EP3541969B1 - Method for producing a strip of a co-fe alloy, strip of a co-fe alloy and sheet metal stack - Google Patents

Description

The invention relates to a method for manufacturing a CoFe alloy strip and a CoFe alloy strip.

Soft magnetic cobalt-iron alloys (CoFe) with a Co content of 49% are used due to their high saturation polarization. One class of CoFe alloys has a composition of 49% Fe, 49% Co and 2% V by weight, which may also contain additions of Ni, Nb, Zr, Ta or B. With such a composition, a saturation polarization of about 2.3 T is achieved with a sufficiently high electrical resistance of 0.4 μΩm at the same time.

Such alloys are used, for example, as highly saturating flux guides or for applications in electrical machines. When used as a generator or motor, stators or rotors are typically manufactured in the form of laminated packages. The material is used in strip thicknesses ranging from 0.50 mm to very thin dimensions of 0.050 mm.

To achieve the magnetic properties, the material is subjected to a heat treatment, also known as final magnetic annealing. This heat treatment takes place above the recrystallization temperature and below the α/γ phase transition, usually in the range from 700°C to 900°C.

In contrast to electrical steel made of iron-silicon (FeSi), strip made of CoFe is typically not offered in a final annealed condition. Final annealed strip is soft due to a recrystallized structure and at the same time brittle due to the adjustment of order and can therefore only be punched inadequately. Furthermore, cutting or stamping processes lead to a significant deterioration in the magnetic properties. For this reason, CoFe sheets undergo final annealing after shaping, either on sheet metal panels, on individual laminations or on finished sheet metal packages.

However, the magnetic final annealing also changes the dimensions of the sheet. This increase in length is in the range of 0.03% to 0.20%.

If the growth is known, an allowance of the punching tool can compensate for isotropic growth within certain limits and/or the laminations or laminations can be reworked, such as in FIG WO 2007/009442 A2 is revealed. Such processes are associated with higher costs and, depending on the geometry, are not always practical.

The pamphlet JP S62 188756 A discloses a foil having a composition (Fe _1-a Co _a ) _100-x M _x , where M is one or more of Ti, V, Cr, Mn, Si, Zr, Nb, Mo, Sn, Pb, Zn, Ta , W, Ni, and Al, a denotes the ratio of Co to Fe of 0.2-0.6, and x is 0.05-10% by weight.

The object is therefore to specify a strip made from a CoFe alloy and a method for producing a strip made from a CoFe alloy which exhibits reduced growth after the final magnetic anneal.

According to the present invention there is provided a method as claimed in claim 1, a method as claimed in claim 7 and a CoFe alloy ribbon as claimed in claim 13.

According to the present invention, there is provided a method of manufacturing CoFe alloy ribbon, comprising the following. First, a melt consisting of 35% by weight ≤ Co ≤ 55% by weight, 0% by weight ≤ V ≤ 3% by weight, 0% by weight ≤ Ni ≤ 2% by weight, 0% by weight % ≤ 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 .-%, remainder Fe and up to 1 wt .-% impurities provided, the impurities one or more of the groups O, N, S, P, Ce , Ti, Mg, Be, Cu, Mo and W. The melt is cast under vacuum and then solidified into a cast block. The ingot is hot-rolled into a slab and then into a hot-rolled strip having a thickness D ₁ .

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 form an intermediate strip with a thickness D ₂ , the intermediate strip is subjected to intermediate annealing at a temperature above 700° C. and cooled to a temperature of above 700° C. to a temperature below 200° C. in a gaseous medium. Intermediate annealing is carried out continuously at a speed of 1 m/min to 10 m/min, the time the strip stays in the heating zone of the continuous furnace at a temperature of 700°C to 1100°C, preferably 800°C to 1000°C between 30 seconds and 5 minutes and the intermediate annealing of the intermediate strip takes place in a continuous process at a temperature of 800°C to 900°C or 1000°C to 1100°C. The heat-treated intermediate strip is cold-rolled with a metallically bright surface to a strip with a thickness D ₃ , the degree of cold deformation (D ₂ -D ₃ )/D ₂ being ≤80%, preferably ≤60% and 0.05 mm ≤D ₃ ≤ is 0.5mm.

After the continuous intermediate annealing of the cold-rolled intermediate strip, no quenching and pickling is carried out, so that the heat-treated intermediate strip has a bright metallic surface. The heat-treated intermediate strip is further processed with this metallically bright surface by further cold rolling. Thus, the manufacturing process is simplified. Furthermore, the degree of cold deformation of the last cold rolling step is limited, which allows the resulting strip to have a growth dl/l ₀ in the longitudinal direction of the strip less than 0.08%, preferably 0.06% and/or in the cross direction of the tape less than 0.08%, preferably 0.06%. l ₀ denotes the initial length before final annealing, dl the absolute change in length after final annealing and dl/l ₀ the relative change in length based on the initial length.

The final magnetic annealing of this CoFe alloy takes place above the recrystallization temperature and below the α/γ phase transition. The recrystallization temperature and the temperature at which the α/γ phase transition takes place depends on the composition of the CoFe alloy. Mostly the magnetic Final annealing carried out in the range from 700°C to 900°C. During the subsequent cooling, an adjustment of order takes place, ie a B2 superstructure is formed. Due to the magnetic final annealing and the associated adjustment of order, there is a permanent change in the dimensions of the sheet at room temperature or a permanent increase in length. A strip with an initial length l ₀ at room temperature before the final anneal thus has a length l ₀ + dl after the final anneal and at the same room temperature. In some embodiments, dl is greater than 0.

