Patent Publication Number: US-7909945-B2

Title: Soft magnetic iron-cobalt-based alloy and method for its production

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates to improved soft magnetic iron-cobalt-based alloys, more particularly to improvements to such alloys with a cobalt content of 10 percent by weight (% by weight) to 22% by weight, to methods for the production of such improved alloys, to methods for the production of finished and semi-finished products from these alloys, and to products containing such alloys, in particular magnetic components for actuator systems. 
     2. Description of Related Art 
     Soft magnetic iron-cobalt-based alloys have a high saturation magnetisation and can therefore be used in the design of actuator systems with high power and/or a small overall volume. Solenoid valves, for example solenoid valves for fuel injection in internal combustion engines, are a typical application of such alloys. 
     Certain soft magnetic iron-cobalt-based alloys with a cobalt content of 10% by weight to 22% by weight are, for example, known from U.S. Pat. No. 7,128,790. However, when using these alloys in high-speed actuators, switching frequency can be limited by the eddy currents which are generated. Improvements in the strength of the magnet cores are also desirable in high-frequency actuator systems designed for continuous duty. 
     SUMMARY 
     The invention is therefore based on the problem of providing an improved alloy which, by virtue of its novel composition, is better suited for use as a magnet core in high-speed actuators than prior alloys described above. 
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     The invention will be more clearly understood by reference to the specific embodiments, which are not intended to limit the scope of the invention, or of the appended claims. 
     According to the invention, this problem is solved by the subject matter of the independent claims. Advantageous further developments can be derived from the dependent claims. 
     According to the invention, a soft magnetic alloy consists essentially of 10% by weight≦Co≦22% by weight, 0% by weight≦V≦4% by weight, 1.5% by weight≦Cr≦5% by weight, 1% by weight≦Mn≦2% by weight, 0% by weight≦Mo≦1% by weight, 0.5% by weight≦Si≦1.5% by weight, 0.1% by weight≦Al≦1.0% by weight, rest iron. 
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic diagram of a solenoid valve with magnetic core made of a soft magnetic alloy according to one embodiment of the invention. 
       FIG. 2  is a flow chart showing steps in the production of semi-finished products made of an alloy according to an embodiment of the invention. 
       FIG. 3  is a graph showing coercitive field strength H c  versus annealing temperature for various soft magnetic alloys according to certain embodiments of the invention. 
       FIG. 4  is a graph showing coercitive field strength H c  versus annealing temperature for further soft magnetic alloys according to certain embodiments of the invention. 
     The terms “essentially” and “consisting essentially of” denote that the composition contains the recited components, as well as any impurities which may be present, such as smelting impurities and the like, and any other components that do not affect the basic and novel characteristics of the alloy. The alloy preferably contains a maximum of 200 ppm of nitrogen, a maximum of 400 ppm of carbon and a maximum of 100 ppm of oxygen. 
     Compared to the binary Co—Fe alloy, the alloy according to the invention has a higher resistivity, resulting in a suppression of eddy currents combined with a minimum reduction of saturation polarisation. This is achieved by the addition of non-magnetic elements. As a result of its Al and Si content, the alloy further has a higher strength. This alloy is suitable for use as a magnet core of a high-speed actuator system, such as in a fuel injector of an internal combustion engine. 
     Cr and Mn significantly increase resistance while only slightly reducing saturation. At the same time, the annealing temperature, which corresponds to the upper limit of the ferritic phase, is reduced. This is, however, not desirable, as it results in poorer soft magnetic properties. 
     Al, V and Si likewise increase electric resistance while also increasing the annealing temperature. In this way, an alloy with a high resistance, high saturation and high annealing temperature and thus with good soft magnetic properties can be specified. 
     As a result of its Al and Si content, the alloy further has a higher strength. The alloy is suitable for cold forming and ductile in the finish-annealed state. The alloy may have an elongation A L &gt;2%, preferably A L &gt;20%. The elongation A L  is measured in tensile tests. This alloy is suitable for use as a magnet core of a high-speed actuator system, such as in a fuel injector of an internal combustion engine. 
