EP4259834A1

EP4259834A1 - Method for fabricating a substantially equiatomic feco-alloy cold-rolled strip or sheet, substantially equiatomic feco-alloy cold-rolled strip or sheet, and magnetic part cut from same

Info

Publication number: EP4259834A1
Application number: EP20824681.9A
Authority: EP
Inventors: Thierry Waeckerle; Rémy BATONNET
Original assignee: Aperam SA
Current assignee: Aperam SA
Priority date: 2020-12-09
Filing date: 2020-12-09
Publication date: 2023-10-18
Also published as: MX2023006853A; CN116783313A; KR20230118634A; US20240035139A1; CA3200783A1; WO2022123297A1; JP2024503576A

Abstract

The invention relates to a substantially equiatomic FeCo-alloy cold-rolled strip or sheet, and to a magnetic part cut from same, as well as to a method for fabricating a FeCo-alloy cold-rolled strip or sheet. A fully recrystallised hot-rolled sheet or strip is prepared, with a thickness of 1.5 - 2.5 mm and the following composition: 47.0% ≤ Co ≤ 51.0%; traces ≤ V + W ≤ 3.0%; traces ≤ Ta + Zr ≤ 0.5%; traces ≤ Nb ≤ 0.5%; traces ≤ B ≤ 0.05%; traces ≤ Si ≤ 3.0%; traces ≤ Cr ≤ 3.0%; traces ≤ Ni ≤ 5.0%; traces ≤ Mn ≤ 2.0%; traces ≤ O ≤ 0.03%; traces ≤ N ≤ 0.03%; traces ≤ S≤ 0.005%; traces ≤ P≤ 0.015; traces ≤ Mo ≤ 0.3%; traces ≤ Cu ≤ 0.5%; traces ≤ Al ≤ 0.01%; traces ≤ Ti ≤ 0.01%; traces ≤ Ca + Mg ≤ 0.05%; traces ≤ rare earths ≤ 500 ppm; the remainder being iron and impurities. A first cold-rolling step is carried out with a reduction rate of 70 to 90%, to bring the strip or sheet to a thickness ≤ 1 mm. Intermediate annealing is carried out when running, leading to a partial recrystallisation of the strip or sheet, running at a speed (V), and where its temperature, in the useful zone of the furnace of useful length (Lu), is between Trc and 900°C, the strip or sheet remaining therein for 15 s to 5 min at a temperature (T) such that 26°C.min ≤ (T – Trc).Lu/V ≤ 160°C.min. The strip or sheet is cooled at least at 600°C/hour. A second step of cold-rolling the annealed strip or sheet is carried out, with a reduction rate of 60 to 80%, to bring the strip or sheet to a thickness of 0.05 to 0.25 mm. And final annealing (Rf) of the cold-rolled strip or sheet is carried out to achieve complete recrystallisation followed by cooling at 100 to 500°C/hour. Magnetic part, such as a magnetic core, obtained from a strip or sheet manufactured by this method.

Description

METHOD FOR MANUFACTURING SUBSTANTIALLY EQUIATOMIC FECO ALLOY COLD-ROLLED STRIP OR SHEET, SUBSTANTIALLY EQUIATOMIC FECO ALLOY COLD-ROLLED STRIP OR SHEET, AND MAGNETIC PART CUT THEREOF

The present invention relates to the field of cold-rolled strips and sheets of magnetic materials and parts cut from such strips and sheets, and more particularly strips and sheets of substantially equiatomic FeCo alloy.

Magnetic cores in FeCo soft magnetic alloy that are substantially equiatomic (therefore containing substantially equal weight and atomic quantities of Fe and Co), to which are often added about 2% of V, have long been known to allow high densities to be obtained. of power (volume or mass) during energy conversions in electrical engineering. In the case where it is sought to reduce as much as possible the magnetic losses, which are a source of heat dissipation, it is known that it is necessary to reduce the thickness of the strips constituting the core, which have been cut from strips or previous sheets.

In industrial practice, it is common to produce equiatomic FeCo cold rolled strips and sheets with a thickness of about 0.1 mm. However, the magnetic losses that are associated with these materials are still considered to be insufficiently lowered. Further lowering can be achieved by producing strips and sheets of high purity in residual elements and inclusions, thanks to the use of new raw materials and the execution of one or multiple reflows during the development of the metal. in the form of an ingot. It is thus possible to obtain, for a strip 0.1 mm thick, low magnetic losses, of the order of 25 W/kg at 400 Hz for a maximum sinusoidal induction of 2 T. This production method is however expensive because it requires at least one additional remelting compared to the usual equiatomic FeCo alloys.

By way of example, the following results are observed on reference metal samples having the following compositions, in weight percentages, summarized in Table 1. The elements not mentioned are, at most, present only as impurities (traces), resulting from the elaboration, and without metallurgical influence.

Table 1: Reference casting compositions Ref 1 to Ref 5

The Ref 1 casting did not undergo remelting, unlike the other castings, but only a development by vacuum induction (VIM, Vacuum Induction melting), which leads to maintaining the usual inclusionary distribution of Fe-Co alloys, in particular oxides vanadium, silicon, aluminum, magnesium, calcium, etc., but also niobium and aluminum nitrides, silicon carbides. Table 1, which sticks to the composition of the samples, cannot account for this inclusion richness using part of the elements in solution in the metal.

The remelting of castings Ref 2 to Ref 5 were carried out on castings first produced by VIM, without addition of N b, by the vacuum arc remelting process, also called VAR (Vacuum Arc Remelting), which has the main effect of eliminating or fragmenting a significant part of the stable precipitates (oxides, carbides, nitrides) of the metal matrix resulting from the VIM, and also of directly eliminating by vacuuming part of the impurities not precipitated in the matrix (S, N, O).

These reference castings were transformed hot, by blooming and passing through the strip mill (hot rolling), into strips 2 mm thick, then annealed, before simple cold rolling to a thickness of 0.1 mm.

In this final state of thickness, washers in the format 36 (external diameter) x 30.5 mm (inner diameter) or 36 (external diameter) x 25 mm (inner diameter), or coiled tori in the format 30 x 20 mm (external and internal diameters respectively) x 10 mm (torus height, corresponding to the strip width) can be made, depending on whether one is interested in a “rotating machine” (washers) or “transformer” (wound torus) application.

In all cases, the materials tested were heat treated for 3 hours under pure hydrogen, at 850°C for samples Ref 1, Ref 2 and Ref 3, at 880°C for samples Ref 4 and Ref 5. Cooling following the heat treatment was in all cases carried out at a rate of 250° C./hour in order to optimize the magnetic performance. It is for this cooling rate that the first magnetocrystalline anisotropy constant K1 (which largely controls the magnetic properties) vanishes.

The wound toroids are representative of what one would observe in a single-phase or three-phase transformer core type application, while the washers are representative of a rotary actuator type application, particularly at high speed.

The results of the coercive field measurements Hc, losses at 2 T and 400 Hz and the increase in losses observed between the washers and the toroids are summarized in table 2

Table 2: Coercive field and magnetic loss measurements performed on the reference samples in Table 1

It can be seen that the use of a reflow makes it possible to reduce the magnetic losses on the toroids by around 30% (comparison of Ref 1 with Ref 2 or Ref 3 in wound toroids), which is very important for many applications. We also see that depending on whether the measurement is taken on the toroids in the rolling direction DL, or whether it is taken on the washers, therefore using all the directions of the sheet, the magnetic losses are 5 to 10 higher. % in the case of tori. This denotes a certain performance anisotropy in the rolling plane.

On the other hand, raising the final annealing temperature, by going from 850 to 880°C, significantly reduces the level of magnetic losses both on toroids and on washers, as shown by the comparisons of Ref 2 and Ref 4 of one hand, and Ref 3 and Ref 5 on the other hand.

The object of the invention is to provide manufacturers of strips or sheets of equiatomic FeCo alloys and of products cut from such strips or sheets with a means of obtaining very low magnetic losses, typically 26.5 W/ kg or lower under an induction of 2 T at 400 Hz, without requiring costly development due to the choice of raw materials as in the succession of metallurgical operations.

To this end, the subject of the invention is a process for manufacturing a cold-rolled strip or sheet of substantially equiatomic FeCo alloy, characterized in that:

- a hot-rolled sheet or strip is prepared with a thickness (RHG) of between 1.5 and 2.5 mm, and whose composition consists, in weight percentages, of:

* 47.0% < Co < 51.0%; preferably 47.0% < Co < 49.5%;

* traces < V + W < 3.0%; preferably 0.5%<V+W<2.5%;

* traces < Ta + Zr < 0.5%;

* traces <Nb<0.5%, preferably traces <Nb<0.1%;

* traces < B < 0.05%; preferably traces <B<0.005%;

* traces < Si < 3.0%;

* trace < Cr < 3.0%;

* trace < Ni < 5.0%; preferably traces <Ni<0.1%;

* trace < Mn < 2.0%; preferably traces < Mn < 0.1%;

* traces < C < 0.02%; preferably traces <C<0.01%;

* traces < O < 0.03%; preferably traces <0 <0.01%;

* traces < N < 0.03%; preferably traces <N<0.01%;

* traces < S < 0.005%; preferably traces <S<0.002%;

*traces < P < 0.015; preferably traces <P<0.007%;

* traces < MB < 0.3%; preferably traces < Mo < 0.1%;

* traces < Cu < 0.5%; preferably traces <Cu<0.1%;

* traces < Al < 0.01%; preferably traces < Al < 0.002%;

* traces < Ti <0.01%; preferably traces <Ti <0.002%; * traces < Ca + Mg <0.05%; preferably traces <Ca + Mg <0.001%;

* traces < rare earths < 500 ppm;

* the rest being iron and impurities resulting from processing;

* said strip or sheet having a recrystallization onset temperature (Trc) and a 100% recrystallized microstructure;

- then we proceed to a first step of cold rolling (LAF1) of the strip, or of the sheet in one or more passes, with an overall reduction rate (TR1) of 70 to 90%, preferably of 65 to 75 %, to bring the strip or sheet to a thickness (e1) less than or equal to 1 mm, preferably less than or equal to 0.6 mm;

