GB2492406A

GB2492406A - A soft magnetic Fe-Co-V-Nb alloy

Info

Publication number: GB2492406A
Application number: GB201111233A
Authority: GB
Inventors: Witold Pieper; Niklas Volbers; Joachim Gerster
Original assignee: Vacuumschmelze GmbH and Co KG
Current assignee: Vacuumschmelze GmbH and Co KG
Priority date: 2011-07-01
Filing date: 2011-07-01
Publication date: 2013-01-02
Anticipated expiration: 2031-07-01
Also published as: GB2492406B; GB201111233D0; DE102012105605A1

Abstract

A soft magnetic alloy comprises (by weight): 47-50 % Co, 1-3 % V, 0-0.2 % Ni, 0.08-0.12 % Nb, 0-0.007 % C, 0-0.1 % Mn, 0-0.1 % Si, with the balance being Fe and impurities. A soft magnetic alloy comprising (by weight): 47-50 % Co, 1-3 % V, 0-0.2 % Ni, 0.08-0.12 % Nb, 0-0.005 % C, 0-0.1 % Mn, 0-0.1 % Si, with the balance being Fe is processed by hot rolling followed by cold rolling and then annealing at a temperature in the range 730-880 0C. The alloy can be hot rolled at a temperature in the range 1100-1300 0C, with a thickness reduction of 90 %. After hot rolling the alloy is preferably quenched to room temperature from 730 0C or more, pickled and then cold rolled with 90 % reduction in thickness. Used for making laminated electric motor stators and rotors.

Description

Soft magnetic alloy and method for producing a soft magnetic alloy.

A ferromagnetic material that can be magnetized, but tends not to remain magnetized is described as magnetically soft. When a magnetically soft material is magnetised in a magnetic field and then removed from the magnetic field, it loses most of the magnetism exhibited while in the field. A magnetically soft material preferably displays a low hysteresis loss, high mag-netic permeability and a high magnetic saturation induction.

Magnetically soft materials are used in various static and ro- tating electrical devices, such as motors, generators, alter-nators, transformers and magnetic bearings.

US 5,501,747 discloses a high strength, soft magnetic iron-cobalt-vanadium based alloy which further comprises 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 having a combination of yield strength, magnetic properties and electrical properties which enables it to be used for the rotating part, such as a rotor, of a rotating electrical ma-chine. When the alloy is annealed at a temperature of not more than about 740DC for not more than about 4 hours, it has a room temperature yield strength of at least 620 MPa.

However, further soft magnetic alloys having a combination of a high yield strength and magnetic properties suitable for ap- plications, such as rotating electrical devices, are desir-able.

A soft magnetic alloy is provided that consists essentially of 47 weight percent «= Co «= 50 weight percent, 1 weight percent «= V «= 3 weight percent, 0 weight percent «= Ni «= 0.2 weight per-cent, 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 per-cent, remainder Fe.

The alloy is based on a 49%Co-2%V-Fe-type alloy which further includes niobium within the range of 0.08 to 0.12 weight per- cent, a maximum carbon content of 0.005 weight percent and op-tionally Ni up to 0.2 weight percent.

The elements manganese and silicon are also optional and may be added in order to reduce the oxygen content of the alloy.

Oxygen is not intentionally added to the alloy, but may be present as an impurity in amounts up to 0.009 weight percent.

Further impurity elements such as one or more of Cr, Cu, Mo, Al, 5, Ti, Ce, Zr, B, N, Mg, Ca or P may be present in a total amount of not more than 0.5 weight percent.

For alloys of the 49%Co-2%V-49%Fe-type, the annealing tempera- ture is generally observed to have opposing effects on the me- chanical properties and the magnetic properties. In particu-lar, the yield strength is observed to increase for decreasing annealing temperatures, whilst the magnetic properties are im- proved by annealing at higher temperatures. The optimum me-chanical properties are achieved at lower temperatures than the optimum magnetic properties.

A combination of a niobium content with 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 with a yield strength that can be adjusted as desired over a range of 200 MPa to 450°C by ap-propriate selection of the annealing conditions. At the same time, soft magnetic properties suitable for soft magnetic parts, such as a rotor or a stator, of a rotating electrical machine can be obtained.