     A soft magnetic cobalt-iron-based alloy for an actuator system is subject to contradictory demands. A higher cobalt content in the binary alloy results in a higher saturation magnetisation J s  of approximately 9 mT per 1% by weight of Co (based on 17% by weight of Co) and therefore permits a reduction in overall volume and increased system integration or higher actuating forces at the same overall volume. At the same time, however, the costs of the alloy increase. As the Co content increases, the soft magnetic properties of the alloy, such as permeability, become poorer. Above a Co content of 22% by weight, saturation is increased less by further Co additions. 
     The alloy should further have a high resistivity and good soft magnetic properties. 
     This alloy therefore has a cobalt content of 10% by weight≦Co≦22% by weight. A lower cobalt content reduces the raw material costs of the alloy, making it suitable for applications where costs are of great importance, such as automotive engineering. Maximum permeability is high within this range, resulting in advantageously low drive currents in actuator applications. 
     In further embodiments, the alloy has a cobalt content of 14% by weight≦Co≦22% by weight and 14% by weight≦Co≦20% by weight. 
     The soft magnetic alloy of the magnet core has a chromium and manganese content which results in a higher resistivity p in the annealed state accompanied by a slight reduction of saturation. This higher resistivity allows shorter switching times in an actuator, because eddy currents are reduced. At the same time, the alloy has a high saturation and a high permeability μ max ,whereby good soft magnetic properties are maintained. 
     The alloy elements Si and Al improve the strength of the alloy without significantly reducing its soft magnetic properties. By the addition of Si and Al, the strength of the alloy can be increased noticeably as a result of solid-solution hardening without any significant reduction of its soft magnetic properties. 
     The aluminium content and the vanadium content according to the invention permit a higher annealing temperature, which improves the soft magnetic properties of coercitive field strength H c  and maximum permeability μ max . A high permeability is desirable, because it results in low drive currents if the alloy is used as a magnet core or flux conductor of an actuator. 
     In one embodiment, the alloy has a silicon content of 0.5% by weight≦Si≦1.0% by weight. 
     The Mo content was kept low to avoid the formation of carbides, which may adversely affect magnetic properties. 
     In addition of Cr and Mn, a minor addition of molybdenum is expedient, as this molybdenum content is characterised by an advantageous relationship between resistance increase and saturation reduction. 
     One embodiment has an aluminium plus silicon content of 0.6% by weight≦Al+Si≦1.5% by weight, whereby the brittleness and processing problems which may arise at a higher total aluminium plus silicon content are avoided. 
     One embodiment has a chromium plus manganese plus molybdenum plus aluminium plus silicon plus vanadium content of 4.0% by weight≦(Cr+Mn+Mo+Al+Si+V)≦9.0% by weight. Compared to the binary Co—Fe alloy, this alloy has a higher resistivity, resulting in a suppression of eddy currents, while saturation polarisation is reduced only minimally and coercitive field strength H c  is increased even less. 
     One embodiment has a chromium plus manganese plus molybdenum plus aluminium plus silicon plus vanadium content of 6.0% by weight≦Cr+Mn+Mo+Al+Si+V≦9.0% by weight. 
     In further embodiments, the soft magnetic alloy consists essentially of 10% by weight≦Co≦22% by weight, 0% by weight≦V≦1% by weight, 1.5% by weight≦Cr≦3% by weight, 1% by weight≦Mn≦2% by weight, 0% by weight≦Mo≦1% by weight, 0.5% by weight≦Si≦1.5% by weight, 0.1% by weight≦Al≦1.0% by weight, rest iron. It may have an aluminium plus silicon content of 0.6% by weight≦Al+Si≦1.5% by weight and/or a chromium plus manganese plus molybdenum plus aluminium plus silicon plus vanadium content of 4.5% by weight≦Cr+Mn+Mo+Al+Si+V≦6.0% by weight. 
     In one embodiment, the alloy consists essentially of V=0% by weight, 1.6% by weight≦Cr≦2.5% by weight, 1.25% by weight≦Mn≦1.5% by weight, 0% by weight≦Mo≦0.02% by weight, 0.6% by weight≦Si≦0.9% by weight and 0.2% by weight≦Al≦0.7% by weight. 
     In one embodiment, the alloy consists essentially of 0% by weight≦V≦2.0% by weight, 1.6% by weight≦Cr≦2.5% by weight, 1.25% by weight≦Mn≦1.5% by weight, 0% by weight≦Mo≦0.02% by weight, 0.6% by weight≦Si≦0.9% by weight and 0.2% by weight≦Al≦0.7% by weight. 
