Soft magnetic alloy and method for producing a soft magnetic alloy

Abstract

A soft magnetic alloy consisting essentially of 47 wt% ≤ Co ≤ 50 wt%, 1 wt% ≤ V ≤ 3 wt%, 0 wt% ≤ Ni ≤ 0.2 wt%, 0.08 wt% ≤ Nb ≤ 0.12 wt%, 0 wt% ≤ C ≤ 0.007 wt%, 0 wt% < Mn ≤ 0.1 wt%, 0 wt% < Si ≤ 0.1 wt%, remainder Fe, wherein (Mn + Si) ≥ 0.02 wt% and the soft magnetic alloy has an induction B(8 A / cm) of at least 2.12 T.

Description

A ferromagnetic material that can be magnetized but tends to remain unmagnetized is described as soft magnetic. When a soft magnetic material is magnetized in a magnetic field and then removed from the magnetic field, it largely loses the magnetism it has exhibited in the field. A soft magnetic material preferably exhibits a low hysteresis loss, a high magnetic permeability and a high saturation magnetic induction. Soft magnetic material is used in various static and rotating electrical devices such as motors, generators, alternators, transformers, and magnetic bearings.The publications DE 10 2005 034 486 A1, U.S. Pat. No. 3,634,072 A and JP H01255645 A each disclose FeCoV alloys.U.S. Pat. No. 5,501,747 discloses a high strength, soft magnetic iron cobalt vanadium based alloy further comprising 0.15 weight percent to 0.5 weight percent niobium and 0.003 weight percent to 0.02 weight percent carbon. This alloy is disclosed as a combination of the yield strength, the magnetic properties and the electrical properties which enables it to be applied to the rotating member such as a rotor of a rotating electrical machine. When annealed at a temperature of no more than 740°C for no more than about 4 hours, the alloy has a yield strength of at least 620 MPa at room temperature.However, other soft magnetic alloys having a combination of a high yield strength and suitable magnetic properties suitable for applications such as rotating electrical equipment are desirable.A soft magnetic alloy is provided consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.005 weight percent, 0 weight percent < Mn ≤ 0.1 weight percent, 0 weight percent < Si ≤ 0.1 weight percent, balance iron, wherein (Mn + Si) ≥ 0.02% weight percent and the soft magnetic alloy has an induction B(8A / cm) of at least 2.12 T.The alloy is based on a 49%Co-2%V-Fe-type alloy further comprising niobium in a range of 0.08 to 0.12 weight percent, a maximum carbon content of 0.005 weight percent, and optionally Ni up to 0.2 weight percent.The elements manganese and silicon may be added to reduce the oxygen content of the alloy. Oxygen is not intentionally added to the alloy, but may be present as an impurity on the order of up to 0.009 weight percent. Other impurity elements such as one or more of Cr, Cu, Mo, Al, S, Ti, Ce, Zr, B, N, Mg, Ca, or P may be contained in a total amount of not more than 0.5 weight percent.For 49%Co-2%V-49%Fe type alloys, it is generally observed that the annealing temperature has adverse effects on mechanical properties and magnetic properties. In particular, it is observed that the yield strength increases for decreasing annealing temperatures, while the magnetic properties are improved during annealing at higher temperatures. The optimum of the mechanical properties is achieved at lower temperatures than the optimum of the magnetic properties.A combination of a niobium content in the range of 0.08 to 0.12 weight percent and a carbon content of less than 0.005 weight percent, or preferably less than 0.003 weight percent, provides a soft magnetic alloy having a yield strength that can be adjusted as desired over a range of 200 MPa to 450 MPa by appropriate selection of the annealing conditions. At the same time, soft magnetic characteristics suitable for soft magnetic parts such as a rotor or a stator of a rotating electric machine can be obtained.An explanation of this behavior is that by reducing the carbon content, the formation of Laves phases (Co / Fe, Nb) is preferred, while the formation of carbides is reduced, thus making it possible to obtain a suitably high yield strength without ending in a deterioration of the magnetic properties, in particular in losses, up to a magnitude in which they are no longer suitable for use in electric machines.In a rotating electric machine, the rotor typically requires a higher yield strength than is required for the stator, as the rotor rotates during operation and is subject to centrifugal forces. It is useful if the yield strength of the rotor is sufficiently high that the material of the rotor remains below its elastic limit despite the centrifugal forces. In contrast, the stator is