LAMINATED CORE AND METHOD FOR THE PRODUCTION OF A HIGH PERMEABILITY SOFT MAGNETIC ALLOY

Abstract

A soft magnetic alloy is provided. The alloy consists essentially of 5 wt %Co25 wt %, 0.3 wt %V5.0 wt %, 0 wt %Cr3.0 wt %, 0 wt %Si3.0 wt %, 0 wt %Mn3.0 wt %, 0 wt %Al3.0 wt %, 0 wt %Ta0.5 wt %, 0 wt %Ni0.5 wt %, 0 wt %Mo0.5 wt %, 0 wt %Cu0.2 wt %, 0 wt %Nb0.25 wt % and up to 0.2 wt % impurities.

Claims

1. A method for the production of a soft magnetic alloy comprising: providing a preliminary product that has a composition consisting essentially of: TABLE-US-00017 5 wt % Co 25 wt %, 0.3 wt % V 5.0 wt %, 0 wt % Cr 3.0 wt %, 0 wt % Si 3.0 wt %, 0 wt % Mn 3.0 wt %, 0 wt % Al 3.0 wt %, 0 wt % Ta 0.5 wt %, 0 wt % Ni 0.5 wt %, 0 wt % Mo 0.5 wt %, 0 wt % Cu 0.2 wt %, 0 wt % Nb 0.25 wt %, 0 wt % Ti 0.05 wt %, 0 wt % Ce 0.05 wt %, 0 wt % Ca 0.05 wt %, 0 wt % Mg 0.05 wt %, 0 wt % C 0.02 wt %, 0 wt % Zr 0.1 wt %, 0 wt % O 0.025 wt %, 0 wt % S 0.015 wt %, residual iron, wherein Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities due to melting, the preliminary product having a cold rolling texture or a fiber texture, the preliminary product having a phase transition from a BCC phase region to a mixed BCC/FCC region to an FCC phase region, as the temperature rises the phase transition between the BCC phase region and the mixed BCC/FCC region taking place at a first transition temperature Tin and, as the temperature continues to rise, the transition between the mixed BCC/FCC region and the FCC phase region taking place at a second transition temperature T.sub.2, where T.sub.2>T.sub.1 and the difference T.sub.2T.sub.1 is less than 45K, wherein the preliminary product is subjected to the following heat treatment: heating the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period ti, followed by cooling from T.sub.1 to room temperature, or wherein the preliminary product is subjected to the following heat treatment: heating the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period ti, followed by cooling the preliminary product to a temperature T.sub.2, followed by heat treating the preliminary product at temperature T.sub.2 for a period t.sub.2, followed by cooling the preliminary product from T.sub.2 to room temperature, wherein T.sub.1>T.sub.2, T.sub.1T.sub.2 and T.sub.2T.sub.1, wherein 920 C.T.sub.1>T.sub.m, 700 C.T.sub.21050 C., and T.sub.m is the solidus temperature. wherein the heating rate over at least the temperature range from T.sub.1 to T.sub.1 is 1 K/h to 100 K/h, and wherein the cooling rate over at least the temperature range from T.sub.2 to T.sub.1 is 1 K/h to 100 K/h.

2. A method according to claim 1, wherein the heating rate over at least the temperature range from 900 C. to T.sub.1 is 1 K/h to 100 K/h.

3. A method according to claim 1, wherein the cooling rate over at least the temperature range from T.sub.1 to 900 C. is 1 K/h to 100 K/h.

4. A method according to claim 1, wherein T.sub.1 lies between T.sub.2 and (T.sub.2+100 C.).

5. A method according to claim 1, wherein the preliminary product is weighted down by an additional weight and the preliminary product with the additional weight is subjected to the heat treatment.

6. A method according to claim 5, wherein the additional weight is at least 20% of the weight of the preliminary product.

7. A method according to claim 1, wherein the preliminary product has the form of a plurality of stacked sheets or one or more laminated cores.

8. A method according to claim 1, wherein the preliminary product has the form of a plurality of stacked sheets that are each coated with an electrically insulated coating.

9. A method according to claim 8, further comprising coating the preliminary product with an oxide layer for electrical insulation.

10. A method according to claim 9, wherein the preliminary product is coated with a layer of magnesium methylate or zirconium propylate that transforms into an insulating oxide layer during heat treatment.

11. A method according to claim 1, wherein following the heat treatment the preliminary product is subjected to further heat treatment in an atmosphere containing hydrogen or water vapor in order to form an electrically insulating layer.

12. A method according to claim 7, wherein following heat treatment at least one laminated core is produced from the stacked sheets by of electrical discharge machining, laser cutting or water jet cutting.

13. A method according to claim 12, wherein following heat treatment the plurality of sheets are: stuck together by an insulating adhesive to form a laminated core, or surface oxidised to form an insulating layer and then stuck or laser welded together to form a laminated core, or coated with an inorganic-organic hybrid coating and then further processed to form a laminated core.

14. A method according to claim 1, wherein 960 C.T.sub.1<T.sub.m.

15. A method according to claim 1, wherein the preliminary product is heat treated for a period of over 15 minutes above T.sub.2 and then cooled to T.sub.2.

16. A method according to claim 1, wherein 15 minutest.sub.120 hours.

17. A method according to claim 1, wherein 30 minutest.sub.220 hours.

18. A method according to claim 1, wherein the preliminary product is cooled at least from T.sub.1 to room temperature and then heated from room temperature to T.sub.2.

