The present invention relates to iron-cobalt alloys, particularly those having a content of about 10 to 35% of Co, as well as pure iron and alloys of iron and silicon which have a content of about 3% Si. These materials are used to form magnetic parts such as transformer cores, in particular for aircraft. Low frequency transformers (<1 kHz) embedded in the aircraft consist mainly of a magnetic core of soft magnetic alloy, laminated, stacked or coiled construction constraints, and primary and secondary windings (s) of copper. The primary current supply is variable over time, periodic but not necessarily purely sinusoidal shape, which does not fundamentally change the purpose of the transformer. Constraints on these transformers are multiple. They should have a volume and / or mass (usually the two are related) the smallest possible, so a volume or mass power density as high as possible. The higher the operating frequency, the lower the magnetic yoke the section and the volume (thus also the mass) of the cylinder head are important, exacerbating the interest of miniaturization in low frequency applications. As the fundamental frequency is often imposed, this amounts to obtain the highest magnetic workflow as possible or if the electrical power delivered is imposed to minimize the passage of magnetic flux section (and therefore the mass of materials), always to increase the power density by reducing the embedded masses. They must have sufficient durability (10 to 20 years minimum depending on the application) to allow profitable. Therefore, the thermal operating regime must be well taken into account with respect to the aging of the transformer. Typically a minimum life of 100,000 hours at 200 ° C is desired. The processor must operate on a power supply network to roughly sinusoidal frequency, with a magnitude of the effective voltage output varies transiently up to 60% from one moment to another, particularly when the power power transformer or with abrupt engagement of an electromagnetic actuator. This results, and by construction, a current surge in the transformer primary across the nonlinear magnetization curve of the magnetic core. The elements of the transformer (insulation and electronic components) must be able to withstand without damage high variations of this inrush current, so-called "effect of inrush." This inrush effect can be quantified by an "index inrush" In which is calculated by the formula In = 2.Bt + Br - Bsat, where Bt is the nominal working induction of the magnetic core of the transformer, is Bsat the core saturation induction and residual induction Br is its The noise emitted by the transformer due to electromagnetic forces and magnetostriction must be low enough to comply with the standards or to meet the requirements of users and staff posted in the vicinity of the transformer. Increasingly, the drivers and co-drivers aircraft wishing to either communicate using helmets but direct way. The thermal efficiency of the transformer is also very important to consider, since it sets both its internal operating temperature and heat flow which must be discharged, for example by means of an oil bath surrounding the windings and cylinder head, associated with oil pump dimensioned accordingly. The thermal power sources are primarily losses by Joule effect from the primary and secondary windings and the magnetic losses resulting from variations in the magnetic flux over time and in the magnetic material. In industrial practice, the volume thermal power to be extracted is limited to a certain threshold imposed by the size and power of the oil pump, and the temperature limit of internal operation of the transformer. Finally, the cost of the transformer must be kept as low as possible to ensure the best technical and economic compromise between cost of materials, design, manufacturing and maintenance, and optimization of electrical power density (mass or volume ) of the device through consideration of the thermal regime of the transformer. In general, it is advantageous to seek specific power density / volume as high as possible. The criteria to be considered to appreciate mainly the saturation magnetization Js and magnetic induction 800 A / B 800 . two technologies currently used for manufacturing low frequency embedded processors. According to a first of these techniques (so-called "in wound core"), the transformer comprises a magnetic circuit wound when power is Single phase. When power is three-phase, the core structure of the transformer is formed by two toroidal cores joined the above type, and surrounded by a third strip-wound core and forming an "eight" around the two preceding toroidal cores. This circuit form requires in practice a small thickness of the magnetic sheet (typically 0.1 mm). Indeed, this technology is used only when the supply frequency forces, taking into account induced currents, to use strips of this thickness, i.e. typically to frequencies of a few hundred Hz. According to the second of these techniques (known as "cut-to stacked core") is used a stacked magnetic circuit, whatever the envisaged electrical sheet thicknesses. This technology is good for any frequency below a few kHz. However care must be taken to deburring, the juxtaposition or even electrical insulation sheets, to reduce both noise gaps (and therefore optimize the apparent power) and limit induced currents between metal sheets. In either of these technologies are used in embedded power transformers, and whatever the thickness of proposed tape, a soft magnetic material with high permeability. Two families of these materials are available in thicknesses from 0.35 mm to 0.1 or even 0.05 mm, and are clearly distinguished by their chemical compositions: Fe-3% Si alloys (the compositions of the alloys are, throughout the text data in% by weight) whose fragility and electrical resistivity are mainly controlled by the Si content; their magnetic losses are quite low (non-oriented alloys NO) at low (grain oriented alloys GO), their saturation magnetization Js is high (of the order of 2T), their cost is very moderate; There are two subfamilies of Fe-3% Si is used for an embedded transformer core technology or to another: o Fe-3% Si grain oriented (GO), used for on-board transformer structures of the type "wound": their high permeability (B800 = 1 .8 - 1 .9 T) is related to their texture {1 10 } <001> very pronounced; these alloys have the advantage of being inexpensive, easy to fit, high permeability but saturation is limited to 2 T, and they exhibit a very strong non-linearity of the magnetization curve which can cause very high harmonics; o Fe-3% Si grain non-oriented (NO), used for on-board transformer structures of type "cut-stacked"; their permeability becomes smaller, their saturation magnetization is similar to GO; - alloys Fe-48% Co-2% V, including the fragility and electrical resistivity are mainly controlled by vanadium; they have their high magnetic permeability not only to their physical characteristics (K1 low) but also cooling after final annealing that rule K1 to a very low value; because of their fragility, these alloys must be shaped in the cold worked condition (by cutting, stamping, bending ...), and only after the workpiece has its final shape (rotor or stator of rotating machine, profile E or I transformer) the material is then annealed in the last step; Moreover, because of the presence of V, the quality of the annealing atmosphere should be perfectly controlled not to be oxidising; Finally, the price of this material, very high (20 to 50 times that of the Fe-3% Si - GO) is related to the presence of Co and is roughly proportional to the Co content; Fe-Co alloys at lower Co contents (typically 18 or 27%) are also available; they have the advantage of being cheaper than the previous ones, as they contain less Co while providing as good a saturation magnetization or in some cases even slightly higher than that of the previous FeCo48V2 alloy; However, their magnetic permeability and magnetic losses are significantly higher than those of equiatomic FeCo alloys. while providing also good saturation magnetization, or in some cases