static and not subject to centrifugal force, so the stator may have a lower yield strength than the rotor.It is advantageous that the yield strength and the magnetic properties of the soft magnetic alloy according to the invention can be adjusted by tempering the parts for the rotor and for the stator at different tempering temperatures such that the same composition can be used both for the rotor and for the stator of an electric machine.In another embodiment, the upper limit of the carbon content is decreased to 0.003 weight percent, so that the soft magnetic alloy has a carbon content of 0 weight percent ≤ C ≤ 0.003 weight percent. In further embodiments, the soft magnetic alloy contains carbon in the range of 0 weight percent < C ≤ 0.005 weight percent or 0 weight percent < C ≤ 0.003 weight percent. Reducing the carbon content may be advantageous for improving the magnetic properties.In another embodiment, the soft magnetic alloy contains nickel in a range of 0 weight percent <Ni ≤ 0.2 weight percent.In some embodiments, the soft magnetic alloy contains manganese and / or silicon within a range of 0 weight percent < Mn ≤ 0.07 weight percent and / or 0 weight percent < Si ≤ 0.05 weight percent.In one embodiment, the soft magnetic alloy comprises a yield strength (0.2% strain) between 200 MPa and 450 MPa in a tempered state. The yield strength can be adjusted as desired by adjusting the annealing conditions, in particular by selecting a suitable annealing temperature.The soft magnetic alloys having a composition within the ranges given above exhibit a linear dependence of the yield strength on the annealing temperature. This property is not demonstrated by the commercially available 49%Co / 49%Fe / 2%V alloys with additions of about 0.05 Nb and 100 ppm C as the HIPERCO 50. These commercially available alloys are referred to as reference alloys in the following.In one embodiment, the soft magnetic alloy comprises a yield strength (0.2% elongation) that is a linear function of the annealing temperatures over an annealing temperature range of 740° C. to 865° C. or 730° C. to 900° C.In one embodiment, the soft magnetic alloy in a tempered state has a yield strength (0.2% strain) that is within ±10% of a linear function of the yield strength (0.2% strain) with respect to the tempering temperature maintained for the soft magnetic alloyIn a tempered state, the soft magnetic alloy may comprise a resistance of at least 0.4 μΩm and / or an induction B(8A / cm) of at least 2.12 T.As discussed above, the soft magnetic alloy includes a combination of mechanical strength and soft magnetic properties suitable for soft magnetic parts of a rotating electric machine. In one embodiment, the soft magnetic alloy is annealed such that, in the annealed state, it has an induction B(8A / cm) of at least 2.12 T and a yield strength of at least 370 MPa. This combination of properties is suitable for a rotor of an electric machine.In a specific embodiment, after annealing at a temperature in the range of 720° C. to 900° C., the soft magnetic alloy has a yield strength in the range of 200 MPa to 450 MPa and a power loss density at 2 T and 400 Hz of less than 90 W / kg. In further embodiments, the power loss density at 2 T and 400 Hz is less than 90 W / kg for a temperature of 720° C. and is less than 65 W / kg for a temperature of 880° C.A stator for an electric motor and a rotor for an electric motor comprising a soft magnetic alloy according to any one of the above-described embodiments are also provided. An electric motor having a stator and a rotor each comprising a soft magnetic alloy having a composition according to any of the embodiments described above is also provided. The rotor and the stator may have the same composition, but different mechanical properties and magnetic properties. This may be provided by annealing the rotor or parts forming the rotor under different annealing conditions compared to the stator or parts of the stator.The rotor and / or the stator may include a plurality of plates or layers stacked together to form a laminate.The electric machine may be a motor, a generator, an alternator, or a transformer.A method of making a soft magnetic alloy is provided, the method comprising providing a melt consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.005 weight percent, 0 weight percent < Mn ≤ 0.1 weight percent, 0 weight percent < Si ≤ 0.1 weight percent, balance Fe, wherein (Mn + Si) ≥ 0.02% weight percent. This melt is cooled and solidified to form a blank. The blank is hot rolled, quenched from a temperature