19. A method according to claim 1, wherein following heat treatment the soft magnetic alloy has: a maximum permeability .sub.max5,000 and/or an electrical resistance 0.25 m, hysteresis losses P.sub.Hys0.07 J/kg at an amplitude of 1.5 T and/or a coercive field strength H.sub.c of 0.7 A/cm and/or an induction B1.90 T at 100 A/cm, or a maximum permeability .sub.max10,000 and/or an electrical resistance 0.25 m and/or hysteresis losses P.sub.Hys0.06 J/kg at an amplitude of 1.5 T and/or a coercive field strength H.sub.c of 0.6 A/cm and an induction B1.95 T at 100 A/cm, or a maximum permeability .sub.max12,000 and/or an electrical resistance 0.30 m and/or hysteresis losses P.sub.Hys0.05 J/kg at an amplitude of 1.5 T and/or a coercive field strength H.sub.c of 0.5 A/cm and/or an induction B2.00 T at 100 A/cm.

20. A method according to claim 1, wherein the preliminary product is heat treated in a hydrogen-containing atmosphere or in an inert gas.

21. A method according to claim 1, further comprising: providing by vacuum induction melting, electroslag re-melting or vacuum arc re-melting of a molten mass consisting essentially of: TABLE-US-00018 5 wt % Co 25 wt %, 0.3 wt % V 5.0 wt %, 0 wt % Cr 3.0 wt %, 0 wt % Si 3.0 wt %, 0 wt % Mn 3.0 wt %, 0 wt % Al 3.0 wt %, 0 wt % Ta 0.5 wt %, 0 wt % Ni 0.5 wt %, 0 wt % Mo 0.5 wt %, 0 wt % Cu 0.2 wt %, 0 wt % Nb 0.25 wt %, 0 wt % Ti 0.05 wt %, 0 wt % Ce 0.05 wt %, 0 wt % Ca 0.05 wt %, 0 wt % Mg 0.05 wt %, 0 wt % C 0.02 wt %, 0 wt % Zr 0.1 wt %, 0 wt % O 0.025 wt %, 0 wt % S 0.015 wt %, residual iron, where Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities, solidifying the molten mass to form an ingot, mechanically deforming the ingot to produce the preliminary product, this mechanically deforming being carried out by means of hot rolling and/or forging and/or cold forming.

22. A method according to claim 21, wherein the ingot is mechanically deformed by hot rolling at temperatures of between 900 C. and 1300 C. to form a slab and then to form a hot strip of thickness D.sub.1, then is mechanically deformed by cold rolling to form a strip of thickness D.sub.2, where 0.05 mmD.sub.21.0 mm and D.sub.2<D.sub.1.

23. A method according to claim 23, wherein a hot strip of thickness D.sub.1 is initially produced by continuous casting and then is mechanically deformed by cold rolling to form a strip of thickness D.sub.2, where 0.05 mmD.sub.21.0 mm and D.sub.2<D.sub.1.

24. A method according to claim 22, wherein the degree of cold deformation by cold rolling is >40%.

25. A method according to claim 22, wherein the ingot is mechanically deformed by hot rolling at temperatures of between 900 C. and 1300 C. to form a billet and then mechanically deformed by cold drawing to form a wire.

26. A method according to claim 25, wherein the degree of cold deformation by cold drawing is >40%.

27. A method according to claim 1, wherein following heat treatment the average grain size is at least 100 m, and the soft magnetic alloy having an induction B.sub.100 (induction B at H=100 A.cm) of at least 1.90 T.

28. A laminated core comprising a plurality of electrically insulated sheets of a soft magnetic alloy that consists essentially of: TABLE-US-00019 5 wt % Co 25 wt %, 0.3 wt % V 5.0 wt %, 0 wt % Cr 3.0 wt %, 0 wt % Si 3.0 wt %, 0 wt % Mn 3.0 wt %, 0 wt % Al 3.0 wt %, 0 wt % Ta 0.5 wt %, 0 wt % Ni 0.5 wt %, 0 wt % Mo 0.5 wt %, 0 wt % Cu 0.2 wt %, 0 wt % Nb 0.25 wt %, 0 wt % Ti 0.05 wt %, 0 wt % Ce 0.05 wt %, 0 wt % Ca 0.05 wt %, 0 wt % Mg 0.05 wt %, 0 wt % C 0.02 wt %, 0 wt % Zr 0.1 wt %, 0 wt % O 0.025 wt %, 0 wt % S 0.015 wt %, residual iron, wherein Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities, wherein the soft magnetic alloy has a maximum permeability .sub.max10,000, an electrical resistance 0.28 m, hysteresis losses P.sub.Hys0.055 J/kg at an amplitude of 1.5 T, a coercive field strength H.sub.c of 0.5 A/cm and an induction B1.95 T at 100 A/cm, and the laminated core has a fill factor F90%.

29. A laminated core according to claim 28, wherein the soft magnetic alloy has a maximum permeability .sub.max12,000.

30. A laminated core according to claim 28, wherein the soft magnetic alloy has hysteresis losses P.sub.Hys0.05 J/kg and/or a coercive field strength H.sub.c of 0.4 A/cm and/or an induction B2.00 T at 100 A/cm.