even somewhat higher than that of the previous FeCo48V2 alloy; However, their magnetic permeability and magnetic losses are significantly higher than those of equiatomic FeCo alloys. while providing also good saturation magnetization, or in some cases even somewhat higher than that of the previous FeCo48V2 alloy; However, their magnetic permeability and magnetic losses are significantly higher than those of equiatomic FeCo alloys. Only these two families of high permeability materials are currently used in the embedded power transformers. Except FeCo equiatomic alloy, high saturation material (pure Fe, Fe-Si or FeCo less than 40% Co) has a magnetocrystalline anisotropy of several tens of kJ / m 3, Which does not allow them to have a high permeability in the case of a random distribution of the final crystallographic orientations. In the case of magnetic sheets to less than 48% Co for middle frequency embedded processors, so it has long been known that the chances of success necessarily require acute texture characterized by the fact that every grain, an axis <100> is very close to the rolling direction. Texture {1 10} <001> so-called "Goss" obtained in the Fe-Si by a secondary recrystallization is illustrated case. However, according to these bibliographic work sheet should not contain cobalt. More recently, it was shown in US-A-3881967 that with four additions to 6% Co and 1 to 1, 5% Si, and also using a secondary recrystallization, high permeabilities could also be obtained from: B 800 = 1, T 98, a gain of 0.02 T /% Co to 800 a / m relative to the best sheet 3% Si Fe current GO (B 10 = 1, 90 T). However, it is obvious that an increase of only 4% of the B 800 is not sufficient to substantially alleviate a transformer. For comparison, an Fe-48% Co-2% V optimized for transformer has a B 800 of about 2.15 ± 0.05 T T, which allows an increase in magnetic flux at 800 A / m for the same yoke section of about 13% ± 3%, to 2500 A / m to about 15 % to 5000 A / m to about 16%. It should also be noted the presence in the Fe 3% Si -GO, large grains due to the secondary recrystallization, and a very small crystal disorientation between authorizing B 80 o 1, 9t coupled to the presence of a magnetostriction coefficient λ 100 very much greater than 0. this makes it very sensitive material constraints of mounting and operation, which brings in industrial practice B 800a Fe 3% Si GO operating in an embedded transformer to about 1: 8 T. This is also the case for the alloys of US-A-3 881 967. In addition, the Fe-48% Co-2 % V amplitude magnetostriction coefficients even 4 to 5 times higher than the Fe-3% Si, and a random distribution of crystal orientations and a small average grain size (a few tens of microns), which makes it very sensitive to low stresses in particular, that cause great variations of the magnetization characteristic J (H), and therefore also of B (H). These changes are consistent improvement when the stress is unidirectional and traction in the direction of degradation when the stress is unidirectional and compression. In operation, by the increase of the magnetization and the saturation induction, it must be considered that the replacement of a 3% Si Fe GO by Fe-48% Co-2% V causes an increase in magnetic flux of constant section of the transformer board of the order of 20 to 25% of the operating range of amplitudes of 800 to 5000 A / m, is therefore about 0.5% increase of the magnetic flux by% Co. the US alloy -A-3881967 enables a 1% increase in the magnetic flux by 1% Co, but as we said, this total increase (4%) was considered too low to justify the development of this material. It was also proposed, in particular in document US-A-3,843,424 to use a Fe-alloy 5 to 35% Co, having less than 2% Cr, and less than 3% Si, and having a Goss texture obtained by primary recrystallization and normal grain growth. Compositions Fe-27% Co-0.6% Cr or Fe-18% Co-0.6% Cr are cited as to achieve 2.08 T 800 A / m and 2.3 T at 8000 A / m. These values ​​allow for operation, with respect to an Fe-3% Si-GO sheet operating at 1 .8 T 800 A / m, and 1 .95 T 5000 A / m, to increase the magnetic flux in a given yoke section from 15% to 800 A / m and 18% at 5000 A / m, and therefore to reduce correspondingly the volume or mass of the transformer. Thus there have been proposed many compositions and methods for manufacturing Fe-Co alloys low (with possible additions of alloying elements) for generally obtaining magnetic inductions at 10 Oe near those accessible with commercial alloys Fe-48% Co-2% V but with Co contents (and thus cost) significantly lower (18 to 25%). However, experience has shown that these materials, when obtained and processed by the usual methods, exhibit high magnetostrictions, at least in some of their directions (taking, for example, DL rolling direction as a reference) . Now, as the direction of the magnetic excitation may vary greatly from one place to another of the magnetic circuit and at the same time, this inhomogeneity of magnetostriction in the different directions may well lead to generation of a noise magnetostriction very significant, although the magnetostriction in a determined direction is weak. In the core technology cut-stacked it is not known that Fe-Ni alloys are used in aircraft transformers. In fact, these materials have a saturation magnetization Js (1, 6 maximum T for the Fe-Ni50) much lower than the Fe-Si (2 T) or Fe-Co (> 2.3 T) above and also exhibit magnetostriction coefficients for FeNi50 of = 7 ppm and λ 100 = 27 ppm. This results in an apparent saturation magnetostriction A sat = 27 ppm for Fe-Ni50 polycrystalline type material "undirected" (that is to say that does not have textured structure). This level of magnetostriction is causing a high noise, and this, added to a saturation magnetization Js fairly moderate, says that this material is not used. In summary, the various problems which the aeronautical transformers designers face may arise as well. In the absence of strong demand on the noise due to the magnetostriction, the compromise between the demands on a weak effect of inrush, high mass density of the transformer, good efficiency and low magnetic losses lead to the use of solutions involving match magnetic cores wound GO Fe-Si, Fe-Co or amorphous iron based or solutions involving magnetic cores cut pieces and stacked NO Fe-Si or Fe-Co. In the latter case, frequently are used stacked cut-E cores or I electrical steel FeSi or NO GO, or FeCo alloys such as Fe49Co49V2. But since these materials have a significant magnetostriction and the magnetization direction does not continue in the same direction in a crystallographic structure in E, the transformer structures deform much and emit a loud noise if their design is made with a level usual working induction (about 70% of Js). To reduce noise emissions, we must: or reduce the induction of labor, but must be increased in the same ratio of the core section, so its volume and mass to retain a power transferred; is acoustically shielded transformer, driving up costs and an increase in the mass and volume of the transformer. In these conditions, it is far from always possible to design a transformer simultaneously meet the constraints of weight and noise specifications. The requirements on low noise magnetostrictive being increasingly widespread, it is not possible to meet with previous technologies other than increasing the volume and weight of the transformer, because it is not known to reduce noise other than reducing the average working induction Bt, so by increasing the core cross-section and the total mass to maintain the same magnetic workflow. B ^ must be lowered to about T 1, instead of 1, 4 to 1, 7 T for Fe-Si-Co or Fe in the absence of requirements on noise. It is also often pad the transformer, thus increasing its weight and its dimensions. Only a zero magnetostrictive material would, at first, to solve the problem, and if they have a higher labor induction that of current solutions. Only 80% Ni-Fe alloys which exhibit Js saturation induction of about 0.75 T and nanocrystalline which Js is 1, T 26 approximately have such a low magnetostriction. But the