above 730° C. and then cold rolled. Subsequently, at least a portion of the ingot is annealed at a temperature in the range of 730° C. to 880° C. After hot rolling, the ingot is cooled to a temperature above 730°C and then quenched to room temperature, or the ingot is cooled and reheated to a temperature above 730°C and then quenched to room temperature.After cold rolling, the blank may be in the form of a plate or a strip. Portions of the blank may be removed by stamping or separating, for example, and the piece or pieces may be annealed at an appropriate selected temperature to obtain the desired mechanical and magnetic properties.In further embodiments, at least a portion of the ingot is annealed at a temperature in the range of 740° C. to 865° C., or in a range of 730° C. to 790° C., or in a range of 800° C. to 880° C. The higher temperature range of 800° C. to 880° C. may be used when a stator is manufactured from a soft magnetic alloy, and the lower temperature range of 730° C. to 790° C. may be used when a rotor is manufactured from the soft magnetic alloy.In a further embodiment, a thickness reduction of the blank of about 90% is produced by hot rolling the blank. This thickness reduction may be selected to select the desired thickness reduction in the subsequent cold rolling step and to select the amount of deformation applied to the soft magnetic alloy during cold rolling.The blank may be hot rolled at a temperature in the range of 1100°C to 1300°C. After hot rolling, the blank can be naturally cooled to room temperature. After hot rolling, the strip may be quenched from a temperature above 730°C to room temperature or below room temperature. This can be done while the strip is cooled from the hot rolling temperature. Alternatively, the strip may be cooled to room temperature and then reheated to a temperature above 730°C and quenched to room temperature or below room temperature.After hot rolling and before cold rolling, the blank may be cleaned, for example, milled and / or mechanically worked, for example, by sandblasting to clean the surface. This improved surface finish of the ingot after cold rolling may also aid in improving the magnetic properties of the alloy after annealing.In one embodiment, a 90% thickness reduction in the ingot is produced by cold rolling the ingot. After cold rolling, the thickness of the ingot is in a range of 0.3 mm to 9.4 mm. This thickness is suitable for producing laminated articles such as laminated rotors and laminated stators for electric machines.A method for manufacturing a semi-finished part is also provided, comprising performing the method according to any of the previously described embodiments and separating a part of the blank to form a semi-finished part.A laminated article may be formed by joining a plurality of semi-finished parts including a soft magnetic alloy according to any one of the above-described embodiments.A rotor for an electric motor may be provided by annealing the soft magnetic alloy or the laminated article according to any one of the above-described embodiments at a temperature of 730° C. to 790° C.A stator for an electric motor may be provided by annealing the soft magnetic alloy or the laminated article according to any one of the above-described embodiments at a temperature of 800° C. to 880° C.Specific examples and embodiments will now be described with reference to the accompanying drawings and tables. FIG. 1 shows a graph of the yield strength as a function of the Nb content for sample alloys with max. 50 ppm carbon. FIG. 2 shows a graph of a range of yield strength as a function of Nb content for sample alloys with max. 50 ppm carbon. FIG. 3 shows a graph of the coercive field strength as a function of the Nb content for sample alloys with max. 50 ppm carbon. FIG. 4 shows a graph of the induction B(8 A / cm) as a function of the Nb content for sample alloys with max. 50 ppm carbon. FIG. 5 shows a graph of the losses at 2 T and 400 Hz as a function of the Nb content for sample alloys with max. 50 ppm carbon. FIG. 6 shows a graph of the yield strength as a function of the carbon content for sample alloys with 0.09-0.11% Nb. FIG. 7 shows a graph of a range of yield strength as a function of carbon content for sample alloys with 0.09-0.11% Nb. FIG. 8 shows a graph of the coercive field strength as a function of the carbon content for sample alloys with 0.09-0.11% Nb. FIG. 9 shows a graph of the induction B(8 A / cm) as a function of the carbon content for sample alloys with 0.09-0.11% Nb. FIG. 10 shows a graph of the losses at 