31. A laminated core according to claim 28, wherein 10 wt %Co20 wt %, or 0.5 wt %V4,0 wt %, or 0.1 wt %Cr2.0 wt %, or 0.1 wt %Si2.0 wt %, and/or the sum being 0.1 wt %Cr+Si+Al+Mn1.5 wt %.

32. A laminated core according to claim 28, wherein the laminated core has at least two sheets that each have a thickness of 0.05 mm to 0.50 mm, the electrical insulation between adjacent sheets having a thickness of 0.1 m to 2.0 m.

33. An electric machine comprising a laminated core according to claim 28.

34. A method for the production of a soft magnetic alloy, the method comprising: providing a preliminary product having a composition consisting essentially of: TABLE-US-00020 5 wt % Co 25 wt %, 0.3 wt % V 5.0 wt %, 0 wt % Cr 3.0 wt %, 0 wt % Si 3.0 wt %, 0 wt % Mn 3.0 wt %, 0 wt % Al 3.0 wt %, 0 wt % Ta 0.5 wt %, 0 wt % Ni 0.5 wt %, 0 wt % Mo 0.5 wt %, 0 wt % Cu 0.2 wt %, 0 wt % Nb 0.25 wt %, 0 wt % Ti 0.05 wt %, 0 wt % Ce 0.05 wt %, 0 wt % Ca 0.05 wt %, 0 wt % Mg 0.05 wt %, 0 wt % C 0.02 wt %, 0 wt % Zr 0.1 wt %, 0 wt % O 0.025 wt %, 0 wt % S 0.015 wt %, residual iron, wherein Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities due to melting, and the preliminary product having a cold rolling texture or a fiber texture, wherein the preliminary product has a phase transition from a BCC phase region to a mixed BCC/FCC region to an FCC phase region, as the temperature rises the phase transition between the BCC phase region and the mixed BCC/FCC region taking place at a first transition temperature T.sub.1 and, as the temperature continues to rise, the transition between the mixed BCC/FCC region and the FCC phase region taking place at a second transition temperature T.sub.2, where T.sub.2>T.sub.1 and the difference T.sub.2T.sub.1 is less than 45K, wherein the preliminary product is subjected to the following heat treatment: heating up the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period t.sub.1, followed by cooling from T.sub.1 to room temperature, or wherein the preliminary product is subjected to the following heat treatment: heating up the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period ti, followed by cooling the preliminary product to a temperature T.sub.2, followed by heat treating the preliminary product at temperature T.sub.2 for a period t.sub.2, followed by cooling the preliminary product from T.sub.2 to room temperature, wherein T.sub.1>T.sub.2, wherein T.sub.1 lies between T.sub.2 and (T.sub.2+100 C.) and T.sub.2 lies below T.sub.1, wherein 700 C.T.sub.21050 C. and T.sub.2<T.sub.1.

35. A method for the production of a soft magnetic alloy, comprising: providing by vacuum induction melting, electroslag re-melting or vacuum are re-melting of a molten mass consisting essentially of: TABLE-US-00021 5 wt % Co 25 wt %, 0.3 wt % V 5.0 wt %, 0 wt % Cr 3.0 wt %, 0 wt % Si 3.0 wt %, 0 wt % Mn 3.0 wt %, 0 wt % Al 3.0 wt %, 0 wt % Ta 0.5 wt %, 0 wt % Ni 0.5 wt %, 0 wt % Mo 0.5 wt %, 0 wt % Cu 0.2 wt %, 0 wt % Nb 0.25 wt %, 0 wt % Ti 0.05 wt %, 0 wt % Ce 0.05 wt %, 0 wt % Ca 0.05 wt %, 0 wt % Mg 0.05 wt %, 0 wt % C 0.02 wt %, 0 wt % Zr 0.1 wt %, 0 wt % O 0.025 wt %, 0 wt % S 0.015 wt %, residual iron, wherein Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities, solidifying the molten mass to form an ingot of a soft magnetic alloy, mechanically deforming the ingot, wherein the ingot is mechanically deformed by hot rolling at temperatures between 900 C. and 1300 C. to form a billet, is then mechanically deformed to form a hot strip of thickness D.sub.1 and then is mechanically deformed by cold working to form a strip of thickness D.sub.2, the degree of cold deformation being >40%, where 0.05 mmD.sub.21.0 mm and D.sub.2<D.sub.1, wherein the strip has a cold rolling texture or a fibre texture, wherein the soft magnetic alloy of the strip has a phase transition from a BCC phase region to a mixed BCC/FCC region to an FCC phase region, as the temperature rises the phase transition between the BCC phase region and the mixed BCC/FCC region taking place at a first transition temperature T.sub.1 and, as the temperature continues to rise, the transition between the mixed BCC/FCC region and the FCC phase region taking place at a second transition temperature T.sub.2, where T.sub.2>T.sub.1 and the difference T.sub.2T.sub.1 is less than 45K, wherein the strip is subjected to the following heat treatment: heating up the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period ti, followed by cooling from T.sub.1 to room temperature, or wherein the strip is subjected to the following heat treatment: heating up the preliminary product to a temperature T.sub.1, followed by heat treating the preliminary product at temperature T.sub.1 for a period t.sub.1, followed by cooling the preliminary product to a temperature T.sub.2, followed by heat treating the preliminary product at temperature T.sub.2 for a period t.sub.2, followed by cooling the preliminary product from T.sub.2 to room temperature, where T.sub.1>T.sub.2, wherein T.sub.1 lies above T.sub.2 and T.sub.2 lies below T.sub.1, where 920 C.T.sub.1<T.sub.m, 700 C.T.sub.21050 C., and T.sub.m is the solidus temperature.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0142] Embodiments of the invention are described in greater detail below with reference to the drawings and the following examples.