- then an intermediate annealing (R1) is carried out as the strip or sheet passes through an annealing furnace, leading to partial recrystallization of the strip or sheet, said strip or sheet passing through said annealing furnace at a speed (V), the partial recrystallization rate being 10 to 50%, preferably 15 to 40%, better 15 to 30%, and where the temperature of the strip or sheet, in the useful zone of the furnace having a useful length (Lu), is between Trc and 900°C, preferably between 700 and 880°C, the strip or sheet remaining in this useful zone (Lu) for 15 s to 5 min at a temperature (T ) such that 26°C.min < (T - Trc).Lu/V < 160°C.min, preferably 50°C.min < (T - Trc).Lu/V < 160°C.min, with T and Trc in °C, Lu in m, V in m/min, and the strip or sheet is cooled on leaving the furnace at a rate of at least 600°C/hour, preferably at least 1000°C/ hour, better still at least 2000° C./hour, up to a temperature less than or equal to 200° C.;

- then a second step of cold rolling (LAF2) of the annealed strip or sheet is carried out, in one or more passes, with an overall reduction rate of 60 to 80%, preferably 65 to 75%, bringing the cold rolled strip or sheet to a thickness (e2) of 0.05 to 0.25 mm;

- then a final annealing (Rf) of the cold-rolled strip or sheet or of a part previously cut from this strip is carried out, for at least 30 min, preferably at least 1 h, at a temperature of 750 to 900°C, preferably from 800 to 900°C, better still between 850 and 880°C, in a neutral or reducing atmosphere, or under vacuum, to obtain complete recrystallization of the strip or sheet or part cut, followed by cooling at a rate of 100 to 500°C/hour, preferably between 200 and 300°C/hour.

According to a variant of the invention, (V + W)/2 + (Ta + Zr)/0.2 > 0.8%, preferably > 1.0%.

According to a variant of the invention, traces < Si < 0.1%.

According to a variant of the invention, traces <Cr<0.1%. According to a variant of the invention, before said first cold rolling step (LAF1) at least one additional cold rolling cycle (LAFi) + intermediate annealing (Ri) is carried out to bring the cold rolled strip or sheet to a thickness between its thickness after hot rolling (BHR) and the entry thickness of the first cold rolling (LAF1), the passage time of the strip in the useful zone of the furnace, located between Trc and 900°C , during each additional annealing (Ri), leading to total recrystallization of the strip or of the sheet, the intermediate annealings (Ri) having a passage time in the zone of length Lu of the furnace, where the temperature of the strip is located between Trc and 900°C, from 10 s to 10 min, and preferably between 15 s and 5 min, better still between 30 s and 5 min, and being followed by cooling of the strip or of the sheet at the outlet of the furnace at a rate of at least 600°C/hour, preferably at least 1000°C/hour, better still at least 2000°C/hour e, up to a temperature less than or equal to 200° C., the strip or sheet having a 100% recrystallized microstructure after the last of said additional annealings (Ri).

After hot rolling and before the first cold rolling (LAF1), the hot rolled strip or sheet can be annealed by cooling the hot rolled strip or sheet from a temperature of between 800 and 1000°C at a rate of at least 600°C/second, preferably at least 1000°C/second, more preferably at least 2000°C/second, down to room temperature.

Said annealing can take place directly after hot rolling, without intermediate reheating.

The atmospheres of the annealing furnaces can be reducing atmospheres, preferably pure hydrogen.

The at least one additional intermediate annealing can be a rolling annealing of the strip or sheet, in an annealing furnace where the temperature of the strip or sheet, in the useful zone of the furnace, is between Trc and 900° C., the strip remaining in this useful zone for 15 s to 5 min, the strip or sheet is cooled on leaving the oven at a rate of at least 600° C./hour, preferably at least 1000° C./hour, better still at least 2000°C/hour, down to a temperature less than or equal to 200°C, and the at least one additional cold rolling (LAFi ) is carried out in one or more passes, with an overall reduction rate of at least 40 %.

After the final static annealing (Rf), an additional annealing can be carried out as the strip or sheet passes, so that the metal reaches at least 700°C and at most 900°C, for at least 10 seconds and at most 1 hour, preferably 10 seconds to 20 minutes, followed by cooling at a rate of at least 1000°C/hour. The invention also relates to a substantially equiatomic FeCo alloy, characterized in that:

- its composition consists of, in weight percentages:

* 47.0% < Co < 51.0%; preferably 47.0% < Co < 49.5%;

* traces < V + W < 3.0%; preferably 0.5%<V+W<2.5%;

* traces < Ta + Zr < 0.5%;

* traces <Nb<0.5%, preferably traces <Nb<0.1%;

* traces < B < 0.05%; preferably traces <B<0.005%;

* traces < Si < 3.0%;

* trace < Cr < 3.0%;

* trace < Ni < 5.0%; preferably traces <Ni<0.1%;

* trace < Mn < 2.0%; preferably traces < Mn < 0.1%;

* traces < C < 0.02%; preferably traces <C<0.01%;

* traces < O < 0.03%; preferably traces <0 <0.01%;

* traces < N < 0.03%; preferably traces <N<0.01%;

* traces < S < 0.005%; preferably traces <S<0.002%;

*traces < P < 0.015; preferably traces <P<0.007%;

* traces < MB < 0.3%; preferably traces < Mo < 0.1%;

* traces < Cu < 0.5%; preferably traces <Cu<0.1%;

* traces < Al < 0.01%; preferably traces < Al < 0.002%;

* traces < Ti < 0.01%; preferably traces <Ti <0.002%;

* traces < Ca + Mg < 0.05%; preferably traces <Ca + Mg <0.001%;

* traces < rare earths < 500 ppm;

* the rest being iron and impurities resulting from processing;

- in that the microstructure of the alloy is completely recrystallized;

- and in that the texture of said alloy is as follows:

* 8 to 20%, preferably 9 to 20%, by surface or by volume, of the {001}<110> component disoriented at a maximum of 15°;

* 8 to 25%, preferably 9 to 20%, by surface or by volume, of the {111}<112> component disoriented at a maximum of 15°;

* 5 to 15%, preferably 6 to 11%, by surface or by volume, of the {111}<110> component disoriented at a maximum of 15°;

* the rest of the material being made up of other texture components, disoriented by at most 15°, each representing a maximum of 15% in surface area or in volume, the covering of the said other components of texture with any one of the components {001}<110>, {111}<112> and {111}<110> not exceeding 10% in area and volume.

According to a variant of the invention, traces < Si < 0.1%.

According to a variant of the invention, traces < Cr < 0.1%.

The invention also relates to a magnetic part cut from a substantially equiatomic FeCo alloy, characterized in that it results from the cutting of a strip or a sheet of alloy of the preceding type.

The invention also relates to a magnetic core in a substantially equiatomic FeCo alloy, characterized in that it is produced from cut-out magnetic parts of the preceding type.

As will have been understood, the invention consists above all in obtaining the strip or the sheet by means of a succession of process steps comprising cold rolling in at least two steps, that is to say at at least two cold rolling passes or at least two groups of successive cold rolling passes, these two passes or groups of passes, which will be called LAF1 and LAF2, being separated by a specific intermediate annealing R1 of only partial recrystallization executed in parade between the two passes or the two groups of passes. Just after these two passes/groups of passes, a final static annealing is finally carried out, which leads to obtaining a fully recrystallized strip. These steps are applied to an alloy of well-defined composition, and the treatment conditions lead to the creation, within the cold-rolled and annealed strip or sheet, of a particular texturing according to three main given texture components and in given proportions.

Also, this sequence of two cold rollings separated by annealing leading only to partial recrystallization, must start on a strip which is 100% recrystallized at the end of the hot rolling and any subsequent treatments.

It is this set of characteristics that gives the strip or sheet its remarkably low magnetic losses.

In the rest of the text, when we speak of a "cold rolling step" and its reduction rate, it should be understood that we will include the case where this cold rolling step is carried out in several passes executed in immediate succession, therefore without intermediate annealing, and that the reduction rate of this “cold rolling step” is the overall rate obtained at the end of all the passes of this step if there are several. When the invention is applied, it is then, surprisingly, not necessary to have a metal having a high chemical purity and a high inclusion cleanliness to obtain the targeted performances, although it is still preferable to start lowest levels of impurities and inclusions possible, in order to obtain even better performances than those of comparable existing products.

This implies that we can use common raw materials, and not necessarily new raw materials containing few residual elements and various impurities, and that we can do without multiple remelting during the production of the ingot. from which the strips or sheets will be obtained. Of course, such operations are not excluded from the process according to the invention, when it is desired to obtain strips or sheets having exceptionally low magnetic losses. But they are no longer necessary to obtain magnetic losses considered to be “low” according to the conventional criteria defined above.

It turns out that the use of the succession of steps according to the invention, applied to a substantially equiatomic FeCo alloy, to which certain alloying elements can also be added in relatively limited quantities, leads to the obtaining of a particular texture where the components {001}<110>, {111}<112> and also, but possibly to a lesser extent, {111}<110>, are present within limits and with a precise maximum disorientation for each of between them.

Remarkably, this texture tolerates relatively high levels of impurities in the alloy, in order to obtain low magnetic losses, and makes it possible to obtain magnetic losses which are even particularly low if the impurities are at a low level, the order of what was necessary with the methods of the prior art used for the manufacture of strips and sheets of equiatomic FeCo alloys to obtain only low magnetic losses.

The invention will be better understood using the following description, given with reference to the following appended figures:

Figure 1 which shows, in W/kg, the magnetic losses under a field of 2 T 400 Hz and the recrystallized fraction of various samples, as a function of the magnitude (T - Trc)/V in °C.min/m;

Figure 2 which shows, in W/kg, the magnetic losses under a field of 2 T 400 Hz and the recrystallized fraction of various samples, as a function of the quantity (T - Trc).Lu/V in °C. min for a useful oven length (Lu) of 2.6m.