     In one embodiment, the alloy consists essentially of 0% by weight≦V≦0.01% by weight, 2.3% by weight≦Cr≦3.5% by weight, 1.25% by weight≦Mn≦1.5% by weight, 0.75% by weight≦Mo≦1% by weight, 0.6% by weight≦Si≦0.9% by weight and 0.1% by weight≦Al≦0.2% by weight. 
     In one embodiment, the alloy consists essentially of 0.75% by weight≦V≦2.75% by weight, 2.3% by weight≦Cr≦3.5% by weight, 1.25% by weight≦Mn≦1.5% by weight, 0% by weight≦Mo≦0.01% by weight, 0.6% by weight≦Si≦0.9% by weight and 0.2% by weight≦Al≦1.0% by weight. 
     These three alloys offer a preferred combination of high electric resistance, high saturation and low coercitive field strength. 
     Alloys of the above compositions have a resistivity ρ&gt;0.50 μΩm or ρ&gt;0.55 μΩm or ρ&gt;0.60 μΩm or ρ&gt;0.65 μΩm. This value provides for an alloy which generates low eddy currents when used as a magnet core of an actuator system. This permits the use of the alloy in actuator systems with higher switching times. 
     The proportion of the elements aluminium and silicon in the alloy according to the invention results in an alloy with a yield point of R p0.2  of 340 MPa. This higher strength of the alloy can increase its service life when used as a magnet core of an actuator system. This is an attractive feature when using the alloy in high-frequency actuator systems, such as fuel injectors in internal combustion-engines. 
     The alloy according to the invention is characterised by good magnetic properties, high strength and high resistivity. In further embodiments, the alloy has a saturation J(400 A/cm)&gt;2.00 T or &gt;1.90 T and/or a coercitive field strength H c &lt;3.5 A/cm or H c &lt;2.0 cm and/or H c &lt;1.0 cm and a maximum permeability μ max &gt;1000 or μ max &gt;2000. 
     The chromium plus manganese plus molybdenum plus aluminium plus silicon plus vanadium content according to the invention lies in the range of 4.0% by weight to 9.0% by weight. This higher content provides for an alloy having a higher electric resistance ρ&gt;0.6 μΩm and a low coercitive field strength H c &lt;2.0 A/cm. This combination of properties is particularly suitable for use in high-speed actuators. 
     The invention further provides for a soft magnetic core or flux conductor for an electromagnetic actuator made of an alloy according to any of the preceding embodiments. This soft magnetic core is available in various embodiments, such as a soft magnetic core for a solenoid valve of an internal combustion engine, a soft magnetic core for a fuel injector of an internal combustion engine, a soft magnetic core for a direct injector of a spark ignition engine or diesel engine or as a soft magnetic component for electromagnetic valve control, for example for inlet and outlet valves. 
     The various actuator systems, such as solenoid valves and fuel injectors, are subject to varying requirements in terms of strength and magnetic properties. These requirements can be met by selecting an alloy with a composition within the range described above. 
     The invention further provides for a fuel injector of an internal combustion engine with a component made of a soft magnetic alloy according to any of the preceding embodiments. In further embodiments, the fuel injector is a direct injector of a spark ignition engine or a direct injector of a diesel engine. 
     In further embodiments, the invention provides for a yoke part for an electromagnetic actuator, for a soft magnetic rotor and a soft magnetic stator for an electric motor and for a soft magnetic component for an electromagnetic valve control on an inlet valve or an outlet valve used in an engine compartment of, for example, a motor vehicle, all these being made of an alloy according to any of the preceding embodiments. 
     The invention further provides for a method for the production of semi-finished products from a cobalt-iron alloy, wherein melting and hot forming processes are first used to produce workpieces from a soft magnetic alloy consisting essentially of 10% by weight≦Co≦22% by weight, 0% by weight≦V≦4% by weight, 1.5% by weight≦Cr≦5% by weight, 1% by weight≦Mn≦2% by weight, 0% by weight≦Mo≦1% by weight, 0.5% by weight≦Si≦1.5% by weight, 0.1% by weight≦Al≦1.0% by weight, rest iron. 
     The alloy of the workpieces may alternatively have a composition according to any of the preceding embodiments. 
     The alloy can be melted using a variety of different methods. In theory, all commonly used technologies are feasible, including melting in the presence of air or by means of VIM (vacuum induction melting). An arc furnace or other inductive technologies can be used for this purpose. VOD (vacuum oxygen decarburisation), AOD (argon oxygen decarburisation) or ERP (electroslag remelting process) improves the quality of the product. 