One explanation for this behaviour is that by reducing the carbon content, the formation of Laves phases (Co/Fe, Nb) is favoured whilst the formation of carbides is reduced, thus enabling a suitably high yield strength to be obtained without resulting in a worsening of the magnetic properties, in par- ticular losses, to such a degree that they are no longer suit-able for use in electric machines.

In a rotating electrical machine, the rotor typically requires a higher yield strength than is required for the stator as the rotor rotates during use and is subjected to centrifugal forces. It may be 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 subjected to centrifugal force so that the stator may have a lower yield strength than that of the rotor.

usefully, the yield strength and the magnetic properties of the soft magnetic alloy according to the invention can be ad-justed by annealing the parts for the rotor and for the stator at different annealing temperatures so that the same composi- tion can be used for both the rotor and the stator of an elec-trical machine.

In a further embodiment, the upper limit of the carbon content is reduced to 0.003 weight percent so that the soft magnetic alloy comprises a carbon content of 0 weight percent «= C «= 0.003 weight percent. In further embodiments, the soft mag-netic alloy includes 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 useful in improving the magnetic properties.

Tn a further embodiment, the soft magnetic alloy includes nickel within the range of 0 weight percent < Ni «= 0.2 weight percent.

As discussed above, manganese and silicon are optional. In some embodiments the soft magnetic alloy includes 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 per-cent.

In an embodiment, the soft magnetic alloy comprises a yield strength (0.2% strain) of between 200 MPa and 450 MPa in an annealed state. The yield strength can be adjusted as desired by adjusting the annealing conditions, in particular, by se-lecting a suitable annealing temperature.

The soft magnetic alloys having a composition within the ranges given above display a linear dependence of the yield strength with annealing temperature. This feature is not dis-played by commercially available 49%Co/49%Ee/2%V alloys with additions of about 0.05 Nb and 100 ppm C such as Hiperco 50.

These commercially available alloys are referred to as refer-ence alloys in the following.

In an embodiment, the soft magnetic alloy comprises a yield strength (0.2% strain) that is a linear function of annealing temperature over an annealing temperature range of 740°C to 865°C or 730°C to 900°C.

In an embodiment, the soft magnetic alloy, in an annealed state, comprises a yield strength (0.2% strain) that lies within ± 10% of a linear function of yield strength (0.2% strain) against annealing temperature obtained for the soft magnetic alloy.

In an annealed state, the soft magnetic alloy may comprise a resistivity of at least 0.4 itQm and/or an induction 3(8 A/rn) of at least 2.12 T. As discussed above, the soft magnetic alloy comprises a combi-nation of mechanical strength and soft magnetic properties that are suitable for the soft magnetic parts of a rotating electrical machine. In an embodiment, the soft magnetic alloy is annealed such that it has, in the annealed state, an induc-tion 3(8 A/rn) of at least 2.12 T and a yield strength of at least 370 MPa. This combinaticn of properties is suitable for a rotor of an electric machine.

In a particular embodiment, after annealing at a temperature in the range of 720°C to 900°C, the soft magnetic alloy com-prises a yield strength in the range of 200 MPa and 450 MPa, and a power loss density at 21 and 400 Hz of less than 90 W/kg. In further embodiments, for an annealing temperature of 720°C, the power loss density at 21 and 400 Hz is Less than 90 W/kg and for an annealing temperature of 880°C is less than 65 W/kg.

A stator for an electric motor and a rotor for an electric no-tor comprising a soft magnetic alloy according to one of the previously described embodiments is also provided. An electric motor comprising a stator and a rotor each comprising a soft magnetic alloy having a composition according to one of the previously described embodiments is also provided. The rotor and the stator may have the same composition, but differing mechanical properties and magnetic properties. This may be provided by annealing the rotor or parts forming the rotor un-der different annealing conditions compared to the stator or parts forming the stator.

The rotor and/or the stator may comprise a plurality of plates or layers that are stacked together to form a laminate.

The electric machine may be a motor, a generator, an alterna-tor, or a transformer.