In the formulas, T and Trc are expressed in °C, Lu in m, V in m/min The invention relates to substantially equiatomic FeCo alloys, the composition of which is as follows. All percentages are percentages by weight. When we speak of the presence of "traces", it must be understood that the element in question may be totally absent, or be present only in the state of impurity, resulting from the simple fusion of the raw materials. and the production of the liquid metal, this content possibly being at the limit of the possibility of the detection of the element by the measuring device used. We include the case where the measuring device would indicate a weak presence of the element whereas its real content would be nil.

The Co content is between 47.0 and 51.0%, preferably between 47.0 and 49.5%

This content is necessarily close to the equiatomic composition of about 49% Co and 49% Fe for an FeCo alloy, containing, in addition, about 2% V.

The equiatomic FeCo binary alloy is known to have, remarkably, both a very high saturation magnetization value Jsat (2.35 T) and a very low magnetocrystalline anisotropy constant K1, that a cooling rate of the order of 250° C./hour (most generally 100 to 500° C./hour, but preferably 200 to 300° C./hour) after the final annealing makes it possible to cancel out or, at least, to greatly reduce it. This low magnetocrystalline anisotropy constant, or even zero, determines, to a large extent, the magnetic properties of the alloy in direct current or in low frequency alternating current.

The V + W content is between traces and 3.0%, preferably between 0.5 and 2.5%.

The presence of V and/or W is intended to reduce the weakening ordering speed below 700°C, which allows the annealing, which very preferentially follows hot forming, to keep the metal good ductility for cold rolling. 2% of V also makes it possible to double the electrical resistivity compared to a FeCo without V, which leads to a considerable reduction in magnetic losses at low and, above all, medium frequencies, therefore particularly appreciable over the entire range of electrotechnical applications, typically from a few tens of Hz for low-frequency terrestrial applications, and a few hundred to a few thousand Hz typically for aeronautical applications (generator, transformer, smoothing inductance). From 2% of V, and depending on the final annealing temperature Rf, one enters the two-phase range a + y, which is unfavorable to the magnetic performance of the alloy. Beyond 3.0% of V, and whatever the temperature of the final annealing Rf, non-magnetic austenite is formed y, and the magnetic performance then becomes clearly mediocre for applications typical of these equiatomic FeCo alloys. The addition of V, and/or of W, which has substantially the same effects, is therefore not recommended if it goes beyond the limit of 3.0% mentioned above for the sum V + W.

The sum of the Ta and Zr contents is between traces and 0.5%.

Ta and Zr, like V and W, slow down the speed of ordering. An addition of 0.2% of Ta has the same effect as 2% of V and W on this point. However, Ta and Zr have no influence on the electrical resistivity, and the addition of V and W is therefore preferred for the usual intended uses for the alloys concerned by the invention.

To properly take into account the respective effects of V and W, on the one hand, and Ta and Zr, on the other hand, on the speed of ordering, it is necessary, preferably, to perform a weighting of the effects of these two groups. elements, according to the formula:

(V + W)/2 + (Ta + Zr)/0.2 > 0.8%, preferably > 1.0%.

But, moreover, the upper limits for the V + W and Ta + Zr contents which were given above must also be respected.

The Nb content is between traces and 0.5%, preferably between traces and 0.1%.

This possible addition of Nb can be interesting to avoid the appearance of embrittling phases during the possible reheating which precedes the annealing of the hot-formed semi-finished product, and thus to allow the success of cold rolling. But Nb is a powerful inhibitor of grain growth, and it makes it much more difficult during final Rf static annealing. The achievement of good magnetic properties is therefore compromised if the Nb content is too high. In addition, Nb easily combines with C, N and O to form carbides, nitrides, carbonitrides or oxides, which help to inhibit grain growth and degrade magnetic properties directly (by entrapment of Bloch walls) or indirectly (by grain size limitation).

Thus, depending on the processes used: preparations with or without remelting, production with oxidation, nitriding, carburization, limited or not, of the liquid metal, execution of reheating, more or less brief, before annealing, or annealing carried out directly after setting in hot form, it is possible to add up to a few 1/100% of Nb, typically up to 0.10% and for example 0.04% or 0.07% Nb. Above 0.5%, the grain growth inhibiting effect is excessive for obtaining the desired magnetic properties.

B content is between traces and 0.05%

It has a role similar to that of Nb, but it is therefore also weakening, and its presence must be limited accordingly. The Si content is between traces and 3.0%, in some cases between traces and 0.1%.

The Cr content is between traces and 3.0%, in some cases between traces and 0.1%.

Si and Cr are renowned for their ability to significantly increase the electrical resistivity of materials. But in the specific case of equiatomic FeCo alloys, this function is, or may be, already ensured by V, W, Ta, Zr. And Cr and Si do not reduce the ordering rate, unlike V, while this reduction is very preferable for the alloys used in the invention.

Cr and Si are therefore tolerable at a rate of at most 3.0% each, if we want to obtain a very high electrical resistivity, but we mainly favor the addition of V to obtain the increase in electrical resistivity since its addition is accompanies other beneficial effects, as has been said. Adding more Cr or Si would lower the saturation induction, and therefore the ability of the material to have a high mass power density, due to the decrease in the Fe and Co contents that this would provide. But it must also be remembered that the sizing of electrical machines such as transformers, actuators, generators, etc. is limited, particularly in the aeronautical field, by the heating due to the Joule effect and the magnetic losses of the magnetic cores. However, the addition of Si and/or Cr tends to reduce the magnetic losses, thus making it possible to increase the frequencies and magnetic inductions of work. We can then increase the power density, or reduce the negative impact of the reduction in induction at saturation. For some particular applications in which the reduction of magnetic losses is of significant importance, the addition of Si and/or Cr can therefore be globally advantageous.

For applications where this reduction in magnetic losses is not particularly desired, it is recommended to limit Cr and Si to 0.1% each, which often corresponds to a simple absence of voluntary addition of these elements during the development .

The Ni content is between traces and 5.0%, preferably between traces and 0.1%.

Ni is a ferromagnetic element, but it is clearly less interesting than Fe and Co for the saturation magnetization Jsat, and has no advantage for the lowering of the magnetocrystalline anisotropy constant K1 and the increase of the resistivity. On the other hand, it provides an improvement in ductility which can be advantageous for cold rolling. An addition of Ni up to 5.0% is tolerated, but in many In this case, it will not be necessary to add Ni, and the preferred maximum content of 0.1% will often simply correspond to the Ni present in the raw materials. Moreover, a lack of addition of Ni contributes to limiting the cost of the alloy.

The Mn content is between traces and 2.0%, preferably between traces and 0.1%.

Mn does not have any particularly favorable or unfavorable properties, other than a reduction in Jsat with no benefits that might outweigh it. Up to 2.0% can be added, but preferably content resulting from the simple fusion of the raw materials, hence the preferred maximum of 0.1%.

The C content is between traces and 0.02%, preferably between traces and 0.01%. The aim is thus to ensure the absence of carbide precipitation, and above all to avoid the formation of clusters of C atoms which would degrade the magnetic properties, by trapping the Bloch walls, as the material is used.

The S content must not exceed 50 ppm (0.005%) because it tends to form, during hot transformation, fine precipitates of sulphides such as MnS, which will be very unfavorable to the magnetic properties of the material, increasing the coercive field Hc (and therefore the losses by hysteresis) and by reducing the magnetic permeability p, therefore by increasing the ampere-turns necessary for the magnetization of the magnetic yoke, which goes in the direction of an increase in heating of the windings by Joule effect and a degradation of the efficiency of the machine. The addition of S has no favorable effect.

P tends to form phosphides (of V for example) which, like sulphides, are precipitates interacting with the Bloch walls (trapping), thus degrading the magnetic properties as for S. The P content is limited to at most 150 ppm (0.015%), and preferably at most 70 ppm (0.007%).

Mo does not bring a significant reduction in the ordering, compared to V. Moreover, this element is relatively expensive and does not carry a magnetic moment, so its addition would reduce the magnetization at saturation (Jsat), while increasing the material price. Its presence in the alloy is typically limited to 0.3%, and preferably to 0.1% maximum.

Like Mo, Cu is relatively expensive, does not carry a magnetic moment, and also tends to promote the formation of copper clusters in iron-rich matrices, which will act as precipitates on the Bloch walls, resulting in degradation. magnetic performance Hc and p. Its presence is typically limited to at most 0.5% in the alloy, and preferably to at most 0.1%, thanks to a judicious choice of raw materials and an absence of voluntary addition. N and O are, like S and P, oxidants on the chemical level, and therefore have great facility in forming non-magnetic precipitates, interacting unfavorably with the Bloch walls, thus significantly degrading Hc (increasing it) and (by reducing it): the more N and O there are in the matrix, the greater the risk that these elements will encounter, when hot, oxidizable elements such as Fe, Co, Mn, V, W, Ta, Zr, Nb , Ti, Ca, Mg, Al, Si, La... present in the matrix either in very large quantities (Fe, Co...) or as unavoidable residuals (Ca, Mg, Ti, Al...). Despite the vacuum melting of the raw materials (VI M) and even the vacuum remelting (VAR) or under slag (ESR) of the ingot or the electrode, it cannot be completely prevented that a small fraction of the metal combines to a few tens of ppm of oxidants such as O and N. The presence of at most 300 ppm of O and 300 ppm of N, and preferably of at most 100 ppm of O and at most 100 ppm N.

Si, Mn but especially Al, Ti, Ca, Mg, or rare earths like La, have a great affinity for oxidants like O, N, S, and even for C, and can then form various precipitates (oxides, nitrides, sulphides, carbides) very degrading for the magnetic properties. Remelting operations (VAR, ESR) make it possible to significantly reduce the number and size of these precipitates, but the more oxidizable elements there are at the start (for example in an ingot resulting from a VIM vacuum treatment), the more it will remain after remelting, and therefore until the final stage of manufacturing the material. It is therefore important to reduce their presence as much as possible at the start.