     The VIM method is preferred for the production of the alloy, as it permits a more precise adjustment of the proportions of the alloy elements, and non-metallic inclusions in the solidified alloy are avoided more easily. 
     The melting process is followed by a variety of process steps depending on the semi-finished product to be produced. 
     In the production of strip from which components are subsequently punched, the ingot resulting from the melting process is first converted into a slab by blooming. The term blooming identifies the conversion of an ingot into a slab with a rectangular cross-section in a hot rolling process at a temperature of, for example, 1250° C. After the blooming process, the scale formed on the surface of the slab is removed by grinding. The grinding process is followed by a further hot rolling process in which the slab is converted into strip at a temperature of, for example, 1250° C. The impurities formed in the hot rolling process on the surface of the strip are then removed by grinding or pickling, and the strip is cold-rolled to its final thickness, which may be in the range of 0.1 mm to 2 mm. Finally, the strip is subjected to a finish-annealing process. During this finish-annealing process, the lattice vacancies caused by the forming processes are rectified, and crystalline grains form in the structure. 
     The process for producing turned components is similar. Here, too, billets with a square cross-section are produced by blooming the ingot. This so-called blooming is performed at a temperature of, for example, 1250° C. The scale produced in the blooming process is then removed by grinding. This is followed by a further hot rolling process whereby the billets are converted into bars or wires up to a diameter of, for example, 13 mm. Straightening and scalping processes then correct distortions in the material on the one hand and remove the impurities formed on the surface in the hot rolling process on the other hand. The material is finally likewise finish-annealed. 
     The finish-annealing process can be carried out in a temperature range between 700° C. and 1100° C. In one implementation, the finish-annealing process is carried out in a temperature range between 750° C. and 850° C. The finish-annealing process can be carried out in the presence of an inert gas or hydrogen or in a vacuum. 
     Conditions such as the temperature and duration of the finish-annealing process can be selected such that the finish-annealed alloy in a tensile test exhibits deformation parameters of an elongation A L &gt;2% or A L &gt;20%. 
     In a further implementation, the alloy is cold-formed prior to finish-annealing. 
     The invention is explained in greater detail with reference to the drawing. 
       FIG. 1  shows an electromagnetic actuator-system  20  with a magnet core  21  made of a soft magnetic alloy according to the invention, which in a first embodiment consists essentially of 18.3% by weight Co, 2.62% by weight Cr, 1.37% by weight Mn, 0.85% by weight Si, 0.01% by weight Mo, 0.21% by weight Al, rest iron. In a further embodiment not illustrated in the drawing, a yoke made of this alloy is specified. 
     A coil  22  is supplied with power from a power source  23 , so that a magnetic field is induced as the coil  22  is excited. The coil  22  is arranged around the magnet core  21  such that the magnet core  21  is moved from a first position  24  indicated by a broken line in  FIG. 1  to a second position  25  by the induced magnetic field. In this embodiment, the first position  24  is a closed position while the second position is an open position. The current flow  26  through the channel  27  is therefore controlled by the actuator system  20 . 
     In a further embodiment, the actuator system  20  is a fuel injector of a spark ignition engine or a diesel engine, or a direct injector of a spark ignition engine or a diesel engine. 
     The soft magnetic alloy of the magnet core  21  has a chromium plus manganese content resulting in the annealed state in a resistivity ρ of 0.572 μΩm. This higher resistivity allows for shorter switching times in the actuator, as eddy currents are reduced. At the same time, the alloy has a high saturation J(400 A/cm), measured at a magnetic field strength of 400 A/cm, of 2.137 T and a permeability μ max  of 1915, whereby good soft magnetic properties are maintained. 
     The alloy elements Si and Al improve the strength of the magnet core  21  without substantially affecting its soft magnetic properties. The yield point R p0.2  of this alloy is 402 MPa. The aluminium content permits a higher annealing temperature, which results in good soft magnetic properties of a coercitive field strength H c  of only 2.57 A/cm and a maximum permeability μ max  of 1915. A high permeability is desirable, because it results in lower drive currents when using the alloy as a magnet core of an actuator. 