Fe-80% Ni alloys have a weak induction of Bt working to provide lighter than conventional transformers transformers. Only nanocrystalline allow this relief in the case of a very low noise asked. When the need for noise reduction is less important, nanocrystalline prove to be a relatively quiet solution, But nanocrystalline pose a major problem in the case of an "embedded processor" solution: their thickness is about 20 μηι and they are wound toroid flexible amorphous state around a rigid support, so that the shape the torus is maintained throughout the heat treatment leading to nanocrystallization. And this support can only be removed after the heat treatment, again for the shape of the torus can be preserved, and also because the core is then often cut in half to allow for better compactness of the transformer using the technology of the circuit wrapped earlier described. Only impregnation resins wound core can maintain the same shape in the absence of the support which is removed after polymerization of the resin. But after a cut C nanocrystalline impregnated and cured toroid, there is a deformation of C that prevents the two parts to be delivered exactly opposite to reconstitute the closed torus, once inserted windings. Constraints of fixing C in the transformer may also lead to their deformation. It is therefore preferable to retain the support, which increases transformer. More nanocrystalline exhibit a saturation magnetization Js significantly lower than other soft materials (iron, FeSi3%, Ni50% Fe, FeCo, amorphous iron core), which requires significantly burden the transformer, since the increase section of the magnetic core will offset the decline of labor induction imposed by Js. Also the "nanocrystalline" solution would be used as a last resort, if the maximum noise level is low and if required a lighter and low noise solution did not appear. which increases the transformer. More nanocrystalline exhibit a saturation magnetization Js significantly lower than other soft materials (iron, FeSi3%, Ni50% Fe, FeCo, amorphous iron core), which requires significantly burden the transformer, since the increase section of the magnetic core will offset the decline of labor induction imposed by Js. Also the "nanocrystalline" solution would be used as a last resort, if the maximum noise level is low and if required a lighter and low noise solution did not appear. which increases the transformer. More nanocrystalline exhibit a saturation magnetization Js significantly lower than other soft materials (iron, FeSi3%, Ni50% Fe, FeCo, amorphous iron core), which requires significantly burden the transformer, since the increase section of the magnetic core will offset the decline of labor induction imposed by Js. Also the "nanocrystalline" solution would be used as a last resort, if the maximum noise level is low and if required a lighter and low noise solution did not appear. since increasing section of the magnetic core will offset the decline of labor induction imposed by Js. Also the "nanocrystalline" solution would be used as a last resort, if the maximum noise level is low and if required a lighter and low noise solution did not appear. since increasing section of the magnetic core will offset the decline of labor induction imposed by Js. Also the "nanocrystalline" solution would be used as a last resort, if the maximum noise level is low and if required a lighter and low noise solution did not appear. The object of the invention is to provide a material to form transformer cores having a very small magnetostriction, including when subjected to a strong induction of labor that would not use a magnetic core mass too large, thus to provide transformers having a specific power density (or bulk) high. In this way, processors they would achieve could advantageously be used in environments such as an aircraft cockpit where low noise magnetostrictive would be beneficial for user comfort. To this end, the invention relates to a sheet or ferrous alloy strip cold rolled and annealed, characterized in that its composition is, in percentages by weight: - traces defined by disorientation less than 15 ° around a crystallographic orientation defined {h 0 kolo} . The invention also relates to a method for producing a ferrous strip or sheet alloy of the foregoing type, characterized in that: - is developed a ferrous alloy whose composition consists of: - traces (these are the guidelines that prove most present in sheet and strip according to the invention) and, in general, no more than 30% of all texture component {hkl} marked, that is to say, a component characterized in that at most 30 % of volume fraction of grains of the material have the orientation {hkl} to less than 15 ° in disorientation of a specific orientation {h 0 kolo} .. After the final recrystallization annealing which allows to obtain the final magnetic properties of the material may be added an additional oxidation annealing the material at a temperature between 400 and 700 ° C, preferably between 400 and 550 ° C, allowing but a high surface oxidation of the material on at least one of its faces, without the risk of intergranular oxidation since it is known to occur at higher temperatures. This oxidation layer has a thickness of 0.5 to 10 μηι and ensures electrical insulation between the stacked parts of the magnetic core transformer, thereby substantially reducing the induced currents and thus the magnetic losses of the transformer. The precise conditions for obtaining this layer oxidation can readily be determined by those skilled in the art using classical experiments, depending on the precise composition of the material and the oxidizing power of the selected treatment atmosphere (air, pure oxygen, oxygen-gas mixture neutral ...) vis-à-vis the material. Conventional composition analysis of the oxide layer and its thickness to determine what conditions for processing a given material (temperature, time, atmosphere) the desired oxidation layer can be obtained. There is described a manufacturing process comprising two cold rolling steps and two or three annealing. But there remain of the invention to perform more like cold rolling stages to those that have been described, which can be separated by intermediate annealing similar to the first mandatory annealed which have been described. It should be understood that each of the cold rate of 50 to 80% reduction rolled, preferably 60 to 75%, it is told which may be carried out progressively, in several successive passes not separated by an intermediate annealing. in addition to the low magnetostriction and low effect of inrush, a transformer mass as small as possible. 1, 8 T, in particular, is a good induction to get as light transformer and low noise as possible. It is well understood that to obtain a low noise magnetostriction of the transformer, it would not be useful to obtain a low magnetostriction only in one or some direction (s) that define with respect to the rolling direction and the direction of field, maintaining a relatively high magnetostriction in the other directions. So we take as user satisfaction criterion the maximum deviation "Max Δλ" between the magnetostriction of amplitudes observed in the measurements carried out on three types of sample from the same material and shown in Figure 1. The examples which follow will be based on this evaluation method These samples are taken from a strip 1 according to the invention or prepared according to a standard method, according to the example. Its rolling direction DL, DT and its direction through its center 45 ° direction is represented by arrows. Three types of samples are taken from the sheet 1 for the achievement of magnetostriction tests. Type 1: 2 elongated rectangular samples (e.g. 120x15 mm) cut such that the direction along the sample 2 is parallel to DL. The magnetic field Ha is applied during the measurement of deformation, by an excitation coil having the same axis as the direction along the sample 2, so also as the sample 2. LONG management ε deformation measurements, called A H // DL are carried out both in the direction of the field (K H " DI Z / / H), and perpendicular