A method for manufacturing a soft magnetic alloy is provided which comprises 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 per-cent, 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 per-cent, remainder Fe. This melt is cooled and solidified to form a blank. The blank is hot rolled, quenched from a temperature of above 730°C, and, afterwards, cold rolled. Subsequently, at least a portion of the blank is annealed at a temperature in the range of 730°C to 880°C.

After cold rolling, the blank may have the form of a plate or ribbon. Pieces of the blank may be removed by stamping or cut-ting, for example, and the piece or pieces annealed at a suitably selected temperature no obtain the desired mechanical and magnetic properties.

In further embodiments, at least a portion of the blank is an-nealed at a temperature in the range of 740°C to 865°C or in the range of 730°C to 790°C or in the range of 800°C to 880°C.

The higher temperature range of 800°C to 880°C may be used when fabricating a stator from the soft magnetic alloy and the lower temperature range of 730°C to 790°C may be used when fabricating a rotor from the soft magnetic alloy.

In a further embodiment, a thickness reduction in the blank of about 90% is produced by the hot rolling of the blank. This thickness reduction may be selected so as to select the de-sired thickness reduction in the subsequent cold rolling step and to select the amount of deformation introduced into 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 may be natu-rally cooled to room temperature. After hot rolling, the strip is quenched from a temperature above 730°C to room temperature or to below room temperature. This may be carried out whilst the strip is cooling from the hot rolling temperature. Alter- natively, the strip may be cooled to room temperature and af-terwards reheated to a temperature above 730°C and quenched to room temperature or to below room temperature.

After hot rolling and before cold rolling, the blank may be cleaned, for example pickled and/or mechanically worked, for example by sand blasting, to clean the surface. This improves the surface finish of the blank after cold rolling and may also aid in improving the magnetic properties of the alloy af-ter annealing.

In an embodiment, a thickness reduction in the blank of 90% is produced by the cold rolling of the blank. After cold rolling, the thickness of the blank may lie in the range of 0.3 rum to 0.4 mm. This thickness is suitable for producing laminated ar-tides such as laminated rotors and laminated stators for electric machines.

A method for manufacturing a semi-finished part is also pro-vided that comprises performing the method according to one of the previously described embodiments and separating a portion of the blank to produce a semi-finished part.

A laminated article may be formed by assembling a plurality of semi-finished parts comprising a soft magnetic alloy according to one of the embodiments described above.

A rotor for an electric motor may be provided by arsiealing the soft magnetic alloy or the laminated article according to one of the previously described embodiments at a temperature of 730 to 790°C.

P. stator for an electric motor may be provided by annealing the soft magnetic alloy or the laminated article according to one of the previously 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.

Figure 1 illustrates a graph of yield strength vs. Nb-content for sample alloys with max. 50 ppm carbon.

Figure 2 illustrates a graph of range of yield strength vs. Nb-content for sample alloys with max. 50 ppm car-bon.

Figure 3 illustrates a graph of coercive field strength vs. Nb-content for sample alloys with max. 50 ppm car-bon.

Figure 4 illustrates a graph of Induction B(8 A/cm) vs. Nb-content for sample alloys with max. 50 ppm carbon.

Figure 5 illustrates a graph of losses at 2 T and 400 Hz vs. Nb-content for sample alloys with max. 50 ppm car-ben.

Figure 6 illustrates a graph of yield strength vs. carbon content for sample alloys with 0.09 -0.11% Nb.

Figure 7 illustrates a graph of range of yield strength vs. carbon content for sample alloys with 0.09 -0.11% Nb.

Figure 8 illustrates a graph of coercive field strength vs. carbon content for sample alloys with 0.09 -0.11% Nb.

Figure 9 illustrates a graph of induction B(8 A/cm) vs. car-ban content for sample alloys with 0.09 -0.11% Nb.

Figure 10 illustrates a graph of losses at 2 T and 400 Hz vs. carbon content for sample alloys with 0.09 -0.11% Nb.

Figure 11 illustrates a graph of coercive field strength vs. Yield strength for (a) a sample alloy with 0.09 - 0.11% Nb and max. 50 ppm carbon, (b) a sample alloy with 0.04 -0.06% Nb and 100-110 ppm carbon (a HIPERCO 50-like composition), (c) VACODUR 50 compar-ison data, (d) HIPERCO 50 comparison data.