The target is therefore at most 100 ppm of Al (0.01%) and preferably at most 20 ppm of Al (0.002%), at most 100 ppm of Ti (0.01%) and preferably at most 20 ppm of Ti (0.002%), at most 50 ppm of Ca + Mg, and preferably at most 10 ppm of Ca + Mg. In the case of addition of rare earths, at most 500 ppm, the particular aim is to obtain a liquid bath in the VIM with a very low chemical activity of oxygen before the addition of the rare earths.

The rest of the alloy is made up of Fe and impurities resulting from the elaboration.

It should be understood that the contents considered as preferred for certain elements are independent of the contents considered as preferred for the other elements. In other words, it is possible, without departing from the invention, to have one or more elements in their preferred range(s) while the other elements would not be in their preferred ranges if they have one.

The composition of the alloy gives it a complete recrystallization temperature which is generally around 700°C, whereas the onset of recrystallization begins around 600°C after the restoration phenomenon (which produced at about 500-600°C). We need to know the time (which we will call "useful time", and which will be designated by "t _u ") during which the material remains in the recrystallization zone of the annealing furnace (in other words, in the zone where the temperature of the oven is at least 600° C.) during the travel of the strip in the annealing oven at the speed V, and which can be measured experimentally or determined by calculation using known models of the skilled person. It is considered, in the context of the invention, that the critical recrystallization temperature Trc, from which the material begins its recrystallization, is Trc=600°C. The useful length (of the furnace) at the recrystallization Lu is Lu=Vt _u and can be measured fairly easily by those skilled in the art during a temperature measurement on a moving strip.

According to the invention, one takes as a starting point a semi-finished product which has been produced (without remelting if one wants to stick to an economic method of production and to final performance of the product simply comparable to that of usual products and not specially improved compared to them, or with remelting if one wants to obtain remarkably good final performances), cast, hot-formed and, preferably, annealed, by usual means, with shaping parameters by forging and /or completely conventional hot rolling. These steps aim to prepare a semi-finished product suitable for being cold rolled to obtain a strip or sheet of equiatomic FeCo alloy (thus containing approximately as much Fe as Co, both in weight percentages and in atomic percentages since these two elements, immediately neighbors in the periodic table of elements, have very similar atomic masses, 55.8 and 58.9 g/mol respectively), whose composition is comparable to that of known equiatomic FeCo alloys. A hot-formed semi-finished product is thus obtained, typically in the form of a strip, with a thickness 6HR of between 1.5 and 2.5 mm, typically of the order of 2 mm. Above 2.5 mm in thickness, there is a risk of no longer being able to extract the heat quickly enough, even by annealing, to avoid ultra-fast and weakening ordering.

At the end of hot rolling, the strip obtained is subjected, not necessarily but very preferentially, to annealing. This treatment makes it possible to avoid to a very large extent the order/disorder transformation in the material, so that the latter remains in an almost disordered structural state, little changed compared to its structural state obtained by hot rolling at a higher temperature. to Trc, and which, therefore, is sufficiently ductile to be able to be cold rolled.

The annealing therefore allows the hot strip to be then assuredly cold rolled without difficulty up to the final thickness of the rolling sequence at cold, regardless of its thickness if it is not greater than 2.5 mm, and regardless of its composition, if it is within the limits set by the invention.

The annealing can be carried out directly at the hot rolling exit, therefore without intermediate heating of the strip, if the temperature of the strip at the end of rolling is sufficiently high and if the hot rolling installation allows it, or, in otherwise, after reheating the strip to a temperature above the order/disorder transformation temperature.

In practice, the weakening ordering being established between 720°C and the ambient temperature, there are two possibilities of carrying out this annealing:

- either the still hot metal, following its hot rolling, is violently cooled (typically at least 200°C/second, preferably at least 1000°C/second, better still at least 2000°C/second), at the water for example, at the outlet of the hot rolling installation, from a temperature of 800 to 1000° C. down to ambient temperature;

- either the hot rolled metal then cooled slowly, therefore fragile, is reheated between 800 and 1000°C, before violent cooling, that is to say at least 200°C/second, preferably at least 1000° C/second, better at least 2000°C/second, down to room temperature.

Such processing is known per se to those skilled in the art.

At the end of this sequence of operations, the metal must be in a 100% recrystallized state, unless this total recrystallization is obtained by one or more additional annealings which will be carried out before the LAF1-R1-LAF2 sequence, this sequence being one of the main elements of the invention, as we have seen.

The hot rolling of equiatomic FeCo alloys in the form of strips is most often carried out around 900°C, and 100% or very close recrystallization is then obtained during the stay of the strip in the coiled state.

In the case where the hot-rolled product is a sheet not intended to be coiled, and if it is realized, during preliminary tests, that 100% recrystallization is not already systematically obtained after hot rolling, it is possible to adjust the conditions of the hot rolling and its ancillary operations to obtain this 100% recrystallized state with certainty, by acting on the duration of the reheating preceding the hot rolling or by slowing down the cooling which follows the hot rolling, for example by placing the sheet under a hood.

Starting from a hot-formed, and optionally annealed, product which is recrystallized to 100% or almost, then makes it possible to then carry out the at least two cold rolling steps and the at least one intermediate annealing according to the invention starting from of one standardized microstructure, on which the effects of the following operations on the texturing of the material will be predictable and controllable.

After hot rolling and any annealing, the metal is preferably and conventionally subjected to an operation of chemical pickling and/or mechanical descaling of the hot rolled strip to prevent the encrustation of scale in the strip surface during subsequent laminations. This operation does not influence the microstructure of the strip and is therefore not an element of the invention.

A first LAF1 cold rolling of this 100% recrystallized semi-finished product with an initial thickness e R is then carried out, in one or more passes, which destroys the initial recrystallized microstructure. Polishing can be done before the first pass or between two passes. The semi-finished product is thus brought to a thickness e1 less than or equal to 1 mm, preferably less than or equal to 0.6 mm, generally between 0.5 mm and 0.2 mm, typically 0.35 mm, and which can go down to 0.12 mm, which corresponds, according to the invention, to an overall reduction rate TR1 at the first cold rolling LAF1 of between 70 and 90%.

An intermediate annealing R1 is then carried out on this semi-finished product, in a passing furnace. This intermediate annealing R1 according to the invention is necessarily carried out on the run in order to be able to obtain, at the outlet of the annealing furnace, sufficiently high forced cooling rates, that is to say at least 600° C./hour, preferably at least 1000°C/hour, better still at least 2000°C/hour, which can only be reached if the strip is unwound, and is therefore not in coil form as it would be in an annealing furnace static.

Intermediate annealing R1 is performed at a temperature such that the alloy is in the disordered ferritic phase. This means that the temperature is between the order/disorder transformation temperature of the alloy and the ferritic/austenitic transformation temperature of the alloy. For a substantially equiatomic Fe-Co alloy such as those concerned by the invention, having a Co content of between 47.0 and 51.0% by weight, the temperature of the atmosphere of the furnace in the useful length Lu of the furnace of annealing must, in practice, be between Trc and 950°C. Lu is the "useful length" of the furnace, i.e. the length of the path of the strip in the furnace over which the strip itself, and not only the atmosphere of the furnace, is actually at a higher temperature at Trc. This can lead to not taking into account, for the determination of the parameters of the intermediate annealing R1 according to the invention, the portions of the furnace closest to its entrance and its exit, in which it is not certain that the temperature effective is sufficient for the passage of the strip therein to be metallurgically effective. Those skilled in the art will be able to determine, using measurements and from current experiments, over what length Lu, in the oven at his disposal, the temperature of the treated strip is actually higher than the temperature Trc, knowing the composition of the strip.

The atmosphere of the annealing furnace is preferably a reducing atmosphere, therefore consisting of pure hydrogen or a hydrogen-neutral gas mixture (argon or nitrogen). A neutral atmosphere (Ar and/or nitrogen for example) would also be possible, but having a reducing atmosphere ensures that parasitic air inlets or insufficient purity of the neutral gas will not risk causing surface oxidation of the strip which would be detrimental to the proper execution of the cold rolling which will follow.

The temperature of the strip in the useful length Lu of the annealing furnace is, as said, between the temperature at the start of recrystallization Trc (which can be considered, with a good approximation, as equal to 600°C, taking into account the compositions of the strip to which the invention is addressed and which are located in a limited range) and 900° C., preferably between 700 and 900° C. to obtain more assuredly a partial recrystallization, but nevertheless sufficient for all the alloy compositions concerned by the invention. The effective temperature of the furnace atmosphere must be chosen accordingly, also taking into account the fact that the strip takes more or less time to heat up after entering the furnace, and that the nature of this atmosphere can also influence this warm-up time. Pure hydrogen is the usual gas which is the most favorable from this point of view, but heat transfers in the furnace can also be improved by setting up a forced convection regime, so that less favorable gaseous atmospheres less heat transfer than pure hydrogen, but more easily manageable from the point of view of the operational safety of the furnace, can be used. Helium would provide even better heat transfers than hydrogen and would pose fewer safety problems, but it is much more expensive and is not reducing.

The strip must remain in this temperature range for a period of 15 s to 5 min. At least for the shortest durations and the highest annealing temperatures R1, this can lead to imposing on the atmosphere of the furnace a temperature a little higher than 900°C, for example 950°C. A person skilled in the art will be able to determine experimentally, depending on the products he processes, their running speed and the precise characteristics of his oven, which temperatures in the oven would be suitable for the strip itself to reach a temperature to the present invention, and this for a period also in accordance with the invention, the objective being to obtain only partial recrystallization of the strip. Concerning the degree of only partial recrystallization obtained following this intermediate annealing R1, it must be between 10 and 50%, preferably between 15 and 40%, better still between 10 and 30%. Too low a recrystallization rate makes intermediate annealing R1 unnecessary, while too high a recrystallization rate degrades the magnetic losses of the final product.