thereto (A H // DL gj_ H ) and hence two values of magnetostriction for sample 2 type 1. Type 2: Sample 3 elongate rectangular (e.g. 120x15 mm) cut such that the direction along the sample 3 is parallel to the axis at 45 ° DL and DT. The magnetic field Ha is applied during the measurement of strain by an excitation coil having the same axis as the direction along the sample 3, also according to the sample management 3. LONG deformation measurements, called edit Chapter Η // 45 °, are carried out as well in the direction of the field (edit Chapter Η // 45 ° ε // Η ), perpendicularly thereto (edit Chapter Η // 45 ° ε ± Η ) and hence two magnetostriction values for sample 3 of type 2. Type 3: Sample 4 rectangular elongate (e.g. 120x15 mm) cut such that the direction along the sample 4 is parallel to DT. The magnetic field Ha is applied during the measurement of deformation, by a same axis as the sample LONG management excitation coil 4, also according to the sample management LONG 4. Strain measurements, labeled A H // DT are performed both in the direction of the field (λ ™ 1 ^), and perpendicular thereto (A H // DT £ j_ H ) and hence two magnetostriction values for sample 4 type 3. In total therefore six different deformation measurements are measured at each level of induction B (measured) of each of three types of sample. For the magnétoctrictif behavior of the material, not only three directions (types) of sampling are used (DL, DT and the direction forming an angle of 45 ° with Dl and DT), but also several induction levels such as, for example 1 T , 1, 5T, 1, 8T. The magnitude Δλ Max measured for an induction amplitude B in the material and can also note Max Δλ (Β) is representative of the isotropic magnetostriction. It is calculated by taking into account the highest value and the lowest value among these six λ values ​​measured on the samples 2, 3, 4 from the same band material 1 as shown in Figure 1. This consideration is the highest value that can be found among the six absolute values ​​of the algebraic differences between each possible pair of magnetostriction measures described above. In other words : M8chDl (B) = M8ch | l H e ^ H (R) - l H e ^ (B) i, j = DL, 45 ° or DT For a sheet or strip is declared according to the invention, it is recognized that the maximum value Max Δλ measured for an induction of 1 T 8 must be at most 25 ppm. The ten tests to be described were performed on samples including a FeCo27 type alloy which we will specify detailed compositions. But we will see that the invention is applicable to quite comparable to all the alloys known under this category in itself and routinely used in transformer cores, without the interest of the texturing very low but not zero which will be described, with means to get it, has so far been identified. Table 1 shows the compositions of various alloys according to the invention and reference alloys, used during the tests. In particular, two FeCo27 alloys from different flows, but very similar compositions so that the test results are directly comparable, were tested. The alloy A was used for the reference tests 1 and 2, the alloy B was used for testing according to the invention 3-9 and the reference tests 10-12. Element ABCDEFGHIJKLMN (%) Invention nvention nvention nvention nvention nvention nvention nvention nvention Reference Reference Reference Invention Invention C 0,010 0,009 0,007 0,023 0,012 0,013 0,011 0,012 0,010 0,008 0,009 0,009 0,012 0,015 Mn 0.256 0.195 0.234 0.261 0.248 0.421 0.532 0.810 0.167 0.208 0.520 0.289 0.368 <0.010 And 0.142 0.153 0.330 0.720 0.031 2.730 0.070 0.013 3.020 0.023 3.07 1.53 0.640 0.083 S 0,0023 0,0042 0,0033 0,0021 0,0048 0,0008 0,0006 0,0028 0,0005 0,0015 0,0007 0,0044 0,0008 < 0,0005 P 0,0025 0,0055 0,0031 0,0029 0,0029 0,0032 0,0047 0,0037 0,0053 0,0031 0,0043 0,0049 0,0041 < 0,0005 Ni 0,030 0,030 0,100 < 0,01 0,130 < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 < 0,01 0,080 < 0,01 Cr 0,514 0,498 1 ,00 0,200 0,011 0,008 0,048 6,06 0,047 0,089 0,007 0,038 0,072 <0,01 Mo < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 0,170 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 Cu 0,009 0,010 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 <0,005 <0,005 < 0,005 < 0,005 Co 27,09 27,32 18,35 10,07 4,21 0,020 < 0,01 27,11 < 0,01 49,0 18,20 38,15 38,82 15,10 V 0,01 0,01 < 0,005 0,51 < 0,005 < 0,005 < 0,005 < 0,005 < 0,005 2,03 < 0,005 < 0,005 < 0,005 < 0,005 Al < 0,001 < 0,001 0,14 < 0,001 < 0,001 0,60 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 <0,001 Nb < 0,001 < 0,001 < 0,001 < 0,001 0,005 < 0,001 < 0,001 < 0,001 < 0,001 0,040 < 0,001 < 0,001 < 0,001 < 0,001 Ti < 0,001 < 0,001 < 0,001 0,080 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 < 0,001 N 0,0015 0,0044 0,0023 0,0036 0,0043 0,0027 0,0041 0,0045 0,0048 0,0018 0,0021 0,0019 0,0027 0,0012 Ca < 0,0003 c 0,0003 < 0,0003 0,0013 < 0,0003 c 0,0003 0,0009 < 0,0003 < 0,0003 0,0007 0,0015 < 0,0003 0,0009 < 0,0003 Mg < 0,0002 c 0,0002 0,0006 < 0,0002 < 0,0002 0,0005 0,0004 < 0,0002 s 0,0002 0,0004 < 0,0002 0,0004 < 0,0004 < 0,0002 Ta < 0,002 < 0,002 0,0025 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 < 0,002 B < 0,0005 < 0,0005 < 0,0005 < 0,0005 < 0,0005 c 0,0005 < 0,0005 0,0007 e 0,0005 < 0,0005 < 0,0005 < 0,0005 < 0,0005 < 0,0005 W < 0,005 < 0,005 < 0,005 < 0,005 0,28 0,005 < 0,005 < 0,005 < 0,005 < 0,005 0,005 < 0,005 < 0,010 < 0,010 Fe 71, 93 71, 70 79,87 88,15 95,06 96,20 99,33 65,81 96,75 48,59 78,19 59,97 84,80 60,00 Table 1: Compositions of the test alloys Were prepared samples of the alloys A and B as follows. Was developed alloy in vacuum induction furnace, and was then cast into an ingot of 30 to 50kg, frustoconical, of diameter ranging from 12 cm to 15 cm, height 20 to 30 cm, that the laminate then was a roughing mill to a thickness of 80 mm, then hot rolled at a temperature of about 1000 ° C to impart a thickness of 2.5 mm. Was then performed on these hot-rolled products as a result of annealing and cold rolling (LAF) to less than 100 ° C under the following conditions: Sample 1: 1 to LAF reduction rate 84%; annealing one parade to 1100 ° C for 3 min; LAF 2 at rates of 50% reduction; 2 Static annealing at 900 ° C, 1 h; Sample 2: 1 to LAF reduction rate 84%; annealing one parade to 1100 ° C for 3 min; LAF 2 at rates of 50% reduction; 2 Static annealing at 700 ° C, 1 h; Sample 3: Annealing 1 to show at 900 ° C for 8 min; LAF 1 to 70% of reduction ratio; annealing two parade for 8 min at 900 ° C; LAF 2 to 70% discount rate; 3 static annealing at 660 ° C, 1 h; Sample 4: Annealing 1-900 ° C in the parade for 8 min; LAF 1 to 70% of reduction ratio; annealing 2-900 ° C in the parade for 8 min; LAF 2 to 70% discount rate; 3 static annealing at 680 ° C, 1 h; Sample 5: Annealing 1-900 ° C in the parade for 8 min; LAF 1 to 70% of reduction ratio; annealing 2-900 ° C for 8 min; LAF 2 to 70% discount rate; annealing 3 static at 700 ° C, 1 h; Sample 6: Annealing 1 to show at 900 ° C for 8 min; LAF 1 to 70% of reduction ratio; annealing 2 to show at 900 ° C for 8 min; LAF 2 to 70% discount rate; 3 static annealing at 720 ° C, 1 h; Sample 7: Annealing 1 parade for 8 min at 900 ° C; LAF 1 to 70% of reduction ratio; annealing two parade for 8 min at 900 ° C; LAF 2 to 70% discount rate; annealing 3 static at 750 ° C, 1 h; Sample 8: Annealing 1 parade for 8 min at 900 ° C; LAF 1 to 70% of reduction ratio; annealing two parade for 8 min at 900 ° C; LAF 2 to 70% discount rate; 3 static annealing at 810 ° C, 1 h. Sample 9: Annealing 1 parade for 8 min at 900 ° C; LAF 1 to 70% of reduction ratio; annealing two parade for 8 min at 900 ° C; LAF 2 to 70% discount rate; annealing 3 static at 900 ° C, 1 h. Sample 10: Annealing 1 parade for 8 min at 900 ° C; LAF 1 to 70% of reduction ratio; annealing two parade for 8 min at 900 ° C; LAF 2 to 70% discount rate; 3 static annealing at 1100 ° C, 1 h. Sample 1 1: 1 in the parade annealing for 8 minutes at 900 ° C; LAF 1 to 80% discount rate; annealing two parade for 8 min at 900 ° C; LAF 2 to 40% of reduction ratio; annealing 3 static at 700 ° C, 1 h. - Sample 12: Annealing 1 parade for 8 min at 900 ° C; LAF 1 to 