Figure 12 illustrates a graph of induction B(8 A/cm) vs. Yield strength for (a) a sample alloy with 0.09 -0.11% Nb and max. 50 ppm carbcn, (b) 0.04 -0.06% Nb and 100-ppm carbon (a HIPERCO 50-like composition), (c) VACODUR 50 comparison data, (d) HIPERCO 50 compari-son data.

Figure 13 illustrates a graph of losses at 2T und 50Hz vs. Yield strength for (a) a sample alloy with 0.09 - 0.11% Nb, max. 50 ppm carbon, and (b) a sample alloy with 0.04 -0.06% Nb, 100-110 ppm carbon (a HIPERCO 50-like composition) Figure 14 illustrates a graph of losses at 2T und 400Hz vs. Yield strength for (a) a sample alloy with 0.09 - 0.11% Nb, max. 50 ppm carbon, (b) a sample alloy with 0.04 -0.06% Nb, 100-110 ppm carbon (a 1-IIFERCO 50-like alloy) , (c) VACODUR 50 comparison data, (d) HIPERCO 50 comparison data.

Figure 15 illustrates optical micrographs of a sample alloy according to the invention and a 1-fiperco 50-like sample alloy after annealing for 4h at 850°C.

Figure 16 illustrates a graph of t oxygen content as a func-tion of carbon content for three sample alloys.

Figure 17 illustrates a graph of yield strength vs annealing temperature.

Figure 18 illustrates a SEM micrograph of a comparison sample.

Figure 19 illustrates a SEM micrograph of a comparison sample.

Figure 20 illustrates a SEM micrograph of a sample alloy ac-cording to the invention.

Figure 21 illustrates a SEM micrograph of a comparison sample.

Table 1 illustrates comparison data for Hiperco 50 and VACODUR 50.

Table 2 illustrates magnetic und mechanical properties of the comparison alloys of table 1 after different an-nealing treatments.

Table 3 illustrates the composition, magnetic and mechanical properties of the sample alloys investigated.

Table 4 illustrates the compositions of the alloys used in the embodiment illustrated in Figure 18.

Table 5 illustrates values of the yield strength illustrated in the graph of Figure 18.

Ps soft magnetic alloy is provided that consists essentially of 47 weight percent «= Co «= 50 weight percent, 1 weight percent «= V «= 3 weight percent, 0 weight percent «= Ni «= 0.2 weight per-cent, 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 per-cent, remainder Fe.

The alloy may be fabricated by providing a melt consisting es-sentially 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, remainder Fe, cooling and solidifying the melt and forming a blank. 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. Sub-sequently 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 so that It lies between the recrystallization temperature of around 720°C arid the phase transformation from the alpha, a, phase to the gamma, y, phase at around 885CC. The annealing temperature is selected within this range so that the semi-finished product has the desired mechanical properties, in particular, the desired yield strength (0.2% strain), Rpo.2, in combination with the desired magnetic properties, in particular, losses.

It is observed that a combination of a niobium content with 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 with a yield strength that can be adjusted as desired over a range of MPa to 45000 by appropriate selection of the annealing temperature. At the same time, good soft magnetic properties, in particular low losses, suitable for soft magnetic parts of rotating electrical machines can be obtained.

The yield strength of 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 prefera-bly less than 0.003 weight percent can be adjusted over a wider range that that achievable with the comparison composi-tion of the reference alloys.

In a further embodiment, the yield strength is linearly de-pendent on the annealing temperature. This behaviour is not displayed by the comparison compositions of the reference al-loys.

Usefully, the yieid strength and the magnetic properties can be adjusted so that the sane composition can be used for both the rotor and the stator of an electrical machine by annealing the parts for the rotor and for the stator at different an-nealing temperatures. For example, parts for a rotor may be annealed at 750°C and have a higher yield strength than parts for the stator which are annealed at 870°C. In this example, the stator has clearly better magnetic properties than the ro-tor.

In a first set of embodiments, a plurality of soft magnetic alloys with a carbon content of 50 ppm maximum and differing niobium contents was fabricated.