[0143] FIG. 1 shows a schematic illustration of the heat treatment according to the invention.

[0144] FIG. 2 shows a graph of coercive field strength H.sub.c plotted against cooling rate. FIG. 3 shows a graph of induction B at 20 A/cm plotted against cooling rate. FIG. 4 shows metallographic sections for determining the grain size in two examples.

[0145] FIG. 5 shows metallographic sections of an example (93/0505) containing Si after annealing in the -region.

[0146] FIG. 6 shows a graph of induction B.sub.20 (B at H=20 A/cm) plotted against grain size.

[0147] FIG. 7 shows a graph of coercive field strength H.sub.c plotted against grain size.

[0148] FIG. 8 shows a graph of remanence B.sub.r and B.sub.20 (B at H=20 A/cm).

[0149] FIG. 9 shows a graph of coercive field strength H.sub.c plotted against cold deformation.

[0150] FIG. 10 shows a graph of induction B (20 A/cm) plotted against cold deformation.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0151] According to the invention, a soft magnetic alloy is provided that has a composition that consists essentially of:

TABLE-US-00006 5 wt % Co 25 wt % 0.3 wt % V 5.0 wt % 0 wt % Cr 3.0 wt % 0 wt % Si 3.0 wt % 0 wt % Mn 3.0 wt % 0 wt % Al 3.0 wt % 0 wt % Ta 0.5 wt % 0 wt % Ni 0.5 wt % 0 wt % Mo 0.5 wt % 0 wt % Cu 0.2 wt % 0 wt % Nb 0.25 wt % 0 wt % Ti 0.05 wt % 0 wt % Ce 0.05 wt % 0 wt % Ca 0.05 wt % 0 wt % Mg 0.05 wt % 0 wt % C 0.02 wt % 0 wt % Zr 0.1 wt % 0 wt % O 0.025 wt % 0 wt % S 0.015 wt %
residual iron, wherein Cr+Si+Al+Mn3.0 wt %, and up to 0.2 wt % of other impurities due to melting. The impurities may, for example, be one or more of the elements B, P, N, W, Hf, Y, Re, Sc, Be or other lanthanides other than Ce. In order to increase the electrical resistance, in addition to the alloy element vanadium, it is also possible to add one or more elements from the group Cr, Si, Al and Mn in an amount that satisfies the following sum:

0.05 wt % Cr+Si+Al+Mn3.0 wt %.

[0152] The alloy may be provided in the form of a preliminary product (precursor product) that has a cold rolling texture or a fibre texture. The preliminary product may be a strip or one or more sheets suitable for the production of a laminate core.

[0153] The soft magnetic alloy or the preliminary product has a phase transition from a BCC phase region (also referred to as the a-region) to a mixed BCC/FCC region (also known as the +-region) to an FCC phase region (also known as the -region), as the temperature rises the phase transition between the BCC phase region and the mixed BCC/FCC region taking place at a first transition temperature T.sub.1 and, as the temperature continues to rise, the transition between the mixed BCC/FCC region and the FCC phase region taking place at a second transition temperature T.sub.2, where T.sub.2>T.sub.1 and the difference T.sub.2T.sub.1 is less than 45K, preferably less than 25K.

[0154] The alloy is preferably melted in vacuum induction furnaces, though it can also be processed by means of vacuum arc re-melting or electroslag re-melting. The molten mass first solidifies into an ingot, from which the oxide skin is removed, and is then forged or hot rolled at temperatures between 900 C. and 1300 C. Alternatively, the removal of the oxide skin can also take place on bars that have previously been forged or hot rolled. The desired dimensions can be achieved by hot working strips, billets or bars. Surface oxides can be removed from hot rolled stock by blasting, grinding or stripping. Alternatively, however, the desired final dimensions can also be achieved by cold working strips, bars or wires. In the case of cold rolled strips, a grinding process can be integrated to remove embedded oxides caused by the hot rolling process. If cold working leads to excessive solidification, one or more intermediate annealing processes may be carried out at temperatures between 400 C. and 1300 C. to alloy recovery and re-crystallisation. The thickness or diameter for intermediate annealing should be selected such that cold working of preferably >40%, particularly preferably cold working of >80% and of >95%, is achieved by the final thickness.

[0155] This is followed by heat treatment according to one of the embodiments of the invention. This heat treatment is also referred to as final magnetic annealing. Final annealing is preferably carried out in a clean, dry hydrogen atmosphere. Annealing in an insert gas or vacuum is also possible.

[0156] In one embodiment the preliminary product is heated to a temperature T.sub.1, then heat treated at temperature T.sub.1 for a period t.sub.1 and then cooled from T.sub.1 to room temperature. In an alternative embodiment the preliminary product is heated to a temperature T.sub.1, then heat treated at temperature T.sub.1 for a period t.sub.1, then cooled to a temperature T.sub.2, then heat treated at temperature T.sub.2 for a period t.sub.2, then cooled from T.sub.2 to room temperature. Temperature T.sub.1 is greater than temperature T.sub.2 . In addition, T.sub.1 is above T.sub.2, i.e. in the FCC phase region, T.sub.2 is below T.sub.1, i.e. in the BCC phase region, and 920 C.T.sub.1<T.sub.m, where T.sub.m is the solidus temperature, and 700 C.<T.sub.21050 C.