This permanent increase in length is reduced by the method according to the invention. According to the invention, the permanent growth dl/l ₀ in the longitudinal direction of the strip is less than 0.08%, preferably 0.06% and/or in the transverse direction of the strip is less than 0.08%, preferably 0.06%. This small permanent growth is not achieved in CoFe alloy strip produced with any of the cold working ratios of the final cold rolling step greater than 80%.

It has been found that an important factor influencing the magnitude of this growth is the degree of cold working (CV): the higher the cold working of the material, the more pronounced the growth in length will be after the final anneal. By using intermediate annealing, the degree of cold working can be reduced in the last step, so that after the final magnetic anneal the strip shows reduced growth in length.

The thickness of the strip, which is achieved by hot rolling and/or cold rolling, as well as the thickness of the strip on which the intermediate annealing is carried out, can be defined more precisely. For example, the strip may have a thickness D ₁ of 1.0 mm ≤ D ₁ ≤ 2.5 mm after hot rolling, and a thickness D ₂ of 0.1 mm ≤ D ₂ ≤ 1.0 mm before intermediate annealing second cold rolling, the strip has a thickness D ₃ of 0.05 mm ≤D ₃ ≤0.5 mm.

In one embodiment, the thickness of the hot-rolled strip is reduced from D ₁ to D ₂ by means of cold rolling and/or the thickness of the intermediate strip is reduced from D ₂ to D ₃ reduced by cold rolling. No further intermediate annealing is therefore carried out.

The conditions of the intermediate anneal in the pass are selected so that the strip can be cold rolled after the intermediate anneal. In one embodiment, after the intermediate annealing, the intermediate strip has a structure in which a ferritically recrystallized portion has an average grain size of less than 10 μm and/or a ferritically recrystallized portion has no grains larger than 10 μm. This structure can be created, for example, by a temperature of 800°C to 900°C.

In one exemplary embodiment, the intermediate strip has a bending number before fracture of at least 20 after the intermediate annealing in a reverse bending test. The flex fatigue test can be used to determine the cold formability of the strip.

Intermediate continuous annealing is 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 with the temperature of 700°C to 1100°C, preferably 800°C to 1000°C is between 30 seconds and 5 minutes. The intermediate strip is continuously annealed 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 annealing temperature and belt speed parameters can be adjusted in order to set the properties shown here.

After the intermediate anneal, the strip may have essentially a deformation microstructure or a mixed microstructure with portions of a former γ-phase in a matrix of an α-phase. For example, a deformation structure can be achieved at a temperature of 800°C to 900°C. A mixed structure with portions of a former γ-phase in a matrix of an α-phase can be achieved at a temperature of 1000°C to 1100°C.

The intermediate annealing can be carried out under an inert gas or a dry hydrogen-containing atmosphere with a dew point lower than -30°C. After the intermediate continuous annealing, the intermediate strip is cooled to a temperature lower than 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.

In an alternative method, the hot rolling strain rate is adjusted so that the cold rolling strain rate remains below a predetermined limit in order to keep the elongation after the final magnetic anneal low. This method of manufacturing a CoFe alloy includes the following. A melt consisting of 35% by weight ≤Co ≤55% by weight, 0% by weight ≤V ≤3% by weight, 0% by weight ≤Ni ≤2% by weight, 0% by weight %≦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% by weight ≤C ≤0.1% by weight, remainder Fe and up to 1% by weight impurities is provided, the impurities being one or more of the groups O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W may include. The melt is cast under vacuum and then solidified into a cast block. The ingot is hot rolled into a slab and then into a strip having a thickness D ₁ where 1 mm ≤ _{D 1} < 2 mm. The strip is then quenched from a temperature above 700°C to a temperature below 200°C. The strip is cold rolled and the thickness reduced from D ₁ to a thickness D ₂ , the degree of cold deformation (D ₁ -D ₂ )/D ₁ being ≤80%, preferably ≤60%. The final thickness D ₂ is 0.05 mm ≤ D ₂ ≤ 0.5 mm.

In this process, the degree of deformation during hot rolling and thus the thickness D ₁ of the strip after hot rolling and before cold rolling is adjusted in such a way that the desired final thickness D ₂ 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 of hot rolling is increased and the degree of deformation of cold rolling is correspondingly reduced.

The heat treatment of the ribbon can take place under a dry atmosphere containing hydrogen.

Both alternative methods may further include forming at least one sheet from the strip. The sheet metal can be stamped from the strip. A plurality of laminations can be joined to form a lamination stack. The strip or the sheet or the laminated core can also be heat-treated at a temperature between 700°C and 900°C, i.e. a final magnetic anneal can be carried out. This heat treatment takes place above the recrystallization temperature and below the temperature of the phase transition α/γ, mostly in the range of 700°C to 900°C. During subsequent cooling, the order is adjusted, i.e. a B2 superstructure is formed, and the desired magnetic properties, for example a saturation polarization of around 2.3 T and an electrical resistance of 0.4 µΩm, are generated.

After this heat treatment of the strip, a growth dl/l ₀ 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 a difference between the longitudinal growth and the transverse direction growth of the tape less than 0.06%, preferably less than 0.04%. l ₀ denotes the initial length before final annealing, dl the absolute change in length after final annealing and dl/l ₀ the relative change in length based on the initial length.

This growth is permanent growth, which is caused by the final magnetic annealing and the adjustment of order associated with it. A strip with an initial length l ₀ at room temperature before final annealing thus has a length l ₀ + dl after final annealing and at the same room temperature.