2 T and 400 Hz as a function of the carbon content for sample alloys with 0.09-0.11% Nb. FIG. 11 shows a graph of coercive field strength as a function of the yield strength for (a) a prob alloy with 0.09-0.11% Nb and max. 50 ppm carbon, (b) a sample alloy containing 0.04-0.06% Nb and 100-110 ppm carbon (a HIPERCO-50-like composition), (c) VACODUR 50 comparative data, (d) HIPERCO 50 comparative data. FIG. 12 shows a graph of the induction B(8 A / cm) as a function of the yield strength for (a) a sample alloy with 0.09-0.11% Nb and max. 50 ppm carbon, (b) 0.04-0.06% Nb and 100-110 ppm carbon (a HIPERCO-50-like composition), (c) VACODUR 50 comparative data, (d) HIPERCO 50 comparative data. FIG. 13 shows a graph of the losses at 2T and 50 Hz as a function of the yield strength for (a) a sample alloy with 0.09-0.11% Nb, max. 50 ppm carbon, and (b) a sample alloy comprising 0.04-0.06% Nb, 100-110 ppm carbon (a HIPERCO-50-like composition). FIG. 14 shows a graph of the losses at 2T and 400 Hz as a function of the yield strength for (a) a sample alloy with 0.09-0.11% Nb, max. 50 ppm carbon, (b) a sample alloy containing 0.04-0.06% Nb, 100-110 ppm carbon (a HIPERCO-50-like composition), (c) VACODUR 50 comparative data, (d) HIPERCO 50 comparative data. Figure 15 shows optical micrographs of a sample alloy according to the invention and a HIPERCO-50-like sample alloy after annealing at 4h and 850°C. FIG. 16 shows a graph of t oxygen content as a function of carbon content for three sample alloys. FIG. 17 shows a graph of the yield strength as a function of the annealing temperature. FIG. 18 shows an SEM micrograph of a comparative sample. FIG. 19 shows an SEM micrograph of a comparative sample. Figure 20 shows an SEM micrograph of a sample alloy according to the invention. FIG. 21 shows an SEM micrograph of a comparative sample.Table 1 shows comparative data for HIPERCO 50 and VACODUR 50.Table 2 shows magnetic and mechanical properties of the comparative alloys of Table 1 after different temper treatments.Table 3 shows compositions, magnetic and mechanical properties of the sample alloys that were tested.Table 4 shows the compositions of the alloys used in the embodiment shown in Fig. 18.Table 5 shows yield strength values shown in the graph of Fig. 18.A soft magnetic alloy is provided consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.005 weight percent, 0 weight percent ≤ Mn ≤ 0.1 weight percent, 0 weight percent ≤ Si ≤ 0.1 weight percent, balance iron.The alloy can be prepared by providing a melt consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.005 weight percent, 0 weight percent ≤ Mn ≤ 0.1 weight percent, 0 weight percent ≤ Si ≤ 0.1 weight percent, balance Fe, by cooling and solidifying the melt and forming a ingot. The blank is then hot rolled, for example at 1200°C, cooled and quenched from a temperature above 730°C to room temperature. The blank is then cold rolled at room temperature to a final thickness of 0.35 mm, for example. Subsequently, at least a portion of the blank is annealed at a temperature in the range of 730° C. to 880° C. to form a semi-finished product.The annealing temperature is chosen to be between the recrystallization temperature of about 720°C and the phase transformation at about 885°C from the alpha, α, phase to the gamma, γ, phase. The annealing temperature is selected within this range such that the semi-finished product has the desired mechanical properties, in particular the desired yield point (0.2% elongation), Rp 0,2, in combination with the desired magnetic properties, in particular losses.It has been observed that a combination of a niobium content in the range of 0.08 to 0.12 weight percent and a carbon content of less than 0.005 weight percent, or preferably less than 0.003 weight percent, provides a soft magnetic alloy having a yield strength that can be adjusted as desired over a range of 200 MPa to 450 MPa by appropriate selection of the annealing temperature. At the same time, good soft magnetic properties can be obtained, in particular with low losses, which are suitable for soft magnetic parts of rotating electrical machines.The yield strength of the soft magnetic alloys having a niobium content within the range of 0.08 to 0.12 weight percent and a carbon content of less than 0.005 weight percent, or preferably less than 0.003 weight percent, can be adjusted over a wider range than the achievable range with the comparative compositions of the reference alloys.In a further embodiment, the yield strength depends linearly on the annealing temperature. This