The speed V of passage of the strip in the oven can be adapted, taking into account the length of the oven, so that the passage time in the homogeneous temperature zone of the oven is from 10 s to 10 min, and preferably between 15 sec and 5 min. In any event, the residence time at a temperature between Trc and 900° C. must be greater than 15 s, better still greater than 30 s, especially if the heat transfer conditions are not optimal. For an industrial furnace of the order of one meter in length, the speed must be greater than 0.1 m/min. For another type of industrial furnace 30 m long, the running speed must be greater than 2 m/min, and preferably from 7 to 40 m/min. In general, the person skilled in the art knows how to adapt the running speeds according to the length of the ovens at his disposal.

An additional condition is that the following relationship be respected during the annealing R1 which precedes the second cold rolling LAF2 which will be described later and which gives the strip its final thickness e2:

26°C.min.m < (T - Trcj.Lu / V < 160°C.min with T and Trc in °C, Lu in m, V speed in m/min, knowing that Trc = 600°C is a good approximation.

Preferably, 50°C.min < (T - Trc). Lu / V < 160°C.min with Trc = 600°C as before.

These two inequalities are also valid for other intermediate thicknesses e1 of the strip than 0.35 mm at the time of the intermediate annealing R1, such as 0.3 mm or 0.5 mm.

Indeed, surprisingly, it turned out that to obtain low magnetic losses on the alloys used in the invention (of the order of 26.5 W/kg at most), it was only necessary to obtain a partial recrystallization of the strip at the end of the intermediate annealing R1, with recrystallization rates as said above (10-50%, preferably 15-40%, better 15-30%), and this independently of the completely recrystallized structure that we will target after the final annealing. For this, it is therefore not necessary to inject an excessive quantity of heat into the strip during the intermediate annealing R1 of partial recrystallization according to the invention. There is, however, a minimum to respect in this matter, because otherwise we do not obtain a significant partial recrystallization of the strip, and this intermediate annealing R1 is then useless: we would, otherwise, then be reduced to a case comparable to that where LAF1 and LAF2 would be chained directly and where, consequently, there would be, in a conventional way, only one cold rolling carried out in several passes without the intermediate annealing of partial recrystallization R1 which is an element essential to the invention.

The inventors have, for example, succeeded in obtaining magnetic losses at the final thickness e2 of 0.1 mm as low as less than 26.5 W/kg at 2 T/400 Hz after a final anneal on a torus wound at 880°C, by moving the strip to the intermediate thickness e1 = 0.35 mm during the intermediate annealing R1 in a furnace of useful length (Lu) 1 m at a speed V of 3 m/min, at a temperature 800° C., for an alloy where the onset of recrystallization (Trc temperature) takes place for annealings of a few minutes around 600° C., which is the case of the alloys concerned by the invention. Such annealing corresponds to (T - Trc).Lu/V = 67°C.min, with T and Trc in °C, Lu in m, V in m/min, therefore lower than 160°C.min and also higher at 50° C.min, therefore corresponding to the preferred requirements of the invention. The recrystallized fraction obtained at the end of the intermediate annealing R1, measured by the EBSD technique (Electron Backscatter Diffraction = Diffraction d'Electrons Rétrosdiffusés), was 40%.

In another example, the inventors succeeded in obtaining magnetic losses at the final thickness of 0.1 mm as low as less than 26.5 W/kg at 2 T/400 Hz, running the tape at intermediate thickness e1 = 0.35 mm during intermediate annealing R1 for partial recrystallization in a furnace with a useful length (Lu) of 2.3 m at a speed of 3.6 m/min, at a temperature of 840°C, for an alloy where the beginning of recrystallization (Trc temperature) takes place for annealings of a few minutes at around 600°C. Such annealing corresponds to (T - Trc).Lu/V = 153°C.min, therefore here again less than 160°C.min and also greater than 50°C.min. The recrystallized fraction obtained at the end of the intermediate annealing R1, measured by the EBSD technique, was 47%.

On the other hand, the same annealing R1 of the strip carried out at a speed of 2 m/min leads to too extensive a recrystallization, and one observes, in the final state, magnetic losses greater than 26.5 W/kg, for a value ( T - Trc).Lu/V = 276°C.min, therefore greater than 160°C.min. The recrystallized fraction obtained at the end of the intermediate annealing R1, measured by the EBSD technique, was 72%.

In yet another example, the inventors succeeded in obtaining magnetic losses at the final thickness of e2 = 0.1 mm as low as less than 26.5 W/kg at 2T/400 Hz, by running the tape at the intermediate thickness e2 = 0.5 mm during the intermediate annealing R1 of partial recrystallization in a furnace of useful length (Lu) 4 m at a speed of 7 m/min, at a temperature of 860°C, for an alloy where the beginning of the recrystallization takes place for annealings of a few minutes around 600°C (Trc). Such annealing corresponds to (T-Trc).Lu/V = 149°C.min, therefore less than 160°C.min and also greater than 50°C.min. The recrystallized fraction obtained at the end of the intermediate annealing R1, measured by the EBSD technique, was 25%.

It should be noted that the processing furnace on the parade used can be of any type. In particular, it may be a conventional resistance furnace or else a heat radiation furnace, a Joule effect annealing furnace, a fluidized bed annealing installation, or any other type of furnace.

On leaving the oven, the strip must be cooled at a sufficiently high rate to avoid a total order-disorder transformation during cooling. However, the inventors were surprised to find that, contrary to what happens with a hot-rolled strip approximately 2 mm thick which must, in the vast majority of cases, be annealed in order to then be able to be rolled cold without difficulty, a thin cold-rolled strip (0.12 to 0.6 mm), intended to be then cold-rolled again, only undergoes a slight partial ordering, to the point that the low degree of brittleness achieved does not require the annealing as mentioned above, and which is carried out, very preferably, after the hot rolling.

The inventors were surprised to find that after an intermediate annealing in the parade as just described, the suitability of the strip for cold rolling and cutting (by shearing, in particular) becomes very good when the disorder/order transformation is not complete. This means, unexpectedly, that such a strip can be cold rolled again despite partial straightening resulting in some degree of brittleness.

So that the disorder/order transformation is not total, the cooling rate must be, above 200° C., at least 600° C./hour, preferably at least 1000° C./hour and, more preferably at least 2000°C/hour. Cooling by forced convection or spraying of cooling fluid is therefore, in practice, necessary to reach the targeted minimum speed. When the strip temperature has dropped to 200°C, the order/disorder transformation no longer changes significantly, and the cooling rate between 200°C and ambient temperature no longer matters from this point of view.

The cooling rate can be as high as is theoretically possible given the thickness of the strip and the cooling means available. However, in practice it is not useful to exceed 50,000° C./hour. A speed of between 2,000° C./hour and 10,000° C./hour is most often sufficient, and forced convection is generally sufficient to obtain it. In addition, the annealing carried out before the last cold rolling (namely the intermediate annealing R1) must (for the first) and can (for the second) respect the two following inequalities, depending on the temperature of the strip T in ° C, the useful length of the furnace Lu (length over which the temperature T of plateau or maximum of the furnace is above the temperature Trc of beginning of recrystallization of the strip for annealings of a few minutes, temperature Trc which one takes equal to 600°C with a good approximation for all the alloys concerned by the invention) in m, the strip speed V in m/min:

* 26°C. min < (T - Trc).Lu/V < 160°C.min

* and, preferably, 50°C.min <(T - Trc).Lu/V <160°C.min.

The reasons for this will be seen later.

Then, after this intermediate annealing at the parade R1, a second cold rolling sequence LAF2 is carried out in one or more passes, which typically gives the strip a thickness e2 of between 0.05 and 0.25 mm, preferably between 0.07 and 0.20mm. e2 is, in general, the target final thickness for cold-rolled strip. The degree of reduction TR2 of this second cold rolling LAF2 is, according to the invention, between 60 and 80%, preferably between 65 and 75%.

If the case of two cold rollings LAF1 and LAF2 and an intermediate annealing R1, with this sequence LAF1-R1-LAF2 following the hot rolling and preceding the final static annealing Rf, is the typical preferred case of the invention, a greater number of cold rollings and intermediate annealings can be provided, in addition to LAF1, R1 and LAF2 executed as just described. These additional cold rolling and intermediate annealings may be denoted by LAFi and Ri, respectively, and are performed from the hot rolled and cooled semi-finished product according to the invention. They must therefore all precede the LAF1-R1-LAF2 sequence mandatory in the invention, and the semi-finished product must be 100% recrystallized after the last of the annealings Ri, so as to start the LAF1-R1-LAF2 sequence according to the invention. on a 100% recrystallized microstructure, for the reasons indicated above with regard to the case where cold rolling(s) and annealing(s) are not carried out before this sequence.

There may be only one additional LAFi-Ri cycle compared to the more usual case of a LAF1-R1-LAF2 sequence of operations, but it should be understood that the invention extends to cases where there would be several such additional cycles LAFi-Ri adding to LAF1-R1-LAF2 and all being executed before LAF1. In any case, the annealing R1 carried out before the last cold rolling LAF2 must be carried out, depending on the maximum strip temperature T, the useful length of the furnace Lu (length over which the plateau or maximum temperature T of the furnace is above Trc temperature strip recrystallization start temperature for annealings of a few minutes, here 600°C), with a strip speed V (in m/min) such as:

* 26°C.min < (T - Trc). Lu / V < 160°C.min

* preferably, 50°C.min < (T - Trc).Lu/V < 160°C.min.