70% of reduction ratio; annealing two parade to 1100 ° C for 8 min; LAF 2 to 70% discount rate; annealing 3 static at 700 ° C, 1 h. The static annealing concluding preparation of which, for all samples, was preceded by a rise in temperature at a rate of 300 ° C / s followed by cooling at a rate of the order of 200 ° C / h, carried out simply leaving the samples in the annealing furnace. The temperature rise speed before the final annealing and cooling after the final annealing were therefore relatively moderate, which contributed in all cases to obtain a final product relatively textured, as discussed in the table 2. differences on magnetostrictive and isotropy observed for samples of the invention and the reference samples will therefore be attributable to other factors, including the fact that for the reference samples, Note that the final annealing tests carried out at 850 ° C for 3 h in another static oven, under a hydrogen atmosphere, with similar parameters to those of the assays described herein, but with a cooling rate after even lower final annealing (60 ° C / h), gave very similar results regarding the level of magnetostriction and isotropic. Cooling after final annealing can be particularly slow drawbacks. All annealing of all samples was carried out under pure hydrogen atmosphere and dry dew point less than -40 ° C. No other gas species were present at more than 3 ppm. Thus, samples 1 and 2 reference has undergone cold rolling directly after the heat treatment, and then a high temperature anneal (1100 ° C) in the austenitic range, then a second cold rolling, and final annealing 900 ° C (test 1) or 700 ° C (test 2) in the ferritic range. The inventive samples 3-9 have started after the hot treatments, be annealed at 900 ° C, and then a first cold rolling and a second annealing at 900 ° C, then a second cold rolling, and a final annealing at a variable temperature depending on the tests, from 660 to 900 ° C. All annealing therefore took place in the ferritic range, in accordance with the invention, and were three in number, against two for the first two reference samples 1 and 2. All the cold rolling were performed with a rate to 70% reduction. 10 The reference sample was first subjected ferritic annealing at 900 ° C as the samples according to the invention and unlike the other two reference samples, then a first cold rolling and intermediate annealing at 900 ° C , so in the ferritic range, then a second cold rolling, and final annealing at a temperature of 1100 ° C, ie in the austenitic range. It has thus undergone a treatment comparable to that of the samples 3 to 9 of the invention, except that the final annealing took place in the austenitic range. All its cold rolling were performed at 70% discount rate, as the samples of the invention. The Reference Sample 1 1, after the heat treatment, underwent annealing at 900 ° C, and then a first cold rolling to 80% instead of 70% as all samples 3-10 (which remains in line with the invention), then a second anneal at 900 ° C, then a second cold rolling to 40%, thus not in accordance with the invention, instead of 70% as all samples 3 to 10, then annealing a final temperature of 700 ° C, so in the ferritic range. The reference sample 12 is quite similar to the sample 10, by passing through the austenitic range, which, however, carried out at a different stage of processing. He first suffered ferritic annealing at 900 ° C, as the samples according to the invention and unlike the first two reference samples, then a first cold rolling and intermediate annealing in the austenitic range to 1100 ° C, and thus not in accordance with the invention and then a second cold rolling, and final annealing at a temperature of 700 ° C, so in the ferritic range. It has thus undergone a treatment comparable to that of the samples 3-9 according to the invention, except that the intermediate annealing took place in the austenitic field. The characteristics of the various samples thus obtained, in terms of the presence of a Goss texture or {1 1 1} <1 10> measured by RX, of mean grain diameter measured by analyzing samples of images, characterized by diffraction backscattered electrons (EBSD), and recrystallized fraction, measured at the surface by the same EBSD technique, and assuming that the surface fraction is the volume fraction) are summarized in table 2. Table 2: Texture, grain size and recrystallization rate of the tested samples depending on their processing conditions The different treatment applied metallurgical lines led to the final grain sizes substantially identical to the references and testing of the invention, that is to say a particle size range from about 300 to 15 μηι more precisely of 16-95 μηι for testing according to the invention, i.e. when all anneals are performed in the ferritic range; of 15-285 μηι for references, ie when at least one step of the process goes out of the ferritic range. This shows that the extent of grain size is similar and has no link with low magnetostrictions obtained. But Test 2, the final annealing was performed at 700 ° C, resulted in a grain size substantially lower than 1 and 10 test reference and 9 according to the invention, et qui est du même ordre de grandeur celles que selon des essais the invention 3 to 8 here ont été aussi à des réalisés températures voisines of 700 ° C. De manière générale, les gammes métallurgiques selon des essais the invention procurent une taille de grains (between 16 and 95 μηι selon les essais) relativement proche de celle des essais de référence et en tout cas structured according to que the fly attendre priori, notamment au vu des conditions du Ricottura final. On que l'exécution will notice a Ricottura to 900 ° C before the first Laminage cooling in selon les essais the invention and testing the 10 de référence n'affecte sensiblement pas, elle seule, la taille des grains in obtenue the issue of ' More surprisingly, the significant differences between the various tests treatment ranges have not led to very significant differences in the final textures of materials, from the viewpoint of the Goss texture of proportion and the proportion of texture {1 1 1} <1 10>. Then the magnetostrictions (measured in ppm) on different samples 1-3, 5, 7-12 cut, in various directions DL, DT and 45 ° DL and DT as shown in Figure 1 (the mentioned direction is the direction of the sheet that is the longer side of the rectangular sample) were observed or measured parallel to the long side of the sample (and therefore also parallel to the direction of the applied magnetic field and the magnetic flux of the induction B generated) and denoted "// H", or perpendicular to the major side of the sample (thus perpendicularly to the direction of the applied magnetic field and the magnetic flux of the induction B generated) and denoted "- 1- H ". Measurements were continuously carried out over a wide range of B and exploited precisely three magnetic induction amplitude B 1, T 2, 1, 5 and T 1, 8 T. The results are summarized in Table 3, where individual samples are designated by their composition A or B and by the temperature of their final annealing. It has not carried out measurements on samples 4 and 6, but it is ensured that they were very similar to those of the inventive samples treated with neighboring final annealing temperatures of them. B direction = 1, 2 = 1 TB, TB = 5 1 8 T Sample measuring the Max Max Max (composition, Essai de Déformation Δλ Δλ Δλ termostato magnétostriction (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) 1 ,2 T 1 ,5 T 1 ,8 T recuit final) e // H +4,5 +3 +11 +9 +5 +18 +12 +10 +22 1 A, 900°C 31 44 66,5 J- H -1 ,5 -4 -20 -5 -10,5 -35 -11 -17,5 -44,5 // H +1 ,2 +7 +8 +21 +13 +14 +30 +21 +21 ,5 2 A, 700°C 22 38,5 54 J- H -10 -4 -4,5 -17,5 -8 -9 -24 -14 -14 // H 0 +2 0 +5 +9 +2,5 +10 +12,5 +8 3 B, 660°C 4 15 20,5 J- H 0 -2 0 -2 -6 -2 -5,5 -8 -6 // H 0 0 0 +0,5 0 0 +5 +4,5 +3 5 B, 700°C 0 2,5 10 J- H 0 0 0 -0,5 -2 0 -5 -5 -2,5 // H 0 0 +1 0 +1 +1 ,5 +2 +5 +6 7 B, 750°C 1 2,5 9 J- H 0 0 0 0 -1 -0,4 -0,5 -3 -2 // H 0 0 0 0,5 +2 +3 +4,5 +5,5 +7,5 8 B, 810°C 0 6 15 J- H 0 0 0 0 -1 -3 -3 -4,5 -7,5 // H 0 -1 0 0 -2 0 -1 -1 ,5 +2,5 9 B, 900°C 1 ,5 3 5 J- H 0 0,5 0 0,5 +1 0 +1 0 -2,5 // H +10 +13 +9,5 +17 +22,5 +17 22,5 +31 +25,5 10 B, 1100°C 20,5 34,5 47 J- H -7,50 -7 -6,50 -12 -10 -10 -16 -14 -14,5 // H 15 8,5 13 25 14 21 ,5 38 23 27 11 B, 700°C 25 38,5 57,5 J- H -8 -3 -10 -12 -7 -17 -18,5 -12,5 -19,5 // H 8 9 10 14,5 15 15,5 22 22 22,5 12 B, 700°C 15,5 25,5 36,5 -4,5 -5 -5,5 -9 -9,5 -10 -14 -14 -14 Table 3: magnetostrictive test results There are very strong differences of magnetostrictive measurement, in terms of absolute value and isotropy between the reference tests 1, 2 where the first annealing was performed in the austenitic range, and testing of the invention 3 9 where all annealing were carried out in the ferritic range, including the optional annealing before the first cold rolling, unrealized in tests 1 and 2 reference. Also shown, according to the test 10, in just beyond the end of process in the ferrite phase, with a final annealing carried out in the austenitic range, bass and isotropic magnetostriction affected is not obtained, although here too we have made a ferritic annealing before the first cold rolling. The Reference 1 1 trial shows that low and isotropic magnetostrictive aim is not, either, obtained when one of the cold rolling is performed at a low discount rate, even if all take place in the annealed ferritic range. The reference test 12 shows that low and isotropic magnetostrictive aim is not, either, obtained when the second of three annealing is performed in the austenitic range. Reference Examples 1 and 2 had an austenitic annealing carried out at baseline, after the first cold rolling, and Reference Example 10 was annealed austenitic done at the very end of treatment. Example 12 thus complete the proof of the harmfulness of austenitic annealing regardless of its position in the treatment. Figures 2 to 12 put those differences highlighted. Figure 2 reflects the results of magnetostrictive reported with reference test 1. It shows that even at low inductions of the order, in absolute value of 0.5 T, the magnetostrictive according DT starts to become significant and growing very rapidly with induction. For DL ​​and for the 45 ° direction DT and DL is from about 1 T that magnetostriction starts to increase substantially and quickly. This leads to significant magnetostrictive deformations of up to several tens of ppm in certain directions inductions of about 2 T, and strong anisotropy of these deformations, all going in the direction of creating a noise magnetostrictive too intense for preferred applications of the proposed invention. Figure 3 reflects the results of magnetostrictive reported with reference test 2. We observe that, compared to test 1, the isotropic magnetostriction improved somewhat, and some extreme values ​​of magnetostriction are a little lower. But from an induction of 1 T, the magnetostrictive starts to become important in the three directions considered. The resulting material would not be suitable, either, to preferred applications of the invention. The size of much smaller grains in the sample of Test 2 in the test sample 1 was therefore not very fundamentally improved results in magnetostriction. Figure 4 reflects the magnetostriction results observed during the test 3 according to the invention. In this case, the shape of the curve changes dramatically. First, almost zero magnetostriction is observed that remains in all directions considered until the induction values ​​exceeding some 1 T. When the magnetostrictive starts to rise to higher fields, its value remains very significantly lower than in the reference tests 1 and 2. Furthermore, the differences between magnetostrictive different directions remain relatively low even for high fields. A T 2 or -2, there is a magnetostriction which is less than 15 ppm and -10 ppm, and this for all considered directions. Figure 5 reflects the results of magnetostriction observed at test 7 of the invention. We found qualitatively very similar magnetostriction curves to those of Test 3 (4), with, again, a magnetostrictive that starts to become significant only for induction of at least ± 1, ± 2 A 5 T. T, the magnetostriction can be less than 5 ppm and never exceeds 10 ppm. It was therefore excellent results for this test that stands the test 3 only by its temperature final annealing of 750 ° C instead of 660 ° C, which resulted in complete recrystallization while n 'was only 90% in test 3. Figure 6 reflects the magnetostriction results observed during the test 8 according to the invention, which had a final annealing temperature of 810 ° C. We found qualitatively very similar magnetostriction curves to those of Test 3 (4) and 7 of the test (Figure 5). Quantitatively, the results are good, with the maximum values ​​of the magnetostriction which are of the order of ± 10 ppm even for ± 2 T inductions, and Δλ max of 15 ppm to 1, 8T. Figures 7-9 compare the magnetostriction measurements taken for tests 5 and 9 according to the invention. Figure 7 shows the tests carried out according to the TD direction, Figure 8 shows the tests carried out in the direction 45 ° and Figure 9 shows the tests carried out according to the TD direction. The results are very similar and excellent for both trials as LD and TD directions of up to ± 1 inductions 8 T. For the 45 ° direction, the magnetostrictive beginning not to be quite negligible from 1 8 T about in the case of test 5, while in test 9 remains very low even beyond 2 T. in general, a temperature final anneal 900 ° C thus gives results best magnetostrictive a final annealing at 700 ° C. The results of the test 9 are particularly noteworthy the strong inductions of 1, 8 T or slightly beyond, as the weakness of magnetostriction as its isotropy. Figure 10 shows the test results 10 reference in which the final annealing was performed at 1100 ° C, so in the austenitic range, while two previous annealed 1 and 2, performed at 900 ° C annealed like all tests 1 and 2 according to the invention had been in the ferritic range. We find magnetostriction curves according to the various directions comparable, qualitatively and quantitatively to those of other reference tests 1 and 2, seen in Figures 3 and 4. It can be concluded that the passage of the alloy in the austenitic range during one of his annealed, even if it occurs at the end of treatment, is a very important factor in the failure to obtain a low and isotropic magnetostriction. Test 1 1, wherein the second cold rolling was carried out with a reduction rate of only 40%, shows, according to Figure 1 1, a conventional parabolic behavior and low isotropic magnetostriction according to the induction so behavior outside the invention, with for example a magnetostrictive according DL more than 35ppm 1, 5T, nearly 60ppm 1, 8T. It can be concluded that the texture of filiation, modulated by the cold rolling reduction rate is actually well controlled by the texture changes during the cold rolling, restricting the invention to certain reduction rate ranges . Figure 12 shows the results of testing 12 of reference wherein the intermediate annealing was performed at 1100 ° C, ie in the austenitic range, while the two annealed 1 and 3 were carried out at 900 ° C as all annealed 1 and 3 tests according to the invention, therefore in the ferritic range. We find magnetostriction curves according to the various directions comparable to those of other reference tests 1, 2 and 10, seen in Figures 3, 4 and 10, but with a fairly large isotropic magnetostriction. But the level of magnetostriction is still too high, even for relatively low inductions. It can be concluded, in conjunction with test 10, the passage of the alloy in the austenitic range during any of its annealed, It was also surprisingly found that the magnetic losses at 400 Hz for different inductions (1, 1, 2 and 1, 5 T) was significantly lower in the case of the materials obtained according to the invention that they are for materials non-oriented reference. One would think that the examples of the invention may present magnetic losses by induced currents unacceptable, either because of their not fully recrystallized structure (tests 3 and 4), or