According to the invention, a strip made of a CoFe alloy is provided which has a composition consisting of 35% by weight ≦Co≦55% by weight, 0% by weight ≦V≦3% by weight, 0% by weight ≦ 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 of the groups O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W. The tape has a thickness d, where 0.05 mm ≤ d ≤ 0.5 mm, a Vickers hardness greater than 300 and an elongation at break less than 5%. After heat treatment of the strip at a temperature between 700°C and 900°C, the strip has a growth dl/l ₀ in the longitudinal direction of the strip less than 0.08%, preferably 0.06% and/or in the transverse direction of the strip less than 0.08%, preferably 0.06%.

This strip thus has mechanical properties that are present in a cold-rolled condition, namely an elongation at break of less than 5% and a Vickers hardness greater than 300. This strip can be further processed, for example to form sheets from the strip and to cut the sheets a laminated core that is heat treated to adjust the magnetic properties. This heat treatment of the strip is referred to as a final magnetic anneal because it serves to adjust the magnetic properties and can be carried out at a temperature between 700°C and 900°C.

This growth is permanent growth, which is caused by the final magnetic annealing and the adjustment of order associated with it. A strip with an initial length l ₀ at room temperature before final annealing thus has a length l ₀ + dl after final annealing and at the same room temperature. In some embodiments, dl is greater than 0.

The strip according to the invention makes it possible to produce sheet metal sections, to subject them to final annealing in order to set an optimal magnetic field and then to obtain a sufficiently high dimensional accuracy so that further correction of the geometry can be dispensed with. The possible disadvantages of subsequent correction of the geometry, eg by grinding, are a deterioration in the magnetic permeability at these points, the risk of eddy currents, since grinding processes can result in smearing of the lamellae, and higher costs. As a result, when used as a stator or rotor, for example, low Air gaps are set, which leads to improved efficiency of the electric machine.

In one embodiment, the band may have a reduced thickness, for example a thickness of 0.05 mm≦d≦0.356 mm. Furthermore, a multiplicity of laminations can form a laminated core.

In one embodiment, after heat treating the ribbon at a temperature between 700°C to 900°C, a difference between the permanent growth in the longitudinal direction and the permanent growth in the transverse direction of the ribbon is less than 0.06%, preferably less than 0.04%. .

The CoFe ribbon according to the invention with significantly reduced growth has the further advantage that a stamping tool can be designed in such a way that it can be used both for other alloys such as SiFe and for CoFe. Given the high costs for such a tool, this leads to an economic advantage.

• 35 bis 55 Gew.-% Co, bis zu 2.5 Gew.-% V, Rest Fe, zum Beispiel 49 Gew.-% Co, 49 Gew.-% Fe und 2 Gew.-% V sowie bis zu 1 Gew.-% Verunreinigungen,
• 45 Gew.-% ≤ Co ≤ 52 Gew.-%, 45 Gew.-% ≤ Fe ≤ 52 Gew.-%, 0.5 Gew.-% ≤ V ≤ 2.5 Gew.-% Rest Fe sowie bis zu 1 Gew.-% Verunreinigungen,
• 35 Gew.-% ≤Co ≤55 Gew.-%, vorzugsweise 45 Gew.-% ≤Co ≤52 Gew.-%, 0 Gew.-% ≤Ni ≤0.5 Gew.-%, 0.5 Gew.-% ≤V ≤2.5 Gew.-%, Rest Eisen sowie bis zu 1 Gew.-% Verunreinigungen,
• 35 Gew.-% ≤Co ≤55 Gew.-%, 0 Gew.-% ≤V ≤2.5 Gew.-%, 0 Gew.-% ≤(Ta + 2Nb) ≤1 Gew.-%, 0 Gew.-% ≤Zr ≤1,5 Gew.-%, 0 Gew.-% ≤Ni ≤5 Gew.-%, 0 Gew.-% ≤ C ≤0,5 Gew.-%, 0 Gew.-% ≤Cr ≤1 Gew.-%, 0 Gew.-% ≤Mn ≤1 Gew.-%, 0 Gew.-% ≤Si ≤1 Gew.-%, 0 Gew.-% ≤Al ≤1 Gew.-%, 0 Gew.-% ≤B ≤0.01 Gew.-%, Rest Fe sowie bis zu 1 Gew.-% Verunreinigungen (nicht Teil der beanspruchten Erfindung),
• 47 Gew.-% ≤ Co ≤ 50 Gew.-%, 1 Gew.-% ≤ V ≤ 3 Gew.-%, 0 Gew.-% ≤ Ni ≤ 0.25 Gew.-%, 0 Gew.-% ≤ C ≤ 0.007 Gew.-%, 0 Gew.-% ≤ Mn ≤ 0.1 Gew.-%, 0 Gew.-% ≤ Si ≤ 0.1 Gew.-%, 0.07 Gew.-% ≤ Nb ≤ 0.125 Gew.-%, 0 Gew.-% ≤ Zr ≤ 0.5 Gew.-%, Rest Fe sowie bis zu 1 Gew.-% Verunreinigungen, oder
• 49 Gew.-% ≤ Co ≤ 51 Gew.-%, 0.8 Gew.-% ≤ V ≤ 1.8 Gew.-%, 0 Gew.-% ≤ Ni ≤ 0.5 Gew.-%, Rest Fe sowie bis zu 1 Gew.-% Verunreinigungen.