     The Mo content was kept low to avoid the formation of carbides, which can lead to a deterioration of the magnetic properties. 
     Table 1 lists compositions of various exemplary alloys according to the invention. 
     From these alloys, semi-finished products were made using a method illustrated in the flow chart of  FIG. 2 . 
     According to the flow chart of  FIG. 2 , the alloy is first subjected to a melting process  1 . 
     Various methods can be used to melt the alloy. In theory, all commonly used technologies, such as melting in the presence of air or by means of VIM (vacuum induction melting), are feasible. Further possible technologies include the arc furnace or inductive technologies. VOD (vacuum oxygen decarburisation), AOD (argon oxygen decarburisation) or ERP (electroslag remelting process) improves the quality of the product. 
     The VIM method is preferred in the production of the alloy, as it permits a more precise adjustment of the proportions of the alloy elements, and non-metallic inclusions in the solidified alloy are avoided more easily. 
     Depending on the semi-finished product to be produced, the melting process is followed by a number of different process steps. 
     In the production of strip from which components are subsequently punched, the ingot resulting from the melting process  1  is first converted into a slab by blooming  2 . The term blooming identifies the conversion of an ingot into a slab with a rectangular cross-section in a hot rolling process at a temperature of 1250° C. After the blooming process, the scale formed on the surface of the slab is removed by grinding  3 . The grinding process  3  is followed by a further hot rolling process  4  in which the slab is converted into strip with a thickness of, for example, 3.5 mm at a temperature of 1250° C. The impurities formed in the hot rolling process on the surface of the strip are then removed by grinding or pickling 5, and the strip is cold-rolled 6 to its final thickness in the range of 0.1 mm to 2 mm. Finally, the strip is subjected to a finish-annealing process  7  at a temperature of &gt;700° C. During this finish-annealing process, the lattice vacancies caused by the forming processes are rectified, and crystalline grains form in the structure. 
     The process for producing turned components is similar. Here, too, billets with a square cross-section are produced by blooming  8  the ingot. This so-called blooming is performed at a temperature of 1250° C. The scale produced in the blooming process  8  is then removed by grinding  9 . This is followed by a further hot rolling process  10  whereby the billets are converted into bars or wires up to a diameter of 13 mm. Straightening and scalping processes  11  then correct distortions in the material on the one hand and remove the impurities formed on the surface in the hot rolling process  10  on the other hand. The material is finally likewise finish-annealed  12 . 
     The coercitive field strength H c  was measured in dependence on annealing temperature for the alloys of Table 1. The results are illustrated in  FIG. 3 . As FIG.  3  shows, the coercitive field strength is initially reduced with rising temperature and then increases at even higher temperatures approaching the biphase region. 
     The selected annealing temperature is determined by composition, so that the coercitive field strength remains low. The alloy  3  described with reference to  FIG. 1  was annealed at a temperature of 760° C. 
       FIG. 4  shows the coercitive field strength for the alloys  1  to  4 ,  8 ,  10 ,  11  and  13 . The alloys  8 ,  10 ,  11  and  13  were cold-formed after hot rolling. The alloys  1  to  4  were hot-rolled only.  FIG. 4  illustrates the effect of various added elements on H c  at various temperatures. The increase of H c  shows the upper limit of the ferritic phase. 
     The alloys  2 ,  10 ,  11  and  13  with a lower H c  at higher annealing temperatures have an aluminium content of at least 0.68% by weight. The alloys  10  and  11  have a particularly low coercitive field strength H c  of less than 1.5 A/cm at annealing temperatures above 850° C. These alloys have an aluminium content of 0.84% by weight and 0.92% by weight respectively and a vanadium content of 2.51% by weight and 1.00% by weight respectively. 
     In these alloys, the phase transition temperature becomes even higher. This offers the advantage that the magnetic properties can be improved even further by using a higher annealing temperature. 
     The following properties: resistivity in the annealed state ρ el , coercitive field strength H c , saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) and a magnetic field strength of 400 A/cm, J(400 A/cm), maximum permeability μ max , yield point R m , R p0.2 , elongation AL and modulus of elasticity were measured for the alloys of Table 1 and are summarised in Table 2. 