An example of such a process, comprising two additional cycles LAFi-Ri, would be, still from the hot-formed strip of thickness e _H R of 2 mm from the previous example, to first proceed to a first rolling at cold LAFi-n°1 at a rate TR(i= 1 ) of at least 40% to achieve a strip thickness ei-n°1 of at most 1.2 mm, then a first intermediate annealing Ri- No. 1 on the parade, for which it is necessary that the passage time in the useful zone of the oven, where the strip is imposed at a temperature between Trc and 900°C, i.e. from 10 s to 10 min, and preferably included between 15 s and 5 min, better still between 30 s and 5 min, and in any case so that the metal is preferably 100% recrystallized, so as to better ensure that after the last intermediate annealing, and therefore before LAF1 , the sheet or strip may be fully recrystallized as required by the invention. This intermediate annealing Ri-n°1 is followed by cooling at a rate greater than 600° C. per hour, and preferably greater than 1000° C. per hour or even 2000° C./hour. In practice, it is not useful to exceed 10,000° C./hour and a speed of between 2,000° C./hour and 3,000° C./hour is generally sufficient. In general, when it is desired to carry out cold rolling after an intermediate annealing on the parade (Ri or R1), such a rapid cooling must be carried out, for the reasons given above, related to the ability of the strip to be cold rolled again, and also its suitability for cutting if this is useful.

Then a second LAFi-n°2 cold rolling is carried out with a TRi-n°2 rate of at least 40% up to a thickness ei-n°2 of at most 0.96 mm, then a second annealing intermediate Ri-n°2 followed by cooling at a rate greater than 600° C. per hour, and preferably greater than 1000° C./hour, or even 2000° C./hour. In practice, it is not useful to exceed 10,000°C/hour and a speed between 2,000°C/hour and 3,000°C/hour is generally sufficient. This Ri-n°2 annealing is characterized by the fact that the passage time in the useful zone of the furnace, where the strip is subjected to a temperature situated between Trc and 900°C, i.e. from 10 s to 10 min, and preferably between 15 s and 5 min, better still between 30 s and 5 min, and also by the fact that the metal is 100% recrystallized at the end of the Ri-n°2 annealing.

At this stage, the typical and mandatory steps of the invention are then carried out:

LAF1-R1-LAF2 and Rf. The first cold rolling LAF1 is carried out, which must be between 70 and 90%, which is chosen here at 80%, which leads to a thickness of the strip e1 of at most 0.19 mm. The 100% recrystallized microstructure from Ri-n°2 is thus destroyed.

The partial recrystallization annealing R1 is then carried out, followed by cooling at a rate greater than 600° C. per hour, and preferably greater than 1000° C./hour, or even 2000° C./hour. In practice, it is not useful to exceed 10,000°C/hour and a speed between 2,000°C/hour and 3,000°C/hour is generally sufficient. This annealing R1 is characterized by the running of a strip of intermediate thickness e1 = 0.19 mm at most in a furnace of useful length 4 m (Lu) at a speed of 12 m/min, at a temperature of 820° C, for an alloy where the beginning of recrystallization takes place for annealings of a few minutes at around 600°C (in other words Trc). Such annealing corresponds to (T - Trc).Lu/V = 73.3°C.min, therefore less than 160°C.min and also more than 50°C. min. It therefore meets the necessary conditions mentioned above for the annealing R1 preceding the last cold rolling.

This is followed by cold rolling LAF2, which is the fourth cold rolling in this example. LAF2 must have a reduction rate between 60 and 80%, and 70% is chosen here, which produces a strip with a final thickness e2 of, at most, 0.06 mm.

Finally, a final static Rf annealing of total recrystallization is carried out, typically between 850 and 890° C. under a reducing atmosphere for several hours, for example at 880° C. under pure hydrogen for 3 h, followed by cooling at a rate of 100 to 500° C./hour, preferably between 200 and 300° C./hour, to greatly reduce or eliminate the magnetocrystalline anisotropy constant K1.

It may therefore be quite sufficient to carry out only two cold rolling sequences, with intermediate annealing of type R1 (partial recrystallization) ending with rapid cooling (at least 600°C/hour as explained above), and with a distribution of the reduction rates TR between the two cold rollings which has been previously indicated and makes it possible to achieve the desired final thickness, before the final static annealing Rf of total recrystallization which will be detailed later.

Conversely, as we have said, it would be possible to carry out before Rf more than two cold rolling sequences (four in the previous example), with the associated intermediate annealings and rapid cooling, again adequately distributing the rates. respective reduction of cold rolling. But, at least from an economic point of view, it is clear that it is in our interest not to multiply the sequences of cold rolling and annealing beyond what would be necessary according to experience, and that the minimum of two very specific cold rolling sequences LAF1 and LAF2, by their restricted and respective ranges of reduction rates TR1 and TR2, separated by an intermediate strip annealing with partial recrystallization R1, no less specific, followed by rapid cooling, also represents the preferred case, LAF1 being carried out on a fully recrystallized and, optionally, annealed hot-rolled semi-finished product.

It should be understood that the conditions:

- 26°C.min < (T - Trc).Lu/V < 160°C.min , with Trc taken equal to 600°C;

- and preferably 50°C.min <(T-Trc).Lu/V <160°C.min; are the conditions that must be met by annealing at the parade R1 preceding the last cold rolling LAF2.

On the other hand, such conditions do not absolutely need to be respected by any additional intermediate annealings Ri because in this case it is only imperative that the recrystallization be complete after the last additional annealing Ri. That it is complete after the other possible additional annealings Ri is only a preference. For these, when it is carried out, the passage time in the useful zone of the oven, where the strip is subjected to a temperature between Trc and 900°C, must be from 10 s to 10 min, and preferably between 15 s and 5 min, better still between 30 s and 5 min.

What is needed is to have a 100% recrystallized state immediately before LAF1 (so after the last additional annealing Ri).

As examples of succession of manufacturing steps comprising several intermediate annealings Ri and which would be in accordance with the invention, the following diagrams can be cited.

Example 1, with two intermediate annealings Ri:

Hot rolling up to a 6HR thickness of 2 mm - LAFi-n°1 at 50% reduction rate up to a thickness of 1 mm - Ri-n°1 up to a recrystallization rate of 100% - LAFi-n°2 at 50% reduction rate up to a thickness of 0.5 mm - Ri- n°2 up to a recrystallization rate of 100% - LAF1 at 70% reduction rate up to a thickness e1 of 0.15 mm - R1 up to a recrystallization rate of 10 to 40% - LAF2 at 66% reduction rate up to a thickness e2 of 0.06 mm - Static Rf at 850°C for 3 hours under hydrogen providing complete recrystallization.

Example 2, with three intermediate annealings Ri:

Hot rolling up to a thickness eHR of 2.5 mm - LAFi-n°1 at 40% reduction rate up to a thickness of 1.5 mm - Ri-n°1 up to a recrystallization rate from 100% - LAFi-n°2 to 40% reduction rate up to a thickness of 0.9 mm - Ri- n°2 up to a recrystallization rate of 100% - LAFi-n°3 to 44 % reduction rate up to a thickness of 0.5 mm - Ri-n°3 up to a recrystallization rate of 100% - LAF1 at 70% reduction rate up to a thickness e1 of 0.15 mm - R1 up to a recrystallization rate of 10 to 40% - LAF2 at 66% reduction rate up to a thickness e2 of 0 .06 mm - Static Rf at 850° C. for 3 h under hydrogen providing complete recrystallization.

Example 3, with two intermediate annealings Ri:

Hot rolling up to a thickness e _H R of 1.5 mm - LAFi-n°1 at 40% reduction rate up to a thickness of 0.9 mm - Ri-n°1 up to a reduction rate recrystallization rate of 100% - LAFi-n°2 at 44% reduction rate up to a thickness of 0.5 mm - Ri-n°2 up to a recrystallization rate of 100% - LAF1 at 70% reduction reduction rate up to a thickness e1 of 0.15 mm - R1 up to a recrystallization rate of 10 to 40% - LAF2 at 66% reduction rate up to a thickness e2 of 0.06 mm - Rf static at 850° C. for 3 h under hydrogen providing complete recrystallization.

Example 4 with intermediate annealing Ri:

Hot rolling up to a thickness e _H R of 1.59 mm - LAFi-n°1 at 40% reduction rate up to a thickness of 0.95 mm - Ri-n°1 up to a reduction rate recrystallization rate of 100% - LAF1 at 70% reduction rate up to a thickness e1 of 0.29 mm - R1 up to a recrystallization rate of 10 to 40% - LAF2 at 65% reduction rate up to at a thickness e2 of 0.1 mm - static Rf at 870° C. for 2 hours under hydrogen providing complete recrystallization.

In all cases (two LAF cold rolling sequences or more), the material having reached the final thickness undergoes a final static Rf annealing on strip, or on parts previously cut and shaped (wound toroids of transformer, rotor and actuator stator), so as this time to completely recrystallize the strip and to develop the ferritic grain growth amply, without ever penetrating into the austenitic domain. This sufficient growth of the ferritic grain, which makes it possible to obtain low magnetic losses, cannot be obtained by strip annealing, which would be too short for that.

Thus, a static Rf annealing is applied typically lasting more than 30 min, preferably more than 1 hour, at a temperature between 750 and 900° C., preferably between 800 and 900° C., and better still between 850 and 880° C., either under vacuum, or under a non-oxidizing protective atmosphere, therefore neutral or reducing, for example under nitrogen, under a nitrogen-hydrogen or argon-hydrogen mixture, under an inert gas such as argon, and preferably under pure hydrogen. The cooling which follows the final Rf annealing can be carried out at any speed, but preferably between 100° C./hour and 500° C./hour, and better still between 200 and 300° C./hour.

The reasons for these limits are that the purpose of this cooling is to optimize the magnetocrystalline anisotropy constant K1 , and that:

For slow cooling, a positive K1 value corresponding to an ordered alloy is obtained;

For very rapid cooling, a negative K1 value corresponding to a disordered alloy is obtained.

The optimum magnetic properties are obtained for zero K1, therefore for optimized cooling rates situated in the aforementioned range, therefore most typically around 250° C./hour.

The following experiments were performed and demonstrate the advantages of the invention.