Various CoFe alloys can be used. In other exemplary embodiments, the CoFe alloy has one of the following compositions:

• 35 to 55% by weight Co, up to 2.5% by weight V, balance Fe, for example 49% by weight Co, 49% by weight Fe and 2% by weight V and up to 1% by weight % impurities,
• 45% by weight ≦Co≦52% by weight, 45% by weight ≦Fe≦52% by weight, 0.5% by weight ≦V≦2.5% by weight, remainder Fe and up to 1% by weight % impurities,
• 35 wt% ≤Co ≤55 wt%, preferably 45 wt% ≤Co ≤52 wt%, 0 wt% ≤Ni ≤0.5 wt%, 0.5 wt% ≤V ≤2.5% by weight, remainder iron and up to 1% by weight 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% by weight, balance Fe and up to 1% by weight impurities (not part of the claimed invention),
• 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% by weight ≤ Co ≤ 51% by weight, 0.8% by weight ≤ V ≤ 1.8% by weight, 0% by weight ≤ Ni ≤ 0.5% by weight, remainder Fe and up to 1% by weight. -% impurities.

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.

The impurities can contain one or more of the group O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W.

Figur 1

zeigt einen Graph von gemessenem mittlerem Wachstum dl/l0 nach einer Schlussglühung von Bändern, die zu unterschiedlichen Dicken d kaltgewalzt werden.

Figur 2

zeigt einen Graph von Dehngrenze R_p0,2 und Zugfestigkeit R_m in Abhängigkeit von der Temperatur der Durchlaufglühung.

Figur 3

zeigt optische Aufnahmen der Gefüge von drei Proben nach einer Zwischenglühung bei unterschiedlichen Temperaturen.

Figur 4

zeigt Magnetisierungskurven B(H) nach verschiedenen Zwischenglühungen und einer Schlussglühung.

Figur 5

zeigt einen Graph der gemessenen Längenänderung in Walzrichtung gegenüber dem Kaltverformungsgrad für zwei verschiedene Proben.

Exemplary embodiments will now be explained in more detail with reference to the drawings and the following examples.

figure 1

shows a graph of measured mean growth dl/l0 after a final anneal of strips cold rolled to different gauges d.

figure 2

shows a graph of yield strength R _p0.2 and tensile strength R _m as a function of continuous annealing temperature.

figure 3

shows optical images of the structures of three samples after intermediate annealing at different temperatures.

figure 4

shows magnetization curves B(H) after various intermediate anneals and a final anneal.

figure 5

Figure 12 shows a graph of the measured length change in the rolling direction versus the degree of cold working for two different samples.

It has been shown that the growth in length of a strip made of a CoFe alloy after a final anneal can be reduced by limiting the degree of cold working.

figure 1 shows a graph of measured average growth dl/l0 after a final anneal in % in the longitudinal direction on the 50% CoFe materials VACOFLUX 50 (49Fe-49Co-2V) and as a comparative example HIPERCO 50 (49Fe-49Co-2V). The samples examined had a gauge after hot rolling of 2mm or greater, and are cold rolled to different final gauges and thus undergo different degrees of cold working. l ₀ denotes the initial length before final annealing, dl the absolute change in length after final annealing and dl/l ₀ the relative change in length based on the initial length.

This change in length or growth is a permanent change in length or growth that is caused by the final magnetic annealing and the associated adjustment of order. A sample with an initial length l ₀ at room temperature before the final annealing thus has a length of l ₀ + dl after the final annealing and at the same room temperature.

While hot-rolled material, ie with 0% cold deformation (KV), still shows a small, persistent increase in length compared to the original length in the range of 0.03% to 0.05% at room temperature, a strip with a strip thickness of 0.35 mm already shows this a sustained growth of over 0.10%. With even higher cold forming, eg on a strip thickness of 0.10 mm, permanent growth of over 0.20% takes place. This permanent change in length growth is likely due to an increasingly distinct texture. These results show that an important factor influencing the size of this growth is the degree of cold working: the higher the cold working of the material, the more pronounced the growth in length after the final anneal.

Consequently, these results indicate that, in principle, the permanent change in elongation can be reduced if the degree of cold working is reduced. In principle, the degree of cold working can be reduced by performing an intermediate anneal between two cold working steps, each with a smaller cold working degree. Due to the adjustment of order through intermediate annealing, however, a CoFe alloy is subsequently brittle and can no longer be processed. Consequently, the brittleness is conventionally eliminated again 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 in the degree of cold deformation for a given final thickness is achieved by introducing intermediate annealing or by reducing the hot-rolled thickness.

According to the invention, intermediate annealing is carried out in a continuous process in such a way that the strain hardening caused by rolling is reduced and at the same time, by avoiding coarse-grained ferrite, a structure that can be rolled is created despite the brittle adjustment of order. Furthermore, after the intermediate annealing, the strip is not quenched, for example in water or oil, and is not pickled, so that the strip is cold-rolled with a bright metallic surface. As a result, the process is simpler and less expensive to carry out.

After intermediate annealing, it is therefore 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 deformation at the final thickness of 0.50 mm or thinner to such an extent that length growth is significantly reduced at the same time. According to the invention, the cold deformation should be at most 80%, preferably up to 60%, as illustrated by the following examples and test results. Table 1 intermediate anneal to thickness final thickness no 1.0mm 0.5mm 0.35mm 0.20mm 0.10mm 0.35mm 83% 65% (*) 30% (*) - - - 0.20mm 90% 80% (*) 60% (*) 43% (*) - - 0.10mm 95% 90% 80% (*) 71% (*) 50% (*) - 0.05mm 98% 95% 90% 86% 75% (*) 50% (*)

Table 1 shows the degree of cold working as a function of the final thickness and intermediate annealing. A hot-rolled thickness of 2 mm was assumed. The states marked with (*) represent states according to the invention.