[0157] For both methods the heating rate over at least the temperature range from T.sub.1 to T.sub.2 is 1 K/h to 100 K/h, preferably 10 K/h to 50 K/h, and the cooling rate over at least the temperature range from T.sub.2 to T.sub.1 is 1 K/h to 100 K/h, preferably 10 K/h to 50 K/h.

[0158] is In one embodiment a laminated core comprising a plurality of sheets is produced from an alloy according to the invention. The following method is used. The soft magnetic alloy is provided in the form of a strip that is coated with an electrically insulating layer made, for example, of an oxide. The strip is cut to length and metal panels are produced. These metal panels are stacked and the stacked metal panels are annealed or heat treated in a bell furnace according to one of these embodiments. The sheets can then be oxidised.

[0159] Following heat treatment the sheets are stuck together, the coated sheets being stacked with an adhesive layer to form a laminate, and cleaned and a laminated core suitable for use in a rotor or stator is formed, e.g. by electrical discharge machining, from the laminate.

[0160] In one embodiment stacks of 50 or 100 sheets (2101400.15 mm.sup.3) are annealed. In almost all tests a ceramic (24421310 mm.sup.3) plate weighing approx. 2 kg was used as the flat base. Once cut to length, the sheets are annealed as described below to ensure the flatness of the sheets and to increase the fill factor in the finished laminated core. In particular, the heating rate and the cooling rate are set to avoid any plastic deformation of the originally flat sheets and thus to obtain adequate flatness during the heat treatment.

[0161] In some embodiments, in addition the heating and cooling rates set, a weight is placed on the stacked sheets or panels. The weight is varied, in most cases a solid NCT3 covering plate (1.4841) (27015020 mm.sup.3) weighing 6.5 kg being used. The self-weight of the stack of sheets was 1.7 kg (50 sheets) or 3.4 kg (100 sheets) depending on the stack height.

[0162] FIG. 1 shows a schematic curve for the test annealing processes. The broken lines indicate the expected range of the two-phase region. This two-phase region is dependent on the composition of the alloy.

[0163] The transition temperatures T.sub.1 and T.sub.2 for a given composition can be determined by means of DSC measurements. Table 1 shows the composition and transition temperatures for four examples.

TABLE-US-00007 TABLE 1 Co V Cr Si 1.sup.st onset Peak 1.sup.st onset Peak T.sub.c Peak T.sub.c Peak Batch 93/ wt % wt % wt % wt % heating ( ) heating cooling ( ) cooling heating cooling 7604988 16.81 2.29 0.01 0.02 989 995 962 957 939 929 7605180 17.11 1.47 0.01 0.28 967 974 949 942 938 881 7605267 17.20 1.54 0.02 0.23 965 974 944 936 938 875 7409992 17.25 1.49 0.02 0.23 964 972 945 937 939 875

[0164] The annealing programme was selected such that the holding temperature Ti at 1000 C. to 1030 C. is above the two-phase region and in the FCC phase region, as shown in FIG. 1. According to DSC, in the batch used (7605180A) the FCC phase region is between 949 C. and 967 C. (1.sup.st onset during cooling or heating). The passage through the two-phase region was varied, increasing from T.sub.0 to T.sub.1 during heating and from T.sub.1 to T.sub.3 during cooling, in each case with heating and cooling rates between 10 K/h and 100 K/h.

[0165] FIG. 2 shows a graph of coercive field strength H.sub.c and FIG. 3 shows a graph of to induction B at H=20A/cm, both plotted against cooling rate.

[0166] Table 2 shows a summary of values for coercive field strength H.sub.c and induction B at 20 A/cm and 100 A/cm for three examples that are heat treated at different heating rates and cooling rates. The induction values are similar in all cases, one advantage is of the slow heating and cooling rates lying in improved sheet flatness.

TABLE-US-00008 TABLE 2 B B Heating Holding Cooling (20 A/cm) (100 A/cm) H.sub.c # rate step rate in T in T in A/cm 1 from 4 h from 1.706 2.009 0.432 920 C. to 1000 C. 1000 C. to 1000 C. at 920 C. at 4 K/h 4 K/h 2 from 4 h from 1.717 1.984 0.378 920 C. to 1000 C. 1000 C. to 1000 C. at 920 C. at 20 K/h 20 K/h 3 from 4 h From 1.722 1.987 0.433 920 C. to 1000 C. 1000 C. to 1000 C. at 920 C. at 100 K/h 50 K/h Batch 7605180A, strip thickness 0.20 mm

[0167] The measured coercive field strength is somewhat lower at slower cooling rates while the measured induction is somewhat higher at slower cooling rates. Consequently, it is possible to improve the soft magnetic properties of these alloys if cooling rates less than 100 K/h, preferably less than 50 K/h or less than 25 K/h, are used.