Table 3 shows the compositions of the five alloys used, given in weight percentages. Alloys 1 and 4 were produced with a single remelting, from new, and therefore expensive, raw materials. The other alloys 2 (which is the one designated by "Ref 1" in table 1 and whose composition is in accordance with that which can be used in the present invention), 3 and 5 were produced without remelting from ordinary raw materials, therefore with as low a cost as possible. As a result, the Mn, S, Ni, Cu, Nb contents of alloy 1, which result from the melting of the raw materials and the conditions for producing the liquid metal and not from an addition of these elements, are lower than those of these same elements in the other alloys and show that, in this case, raw materials of very good purity were used. All of these alloys have compositions in accordance with what the invention requires. The elements not explicitly mentioned are present at most only in the state of impurities without metallurgical effect. We have also indicated their recrystallization start temperatures Trc, which are involved in determining the parameters of the intermediate annealing R1 preceding the last cold rolling LAF2: as we said, they are all very close to 600°C, as c This is the case for the alloys of the general composition used in the invention.

Table 3: Compositions of the alloys of the experiments

The ingots (dimensions 200 x 500 x 2500 mm) made of these alloys were hot rolled, then subjected to annealing, without which experience shows that the strips are at high risk of breaking during cold rolling if this is carried out on products with an initial thickness of more than 2 mm.

To this end, they successively underwent heating between 800 and 1200°C, blooming in the form of bars with a section of 100 x 350 mm and a few m long, then hot machining and very slow cooling. A very slow reheating (16 h) up to 1200°C then took place, followed by hot rolling on a strip mill, which reduced the thickness of the product from 100 to 2 mm in 16 successive passes. At the end of the last pass ending at 950°C, annealing was carried out under a water jet at a speed of the order of 1000°C/second, then cold winding of the hot strip as well as obtained.

The microstructure of the strip is 100% recrystallized, and is a mixture of primary ferrite and quench martensite from the austenitic phase (which was in equilibrium with the primary ferrite at 950°C), a mixture to which secondary ferrite is added conversion, formed from austenite. Then the hot strips underwent either a simple cold rolling, or a double cold rolling LAF1 and LAF2 with intermediate annealing R1, to obtain cold strips.

Finally, these cold strips underwent a final static Rf anneal under pure hydrogen, followed by a forced cooling at 250° C./hour.

The parameters and the results of the experiments carried out on alloys 1 to 5 of table 3, demonstrating the interest of the invention, are summarized in table 4. The intermediate annealings were carried out in a furnace 2.3 m in length useful heating.

10

Table 4: Results of the tests according to the invention and of the comparative tests The example of the first two lines of the table relating to alloy 5 clearly shows the favorable contribution (which here is sufficient on the washers but insufficient on the toroids for a (T-Trc).LuZV of 42°C.min) of a double cold rolling process compared to a single cold rolling process. The third line of the table, which corresponds to a value of (T-Trc).Lu/V located in the preferred range 50-160°C.min, shows the additional advantage that there is to be placed in this range preferred to further reduce magnetic losses, here by an additional 4%.

Tests with simple lamination, whether or not there was a reflow, are considered as reference tests. In particular, the tests carried out on alloy 1 with simple rolling and an ingot having undergone ESR remelting are typical of materials intended for transformer cores, for which losses less than or equal to 26.5 W/kg under 2 T and 400 Hz are desired, and achieved in this case at the cost of performing an expensive reflow. The test carried out on alloy 2 not remelted but with simple cold rolling is typical of a material intended for the rotors of rotating machines. As they do not include intermediate annealing, the relationship T-Trc).Lu/V has no meaning in their case, hence the expression “not relevant” in the corresponding cells of Table 4.

It is also interesting to note, with regard to the tests carried out on alloy 2, that an increase in the running speed in the annealing furnace from 3.4 m/min to 3.6 m/min makes it possible to reduce the losses at 2 T/400 Hz, to the point that on washers, we go from a value of 27 W/kg, considered almost acceptable but still too high, to a value of 25.8 W/kg, considered suitable. The reason for this is that this acceleration of the scrolling speed made it possible to lower the value of (T-Trc).LuA/ below 160°C.min which is the maximum required by the invention. This shows that it is relevant to consider this parameter.

The examples presented show that, even with alloys which are not particularly pure due to the absence of remelting and a not particularly careful choice of raw materials, the execution of a double cold rolling with intermediate annealing, if the precise conditions of the invention are respected, makes it possible to maintain low magnetic losses after a final annealing carried out under conventional conditions (850° C., 3 h, or better 880° C., 3 h or 860° C., 2 h) . Thus, for electrotechnical applications of all types, requiring both high power density (which equiatomic FeCo alloys can achieve) and low magnetic losses at 2 T, 400 Hz, of the order of 26.5 W / kg, or even lower for the most demanding applications on this point, it turns out that the invention makes it possible to obtain these results without necessarily resorting to costly operations such as the selection of high purity raw materials and the remelting of ESR or VAR ingots.

An explanation for this state of affairs could be the following, in view of the experiments that we will describe.

Unremelted ingots of the Alloy 2, Alloy 3 and Alloy 5 compositions of Table 3 were used, to which conventional application of hot transformation of the ingot by blooming between 1100 and 1200° C., then hot rolling between 1000 and 1200° C. °C on a strip mill up to a thickness of 2 mm, then annealing to 900°C at the hot rolling exit with a cooling rate of 1000°C/second, before cold rolling them to a thickness of 0.1 mm, either by simple cold rolling with a reduction rate of 95%, or by double cold rolling up to a thickness of 0.35 mm (reduction rate 82.5%) then at a thickness of 0.1 mm (reduction rate 71.4%), therefore also with an overall reduction rate of 95%, with intermediate annealing at 840°C for a strip speed of 3.6 m/min for alloy 2, 4.4 m/min for alloy 3, 4.2 m/min for alloy 5 in a furnace of homogeneous useful heating length Lu of 2.3 m. These three cases are described in table 4, and all allow magnetic losses at 2 T/400 Hz to be obtained below 26.5 W/kg

It appeared that, all other things being equal, the double cold rolling (LAF1 and LAF2) and the intermediate annealing R1 gave the strip in the work-hardened state a substantially modified texture. And this significant difference in texture remains, without notable change, after the final annealing of complete Rf recrystallization carried out under the conditions prescribed by the invention. Table 5 shows the volume fraction (in %) of texture component {hkl}<uvw> calculated with a maximum dispersion of 15° on the three Euler angles, with respect to the ideal orientation, in cases where the cold-rolled strip is simply in the work-hardened condition or is in the fully recrystallized condition after a final anneal at 850°C for 3 hours. For intermediate annealing, the useful length Lu of the furnace is 2.3 m.

Table 5: Volume fraction (in %) of texture component {hkl}<uvw> calculated with a maximum dispersion of 15° on the three Euler angles, compared to the ideal orientation for different tests

It clearly appears, in view of these results, that in the work-hardened state after simple cold rolling, the component A of the texture is clearly stronger, typically twice as strong, as the other main components B and C of the texture. . On the other hand, after the double cold rolling according to the invention, the three components have amplitudes close to each other, between approximately 8 and 14%. This is observed on the three series of tests.

On the test during which a final annealing was carried out after a simple cold rolling, the A component is even more predominant than in the work-hardened state (40% against 25%), and is approximately 8 times stronger than the components B and C. On the other hand, with the double cold rolling and the intermediate annealing according to the invention, the ratios between the components A, B and C are almost not affected compared to what they were at the time of the invention. hardened state, and the amplitudes of these components remain close, even very close, to each other (between 7 and 16% approximately each), and component A is no longer necessarily predominant.

These results show that the metallurgical process (double cold rolling range, with intermediate annealing leading to partial recrystallization) of the invention can, moreover, be clearly identified on the final product (after a final annealing completing the recrystallization, carried out typically at 850°C for 3h) by the quantified characterization of its main texture components; and that without ambiguity. Indeed, the case of the invention corresponds to the fact that, after the final Rf annealing, the texture of the microstructure of the material, characterized by EBSD, is as follows:

- 8 to 20%, preferably 9 to 20%, by surface or by volume, of component {001}<110> disoriented at a maximum of 15° (component A of Table 5);

- 8 to 25%, preferably 9 to 20%, by surface or by volume, of {111}<112> component disoriented at a maximum of 15° (component B of Table 5);

- 5 to 15%, preferably 6 to 11%, by surface or by volume, of {111}<110> component disoriented at a maximum of 15° (component C of Table 5);

- the rest of the material being made up of other texture components, disoriented by at most 15°, each representing a maximum of 15% in surface area or in volume, the covering of said other texture components with any of the components {001} <110>, {111}<112> and {111}<110> not exceeding 10% of the surface or volume of any of these three preceding components.

It should be noted that due to the disorientation of each identified texture component around its {hkl}<uvw> crystallographic orientation, such as 15°, two different crystallographic components may partially overlap (see for example references [1] to [5] cited below). So, if a given texture component X is found to represent a proportion close to (but less than) 15% of the material, it is possible that part of this 15% actually comes from one of the main components A, B, C which has some of its crystallographic orientations in common.

If we want to distinguish the orientations or texture components A, B or C from the rest of the crystallographic orientations or minor texture components X, and thus make it possible to unambiguously link the proportions of these components A, B, C to the advantageous magnetic properties of In accordance with the invention, it is necessary to be able to separate these representative components A, B or C sufficiently precisely from the other minor components X, and therefore to define a criterion of low overlap between these 2 types of components.

Detailed crystallographic analyses, known to those skilled in the art, such as typically the well-known technique of EBSD (references [6] and [7] cited later) make it possible to identify each of the texture components clearly distinguishing themselves from the random distribution, and to determine the magnitude of any overlaps between components. In the invention we define that the overlap of crystallographic orientations between one of the components A, B or C on the one hand and a minor texture component X on the other hand must not exceed 10% of the area or volume fraction.