A strip of the VACODUR 49 alloy was used as the material, with a composition of 48.6% by weight Co, 1.86% by weight V, 0.09% by weight Nb, C <0.0070% by weight. %, 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. The strip could then be cold-rolled to a thickness of 0.35 mm.

Intermediate continuous annealing was tested in a continuous furnace with an annealing zone 6 m long. The temperatures chosen were 850° C., 900° C., 950° C., 1000° C. and 1050° C. at a speed of 6 m/min. The anneal was performed under dry H ₂ . The different temperatures of the intermediate annealing in the run are referred to below as variants 1 to 5.

Table 2 shows the measured mechanical properties of the continuously annealed strips of variants 1 to 5. The tensile specimens were taken along the direction of rolling. The bending cycles were determined on strips (longitudinal/transverse to the rolling direction). A bend test 900°C 6m/min transverse was not available.

figure 2 shows a graph of yield point R _p0.2 and tensile strength R _m of the tensile specimens versus the temperature T of the continuous annealing at 6 m/min. The condition Ref. denotes the condition of a sample without continuous annealing and thus a comparative condition.

The mechanical properties of these samples with a thickness of 0.35 mm show that all continuously annealed variants (1-5) result in a high elongation at break of the material. In variants 1, 3, 4 and 5, the difference between R _m and Rp _0.2 is relatively large (>400 MPa), which indicates good plastic deformability. Table 2 variant Intermediate annealing in the run Hardness HV10 Modulus of elasticity GPa R _p0.2 MPa R _m MPa R _m - R _p0.2 MPa A% #Bending change Sampling longitudinal / transverse reference hard as rolled 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 / not applicable 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

A further proof of the different ductility succeeds via the number of bending cycles in the bending cycle test. The states marked as variants 1, 4 and 5 show a high number of possible bending cycles in both directions.

A metallographic examination shows that the different variants have very different structures, which can be divided into three groups.

In Variant 1, intermediate annealing at low temperatures only leads to incomplete recrystallization. For example, the present structure was achieved at a temperature of 850°C.

In variants 2 and 3, intermediate annealing at 900°C or 950°C leads to a ferritic, recrystallized, coarse-grained structure.

In variants 4 and 5, an intermediate annealing in the two-phase area α/γ leads to a mixed structure with parts of the former γ-phase in an α-matrix. By way of example, the present structure was achieved at a temperature of 1000°C.

figure 3 shows optical images of the structures of three samples after intermediate annealing at different temperatures. Variant 1 was heat treated at 850°C 6m/min and shows good rollability, N > 20, a deformation structure and the beginning of recrystallization. Variant 3 was heat treated at 950°C 6 m/min and shows poor rollability, N = 2 - 7 and is ferritic recrystallized. Variant 4 was heat-treated at 1000°C at 6 m/min and shows good rollability, N > 20, a non-uniform ferrite, mixed structure with portions of the former γ-phase in an α-matrix.

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-high mill. A strong Hardening of the material is shown as early as the first stitch, indicating that the material is in the ordered state. Table 3 variant continuous annealing tape thickness Hardness HV Modulus of elasticity GPa R _p0.2 MPa R _m MPa A % reference roll 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

The strips, which were manufactured according to variants 1, 4 and 5, could be rolled up to a thickness of 0.10 mm. In contrast, variants 2 and 3 showed strong 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.

Surprisingly, the tests showed that it is possible to roll a CoFe strip after continuous annealing, as long as the formation of a coarse-grained structure is avoided.

The growth in length after a further heat treatment to adjust the magnetic properties at a temperature between 700°C and 900°C, ie after a final anneal, is examined.

Table 4 shows the growth in length (measured in longitudinal direction) after final magnetic annealing of VACODUR 49, hot-rolled thickness 2 mm. Both variants, ie variants 1 and 4, therefore exhibit significantly reduced growth with a small strip thickness. Table 4 Reference: Version 1: Variant 4: no intermediate glow Intermediate annealing at 0.35 mm at 850°C 6 m/min Intermediate annealing at 0.35 mm at 1000°C 6 m/min final thickness KV dl/l ₀ KV dl/l ₀ KV dl/l ₀ 0.35mm 83% 0.129% 0% 0.035% 0% 0.032% 0.20mm 90% 0.145% 43% 0.055% 43% 0.037% 0.10mm 95% 0.195% 71% 0.054% 71% 0.000% 0.055mm - - - - 84% 0.159%

The tape obtained in this way was characterized with regard to length growth with an intermediate thickness of 0.25 mm and with different final thicknesses of 0.20 mm and 0.10 mm. The measurement was carried out on individual strips with a length of 165 mm, the length of which was measured exactly before and after the final annealing (6h 880°C under H ₂ ). The change in length dl can be determined from the difference in the measured lengths. If you put this in relation to the initial length l ₀ , you get the relative increase in length dl/l ₀ . The measurements listed in Table 4 were always carried out in the longitudinal direction, ie the growth was determined along the direction of rolling.

With the conventionally produced reference material, i.e. without intermediate annealing, the increase in length at a thickness of 0.35 mm is already 0.129%. With increasing cold deformation, the growth increases up to 0.195% at a thickness of 0.10 mm.