[0168] It has been found experimentally that heating or cooling sheets too quickly results in wavy sheets that also exhibit a type of plastic deformation within the sheets. When passing through the two-phase region, the body-centred -phase (BCC) transforms into the more closely packed face-centred se (FCC) as it is heated. This leads to a contraction of the sheets. A retransformation, during which the original geometry is ideally restored, then takes place during cooling. It can be assumed that the deformation observed is due to incomplete transformation and retransformation. The best results were achieved at heating and cooling rates of 20 K/h and 10 K/h. At higher rates, e.g. 50 K/h, slight waviness was observed with 50 sheets, and with 100 to sheets the sheets were unusable at rates of even 35 K/h.

[0169] It has been established that heating and cooling rate as well as weight can be set so as to obtain flat sheets. If no or only minimal weight is applied to the stack of sheets, significant waviness can occur. If annealing is carried out under the same conditions, is i.e. with the same low heating and cooling rates of 10 K/h, but with a solid weight of 6.5 kg, a completely flat stack of sheets is obtained. It is possible to separate all the sheets from one another without difficulty despite the heavy weight.

[0170] The results of the tests are summarised in Table 3, the following annealing evaluations being used: [0171] Very good: the sheets are absolutely flat and exhibit no edge waviness [0172] Good: the sheets are generally flat and exhibit minimal edge waviness [0173] Poor: the sheets exhibit plastic deformation over at least half their surface [0174] Very poor: the sheets show plastic deformation over their entire surface

TABLE-US-00009 TABLE 3 dT/dt dT/dt Weight heating cooling T.sub.0 T.sub.1 = T.sub.max T.sub.2 = T.sub.0 # Sheets in kg in K/h in K/h Evaluation in C. in C. in C. 50 0 none 10 10 Very poor 900 1000 900 50 0.3 1) 50 25 Very poor 930 1030 930 50 8.0 2) 10 10 Very good 900 1000 900 50 6.5 3) 50 50 Good 900 1000 900 50 6.5 3) 50 25 Good 900 1000 900 50 6.5 3) 100 25 Poor 900 1000 900 50 6.5 3) 100 50 Poor 900 1000 900 100 6.5 3) 20 20 Very good 920 1000 920 100 6.5 3) 35 35 Poor 930 1000 930 100 6.5 3) 100 50 Very poor 900 1000 900 1) Very low, uneven weighting with 4 small ceramic plates 2) Even weighting with 4 large ceramic plates of 2 kg each 3) Even weighting with 1 solid NCT3 plate weighing 6.5 kg

[0175] In one of the annealing tests (100 sheets, 20 K/h) a solid NCT3 plate was used as both the base and the weight. The sheets were of very good quality following annealing. These results show that the slow passage through the two-phase region is to conducive to the setting of good soft magnetic properties.

[0176] In a further group of examples the influence of the annealing temperature T.sub.1, shown in FIG. 1, was investigated more closely. Table 4 shows the compositions of the examples.

[0177] It was found that the precise setting of the annealing temperature can be used to improve magnetic properties, in particular induction values. Grain size can also be set by setting the annealing temperature appropriately.

[0178] Annealing in the y-region was found to have a positive influence on induction values B20=B(20 A/cm), on coercive field strength H.sub.e and on maximum permeability .sub.max. An influence on the resulting grain size was also observed.

[0179] Here four compositions were tested in a strip thickness of 0.35 mm with different compositions, see Table 4. The contents of those elements not listed did not exceed 0.02 wt %.

TABLE-US-00010 TABLE 4 Actual composition (wt %) Batch Nominal composition Fe Co V Cr Si 93/0328 Fe-17Co-1,0V-1Cr Residual 17.08 0.98 1.04 93/0329 Fe-17Cr-1.5V-0.5Cr Residual 17.12 1.46 0.54 93/0330 Fe-17Co-2.0V Residual 17.19 1.97 93/0505 Fe-17Co-1.4V-0.4Si Residual 16.97 1.39 0.40

[0180] These example have approx. 17% Co and additions of 1 to 2% V: [0181] batches 93/0328 and 932/0329 also containing 0.5% to 1.0% Cr, [0182] batch 93/0330 being a purely ternary Fe-Co-V without added Cr or Si, and [0183] batch 93/0505 also having 0.4% Si in addition to FeCoV.

[0184] The annealing processes were carried out at different temperatures in the range from 850 C. to 1150 C. The majority of the annealing processes took place at high is temperatures of at least 1000 C. in the -region, though some took place at lower temperatures in the -region. The exact position of the two-phase region is indicated in Table 5. A large variation is apparent here, i.e. the upper phase limit +.fwdarw. is between 928 C., with the addition of significant Cr, and 970 C., with the addition of Si. The width of the two-phase region also varies strongly, ranging from 17 C. to 35 C.

[0185] Heating from 600 C. was typically carried out at 150 K/h. The cooling phase involved furnace cooling (approx. 100 to 150 K/h), an even slower cooling rate being expected at temperatures below 600 C.