their fine grain microstructure. However, the results presented in Table 4 show otherwise. They were obtained on samples of 0.2 mm thick, 100 mm long and 20 mm wide cut to DL, immersed in a magnetic field of frequency 400 Hz fundamental and by controlling the magnetic flux density in a sinusoidal temporal form. Measurements were made for the maximum amplitudes of the induction B of intensity equal to 1, 1, 2, 1, 5 or 1, 8 T. The magnetic losses are in W / kg. Table 4: magnetic losses at 400 Hz measured on different samples As shown, the magnetic losses of the samples produced according to the invention and having reduced grain size and a non-fully recrystallized structure (tests 3 and 4) or fully recrystallized with a final anneal of 700 ° C or more are not particularly high, and remain competitive relative to that obtained for the reference samples. Especially, the samples according to the invention 100% recrystallized and products with a final annealing at 720 ° C and more (up to 810 ° C, 8 or better 900 ° C test test 9) have magnetic losses still substantially improved compared to the reference samples, including that of test 1 which has a high grain size and a 100% recrystallized structure. This advantage of the magnetic losses is, for the Nothing, not clearly explained by the inventors. It is even more remarkable when considered at higher inductions 1, 5 T as 1, 8 T (see Table 4), since the magnetic losses vary with the square of the induction. This is again an advantage for use in the aeronautical embedded processors, whose size is strongly linked to the disposal of various losses (Joule effect and magnetic). Note that surprisingly, while the large grain size of the reference test 10 was a priori in the sense of obtaining the lowest magnetic losses, is the test of the invention 9 has the lowest magnetic losses. In general, the results are even more favorable in terms of magnetic losses that the temperature of the final ferritic annealing is higher, the best results being obtained for the test sample 9 which was annealed at 900 ° C . For the magnetostriction, the ferritic annealing temperatures between 800 and 900 ° C show a deformation anisotropy weak to very weak and goodwill Max Δλ magnetostriction amplitudes not exceeding, in all cases, not 6 ppm to 1, 5T 15 ppm to 1, 8T, therefore significantly better than those of samples of reference tests. In general, we define the invention by saying, in particular, that all annealed must take place in the ferritic region, at a minimum temperature of 650 ° C and a maximum temperature which, taking into account the actual composition of the alloy, is well within the purely ferritic range, without a conversion of at least part of the ferrite into austenite occurs. We saw above what was the maximum temperature depending on the contents of Si, Co and C of the alloy. The strips obtained according to the invention can be used to form transformer cores which are both of the type "cut-stacked" as the type "wound" as defined above. In the latter case, for carrying out the winding must use very thin strips of the order of 0.1 to 0.05 mm thick for example. As said, an annealing carried out before the first cold rolling is preferably practiced in the context of the invention. However, this annealing is not essential, especially if the hot rolled band has stayed long in coiled state during its cooling. In this case, the coiling temperature is often in the range of 850-900 ° C, the duration of the stay can be quite sufficient to get you on the microstructure of the band at this stage very similar effects those that would provide a real annealing in the ferritic range executed in the conditions that were said to optional annealing before the first cold rolling. Table 5 reminds the results obtained in tests 1 and 9 described above on the isotropic magnetostriction and magnetic loss at 1, 5 T, 400 Hz, and it adds information on the ability to cold rolling or to sample warm before it is applied to them a treatment according to the method of the invention, and the saturation magnetization Js of the final product. These results are also compared to those obtained during testing numbered 13 to 24, wherein the alloys of compositions conforming (13 to 19 and 23, 24) or not (20-22) of the invention were also tested. The compositions of these new alloys are also included, with those of Tests 1 and 9 for recall. Samples K and L of the tests 21 and 22 which have proven unsuitable for cold rolling or warm (breakage due to brittleness, from the middle of the belt toward the edges), these trials have not been prosecuted -delà attempting rolling, hence the lack of results regarding in table 5. For all these samples, the final thickness is 0.2 mm. As we have seen, Sample A (run 1) suffered without prior annealing, LAF 1 to 84% reduction rate, then R1 annealing parade to 1100 ° C for 3 min, then a LAF 2 to 50% reduction rate, then a static R2 annealing at 900 ° C for 1 h. Samples B to H (tests 2-18) underwent R1 annealing show at 900 ° C for 8 min and then a LAF 1 to 70% reduction rate, then R2 annealing show at 900 ° C for 8 min at 900 ° C and a LAF 2 to 70% reduction rate, then a static R3 annealing at different temperatures and durations, denoted in table 5. The sample I (test 19) has undergone an annealing R1 to show at 900 ° C for 8 min and then a warm rolling 1 to 150 ° C with a 70% reduction rate, then R2 annealing parade 900 ° C for 8 min and then a warm rolling 2 to 150 ° C with a 70% reduction rate and a static R3 annealing at 850 ° C for 30 min. The sample J (test 20) has undergone a static R1 annealed at 935 ° C for 1 h, then a LAF 1 to 70% reduction rate, then R2 annealing show at 900 ° C for 8 min and then a LAF 2 to 70% reduction rate, then a static R3 annealing at 880 ° C for 1 h. As we have seen, the reference test conducted on 1 FeCo27 A type of alloy has not yielded satisfactory results, the point of view of isotropic magnetostriction see high values ​​of Max Δλ observed. This is apparently linked to the fact that one of its annealed (R1) was carried out at an elevated temperature (1100 ° C) in the austenitic range. The test according to the invention 9, performed on the alloy B which is also a FeCo27, for which all the annealing took place in the ferritic field, by contrast, leads excellent isotropic magnetostriction. We find this good isotropic magnetostriction on testing 13 and 14 which relate to FeCo alloys with lower Co contents than 27%: respectively 18 and 10%, and whose composition and treatments are, moreover, consistent the other requirements of the invention. Example 13 also presents contents of Si, Cr, Al, Ca, Ta relatively significant. Example 14 also presents contents of Si, V and Ti significant. But these levels are within the limits defined for the invention. Similarly, a good isotropy of magnetostriction is present on the test 23 which relates to a FeCo alloy having a Co content of almost 39%, which is significantly higher than 27% but within the limit of 40% maximum fixed for the invention, and a Si content that is significant, but is not really high as to compromise the ability to cold rolling or warm. The loss magnetic and the saturation magnetization are of the same order of magnitude as for the other samples treated according to the invention. 