Figure 1 illustrates a graph cf yield strength vs. Nb-content for sample alloys with a maximum carbon content of 50 ppm which were annealed at five different temperatures, 750°C, 780°C, 820°C, 850°C and 871°C. The yield strength is highest for the alloys annealed at a lower temperature decreases with increasing temperature. There is general increase in the yield strength measured for an increase in niobium content.

Figure 2 illustrates a graph of the range of yield strength obtainable by varying the annealing temperature vs. Nb-content for the samples of figure 1. The difference in the yield strength achievable by appropriate selection of the annealing temperature ranges between 126 and 166 MPa and is a little smaller for niobium contents of greater than around 0.2 weight percent.

The magnetic properties of these sample alloys are illustrated in Figures 3 to 5.

Figure 3 illustrates a graph of coercive field strength vs. Nb-content, Figure 4 illustrates a graph of induction 3(8 A/cm) vs. Nb-oontent and Figure 5 illustrates a graph of losses at 2 T and 400 Hz vs. Nb-content for samples illu-strated in figures 1 and 2.

Figure 3 illustrates that the coercive field strength increas-es with increasing niobium content. Up to a niobium content of 0.12 weight percent, the increase in the coercive field strength after a heat treatment at 871°C is relatively small.

Therefore, a coercive field strength of less than 0.4 A/vm can be achieved with a niobium content of around 0.1 weight per-cent.

As is illustrated in figure 4, for an annealing temperature of 750° C, which leads to the highest yield strength, the magnet-ic induction decreases with increasing niobium content. The value of the induction which can be achieved after a treatment at 871°C remains, however, relatively constant up to a niobium content of around 0.1 so that an induction of more than 2.15 T can be achieved with a niobium content of 0.13 weight percent.

Figure 5 illustrates that the losses increase with increasing niobium content. However, the losses are relatively constant for niobium contents of between 0.04 and 0.11 for the samples annealed at 871°C.

In a second set of embodiments, the effect of the carbon con-tent on the mechanical and magnetic properties of alloys with a niobium content in the range of 0.09 to 0.11 weight percent is investigated.

Figure 6 illustrates a graph of yield strength vs. carbon con- tent for sample alloys with 0.09 -0.11% Nb and Figure 7 illu-strates a graph of range of yield strength vs. carbon content for these sample alloys.

The samples of the second set of embodiments were annealed at the five different temperatures, 750°C, 780°C, 82000, 85000 and 87100, used for the first set of embodiments.

Figure 6 illustrates that the yield strength of the samples increases with increasing carbon content and that for an an-nealing temperature of 871°C the yield strength increases from around 250 MPa for a carbon content of 30 ppm to 400 MPa for a carbon content of 180 ppm. For an annealing temperature of 750°C, the yield strength increases from around 400 MPa for 30 ppm carbon to 475 MPa for a carbon content of 180 ppm.

Figure 7 illustrates that the range over which the yield strength can be adjusted for a given carbon content decreases with increasing carbon content so that for carbon contents of less than around 50 ppm, the yield strength is adjustable over a range of around 150 MPa. However, for a higher carbon con- tent of around 100 ppm, the yield strength can only be ad- justed within a range of around 120 MPa. Above a carbon con-tent of around 100 ppm, the range decreases to less than 100 MPa.

Magnetic properties measured for samples of this second set of embodiments are illustrated in figures 8 to 10.

Figure 8 illustrates a graph of coercive field strength vs. C-content, Figure 9 illustrates a graph of magnetic induction B(8 A/cm) vs. C-content and Figure 10 illustrates a graph of losses at 2 T and 400 Hz vs. C-content for samples with a Nio-bium content of 0.09 -0.11 weight percent.

Figure 8 illustrates that the coercive field strength remains relatively constant for all of the annealing temperatures for carbon contents of up to about 60 ppm. Figure 9 illustrates that the induction remains relatively constant for carbon con-tents of up to 130 ppm for samples heated 871° C. Figure 10 illustrates that the losses increase with increasing carbon content.

