annealing of 6 hours at 880°C in a dry H₂ atmosphere.

[0069] In the Fig. 4 refers to: (a) a sample with a strip thickness of 0.35 mm, on which no continuous annealing is carried out, (reference) (b) a sample with a strip thickness of 0.35 mm, undergoing continuous annealing at 850°C and 6 m / min (reference) (c) a sample which is subjected to continuous annealing at 850°C and 6 m / min at a strip thickness of 0.35mm and is subsequently cold-formed to a strip thickness of 0.20mm (according to the invention). (d) a sample with a strip thickness of 0.35 mm, on which no continuous annealing is carried out, (reference) (e) a sample with a strip thickness of 0.35 mm, undergoing continuous annealing at 1050°C and 6 m / min (reference) (f) a sample which is subjected to continuous annealing at 1050°C and 6 m / min at a strip thickness of 0.35mm and is subsequently cold-formed to a strip thickness of 0.20mm (according to the invention).

[0070] These results show that the inventive method has little influence on the magnetization curve, so that tape with suitable magnetic properties can be provided.

[0071] The second approach according to the invention consists of reducing the hot-rolled thickness so that, at a final thickness of 0.50 mm or less, the cold forming of the final thickness is a maximum of 80%. The thickness of the hot-rolled strip for CoFe alloys is typically between 2 mm and 4 mm. By reducing it to 1 mm, a reduction in the degree of cold forming and thus in the length growth can be achieved at a final thickness of 0.35 mm.

[0072] Hot-rolled strips were produced in the thicknesses according to Table 6 (WW thickness) and each was cold-rolled to different final thicknesses. Table 6 Final thickness WW thickness 3.5 mm WW thickness 2.0 mm WW thickness 1.5 mm WW thickness 1.0 mm 0.35 mm 90 % 83 % 77 % (*) 65 % (*) 0.20 mm 94 % 90 % 87 % 80 % (*) 0.10 mm 97 % 95 % 93 % 90 % 0.05 mm 99 % 98 % 97 % 95 %

[0073] Table 6 shows the degree of cold forming as a function of final thickness and hot rolling thickness (without intermediate annealing). The conditions marked with (*) represent strips according to the invention.

[0074] Fig. Figure 5 shows a graph of the length growth (dI / I0) of strips of varying hot-rolled thickness made from VACOFLUX 50 along the rolling direction after final annealing against the degree of cold working (D1-D2) / D1. The change in length in the rolling direction versus the degree of cold working is shown for two different samples, A and B, after magnetic final annealing. With a constant cold-rolled thickness D2 of 0.35 mm, the hot-rolled thickness D1 was varied between 1.0 mm and 3.5 mm. For each data point, the corresponding hot-rolled thickness (WW thickness) is marked with an arrow.

[0075] These results show that reducing the WW thickness D1 from 3.5 mm to 2.0 mm already leads to a significant reduction in growth on a sample with a final thickness D2 of 0.35 mm. For an WW thickness of 1.0 mm or less, it is possible to achieve a length growth of < 0.08% after final annealing at a final thickness of 0.35 mm.

[0076] In a further investigation, a 1.5 mm thick hot-rolled strip of VACOFLUX 50 was rolled to a final thickness of 0.50 mm and subjected to a magnetic final annealing (4 h at 820°C, H2). The length growth in this test was only 0.045%. Overall, it can be seen that for a final thickness of 0.50 mm or less, a significant reduction in length growth can be achieved with a correspondingly small hot-rolling thickness.

[0077] In summary, in a specific example, the tape according to the invention is produced via the following method: - Hot rolling to a thickness of 2.5 mm to 1.0 mm - Quenching from temperatures above 700°C - Rollers at intermediate thickness (1.0 mm to 0.20 mm) - Continuous annealing at 700°C to 1100°C, preferably in such a way that no coarse-grained ferritic structure is formed, but rather an incompletely recrystallized or a fine-grained recrystallized ferritic structure. - Rolls with a final thickness of up to 80% cold forming, preferably with up to 60% cold forming

[0078] Alternatively, if the hot strip thickness is below 2 mm, continuous annealing can be omitted as long as the cold forming is up to 80%, preferably up to 60%.