In contrast, variant 1 according to the invention has a significantly reduced change in length at the final thickness of 0.10 mm. So was post on the tape the final magnetic anneal at 0.10 mm measured an average growth dl/l ₀ in the longitudinal direction of 0.054%.

Variant 4 tape also showed reduced growth. An average growth dl/l ₀ in the longitudinal direction of 0.000% was measured, with the individual values being between +0.013% and -0.010%.

If the cold working after intermediate annealing becomes too high, the growth increases again significantly. In the exemplary embodiment variant 4 (intermediate annealing 1000° C. 6 m/min at 0.35 mm) a very pronounced length growth dl/l ₀ of 0.159% in the longitudinal direction is obtained at the final thickness of 0.055 mm, ie with 84% cold deformation.

The anisotropy of the growth, i.e. the difference between the growth in length along and across the ribbon, is examined.

Table 5 shows the growth in length of the VACODUR 49 samples after additional final annealing of 6 hours at 880°C, measured on tensile samples or longitudinal strips 165 mm x 20 mm. The as-rolled condition, 0.10 mm, was measured on a comparable sample made of VACOFLUX 48, also after final annealing of 6 hours 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 glow 0.35mm 0.129% 0.106% 0.023% 0.10mm 0.210% 0.110% 0.100% 1 850°C, 6 m/min 0.35mm 0.035% 0.051% 0.016% 0.10mm 0.054% 0.052% 0.002% 4 1000°C, 6 m/min 0.35mm 0.032% 0.058% 0.026% 0.10mm 0.000% 0.056% 0.056%

Variant 1 of Table 5 shows 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% for a strip thickness of 0.10 mm. It is thus possible to stock punching tools symmetrically. Stamped round parts remain round after final annealing.

Variant 4 of Table 5 still has a slight anisotropy, but also shows a clearly small increase in length in terms of absolute value. The difference between longitudinal and transverse directions |longitudinal - transverse| is, at about 0.06% of the original length, much less than the difference observed in conventionally manufactured tape, which is about 0.10%.

Magnetically, both variants show properties in the final thickness that correspond to what is obtained in the starting material with a thickness of 0.35 mm without continuous annealing. The following figure shows the new curves after final magnetic annealing for different strip thicknesses.

figure 4 shows magnetization curves and the influence of further cold working on the new curve B(H) of continuously annealed strip (850°C, 1050°C; 6 m/min each). The measurements were carried out on stamped rings after a final anneal of 6 hours at 880°C in a dry H ₂ atmosphere.

1. (a) eine Probe mit einer Banddicke von 0,35mm, bei dem keine Durchlaufglühung durchgeführt wird, (Referenz)
2. (b) eine Probe mit einer Banddicke von 0,35mm, bei dem eine Durchlaufglühung bei 850°C und 6 m/min durchgeführt wird,(Referenz)
3. (c) eine Probe, die bei einer Banddicke von 0,35mm einer Durchlaufglühung bei 850°C und 6 m/min unterzogen wird und anschließend zu einer Banddicke 0,20mm kaltverformt wird (erfindungsgemäß).
4. (d) eine Probe mit einer Banddicke von 0,35mm, bei dem keine Durchlaufglühung durchgeführt wird, (Referenz)
5. (e) eine Probe mit einer Banddicke von 0,35mm, bei dem eine Durchlaufglühung bei 1050°C und 6 m/min durchgeführt wird,(Referenz)
6. (f) eine Probe, die bei einer Banddicke von 0,35mm einer Durchlaufglühung bei 1050°C und 6 m/min unterzogen wird und anschließend zu einer Banddicke 0,20mm kaltverformt wird (erfindungsgemäß).

In the figure 4 designated:

1. (a) a sample with a strip thickness of 0.35mm, on which no continuous annealing is carried out, (reference)
2. (b) a sample with a strip thickness of 0.35mm, which is subjected to continuous annealing at 850°C and 6 m/min (reference)
3. (c) a sample which, with a strip thickness of 0.35 mm, is subjected to continuous annealing at 850° C. and 6 m/min and is then cold-worked to a strip thickness of 0.20 mm (according to the invention).
4. (d) a sample with a strip thickness of 0.35mm on which no continuous annealing is carried out (reference)
5. (e) a sample with a strip thickness of 0.35mm, which is subjected to continuous annealing at 1050°C and 6 m/min (reference)
6. (f) a sample which, with a strip thickness of 0.35 mm, is subjected to continuous annealing at 1050° C. and 6 m/min and is then cold-worked to a strip thickness of 0.20 mm (according to the invention).

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

The second approach according to the invention is to reduce the hot rolling gauge so that with a final gauge of 0.50 mm or thinner, the cold working on the final gauge is a maximum of 80%. In the case of CoFe alloys, the thickness of the hot-rolled strip is typically 2 mm to 4 mm. With a final thickness of 0.35 mm, a reduction to 1 mm can reduce the degree of cold deformation and thus the growth in length.

Hot-rolled strips were produced in the thicknesses according to Table 6 (WW thickness) and 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 0.35mm 90% 83% 77% (*) 65% (*) 0.20mm 94% 90% 87% 80% (*) 0.10mm 97% 95% 93% 90% 0.05mm 99% 98% 97% 95%

Table 6 shows degree of cold working as a function of final gauge and hot-rolled gauge (without intermediate annealing). The states marked with (*) represent tapes according to the invention.

figure 5 shows a graph of growth in length (dl/l ₀ ) of strips of different hot-rolled gauges made of VACOFLUX 50 along the rolling direction after final annealing versus the degree of cold deformation (D ₁ -D ₂ )/D ₁ . The change in length in the rolling direction versus the degree of cold deformation is shown for two different samples A and B after final magnetic annealing. With a constant cold-rolled thickness D ₂ of 0.35 mm, the hot-rolled thickness D ₁ was varied between 1.0 mm and 3.5 mm. For each data point, the associated hot rolled thickness (WW thickness) is marked with an arrow.