24 concerning the test, it relates to an alloy of 15% Co and devoid of significant levels of other alloying elements, especially Cr. He also has a particularly low and isotropic magnetostriction. The magnetic losses and the saturation magnetization are of the same order of magnitude as for the other samples treated according to the invention. In particular, with respect to the test 13, the absence of Cr in Test 24, the absence tending to increase the saturation magnetization is offset by the presence somewhat less of Co, which itself is in the direction of a reduction of the saturation magnetization. Similarly, the absence of Cr in Test 24 goes in the direction of increasing magnetic losses with respect to the test 13 but the lower content of Co in the test 24 is consistent with a decrease of the same magnetic losses. So compositional differences of the alloy between tests 13 and 24 tend to offset each other, from the viewpoint of magnetic losses and Js. Regarding the reference test 20, it was performed on a FeCo alloy to 49% Co, thus above the upper limit of 40% allowed by the invention. All its annealing were carried out in the ferritic range. Its magnetic losses are very suitable, but the magnetostriction does not have the desired isotropy. As we said, these levels are too high Co, the order-disorder transition during heat treatment is probably too quick and sharp, and the number of annealing required by the invention is not compatible with this composition of the alloy. The presence of 0.04% Nb, though still less than the maximum limit tolerated by the invention, may have also contributed to disturb the texture descent mechanism, which has said it could be an explanation for the Regarding the reference test 21, the Si content is too high with respect to the Co content, and the condition "If 0.6% Al <4.5 to 0.1% Co, if Co <35%" required by the invention is not satisfied. The result is, as explained above, the alloy is not suitable to be cold-rolled or warm, as experience confirms this. Regarding the reference test 22, it is in the case where Co est≥ 35% and where If, ​​according to the invention, therefore, should not exceed 1% for good rollability cold or lukewarm. However, the Si content in this test is 1, 53%: again it was confirmed that good laminabiité cold or lukewarm alloy is obtained under certain conditions of membership, which must be incorporated into the definition of the invention. The test 15 according to the invention shows a relatively low Co (4.21%) is not inconsistent with the achievement of good isotropic magnetostrictive sought, if the contents of Si and Al are low enough. The presence of 0.005% Nb do not mind getting the desired results. The test 16 according to the invention relates to an Fe-Si-Al alloy to very low Co. In his case, the desired isotropic magnetostriction is obtained, together with low magnetic losses. The test 17 according to the invention relates to an alloy which is substantially pure Fe to 99%, with relatively low presence of Mn, Ca, Mg. The isotropy of magnetostriction is less than in the other tests according to the invention, but it is still very good in absolute terms, as Max Δλ 1, T 8 remains <25 ppm as required on sheets or strips according to 'invention. The magnetic losses are also somewhat higher than for the other tests according to the invention, but remain at a good level, and are lower than those observed on the reference test 1. The test 18 according to the invention relates to a FeCo27 type alloy with a high Cr content (6%) and also containing Mn (0.81%) and a little of Mo and B. The good isotropy of magnetostriction is confirmed, and the magnetic losses are as low as for the test 16 despite the presence of 7 ppm of B. the magnetization saturation remains of the order of that found in the other tests, such as contents of Cr, Mn and MB are not so high as to deteriorate undesirably. The test 19 according to the invention relates to a Fe-Si alloy to 3.5% of Si and containing no Al, and shows that the process conditions according to the invention are also applicable with advantage to this type of 'FeSi3 alloys to achieve the desired magnetostriction isotropy. In addition, this example has particularly low magnetic losses. Table 6 presents the experimental results obtained by varying the processing conditions, the composition of the alloy treated sample and the final thickness. Was taken up the results of tests 1 and previous 9, and added fresh tests 25-31 performed on alloys having the compositions B (FeCo27), I (FeSi3) and C (FeCo18) explained in Table 5. Max seconds Time Rate Time Rate Thickness Temperature Time No annealing Annealing reduction reduction 1 8 T final annealing alloy R3 R3 LAF test R1 1 R2 LAF 2 (mm) (°C) (min) (ppm) (my my) (%) 1 A 0.2 0 84 3 50 900 60 66.5 Reference 9 B 0,2 8 70 8 70 900 60 6 Invention 25 B 0,2 8 70 8 70 900 240 7 Invention 26 B 0,2 8 70 8 70 900 1440 5 Invention 27 B 0,2 8 70 8 70 920 60 2,7 Invention 28 B 0,2 8 70 8 70 920 240 5,4 Invention 29 B 0,2 8 70 8 70 920 1440 6 Invention 30 I 0,2 60 70 60 70 850 180 16 Invention 31 C 0,5 5 60 5 50 900 60 18,5 Invention Table 6: Influence of processing conditions on the isotropy of the magnetostriction for different alloy compositions and sample final thicknesses If we compare the results of the different tests of the invention, carried out on samples of the same composition, it is seen that varying the parameters of the LAF and annealed within the definition of the invention still allows to obtain isotropy of the unusually good magnetostrictive in all cases. It may be noted that for the alloy I (type FeSi3), a comparison between the tests 19 and 30 can be deduced that increasing the temperature and duration of the final annealing R3 in the test 30 has caused some degradation of this isotropy, which still remains within the limits of the objectives. We think we can link this decline to the fact that Goss texture component was probably stronger in the test 30 and close to the preferred upper limit of 30%, also due to differences in the hot rolling process. It may also be noted that, regarding the alloy C (type FeCo18), a final thickness of 0.5 mm obtained before the final annealing R3 conduit for R3 identical final annealing conditions, some degradation of the isotropy of magnetostriction (see Trial 31). This could be remedied by increasing, for this thickness, length and / or the temperature of the final annealing remaining within the limits set by the definition of the invention. Generally, it is seen in the light of the various tests, the samples of the magnetic properties (magnetic loss and magnetostriction in particular) are relatively dependent on the precise conditions of the final annealing, contrary to what is often seen in the prior art. The use of a multiple rolling with an intermediate annealing between each rolling, and a final anneal after the last cold rolling (as opposed to a single cold rolling followed by a final annealing), conjugated to obtain a final product very highly or totally recrystallized, could be a factor in favor of this broad tolerance in the manufacturing conditions, which is obviously very advantageous. The persistence, throughout manufacturing, proportions, at most,0 kolo} ), that the method according to the invention allows to obtain, could also contribute to this result. The inventors are, however, yet at the stage of hypotheses to explain the remarkable properties obtained both on the isotropy of the magnetostriction and the magnetic characteristics through the application of the inventive method . Tapes and sheets according to the invention possible to manufacture, in particular, after cutting, the transformer cores compounds of stacked sheets or wound without requiring changes in the overall design of the nuclei of these types usually used. One can take advantage of the properties of these sheets to make transformers produce a low noise magnetostrictive over existing transformer design and similar design. Transformers for aircraft designed to be implanted in a cockpit are a typical application of the invention. We can also use these sheets to form nuclei of higher mass processors, so for transformers particularly high power, while maintaining a magnetostrictive noise remains within acceptable limits. The transformer cores according to the invention may be integrally formed of sheets made from strips or sheets according to the invention, or only partially in the case where it determines that their combination with other materials would be advantageous technically and financially. CLAIMS 1 .- sheet or ferrous alloy strip cold rolled and annealed (1), characterized in that its composition is, in percentages by weight: - traces defined by disorientation less than 15 ° around a crystallographic orientation defined {h0kolo}. 4. A process for producing a strip or sheet ferrous alloy (1) according to one of claims 1 to 3, characterized in that: -on developing a ferrous alloy whose composition consists of: - traces