[0079] The tape according to the invention has the following properties: - Composition like usual CoFe ribbons with approximately equal proportions of iron and cobalt and about 2 wt% vanadium addition. - Final thickness of the strip 0.50 mm or thinner, preferably 0.356 mm or thinner - Vickers hardness > 300 HV - Elongation at break < 5% - Longitudinal growth after magnetic final annealing < 0.08%, preferably < 0.06% - Transverse growth after magnetic final annealing < 0.08%, preferably < 0.06% - Difference between longitudinal and transverse growth < 0.06%, preferably < 0.04%

Claims

[1] Method for producing a CoFe alloy, comprising: Providing a melt consisting of 35 wt% ≤ Co ≤ 55 wt%, 0 wt% ≤ V ≤ 3 wt%, 0 wt% ≤ Ni ≤ 2 wt%, 0 wt% ≤ Nb ≤ 0.50 wt%, 0 wt% ≤ Zr + Ta ≤ 1.5 wt%, 0 wt% ≤ Cr ≤ 3 wt%, 0 wt% ≤ Si ≤ 3 wt%, 0 wt% ≤ Al ≤ 1 wt%, 0 wt% ≤ Mn ≤ 1 wt%, 0 wt% ≤ B ≤ 0.25 wt%, 0 wt% ≤ C ≤ 0.1 wt%, balance Fe, and up to 1 wt% impurities, wherein the impurities are one or more of the may contain group O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W Pouring the molten metal under vacuum and subsequent solidification into a cast block, Hot rolling of the cast ingot into a slab and then into a hot-rolled strip with a thickness D1, followed by quenching of the strip from a temperature above 700°C to a temperature below 200°C, Cold rolling of the hot-rolled strip to an intermediate strip with a thickness D2, Intermediate annealing of the intermediate strip in a continuous process at a temperature above 700°C, wherein the intermediate strip is cooled at a temperature above 700°C to a temperature below 200°C in a gaseous medium, Cold rolling of the heat-treated intermediate strip with a metallically bright surface to a strip with a thickness D3, wherein the degree of cold forming is (D2-D3) / D2 ≤ 80%. [2] Method according to claim 1, wherein the degree of cold forming (D2-D3) / D2 is ≤ 60%. [3] Method according to claim 1 or claim 2, wherein 1.0 mm ≤ D1 ≤ 2.5 mm. [4] Method according to any one of claims 1 to 3, wherein 0.1 mm ≤ D2 ≤ 1.0 mm. [5] Method according to any one of claims 1 to 4, wherein 0.05 mm ≤ D3 ≤ 0.5 mm. [6] Method according to any one of claims 1 to 5, wherein the thickness of the hot rolled strip is reduced from D1 to D2 by means of cold rolling. [7] Method according to any one of claims 1 to 6, wherein the thickness of the intermediate strip is reduced from D2 to D3 by means of cold rolling. [8] Method according to any one of claims 1 to 7, wherein after intermediate annealing the intermediate strip has a microstructure in which a ferritically recrystallized portion has a mean grain size of less than 10 µm. [9] Method according to any one of claims 1 to 8, wherein after intermediate annealing the intermediate strip has a microstructure in which a ferritically recrystallized portion has no grains larger than 10 µm. [10] Method according to any one of claims 1 to 9, wherein after intermediate annealing the intermediate strip exhibits a bending number to breakage of at least 20 in a flexural fatigue test. [11] Method according to any one of claims 1 to 10, wherein the intermediate annealing is carried out continuously at a speed of 1 m / min to 10 m / min. [12] Method according to any one of claims 1 to 11, wherein the dwell time of the belt in the heating zone of the continuous furnace at a temperature of 700°C to 1100°C is between 30 seconds and 5 minutes. [13] Method according to claim 12, wherein the dwell time of the belt in the heating zone of the continuous furnace at a temperature of 800°C to 1000°C is between 30 seconds and 5 minutes. [14] Method according to any one of claims 1 to 13, wherein the intermediate annealing of the intermediate strip is carried out continuously at a temperature of 800°C to 900°C or 1000°C to 1100°C. [15] Method according to any one of claims 1 to 14, wherein after intermediate annealing the strip essentially has a deformation microstructure or a mixed microstructure with proportions of a former γ-phase in an α-matrix. [16] Method according to any one of claims 1 to 15, wherein after intermediate annealing in a continuous process the intermediate strip is cooled to a temperature less than 200°C in air. [17] Method according to any one of claims 1 to 16, wherein the intermediate annealing is carried out under an inert gas or a dry hydrogen-containing atmosphere.

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