behavior is not shown by the comparative compositions of the reference alloys.Advantageously, the yield strength and the magnetic properties can be adjusted such that the same composition can be used for both the rotor and the stator of an electric machine by tempering the parts for the rotor and for the stator at different tempering temperatures. For example, parts for a rotor may be annealed at 750° C. and have a higher yield strength than the parts for the stator that are annealed at 870° C. This example of the stator has significantly better magnetic properties than that of the rotor.In a first set of embodiments, a plurality of soft magnetic alloys having a carbon content of at most 50 ppm and different niobium contents were produced.FIG. 1 shows a graph of yield strength versus Nb content for sample alloys having a maximum carbon content of 50 ppm annealed at five different temperatures, 750° C., 780° C., 820° C., 850° C., and 871° C. The yield strength is highest for alloys annealed at a lower temperature and decreases with increasing temperature. There is a general increase in yield strength, which is measured for an increase in niobium content.FIG. 2 is a graph of a range of yield strength obtainable by varying the annealing temperature depending on the Nb content for the samples of FIG. 1. The difference in yield strength 126 MPa and 166 MPa, which is achievable by appropriate selection of the annealing temperature ranges and is slightly less for niobium contents greater than about 0.2 weight percent.The magnetic properties of these sample alloys are shown in Figs. 3 to 5.FIG. 3 shows a graph of coercive field strength as a function of the Nb content, FIG. 4 shows a graph of induction B(8 A / cm) as a function of the Nb content, and FIG. 5 shows a graph of losses at 2 T and 400 Hz as a function of the Nb content of the samples shown in FIGS. 1 and 2.FIG. 3 shows that the coercive field strength increases with increasing niobium content. Up to a niobium content of 0.12 percent by weight, the increase in coercive field strength after a heat treatment at 871° C. is relatively small. Therefore, a coercive force of less than 0.4 A / cm can be achieved with a niobium content of about 0.1 weight percent.As shown in FIG. 4, the magnetic induction falls as the niobium content increases at a annealing temperature of 750° C., which results in the highest yield point. However, the value of induction that can be achieved after treatment at 871°C remains relatively constant up to a niobium content of about 0.1, so that induction of greater than 2.15 T can be achieved with a niobium content of 0.13 weight percent.FIG. 5 shows that the losses increase with increasing niobium content. However, the losses are relatively constant at niobium contents between 0.04 and 0.11 for sample annealing at 871°C.In a second set of embodiments, the effect of carbon content on the mechanical and magnetic properties of alloys having a niobium content in the range of 0.09 to 0.11 weight percent is studied.FIG. 6 shows a graph of yield strength versus carbon content for sample alloys with 0.09-0.11% Nb and FIG. 7 shows a graph of a range of yield strength versus carbon content for these sample alloys.The samples of the second set of embodiments were annealed at five different temperatures, 750° C., 780° C., 820° C., 850° C. and 871° C., which were used for the first set of embodiments.FIG. 6 shows that the yield strength of the samples increases with increasing carbon content and that for a tempering temperature of 871° C., the yield strength increases from about 250 MPa for a carbon content of 30 ppm to 400 MPa for a carbon content of 180 ppm. For a annealing temperature of 750° C., the yield strength increases from about 400 MPa for 30 ppm carbon to 475 MPa for a carbon content of 180 ppm.FIG. 7 shows that the range over which the yield strength can be adjusted for a given carbon content drops with decreasing carbon content, so that for carbon contents of less than about 50 ppm, the yield strength is adjustable over a range of about 150 MPa. However, for higher carbon contents of about 100 ppm, the yield strength can only be adjusted within a range of about 120 MPa. Above a carbon content of about 100 ppm, the range falls to less than 100 MPa.Magnetic properties measured for samples from this second set of embodiments are shown in Figures 8-10.FIG. 8 shows a graph of coercive field strength as a function of the C content, FIG. 9 shows a graph of magnetic induction B(8 A / cm) as a function of the C content, and FIG. 10 shows a graph of