     The resistivity p of each alloy lies above 0.5 μΩm. This results in a suppression of eddy currents, making the alloys suitable for application as actuators with short switching times. The yield point for the alloys  1  to  7  was measured in the finish-annealed state and lies above 340 MPa for each alloy. These alloys can therefore be used in applications involving higher mechanical loads. 
     Table 2 indicates that the alloys, notwithstanding the high proportion of non-magnetic elements added, have a high saturation J(400 A/cm)&gt;2.0 T, a high resistivity ρ&gt;0.5 μΩm and a high yield point R p0.2 , &gt;340 MPa. These alloys are therefore particularly suitable for magnet cores in high-speed actuator systems, such as fuel injectors. 
     1 st  EMBODIMENT 
     An alloy according to a first embodiment consists essentially of 18.1% by weight Co, 2.24% by weight Cr, 1.40% by weight Mn, 0.01% by weight Mo, 0.83% by weight Si, 0.24% by weight Al, rest iron and was produced as described above. The alloy was annealed at 760° C. and in the annealed state has a resistivity ρ el  of 0.542 μΩm, a coercitive field strength H c  of 2.34 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.029 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.146 T, a maximum permeability μ max  of 2314, a yield point R m  of 623 MPa, R p0.2  of 411 MPa, an elongation AL of 29.6% and a modulus of elasticity of 220 GPa. 
     2 nd  EMBODIMENT 
     An alloy according to a second embodiment consists essentially of 18.2% by weight Co, 1.67% by weight Cr, 1.39% by weight Mn, 0.01% by weight Mo, 0.82% by weight Si, 0.68% by weight Al, rest iron and was produced as described above. The alloy was annealed at 800° C. and in the annealed state has a resistivity ρ el  of 0.533 μΩm, a coercitive field strength H c  of 1.94 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.019 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.151 T, a maximum permeability μ max  of 1815, a yield point R m  of 661 MPa, R p0.2  of 385 MPa, an elongation AL of 25.4% and a modulus of elasticity of 221 GPa. 
     3 rd  EMBODIMENT 
     An alloy according to a third embodiment consists essentially of 18.3% by weight Co, 2.62% by weight Cr, 1.37% by weight Mn, 0.01% by weight Mo, 0.85% by weight Si, 0.21% by weight Al, rest iron and was produced as described above. The alloy was annealed at 760° C. and in the annealed state has a resistivity ρ el  of 0.572 μΩm, a coercitive field strength H c  of 2.57 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.021 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.137 T, a maximum permeability μ max  of 1915, a yield point R m  of 632 MPa, R p0.2  of 402 MPa, an elongation AL of 28.0% and a modulus of elasticity of 217 GPa. 
     4 th  EMBODIMENT 
     An alloy according to a fourth embodiment consists essentially of 18.3% by weight Co, 2.42% by weight Cr, 1.45% by weight Mn, 0.01% by weight Mo, 0.67% by weight Si, 0.23% by weight Al, rest iron and was produced as described above. The alloy was annealed at 730° C. and in the annealed state has a resistivity ρ el  of 0.546 μΩm, a coercitive field strength H c  of 2.73 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.037 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.156 T, a maximum permeability μ max  of 2046, a yield point R m  of 605 MPa, R p0.2  of 395 MPa, an elongation AL of 29.5% and a modulus of elasticity of 223 GPa. 
     5 th  EMBODIMENT 
     An alloy according to a fifth embodiment consists essentially of 15.40% by weight Co, 2.34% by weight Cr, 1.27% by weight Mn, 0.85% by weight Si, 0.23% by weight Al, rest iron and was produced as described above. The alloy was annealed at 760° C. and in the annealed state has a resistivity ρ el  of 0.5450 μΩm, a coercitive field strength H c  of 1.30 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.986 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.105 T and a maximum permeability μ max  of 3241. 
     6 th  EMBODIMENT 
     An alloy according to a sixth embodiment consists essentially of 18.10% by weight Co, 2.30% by weight Cr, 1.37% by weight Mn, 0.83% by weight Si, 0.24% by weight Al, rest iron and was produced as described above. The alloy was annealed at 760° C. and in the annealed state has a resistivity ρ el  of 0.5591 μΩm, a coercitive field strength H c  of 1.39 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.027 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.138 T and a maximum permeability μ max  of 2869. 
     7 th  EMBODIMENT 