In a third set of embodiments, the magnetic properties of an alloy comprising 0.09 to 0.11 weight percent niobium and a maximum of 50 ppm of carbon are compared with two reference samples commercially available under the names VACODUR 50 and HIPERCO 50. Table 1 illustrates the comparison data for the comparison samples. Table 2 illustrates magnetic und mechani-cal properties of the comparison alloy Hiperco 50 of table 1 and an alloy according to the invention after different an-nealing treatments.

The magnetic properties are illustrated in graphs as a depen-dence of the yield strength.

Figure 11 illustrates a graph of coercive field strength vs. Yield strength for (a) sample alloys with 0.09 -0.11% Nb and max. 50 ppm C, (b) sample alloys with 0.04 -0.06% Nb, 100-110 ppm C (a HIPERCO 50-like alloy), (c) VACODUR 50 comparison da-ta, (d) HIPERCO 50 comparison data.

Figure 11 illustrates that the coercive field strength of the alloy according to the invention is lower in nearly the entire yield strength range than the samples with a higher carbon content.

Figure 12 illustrates a graph of induction 5(8 A/cm) vs. yield strength for (a) sample alloys with 0.09 -0.11% Nb and max.

ppm C, (b) sample alloys with 0.04 -0.06% Nb and 100-110 ppm C (a HIPERCO 50-like alloy), (c) VACODUR 50 comparison da-ta, (d) 1-IIPERCO 50 comparison data.

Figure 12 illustrates that the low carbon content alloys have a magnetic induction of greater than 2.22T up to a yield strength of around 300 MPa.

Figure 13 illustrates a graph of losses at 21 urid 50Hz vs. yield strength for (a) sample alloys with 0.09 -0.11% Nb and max. 50 ppm C, und (b) sample alloys with 0.04 -0.06% Nb and 100-110 ppm C (a HIPERCO 50-like alloy) Figure 14 illustrates a graph of losses at 2T und 400Hz vs. yield strength for (a) sample alloys with 0.09 -0.11% Nb and max. 50 ppm C, (b) sample alloys with 0.04 -0.06% Nb and 100- 110 ppm C (HIPERCO 50-like), (c) VACODUR 50 comparison data, (d) HIPERCO 50 comparison data.

Figures 13 and 14 illustrate losses at 50 Hz and 400 Hz. In both cases, the losses are lower for the samples with a low carbon content then for the samples with a higher carbon con-tent.

Table 3 summarizes the composition, annealing conditions, mag- netic properties and mechanical properties of the sample al-loys produced and investigated.

In a third set of embodiments, the development of the micro- structure in an alloy according to the invention was investi-gated. The sample 93/8603 is according to the invention and sample 93/8 605 has a composition similar to the commercial Hi-perco 50 alloy and is a comparison alloy.

The mechanical properties, magnetic properties and the meas-ured grain size of these two alloys after annealing treatments at different temperatures are summarised in table 2.

After annealing at 750° 0, sample 1 has a high yield strength of 474 MPa and a coercive field strength of 1.9 A/cm whereas the Hiperco-like comparison alloy has yield strength of 422 MPa and a coercive field strength of 1.17 A/cm. The grain size of 7 to 10 pm of sample 1 is fine and not completely re- crystallized whereas the Hiperco-like comparison alloy is corn-pletely re-crystaliLised and has slightly larger grains.

For a higher annealing temperature of 750° C, both alloys are completely re-crystallised 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 comparison sample.

For an annealing temperature of 850°C, the mechanical and mag-netic properties of both samples are similar.

Figure 15 illustrates 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 homogenous microstructure with grains having average size of 27 to 30 pm. The Hiperco-like comparison alloy has some isolated huge grains and a more in-homogeneous microstructure is observed. If the large grains are ignored, the average grain sizes around 18 to 22 Elm.

In a fourth set of embodiments, a possible effect of the car-bon content on the oxygen content was investigated.

Figure 16 illustrates a graph of oxygen content as a function of carbon content for the sample alloys 93/8285 -8288, 93/8485 -93/8491, 93/8598 -8600. Figure 16 illustrates that the oxygen content tends to increase for lower carbon contents which may lead to the formation of oxide inclusions in the al-by.