losses at 2 T and 400 Hz as a function of the C content for samples having a niobium content of 0.09-0.11 percent by weight.FIG. 8 shows that the coercive field strength remains relatively constant for all annealing temperatures for carbon contents up to about 60 ppm. Figure 9 shows that induction remains relatively constant for carbon contents up to 130 ppm for samples heated to 871°C. FIG. 10 shows that the losses increase with increasing carbon content.In a third set of embodiments, the magnetic properties of an alloy having 0.09 to 0.11 weight percent and a maximum of 50 ppm carbon are compared to two reference samples commercially available under the names VACODUR 50 and HIPERCO 50. Table 1 shows the comparative data for the comparative samples. Table 2 shows magnetic and mechanical properties of the comparative alloy HIPERCO 50 of Table 1 and an alloy according to the invention after different tempering treatments.The magnetic properties are shown in the graphs as a function of the yield strength.FIG. 11 shows a graph of coercive field strength as a function of yield strength for (a) sample alloys with 0.09-0.11% Nb and max. 50 ppm C, (b) sample alloys containing 0.04-0.06% Nb and 100-110 ppm C (a HIPERCO-50-type alloy), (c) comparative data of VACODUR 50, (d) comparative data of HIPERCO 50.Figure 11 shows that the coercive field of the alloy according to the invention is lower than that of the samples having a higher carbon content in almost the whole yield strength range.FIG. 12 shows a graph of the induction B(8 A / cm) as a function of the yield strength for (a) sample alloys with 0.09-0.11% Nb and max. 50 ppm C, (b) sample alloys containing 0.04-0.06% Nb and 100-110 ppm C (a HIPERCO-50-type alloy), (c) comparative data of VACODUR 50, (d) comparative data of HIPERCO 50.Figure 12 shows that the low carbon alloys have a magnetic induction of greater than 2.22T to a yield strength of about 300 MPa.FIG. 13 shows a graph of the losses at 2T and 50 Hz as a function of the yield strength for (a) sample alloys with 0.09-0.11% Nb, max. 50 ppm C, and (b) sample alloys comprising 0.04-0.06% Nb, 100-110 ppm C (a HIPERCO-50-type alloy).FIG. 14 shows a graph of the losses at 2T and 400 Hz as a function of the yield strength for (a) sample alloys with 0.09-0.11% Nb and max. 50 ppm C, (b) sample alloys containing 0.04-0.06% Nb and 100-110 ppm C (HIPERCO-50-like), (c) comparative data of VACODUR 50, (d) comparative data of HIPERCO 50.FIGS. 13 and 14 show losses at 50 Hz and 400 Hz. In both cases, the losses are lower for the samples with a low carbon content than for the samples with a higher carbon content.Table 3 summarizes the composition, annealing conditions, magnetic properties, and mechanical properties of the sample alloys that were prepared and tested.In a third set of embodiments, the development of microstructure in an alloy according to the invention has been studied. Sample 93 / 8603 is a sample according to the invention and Sample 93 / 8605 has a composition similar to the commercial HIPERCO 50 alloy and is a comparative alloy.The mechanical properties, magnetic properties and the measured grain size of these two alloys after annealing treatments at different temperatures are summarized in Table 2.After annealing at 750° C., the sample 1 has a high yield strength of 474 MPa and a coercive force of 1.9 A / cm, while the HIPERCO-like comparative alloy has a yield strength of 422 MPa and a coercive force of 1.17 A / cm. The grain size of 7 to 10 μm for sample 1 is fine and not completely recrystallized, while the HIPERCO-like comparative alloy is completely recrystallized and has a slightly larger grain size.For a higher annealing temperature than 750°C, both alloys are completely recrystallized and the mechanical and magnetic properties of the two samples are similar.After annealing at 820°C, sample 1 has a lower yield strength but better magnetic values than the HIPERCO-like comparative sample.At a annealing temperature of 850°C, the mechanical and magnetic properties of both samples are similar.Figure 15 shows optical micrographs of a sample alloy according to the invention and a reference (HIPERCO-50-like) sample alloy after annealing for 4h at 850°C.Sample 1 has a relatively homogeneous microstructure with grains having an average size of 27 to 30 μm. The HIPERCO-like comparative alloy has some isolated giant grains and a more inhomogeneous microstructure is observed. If the large grains are ignored, the average grain size is about 18 to 22 μm.In a fourth set of embodiments, a possible effect of carbon