     An alloy according to a seventh embodiment consists essentially of 21.15% by weight Co, 2.31% by weight Cr, 1.38% by weight Mn, 0.84% by weight Si, 0.23% by weight Al, rest iron and was produced as described above. The alloy was annealed at 760° C. and in the annealed state has a resistivity ρ el  of 0.5627 μΩm, a coercitive field strength H c  of 1.93 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 2.066 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.165 T and a maximum permeability μ max  of 1527. 
     The eighth to thirteenth embodiments contain slightly more added elements in total, i.e. between 6 and 9% by weight. In the annealed state, these alloys have a resistivity ρ el ≧0.60 μΩm. 
     8 th  EMBODIMENT 
     An alloy according to an eighth embodiment consists essentially of 18.0% by weight Co, 2.66% by weight Cr, 1.39% by weight Mn, 0.01% by weight Mo, 0.87% by weight Si, 0.17% by weight Al, 1.00% by weight V, rest iron and was produced as described above. This alloy was cold-formed after hot rolling. The alloy was annealed at 780° C. and in the annealed state has a resistivity ρ el  of 0.627 μΩm, a coercitive field strength H c  of 1.40 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.977 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.088 T, a maximum permeability μ max  of 2862, a yield point R m  of 605 MPa, R p0.2  of 374 MPa, an elongation AL of 29.7% and a modulus of elasticity of 222 GPa. 
     9 th  EMBODIMENT 
     An alloy according to a ninth embodiment consists essentially of 18.0% by weight Co, 2.60% by weight Cr, 1.35% by weight Mn, 0.99% by weight Mo, 0.84% by weight Si, 0.17% by weight Al, ≦0.01% by weight V, rest iron and was produced as described above. This alloy was cold-formed in addition. The alloy was annealed at 780° C. and in the annealed state has a resistivity ρ el  of 0.604 μΩm, a coercitive field strength H c  of 2.13 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.969 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.092 T, a maximum permeability μ max  of 1656, a yield point R m  of 636 MPa, R p0.2  of 389 MPa, an elongation AL of 29.2% and a modulus of elasticity of 222 GPa. 
     10 th  EMBODIMENT 
     An alloy according to a tenth embodiment consists essentially of 18.0% by weight Co, 1.85% by weight Cr, 1.33% by weight Mn, ≦0.01% by weight Mo, 0.86% by weight Si, 0.84% by weight Al, 2.51% by weight V, rest iron and was produced as described above. This alloy was then cold-formed. The alloy was annealed at 870° C. and in the annealed state has a resistivity ρ el  of 0.716 μΩm, a coercitive field strength H c  of 0.95 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.920 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.015 T and a maximum permeability μ max  of 4038. 
     This alloy of the tenth embodiment offers a particularly advantageous combination of a high resistivity ρ el  of 0.716 μΩm, a low coercitive field strength H c  of 0.95 A/cm and a high saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.920 T. 
     11 th  EMBODIMENT 
     An alloy according to an eleventh embodiment consists essentially of 12.0% by weight Co, 2.65% by weight Cr, 1.38% by weight Mn, ≦0.01% by weight Mo, 0.85% by weight Si, 0.92% by weight Al, 1.00% by weight V, rest iron and was produced as described above and then cold-formed. The alloy was annealed at 820° C. and in the annealed state has a resistivity ρ el  of 0.658 μΩm, a coercitive field strength H c  of 0.72 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.880 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 2.008 T, a maximum permeability μ max  of 5590, a yield point R m  of 525 MPa, R p0.2  of 346 MPa, an elongation AL of 33.5% and a modulus of elasticity of 216 GPa. 
     This alloy of the eleventh embodiment offers a particularly advantageous combination of a high resistivity ρ el  of 0.658 μΩm, a low coercitive field strength H c  of 0.72 A/cm and a high saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.880 T. 
     12 th  EMBODIMENT 
     having a Co content of more than 22% by weight, the twelfth alloy does not correspond to the invention. 
     13 th  EMBODIMENT 
     An alloy according to a thirteenth embodiment consists essentially of 18.0% by weight Co, 3.00% by weight Cr, 1.32% by weight Mn, &lt;0.01% by weight Mo, 0.86% by weight Si, 0.84% by weight Al, 2.01% by weight V, rest iron and was produced as described above and then cold-formed after hot rolling. The alloy was annealed at 820° C. and in the annealed state has a resistivity ρ el  of 0.769 μΩm, a coercitive field strength H c  of 1.14 A/cm, a saturation J at a magnetic field strength of 160 A/cm, J(160 A/cm) of 1.896 T and at a magnetic field strength of 400 A/cm, J(400 A/cm) of 1.985 T, a maximum permeability μ max  of 3499, a yield point R m  of 674 MPa, R p0.2  of 396 MPa, an elongation AL of 33.3% and a modulus of elasticity of 218 GPa. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Co 
                   