To provide a light desoxidation effect, 0.05 weight percent manganese and 0.05 weight percent silicon were added to some of the alloys. However, when these elements were omitted, an increase in the oxygen content was not observed. However, no disadvantageous effect on the magnetic properties was ob-served.

In a fifth set of embodiments, the effect of the yield strength as a function of temperature was investigated for a sample having a composition according to the invention and a comparison Hiperco-like sample.

Figure 17 illustrates a graph of yield strength vs annealing temperature. Figure 17 illustrates that for the sample accord-ing to the invention, the relationship between the yield strength and the annealing temperature is generally linear, whereas for the comparison Elperco-like sample, there is a steep drop in the yield strength between 780°c and 820° C. The linear form of the decrease in yield strength with in-creasing temperature is useful in that any variation in the annealing temperature within the furnace during production of the semi-finished parts leads to predictable rather unpredict- able results. Therefore, variations in temperature can be com-pensated.

Table 4 illustrates the compositions of the alloys used in the embodiment illustrated in Figure 17 and Table 5 illustrates values of the yield strength illustrated in the graph of Fig-ure 18.

Figure 18 illustrates a SEM (Scanning Electron Microscopy) mi-crograph of a first comparison sample with 0.26 weight percent niobium and 31 ppm carbon. The sample was annealed at 750°C for 3 hours. This comparison sample includes mainly Laves phases which can be seen in the miorograph as the bright and comparatively large inclusions having a size of greater than around 50 nm.

Figure 19 illustrates a SEM micrograph of a second comparison sample with a lower niobium content of 0.1 weight percent and a higher carbon content of 190 ppm. This sample was also an- nealed at 750°C for 3 hours. In contrast to the first compari- son sample, the second comparison sample includes mainly car-bides as shown by the much smaller brighter inclusions. These inclusions differ from the Laves phase inclusions by their smaller size of less than 50 nm.

Figure 20 illustrates a SEN raicrograph 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 includes mainly Laves phases as is illustrated by the bright inclusions within the grains.

Figure 21 illustrates a SEN micrograph of a third comparison alloy with a lower niobium content of 0.06 weight percent and a higher carbon content of 100 ppm which was annealed at 750°C for 3 hours. This comparison alloy includes mainly carbide phases as is illustrates by the smaller bright inclusions.