content on oxygen content was studied.FIG. 16 shows a graph of oxygen content as a function of carbon content for sample alloys 93 / 8225-8288, 93 / 8485-8491, 93 / 8598-8600. Figure 16 shows that the oxygen content tends to increase at lower carbon contents, which may lead to the formation of oxide inclusions in the alloy.To achieve a slight deoxidation effect, 0.05 weight percent manganese and 0.05 weight percent silicon were added in some alloys. However, when these elements are omitted, an increase in oxygen content was not observed. However, no adverse effect was observed for the magnetic properties.In a fifth set of embodiments, the effect of yield strength as a function of temperature was examined for a sample having a composition according to the invention and for a comparative HIPERCO-like sample.FIG. 17 shows a graph of the yield strength as a function of the annealing temperature. Figure 17 shows that for the sample according to the invention the relationship between yield strength and annealing temperature is generally linear, while for the comparative HIPERCO-like sample a sharp drop in yield strength occurs between 780°C and 820°C.The linear shape of the drop in yield strength with increasing temperature is advantageous since the annealing temperature within the furnace during the production of the semifinished parts leads to more predictable results than to unpredictable results. Therefore, variations in temperature can be compensated for.Table 4 shows the compositions of the alloys used in the embodiment shown in Fig. 17, and Table 5 shows yield strength values shown in the graph of Fig. 18.FIG. 18 shows an SEM (scanning electron microscopy) micrograph of a first comparative sample with 0.26 percent by weight niobium and 31 ppm carbon. The sample was annealed at 750°C for 3 hours. This comparative sample mainly includes Laves phases seen in the micrograph as bright and comparatively large inclusions having a size greater than about 50 nm.FIG. 19 shows an SEM micrograph of a second comparative sample with a lower niobium content of 0.1 weight percent and a higher carbon content of 190 ppm. This sample was also annealed at 750°C for 3 hours. Unlike the first comparative sample, the second comparative sample mainly includes carbides as shown by the much smaller lighter inclusions. These inclusions differ from the Laves phase inclusions by their smaller size of less than 50 nm.Figure 20 shows an SEM micrograph of an alloy according to the invention with a niobium content of 0.11 weight percent and a carbon content of 23 ppm. This sample was also annealed at 750°C for 3 hours. The alloy mainly includes Laves phases as shown by the bright inclusions within the grains.FIG. 21 shows an SEM micrograph of a third comparative alloy having a lower niobium content of 0.06 weight percent and a higher carbon content of 100 ppm, annealed at 750° C. for 3 hours. This comparative alloy mainly includes carbide phases as shown by the smaller bright inclusions. Table 1 Table 1Hiperco 5075031,132,1268642978831,022,1508541182040,932,1508038787120,462,19767188VACODUR 5075031,6282,0509046882030,9982,10875383Table 2Table 2AnnealingRp0.2 MPaHcA / cmB(3A / cm) TGrain size μmRp0.2 MPaHc AlcmB(3A / cm) TGrain size μm2h 730°C4741,901,5207 - 104221,171,9359 - 123h 750°C4171,191,9358 - 164101,021,98910 - 12,54h 820°C3180,662,018-3660,711,973-4h 850°C2730,542,02527 - 302820,612,02418 - 22Table 4 Table 437602391-1Remainder: Remainder:48,551,800,09< 0,0030Hiperco 50Remainder: Remainder:43,551,870,050,0070Table 5Table 574039278033737602391-10,35820294865247740442780415Hiperco 500,35820236865242

Claims

A soft magnetic alloy consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.007 weight percent, 0 weight percent < Mn ≤ 0.1 weight percent, 0 weight percent < Si ≤ 0.1 weight percent, balance Fe, wherein (Mn + Si) ≥ 0.02% weight percent, and the soft magnetic alloy has an induction B(8A / cm) of at least 2.12 T.The soft magnetic alloy of claim 1, having a carbon content of 0 weight percent ≤ C < 0.005 weight percentThe soft magnetic alloy of claim 1, having a carbon content of 0 weight percent < C ≤ 0.005 weight percent.The soft magnetic alloy of claim 3 having a carbon content of 0 weight percent < C < 0.003 weight percent.Soft magnetic alloy according to one of the preceding claims, having a nickel content of 0.01 percent by weight < Ni ≤ 0.2 percent by weight.Soft magnetic alloy according to one of the preceding claims, having a manganese content of 0 percent by weight < Mn ≤ 0.07 percent by weight.Soft magnetic alloy according