From these results it can be seen that the step from the WW thickness D ₁ of 3.5 mm to 2.0 mm already leads to a significant reduction in growth on a sample with a final thickness D ₂ of 0.35 mm. For a WW thickness of 1.0 mm or thinner, it is possible to obtain < 0.08% growth in length after final annealing at a final thickness of 0.35 mm.

In a further investigation, a WW strip with a thickness of 1.5 mm was rolled from VACOFLUX 50 to a final thickness of 0.50 mm and subjected to final magnetic annealing (4h 820°C, H ₂ ). The increase in length in this test was only 0.045%. Overall, it can be seen that for a final thickness of 0.50 mm or thinner with a correspondingly small hot-rolled thickness, a strong reduction in length growth can be achieved.

• Warmwalzen an Dicke 2,5 mm bis 1,0 mm
• Abschrecken von Temperaturen oberhalb 700°C
• Walzen an Zwischendicke (1,0 mm bis 0,20 mm)
• Glühung im Durchlauf bei 700°C bis 1100°C, vorzugsweise derart, dass kein grobkörniges ferritisches Gefüge entsteht, sondern ein unvollständig rekristallisiertes oder ein feinkörnig rekristallisiertes ferritisches Gefüge
• Walzen an Enddicke mit einer Kaltverformung von bis zu 80%, vorzugsweise mit einer Kaltverformung von bis zu 60%

In summary, in a specific example, the tape of the present invention is made through the following route:

• Hot rolling to thickness 2.5mm to 1.0mm
• Quenching from temperatures above 700°C
• Rolling to Intermediate Thickness (1.0mm to 0.20mm)
• 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
• Rolling to final gauge with a cold reduction of up to 80%, preferably with a cold reduction of up to 60%

Alternatively, in the case of a hot strip thickness of less than 2 mm, continuous annealing can also be dispensed with as long as cold working is up to 80%, preferably up to 60%.

• Zusammensetzung wie übliche CoFe-Bänder mit in etwa gleichen Anteilen von Eisen und Kobalt und ca. 2 Gew.-% Vanadiumzusatz.
• Enddicke des Bands 0,50 mm oder dünner, vorzugsweise 0,356 mm oder dünner
• Vickershärte > 300 HV
• Bruchdehnung < 5%
• ein bleibendes Wachstum in Längsrichtung nach magnetischer Schlussglühung < 0,08%, vorzugsweise < 0,06 %
• ein bleibendes Wachstum in Querrichtung nach magnetischer Schlussglühung < 0,08%, vorzugsweise < 0,06 %
• Differenz zwischen dem bleibenden Wachstum in Längs- zu dem bleibenden Wachstum in Querrichtung < 0,06 %, vorzugsweise <0,04 %

The tape according to the invention has the following properties:

• Composition as usual CoFe ribbons with roughly equal proportions of iron and cobalt and approx. 2% by weight added vanadium.
• Final gauge of tape 0.50 mm or thinner, preferably 0.356 mm or thinner
• Vickers hardness > 300 HV
• Elongation at break < 5%
• a permanent longitudinal growth after magnetic final annealing < 0.08%, preferably < 0.06%
• a permanent growth in the transverse direction after magnetic final annealing < 0.08%, preferably < 0.06%
• Difference between permanent growth in the longitudinal direction and permanent growth in the transverse direction < 0.06%, preferably < 0.04%

Claims (15)

1. Method for producing a strip from a CoFe alloy according to claim 13, comprising:

   the provision of a melt consisting of 35 % w/w ≤ Co ≤ 55 % w/w, 0 % w/w ≤ V ≤ 3 % w/w, 0 % w/w ≤ Ni ≤ 2 % w/w, 0 % w/w ≤ Nb ≤ 0.50 % w/w, 0 % w/w ≤ Zr + Ta ≤ 1.5 % w/w, 0 % w/w ≤ Cr ≤ 3 % w/w, 0 % w/w ≤ Si ≤ 3 % w/w, 0 % w/w ≤ Al ≤ 1 % w/w, 0 % w/w ≤ Mn ≤ 1 % w/w, 0 % w/w ≤ B ≤ 0.25 % w/w, 0 % w/w ≤ C ≤ 0.1 % w/w, rest Fe and up to 1% w/w impurities, wherein the impurities can comprise one or more of the groups of O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W,

   the decanting of the melt under vacuum followed by solidifying to form an ingot,

   the hot-rolling of the ingot to form a slab and then a hot-rolled strip with a thickness D₁, followed by the quenching of the strip from a temperature above 700°C to a temperature of less than 200°C,

   the cold-rolling of the hot-rolled strip to form an intermediate strip with a thickness D₂,

   the intermediate annealing of the intermediate strip in a continuous process at a temperature above 700°C, wherein the intermediate strip is cooled in a gaseous medium from a temperature above 700°C to a temperature of less than 200°C, wherein the intermediate annealing in a continuous process is carried out at a speed of 1 m/min to 10 m/min, the dwell time of the strip in the heating zone of the continuous furnace with the temperature of 700°C to 1100°C, preferably 800°C to 1000°C, is between 30 seconds and 5 minutes and the intermediate annealing of the intermediate strip in a continuous process is carried out at a temperature of 800°C to 900°C or 1000°C to 1100°C,