                 Cr 
                 Mn 
                 Si 
                 Mo 
                 Al 
                 V 
               
               
                   
                   
                 (% by 
                 Total added 
                 (% by 
                 (% by 
                 (% by 
                 (% by 
                 (% by 
                 (% by 
               
               
                 Alloy 
                 Fe 
                 weight) 
                 alloys 
                 weight) 
                 weight) 
                 weight) 
                 weight) 
                 weight) 
                 weight) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 1 
                 Rest 
                 18.1 
                 4.73 
                 2.24 
                 1.40 
                 0.83 
                 0.01 
                 0.24 
                 &lt;0.01 
               
               
                 2 
                 Rest 
                 18.2 
                 4.58 
                 1.67 
                 1.39 
                 0.82 
                 0.01 
                 0.68 
                 &lt;0.01 
               
               
                 3 
                 Rest 
                 18.3 
                 5.09 
                 2.62 
                 1.37 
                 0.85 
                 0.01 
                 0.21 
                 &lt;0.01 
               
               
                 4 
                 Rest 
                 18.3 
                 4.78 
                 2.42 
                 1.45 
                 0.67 
                 0.01 
                 0.23 
                 &lt;0.01 
               
               
                 5 
                 Rest 
                 15.40 
                 4.69 
                 2.34 
                 1.27 
                 0.85 
                 0.001 
                 0.23 
                 &lt;0.01 
               
               
                 6 
                 Rest 
                 18.10 
                 4.74 
                 2.30 
                 1.37 
                 0.83 
                 0.001 
                 0.24 
                 &lt;0.01 
               
               
                 7 
                 Rest 
                 21.15 
                 4.76 
                 2.31 
                 1.38 
                 0.84 
                 0.001 
                 0.23 
                 &lt;0.01 
               
               
                 8 
                 Rest 
                 18.0 
                 6.18 
                 2.66 
                 1.39 
                 0.87 
                 &lt;0.01 
                 0.17 
                 1.00 
               
               
                 9 
                 Rest 
                 18.0 
                 6.18 
                 2.60 
                 1.35 
                 0.84 
                 0.99 
                 0.17 
                 &lt;0.01 
               
               
                 10  
                 Rest 
                 18.0 
                 7.38 
                 1.85 
                 1.33 
                 0.86 
                 &lt;0.01 
                 0.84 
                 2.51 
               
               
                 11  
                 Rest 
                 12.0 
                 6.78 
                 2.65 
                 1.38 
                 0.85 
                 &lt;0.01 
                 0.92 
                 1.00 
               
               
                 12* 
                 Rest 
                 25.0 
                 5.58 
                 1.57 
                 0.96 
                 0.93 
                 &lt;0.01 
                 1.02 
                 1.00 
               
               
                 13  
                 Rest 
                 18.0 
                 8.18 
                 3.00 
                 1.32 
                 0.86 
                 &lt;0.01 
                 0.84 
                 2.01 
               
               
                   
               
               
                 *not according to invention 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Annealing 
                   
                   
                   
                   
                   
                   
                   
                   
                 Mod. of 
               
               
                   
                 Temperature 
                 ρ 
                 H c   
                 J(160) 
                 J(400) 
                   
                 R m   
                 Rp 0.2   
                 AL 
                 Elasticity 
               
               
                 Alloy 
                 (° C.) 
                 (μΩm) 
                 (A/cm) 
                 (T) 
                 (T) 
                 μ max   
                 (Mpa) 
                 (Mpa) 
                 (%) 
                 (Gpa) 
               
               
                   
               
             
            
               
                 1 
                 760 
                 0.542 
                 2.34 
                 2.029 
                 2.146 
                 2314 
                 623 
                 411 
                 29.6 
                 220 
               
               
                 2 
                 800 
                 0.533 
                 1.94 
                 2.019 
                 2.151 
                 1815 
                 661 
                 385 
                 25.4 
                 221 
               
               
                 3 
                 760 
                 0.572 
                 2.57 
                 2.021 
                 2.137 
                 1915 
                 632 
                 402 
                 28.0 
                 217 
               
               
                 4 
                 730 
                 0.546 
                 2.73 
                 2.037 
                 2.156 
                 2046 
                 615 
                 395 
                 29.5 
                 223 
               
               
                 5 
                 760 
                 0.545 
                 1.30 
                 1.986 
                 2.105 
                 3241 
                 — 
                 — 
                 — 
                 — 
               
               
                 6 
                 760 
                 0.559 
                 1.39 
                 2.027 
                 2.138 
                 2869 
                 — 
                 — 
                 — 
                 — 
               
               
                 7 
                 760 
                 0.563 
                 1.93 
                 2.066 
                 2.165 
                 1527 
                 — 
                 — 
                 — 
                 — 
               
               
                 8 
                 780 
                 0.627 
                 1.40 
                 1.977 
                 2.088 
                 2862 
                 605 
                 374 
                 29.7 
                 222 
               
               
                 9 
                 780 
                 0.604 
                 2.13 
                 1.969 
                 2.092 
                 1656 
                 636 
                 389 
                 29.2 
                 222 
               
               
                 10  
                 870 
                 0.716 
                 0.95 
                 1.920 
                 2.015 
                 4038 
                 — 
                 — 
                 — 
                 — 
               
               
                 11  
                 820 
                 0.658 
                 0.72 
                 1.880 
                 2.008 
                 5590 
                 525 
                 346 
                 33.5 
                 216 
               
               
                 12* 
                 870 
                 0.628 
                 1.25 
                 1.989 
                 2.075 
                 1793 
                 — 
                 — 
                 — 
                 — 
               
               
                 13  
                 820 
                 0.769 
                 1.14 
                 1.896 
                 1.985 
                 3499 
                 674 
                 396 
                 33.3 
                 218 
               
               
                   
               
               
                 *not according to invention