to one of the preceding claims, having a silicon content of 0 percent by weight < Si ≤ 0.07 percent by weight.The soft magnetic alloy of any preceding claim, wherein the soft magnetic alloy has a yield strength (0.2% strain) between 200 MPa and 450 MPa in a tempered state.The soft magnetic alloy of any preceding claim, wherein in a tempered state the soft magnetic alloy has a yield strength (0.2% strain) that is between ±10% of a linear function of the yield strength (0.2% strain) with respect to the tempering temperature.The soft magnetic alloy of any preceding claim, wherein the soft magnetic alloy has a yield strength (0.2% elongation) that is a linear function of the annealing temperature over an annealing temperature range of 740°C to 865°C.The soft magnetic alloy of claim 10, wherein the soft magnetic alloy has a yield strength (0.2% strain) that is a linear function of the annealing temperature over an annealing temperature range of 730°C to 900°C.The soft magnetic alloy of any preceding claim, wherein the soft magnetic alloy has a resistance of at least 0.4 μΩm.The soft magnetic alloy of any preceding claim, wherein the soft magnetic alloy has a yield strength of at least 370 MPa.The soft magnetic alloy of any preceding claim, wherein after annealing at a temperature in the range of 720°C to 900°C, the soft magnetic alloy has a yield strength in the range of 200 MPa to 450 MPa and a power loss density at 2 T and 400 Hz of less than 90 W / kg.The soft magnetic alloy of any preceding claim, wherein the soft magnetic alloy has a composition selected such that the yield strength of the soft magnetic alloy is adjustable over a range of at least 130 MPa after being annealed at 750°C or 871°C.A stator for an electric motor comprising the soft magnetic alloy according to any one of claims 1 to 15.A rotor for an electric motor comprising the soft magnetic alloy according to any one of claims 1 to 15.An electric motor comprising the stator of claim 16 and the rotor of claim 17.A method for making a soft magnetic alloy comprising: - providing a melt consisting essentially of 47 weight percent ≤ Co ≤ 50 weight percent, 1 weight percent ≤ V ≤ 3 weight percent, 0 weight percent ≤ Ni ≤ 0.2 weight percent, 0.08 weight percent ≤ Nb ≤ 0.12 weight percent, 0 weight percent ≤ C ≤ 0.005 weight percent, 0 weight percent < Mn ≤ 0.1 weight percent, 0 weight percent < Si ≤ 0.1 weight percent, balance Fe, wherein (Mn + Si) ≥ 0.02% weight percent, - cooling and solidifying the melt to form a ingot, - hot rolling the ingot followed by - cold rolling the ingot, and subsequently - annealing at least a portion of the ingot at a temperature in the range of 730°C to 880°C, wherein after hot rolling, the blank is cooled to a temperature above 730° C. and then quenched to room temperature or the blank is cooled and reheated to a temperature above 730° C. and then quenched to room temperature.The method of claim 19, wherein at least a portion of the ingot is annealed at a temperature in the range of 740°C to 865°C.The method of claim 19, wherein at least a portion of the ingot is annealed at a temperature in the range of 730°C to 790°C or in the range of 800°C to 880°C.The method of any of claims 19 to 21, wherein a thickness reduction in the blank of 90% is produced by hot rolling the blank.The method of any one of claims 19 to 22, wherein the blank is hot rolled at a temperature in a range of 1100°C to 1300°C.The method of any of claims 19 to 23, further comprising pickling the ingot prior to cold rolling.The method according to any one of claims 19 to 24, wherein a thickness reduction in the blank to 90% is produced by cold rolling the blank.The method according to any one of claims 19 to 25, wherein after the cold rolling, the thickness of the ingot is in the range of 0.3 mm to 0.4 mm.A method of manufacturing a semi-finished part comprising the method of any one of claims 19 to 26 and comprising separating a portion of the blank to produce a tool part.The method of claim 27, further comprising assembling a plurality of semi-finished parts produced by the method of claim 26 and forming a laminated soft magnetic article.A method of manufacturing a rotor for an electric motor, comprising the soft magnetic alloy according to any one of claims 1 to 15 and annealing at a temperature of 730 to 790°C.A method of manufacturing a stator for an electric motor, comprising providing the soft magnetic alloy according to any one of claims 1 to 15 and annealing at a temperature of 800°C to 880°C.

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