   the cold-rolling of the heat-treated intermediate strip with a metallic bright surface to form a strip with a thickness D₃, wherein the degree of cold deformation (D₂-D₃)/D₂ is ≤ 80%, preferably < 60%, and 0.05 mm ≤ D₃ ≤ 0.5 mm.
2. Method according to claim 1, wherein 1.0 mm ≤ D₁ < 2.5 mm and/or 0.1 mm ≤ D₂ ≤ 1.0 mm.
3. Method according to claim 1 or claim 2, wherein after the intermediate annealing the intermediate strip has a structure in which a ferritically recrystallised component has an average grain size of less than 10 µm, or in which a ferritically recrystallised component has no grains with a size of more than 10 µm.
4. Method according to any of claims 1 to 3, wherein after the intermediate annealing the strip substantially has a deformation structure or a mixed structure with components of a former γ-phase in an α-matrix.
5. Method according to any of claims 1 to 4, wherein after the intermediate annealing in a continuous process the intermediate strip is cooled in air to a temperature of less than 200°C.
6. Method according to any of claims 1 to 5, wherein the intermediate annealing is carried out in an inert gas or in a dry hydrogenous atmosphere.
7. Method for producing a strip from a CoFe alloy according to claim 13, comprising:

   the provision of a melt consisting of 35 % w/w ≤ Co ≤ 55 % w/w, 0 % w/w ≤ V ≤ 3 % w/w, 0 % w/w ≤ Ni ≤ 2 % w/w, 0 % w/w ≤ Nb ≤ 0.50 % w/w, 0 % w/w ≤ Zr + Ta ≤ 1.5 % w/w, 0 % w/w ≤ Cr ≤ 3 % w/w, 0 % w/w ≤ Si ≤ 3 % w/w, 0 % w/w ≤ Al ≤ 1 % w/w, 0 % w/w ≤ Mn ≤ 1 % w/w, 0 % w/w ≤ B ≤ 0.25 % w/w, 0 % w/w ≤ C ≤ 0.1 % w/w, rest Fe and up to 1% w/w impurities, wherein the impurities can comprise one or more of the groups of O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W,

   the decanting of the melt under vacuum followed by solidifying to form an ingot,

   the hot-rolling of the ingot to form a slab and then a hot-rolled strip with a thickness D₁, wherein 1 mm ≤ D₁ ≤ 2 mm, followed by the quenching of the strip from a temperature above 700°C to a temperature of less than 200°C,

   the cold-rolling of the strip and the reduction of the thickness Di to a thickness D₂, wherein the degree of cold deformation (D₁-D₂)/D₁ is ≤ 80%, preferably ≤ 60%, wherein 0.05 mm ≤ D₂ ≤ 0.5 mm.
8. Method according to any of claims 1 to 7, further comprising:
   the forming of at least one sheet from the strip.
9. Method according to claim 7 or claim 8, further comprising:
   the joining of a plurality of sheets to form a laminated core.
10. Method according to any of claims 1 to 9, further comprising:
    the heat treatment of the strip at a temperature between 700°C and 900°C.
11. Method according to claim 10, wherein after the heat treatment of the strip a permanent growth dl/l₀ in the longitudinal direction of the strip is less than 0.08% and/or in the transverse direction of the strip less than 0.08%, wherein l₀ denotes the starting length before the heat treatment, dl the absolute length change after the heat treatment and dl/l₀ the relative length change with reference to the starting length, or wherein after the heat treatment of the strip a difference between the permanent growth in the longitudinal direction and the permanent growth in the transverse direction of the strip is less than 0.06%, preferably less than 0.04%.
12. Method according to claim 10 or claim 11, wherein the heat treatment of the strip is carried out in a dry hydrogenous atmosphere.
13. Strip from a CoFe alloy,
    consisting of 35 % w/w ≤ Co ≤ 55 % w/w, 0 % w/w ≤ V ≤ 3 % w/w, 0 % w/w ≤ Ni ≤ 2 % w/w, 0 % w/w ≤ Nb ≤ 0.50 % w/w, 0 % w/w ≤ Zr + Ta ≤ 1.5 % w/w, 0 % w/w ≤ Cr ≤ 3 % w/w, 0 % w/w ≤ Si ≤ 3 % w/w, 0 % w/w ≤ Al ≤ 1 % w/w, 0 % w/w ≤ Mn ≤ 1 % w/w, 0 % w/w ≤ B ≤ 0.25 % w/w, 0 % w/w ≤ C ≤ 0.1 % w/w, rest Fe and up to 1% w/w impurities, wherein the impurities can comprise one or more of the groups of O, N, S, P, Ce, Ti, Mg, Be, Cu, Mo and W,
    wherein the strip has a thickness d, 0.05 mm ≤ d ≤ 0.5 mm, a Vickers hardness HV10 of more than 300 and an elongation at break of less than 5% and, after a heat treatment of the tape at a temperature between 700°C and 900°C, a permanent growth dl/l₀ 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%, wherein l₀ denotes the starting length before the heat treatment, dl the absolute length change after the heat treatment and dl/l₀ the relative length change with reference to the starting length.
14. Strip according to claim 13, wherein 0.05 mm ≤ d ≤ 0.356 mm.
15. Laminated core having a plurality of sheets which form the laminated core, wherein the sheets are formed from the strip according to claim 13 or claim 14.

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