TABLE-US-00011 TABLE 5 + .fwdarw. .sup.1) + .fwdarw. .sup.2) Width + Batch Nominal composition in C. in C. in C. 93/0328 Fe-17Co-1.0V-1Cr 893 928 35 93/0329 Fe-17Cr-1.5V-0.5Cr 925 945 20 93/0330 Fe-17Co-2.0V 950 973 23 93/0505 Fe-17Co-1.4V-0.4Si 953 970 17 .sup.1) 1st onset heating in DSC, .sup.2) 1st onset cooling in DSC

[0186] With both charges, the annealing processes in the a-region (850 C., 910 C.) resulted, as expected, in relatively low induction values B20 =B(20 A/cm) of less than 1.7 T, high H.sub.c values greater than 0.6 A/cm and lower maximum permeabilities .sub.max below 5100 (see Tables 6 and 7). Table 6 shows the magnetic values and grain sizes d.sub.K for alloy 93/0328 with added Cr (Fe-17Co-1V-1Cr). Table 7 shows the magnetic values to and grain sizes for alloy 93/0329 with added Cr (Fe-17Co-1.5V-0.5Cr).

TABLE-US-00012 TABLE 6 T.sub.Max B20 B100 H.sub.c in Br d.sub.k 93/0328 Annealing in C. in T in T A/cm max in T in m 4 h 850 C. 850 1.656 1.918 0.93 3890 0.95 63-76 10 h 910 C. 910 1.623 1.887 0.63 4902 1.02 107-125 10 h 910 C. + 930 1.771 2.036 0.47 6912 1.16 >1500 70 h 930 C. 4 h 1000 C. 1000 1.768 2.011 0.66 5130 1.16 210-430 4 h 1050 C. 1050 1.767 2.012 0.63 5387 1.18 180-350 4 h 1100 C. 1100 1.726 1.980 0.68 4958 1.10 210-350 4 h 1150 C. 1150 1.692 1.956 0.68 4863 1.09 180-350 B20 = B(20 A/cm), B100 = B(100 A/cm)

TABLE-US-00013 TABLE 7 T.sub.Max B20 B100 Hc in Br d.sub.k 93/0329 Annealing in C. in T in T A/cm max in T in m 4 h 850 C. 850 1.651 1.911 1.04 3584 0.88 75 10 h 910 C. 910 1.620 1.881 0.62 5090 1.13 151 4 h 1000 C. 1000 1.803 2.035 0.51 7929 1.38 (+10 h 910 C.) (1.807) (2.038) (0.38) (16,658) (1.53) 250 4 h 1050 C. 1050 1.809 2.039 0.50 7943 1.39 302 4 h 1100 C. 1100 1.797 2.031 0.52 7497 1.35 214 4 h 1150 C. 1150 1.778 2.018 0.47 7860 1.35 254 B20 = B(20 A/cm), B100 = B(100 A/cm)

[0187] Annealing in the -region (up to 1050 C.) results in appreciably higher B20 values above 1.75 T. In the example with 1% Cr (Table 6) a further increase in annealing temperature (1100 C., 1150 C.) results in a clear drop in induction B20 by up to 80 mT compared to the best annealing at 930 C. In contrast, the example with 0.5% Cr (Table 7) is appreciably more stable in this respect, the drop in comparison to the to best annealing at 1050 C. being only approx. 30 mT.

[0188] FIG. 4 shows metallographic sections for determining grain size in batch 93/0328 (on the left: 10 h 910 C. (), on the right: 10 h 910 C.+70 h 930 C. ()).

[0189] As far as grain size d.sub.k is concerned, the only finding for both batches is that annealing in the -region results in larger grains (>180 m) than annealing in the -region (<180 m). Furthermore, no further relationship between B20 and grain size can be established since annealing batch 93/0328 at 1050 C. and 1150 C. leads to the same grain sizes of 180 m to 350 m but to very different B20 values of 1.767 T and 1.692 T.

[0190] However, the sample annealed for a very long time at 930 C. clearly reveals a relationship between coercive field strength H.sub.c and grain size as both the lowest H.sub.c in the batch (0.47 A/cm) and by far the largest grains (>1500 pm) occurred in this state.

[0191] In the ternary alloy 93/0330 with Fe-17Co-2V (Table 8) two annealing processes were carried out in the -region (850 C., 910 C.) and four annealing processes were carried out in the -region (1000 C., 1050 C., 1100 C., 1150 C.) (cf. Table 8). It was also confirmed here that the increase in induction B20 does not occur until annealing to reaches the -region. In addition, this value falls again at very high annealing temperatures of 1100 C. or more.

TABLE-US-00014 TABLE 8 T.sub.Max B20 B100 Hc in Br d.sub.k 93/0330 Annealing in C. in T in T A/cm max in T in m 4 h 850 C. 850 1.648 1.906 1.05 3533 0.87 10 h 910 C. 910 1.615 1.873 0.68 4868 1.11 4 h 1000 C. 1000 1.801 2.038 0.41 10,618 1.44 300-350 4 h 1050 C. 1050 1.812 2.040 0.35 12,670 1.50 250-350 4 h 1100 C. 1100 1.786 2.028 0.38 10,051 1.41 300-430 4 h 1150 C. 1150 1.756 2.005 0.36 10,568 1.44 300-430 B20 = B(20 A/cm), B100 = B(100 A/cm)

[0192] In this batch it also becomes clear that remanence Br increases appreciably as a result of annealing in the -region, i.e. the loop becomes appreciably more rectangular (Br>1.4 T).

[0193] In example 93/0505 with added Si (Fe-17Co-1.5V-0.5Cr) only annealing in the -region was observed (1000 C., 1050 , 1100 C.). Table 9 shows the magnetic values and grain sizes for alloy 93/0505.