Claims

<claim-text>Claims 1. 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 per-cent, 0.08 weight percent «= Nb «= 0.12 weight percent, 0 weight percent «= C «= 0.007 weight percent, 0 weight per-cent «= Mn «= 0.1 weight percent, 0 weight percent «= Si «= 0.1 weight percent, remainder Fe.</claim-text> <claim-text>2. The soft magnetic alloy according to claim 1, comprising a carbon content of 0 weight percent «= C < 0.005 weight per-cent.</claim-text> <claim-text>3. The soft magnetic alloy according to claim 1, comprising a carbon content of 0 weight percent < C «= 0.005 weight per-cent.</claim-text> <claim-text>4. The soft magnetic alloy according to claim 3, comprising a carbon content of 0 weight percent < C < 0.003 weight per-cent.</claim-text> <claim-text>5. The soft magnetic alloy according to one of the preceding claims, comprising a nickel content of 0 weight percent C Ni «= 0.2 weight percent.</claim-text> <claim-text>6. The soft magnetic alloy according to one of the preceding claims, comprising a manganese content of 0 weight percent C Mn «= 0.07 weight percent.</claim-text> <claim-text>7. The soft magnetic alloy according to one of the preceding claims, comprising a silicon content of 0 weight percent < Si «= 0.07 weight percent.</claim-text> <claim-text>8. The soft magnetic alloy according to one of the preceding claims, wherein the soft magnetic alloy comprises a yield strength (0.2% strain) of between 200 P4Pa and 450 MBa in an annealed state.</claim-text> <claim-text>9. The soft magnetic alloy according to one of the preceding claims comprising, wherein in an annealed state, the soft magnetic alloy comprises a yield strength (0.2% strain) that lies within ± 10% of a linear function of yield strength (0.2% strain) against annealing temperature.</claim-text> <claim-text>10.The soft magnetic alloy according to one of the preceding claims, wherein the soft magnetic alloy comprises a yield strength (0.2% strain) that is a linear function of an-nealing temperature over an annealing temperature range of 740°C to 865°C.ll.The soft magnetic alloy according to claim 10, wherein the soft magnetic alloy comprises a yield strength (0.2% strain) that is a linear function of annealing temperature over an annealing temperature range of 730°C to 900°C.12.The soft magnetic alloy according to one of the preceding claims, wherein the soft magnetic alloy comprises a resis-tivity of at least 0.4 pflm.l3.The soft magnetic alloy according to one of the preceding claims, wherein the soft magnetic alloy comprises an in-duction B(8 A/rn) of at least
2.12 T. l4.The soft magnetic alloy according to one of the preceding claims, wherein the soft magnetic alloy comprises an in-duction 3(8 A/rn) of at least 2.12 T and a yield strength of at least 370 MPa.15.The soft magnetic alloy according to one of the preceding claims, wherein after annealing at a temperature in the range of 72000 to 90000, the soft magnetic alloy comprises a yield strength in the range of 200 ?4Pa and 450 ?lPa, and a power loss density at 2T and 400 Hz of less than 90 W/kg.l6.The soft magnetic alloy according to one or the preceding claims, wherein the soft magnetic alloy comprises a compo-sition which is selected so that the yield strength of the soft magnetic alloy is adjustable over a range of at least MPa after having been annealed at 750°C or at 87100.17.A stator for an electric motor, comprising the soft mag-netic alloy according to one of claims 1 to 16.18.A rotor for an electric motor comprising the soft magnetic alloy according to one of claims 1 to 16.19.An electric motor comprising the stator of claim 17 and the rotor of claim 18.20.A method for manufacturing a soft magnetic alloy, compris-i ng 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 per-cent, 0.08 weight percent «= Nb «= 0.12 weight percent, 0 weight percent «= C «= 0.005 weight percent, 0 weight per-cent «= Mn «= 0.1 weight percent, 0 weight percent «= Si «= 0.1 weight percent, remainder Fe, cooling and solidifying the melt and forming a blank, hot rolling the blank followed by cold rolling the blank, and subsequently annealing at least a portion of the blank at a tempera-ture in the range of 730°C to 880°C.21.The method according to claim 20, wherein at least a por-tion of the blank is annealed at a temperature in the range of 740°C to 865°C.22.The method according to claim 20, wherein at least a por-tion of the blank is annealed at a temperature in the range of 730°C to 790°C or in the range of BOODC to 880°C.23.The method according to one of claims 20 to 22, wherein a thickness reduction in the blank of 90% is produced by the hot rolling of the blank.24.The method according to one of claims 20 to 23, wherein the blank is hot rolled at a temperature in the range of 1100°C to 1300°C.25.The method according to one of claims 20 to 24, wherein after hot rolling, the blank is cooled to a temperature of 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, 26.The method according to one of claims 20 to 25, further comprising pickling the blank before cold rolling.27.The method according to one of claims 20 to 26, wherein a thickness reduction in the blank of 90% is produced by the cold rolling of the blank.2B.The method according to one of claims 20 to 27, wherein after cold rolling, the thickness of the blank lies in the range of 0.3 mm to 04 mm.29.A method for manufacturing a semi-finished part comprising performing the method according to one of claims 20 to 28 and separating a portion of the blank to produce a semi-finished part.30.The method according to claim 29, further comprising assembling a plurality of semi-finished parts manufactured by the method according to claim 28 and forming a lami-nated soft magnetic article.31.A method for manufacturing a rotor for an electric motor comprising providing the soft magnetic alloy according to one of claims 1 to 16 and annealing at a temperature of 730 to 790°C.32.A method for manufacturing a stator for an electric motor comprising providing the soft magnetic alloy according to one of claims 1 to 16 and annealing at a temperature of 800°C to 880°C 33.A soft magnetic alloy substantially as described herein with reference to the embodiments.34.A method for manufacturing a soft magnetic alloy substan- tially as described herein with reference to the embodi-ments.35.A method for manufacturing a semi-finished product from a cobalt-iron-vanadium based alloy substantially as de-scribed herein.</claim-text>