[0194] As for the other batches, very high B20 induction values of up to 1.79 T were measured, though they also fell again appreciably at 1100 C. The H.sub.c values of approx. 0.3 A/cm, which are very low in comparison with the other compositions tested, and the very high permeability of greater than 10,000 can possibly be explained by the relatively large-grained structure (cf. Table 9 and FIG. 5).

TABLE-US-00015 TABLE 9 T.sub.Max B20 B100 Hc in Br d.sub.k 93/0505 Annealing in C. in T in T A/cm max in T in m 4 h 1000 C. 1000 1.787 2.029 0.32 12,668 1.32 350-710 4 h 1050 C. 1050 1.760 2.020 0.26 14,272 1.24 300-360 4 h 1100 C. 1100 1.692 1.969 0.33 10,819 1.20 Non- homogenous, up to >1500 B20 = B(20 A/cm), B100 = B(100 A/cm)

[0195] is In all the batches tested, the high induction values (B20>1.75 T) occurred only with annealing in the -region (FCC).

[0196] It was observed that after annealing the induction values were no more than just above the phase transition +.fwdarw. (FCC+BCC.fwdarw.FCC). This correlates with a clear coarsening in structure.

[0197] Table 10 shows a summary of the grain sizes measured in the batches tested taking into account all annealing processes with a duration of between 4 and 10 h. FIG. 6 shows a graph of induction B.sub.20 (B at H=20 A/cm) plotted against grain size. FIG. 7 shows a graph of coercive field strength H.sub.c plotted against grain size. FIG. 8 shows a relationship between remanence B.sub.r and B.sub.20(B at H=20 A/cm) in all states tested. The solid symbols correspond to annealing in the -region (FCC), the hollow symbols to annealing in the -region (BCC).

TABLE-US-00016 TABLE 10 Grain sizes after annealing Annealing in the -region Annealing in the -region (4-10 h) in m (BCC) (FCC) Batch From To From To 93/0328 63 125 210 350 93/0329 75 151 214 302 93/0330 300 430 93/0505 300 >1500

[0198] Increasing annealing temperature too much (to 1100 C. or higher) resulted in a fall in to the induction values observed. The four batches behaved differently, i.e. while batches 93/0329 and 93/0330 were still exhibiting very high B.sub.20 values greater than 1.75 T at 1150 C., this value had already dropped to 1.69 T at 1150 C. and 1100 C. for batches 93/0328 and 93/0505. It proved impossible to detect any direct correlation between this effect and grain size.

[0199] Alloy 93/05050 with added Si shows appreciably larger grains than the compositions without Si. Accordingly, it also has the smallest H.sub.e values, even the ternary FeCoV molten mass from batch 93/0330 showing almost as high H.sub.c values despite appreciably smaller grain size.

[0200] If one disregards states with very coarse grains of 1 mm or more, direct relationships between the magnetic characteristics and grain size emerge (cf. FIG. 4 (B.sub.20) and FIG. 5 (H.sub.c)). Moreover, FIG. 6 shows that there is a link between high induction B20 and high remanence B.sub.r. Indeed, above a remanence of 1.3 T all states from this test show an induction B20 of at least 1.75 T auf. The increase in induction Is therefore associated with a breakdown of the hysteresis loop.

[0201] The influence of the degree of cold deformation on magnetic properties was examined in further embodiments. Low H.sub.c and high B values proved advantageous in soft magnetic terms.

[0202] During rolling lateral expansion of the strip can be ignored and the degree of cold deformation KV of the final thickness D.sub.2 is defined as the percentage reduction in thickness in relation to a non-cold-deformed initial thickness D.sub.1. The following formula applies:

[00001]$\mathrm{KV}\left[\%\right]=\frac{D_1-D_2}{D_1}.Math.100$

[0203] The non-cold-deformed initial thickness D.sub.1 may, for example, by produced by means of hot rolling or by intermediate annealing (ZGL). D.sub.1 was varied within a range of 1.9 mm to 6.4 mm and D.sub.2 was varied within a range of 0.35 mm to 0.10 mm. Three different heat treatments were used, annealing variants step 1+step 2 and step 1+controlled cooling. The cooling rate of the annealing process for 4 h at 1050 C. was 150 C./h. OK signifies furnace cooling, which also corresponds to a cooling rate of 150 C./h. RT signifies room temperature.

[0204] FIG. 9 shows a graph of coercive field strength H.sub.c plotted against cold deformation. FIG. 10 shows a graph of induction B.sub.20 (B at H=20 A/cm) plotted against cold deformation.

[0205] FIG. 9 indicates that induction B at a field strength H of 20 A/cm increases with cold deformation. The maximum cold deformation KV achieved is 98%. The B values can be improved by increasing cold deformation and it is possible to compensate for the deterioration of H.sub.c as cold deformation increases by means of appropriate cooling after step 1 over the two-phase region.

[0206] In summary, a high permeability soft magnetic alloy is provided that both has better soft magnetic properties, e.g. appreciably higher permeability and lower hysteresis losses, and offers higher saturation than existing, commercially available FeCo alloys. At the same time, however, this new alloy also offers significantly lower hysteresis losses than previously known commercially available alloys with Co contents between 10 and 30 wt % and, above all, an appreciably higher level of permeability never previously achieved for this type of alloy. The alloy according to the invention can also be produced cost effectively on an industrial scale, particularly in the form of flat sheets and of a laminated core that may have a fill factor greater than 90% or 94% owing to the flat sheets.