For example if next to the component A-{100}<011> disoriented at 15° around the ideal component (100)[001], we seek to identify a component X-{hkl}<uvw> quite close in disorientation , such that for example X1 -{210}<011 > disoriented at 15° around the ideal component (210)[001] which forms an angle of 26.56° with respect to (100)[001] (there is therefore an overlap since 26.56° < 2x15°), the overlap of the surface or volume fractions of crystallographic orientations of A and of X1 must not exceed 10% of the total surface or volume fraction. If in this case of example of X1 and A there is an excess of 10% in overlap, then we will choose a component X2 a little further from A and satisfying the criterion of <10%, such as for example X2-{320 }<011> disoriented at 15° around the ideal component (320)[001] which forms an angle of 33.69 degrees with respect to (100)[001],

Useful bibliographical references for a good understanding of the concepts and techniques that have just been mentioned are, in particular:

[1] Norbert Broil, “Characterization of crystallized solids by X-ray diffraction”, Engineering techniques P 1080

[2] A. Guinier, “Theory and technique of radiocrystallography”, 1956 Dunod, Paris

[3] H. J. Bunge, “Texture analysis in material science”, 1982 Butterworths Publ. London

[4] B. Jouffrey and R.A. Portier, “Diffraction in metals and alloys: diffraction conditions”, Engineering techniques M 4 126

[5] H. J. Bunge and C. Esling, “Texture and anisotropy of materials” Engineering techniques, M 605-1

[6] T. Baudin, "EBSD analysis - Principle and orientation maps", Engineering techniques M 3040 (2010)

[7] T. Baudin et al., “Analysis of crystallographic textures and microstructures”, Reflets de la Physique n°44-45, p.80

(http://dx.doi.orq/10.1051/refdp/20154445080).

The three texture components considered are those which are the most characteristic for the invention, because they are the most sensitive to the passage from a single cold rolling to a double cold rolling, and are typically those which have the highest proportions. high in the final product. Tests were carried out from alloy 2, of composition given in Table 3, by the same procedure as during the preceding tests. He therefore underwent the following treatment:

Casting without VAR remelting of an ingot with a section of 200 x 800 mm ² ;

Hot rolling of the ingot at a temperature of 950 to 1200°C followed by cooling (annealing) at a speed of the order of 1000°C/second to obtain a hot strip 2.0 mm thick e _H R 100% recrystallized;

Cold rolling LAF1 of said annealed hot strip, at a reduction rate of 83% to obtain a cold strip with a thickness e1 of 0.35 mm;

Intermediate annealing R1 of partial recrystallization carried out by running under pure hydrogen at a temperature between 760 and 810°C, in a furnace with a useful length Lu of 2.3 m, in which the strip runs at a variable speed V according to the tests ( between 2.3 and 6.5 m/min), the temperature T in the useful zone also being variable according to the tests, so that the effects of the quantity (T - Trc).Lu/V on the magnetic losses at 2 T and 400 Hz, after the final annealing Rf as well as the rate of recrystallization after R1, measured by the EBSD method (Electron Back Scattered Diffraction, backscattered electron diffraction) can be evaluated; this annealing R1 is followed by cooling down to ambient temperature at a rate of 2500° C./hour;

LAF2 cold rolling at a reduction rate of 71% to obtain a cold strip with a final thickness e2 0.10 mm;

Final static Rf annealing at a temperature of 850°C for 3 hours under pure hydrogen leading to complete recrystallization, followed by cooling to room temperature at a rate of 250°C/hour.

For these tests, the value of (T - Trc).Lu/V was taken into account, knowing the value of the speed V of the strip and the recrystallization threshold Trc (around 600° C.). Lu (determined experimentally beforehand by installing thermocouples in the oven) is 2.3 m in the present case, and is a quantity to be considered as being within the scope of the invention.

Magnetic losses were measured on 0.1 mm thick washers with inside/outside diameters of 25/36 mm or 29.5/36 mm.

Table 6 shows the magnetic hysteresis characteristics measured in direct current: maximum induction of the cycle Bm for a maximum field of 20 Oe, the remanence Br of this same cycle at a maximum field of 20 Oe, the ratio of Br and of the induction maximum Br/Bm, the coercive force Hc, as a function of the annealing conditions on the run (temperature T and strip speed V). It also shows the magnetic losses observed at 2 T, 400 Hz, as well as an index equal to (T - 600). tu, which is representative of the quantity of energy supplied during the intermediate annealing and is defined with respect to the temperature at the start of recrystallization Trc of the material, which is here 600°C. Lu is the "useful length" of the oven, i.e. the length of the path of the strip in the oven over which the strip is at a temperature higher than Trc, and the "useful time" t _u (in min ) is the time the strip stays in this useful length of the oven. It also shows the surface or volume (which is equivalent) proportions of the three characteristic texture components of the invention.

Table 6: Magnetic characteristics measured on samples (washers

15 with a thickness of 0.1 mm) of the alloy 2 having undergone a double cold rolling, an intermediate annealing R1 (with Lu = 2.3m) and a final annealing Rf, depending on the intermediate annealing conditions, and fractions volume of texture components {001 }< 110> , {111}<112> and {111}<110>

20 Figures 1 and 2 show, for the examples which were 100% recrystallized before LAF1, the magnetic losses at 2 T and 400 Hz and the recrystallized fraction of the samples as a function of the quantities (T - 600)/V and (T - 600).Lu/V respectively, as defined above, 600°C being the value of Trc. It appears (FIG. 1) that these magnetic losses after LAF2 and Rf, all other things being equal, are lower the lower the magnitude (T - 600)/V (V being the speed of the strip). If we want to obtain losses of the order of 26.5 W/kg at most, to remain within the initial objective of the invention which was to maintain losses of the order of 26 W/kg without requiring a choice care of the raw materials associated with a complex elaboration of the ingot from which the strips are made, it is very preferable, for this specific example, not to exceed a value of (T - 600)/V of 80°C.min/ m, and preferably 60°C.min/m (corresponding to losses <26W/kg) if it is desired to obtain magnetic losses less than or equal to 26.5 W/kg. This relatively low maximum value of (T - 600)/V (in relation to the energy injected into the metal during R1) goes hand in hand with relatively low recrystallization rates after R1, which we can estimate should not not exceed 50%, preferably 40%, better 30%. The best examples have recrystallization rates on the order of 15-17%. A minimum rate of 10%, better 15%, is necessary for intermediate annealing to be useful.

The first example in Table 6 has a recrystallization rate at R1 of 40%, and magnetic losses of 26 W/kg at 2 T, 400 Hz after final annealing, which is just below the accepted maximum of 26, 5W/kg. It illustrates the fact that a value of (T-600)/V between 60 and 80 °C.min/m may be suitable for the present case, but not optimal.

The maximum value considered acceptable of (T - 600)/V is only indicative because it is valid for this series of examples, in this reduced range of intermediate annealing temperatures 760-810°C. This limit of 80°C.min/m, preferably 60°C.min/m, corresponds to a scroll annealing furnace with a useful length Lu of 2.6 m. But (figure 2) the calculation of this admissible limit can be generalized to any useful length Lu according to: (T - Trc).Lu/V < 60. Lu = 160°C.min, with Trc = 600°C. Thus, if the furnace considered is three times longer, the limit of 160°C.min being invariant for this strip of thickness 0.35 mm, it will be necessary either to reduce the temperature T of the furnace, or to increase the speed of strip V to respect (T - Trc). Lu/V < 160 °C. min and thus not recrystallize the strip too much during annealing R1, allowing magnetic losses at the final thickness of 0.1 mm to be less than or equal to 26.5 W/kg on washers annealed for a few hours at 850°C , or even better if the annealing is carried out above 850°C (but below 900°C).

Other examples are given in Table 5 on three different castings, following the same metallurgical range (same cold rolling reduction rate, same hot transformations and same thickness after hot rolling) with annealing intermediate annealing varying from 3.6 to 4.4 m/min in a furnace with a useful length of 2.3 m, and a temperature of the homogeneous zone of the furnace of 840°C during the intermediate annealing on the march (therefore above of the first temperature zone considered above). It is therefore verified on these examples, compared to the examples previously cited where Lu = 2.6m, that to maintain (T - 600). 'we reduce Lu, all other things being equal. This first inequality therefore makes it possible to take into account the useful length Lu of the furnace in the use of the invention.

In other words, empirically and unexpectedly, we see that it is necessary to be placed, during the intermediate annealing R1 preceding the last cold rolling, above the temperature of complete recrystallization Trc, which is of the order of 600° C for the alloys concerned by the examples given, but that once this temperature has been exceeded, it is also not necessary to provide an excessive total quantity of heat to the metal so as not to obtain excessive recrystallization. These requirements are achieved by combining the temperature and the duration of the intermediate annealing R1, this last parameter being represented by the running speed in the furnace for a given length of furnace. Taking into account the parameter (T - Trc).Lu/V under the conditions which have been said makes it possible to take these parameters into account to quantify the heat input to the strip and ensure that, taking into account the kinetics recrystallization, the rate of recrystallization provided by R1 remains within the prescribed limits, although the temperature Trc is exceeded during R1.

If the intermediate annealing R1 preceding the last cold rolling LAF2 is insufficient to initiate recrystallization while the strip is at an intermediate thickness between the thickness of the hot-rolled strip and the final thickness of the cold-rolled strip, then this intermediate annealing R1 does not have the desired metallurgical effect, and everything happens as if, from the point of view of the problems that the invention aims to solve, there was no intermediate annealing, and that the or the cold rollings subsequent to the first of them constituted only additional passes constituting, taken together, a single cold rolling stage.

If more than three cold rolling sequences are performed and therefore at least two intermediate annealings Ri and R1, it is the last intermediate annealing R1, that is to say the one carried out before the last cold rolling LAF2 which precedes the final annealing Rf, which must satisfy these conditions required by the invention on the rate of recrystallization of the semi-finished product before Rf.

If we try to correlate the measurements of magnetic losses with some of the most classic microstructural characteristics such as the grain size, the share of fiber texture a or y. we don't get a clear result. However, it can be hypothesized that the more advanced texture isotropy provided by double cold rolling (see Table 5) would contribute to this improvement.

On the other hand, the experiment shows that an influence of the fraction recrystallized at the end of the intermediate annealing R1 is observed. This recrystallized fraction should not be too high. In other words, the stay of the strip in the useful length Lu of the annealing furnace, for a given temperature T greater than Trc, must not be too prolonged, which moreover reflects the relationship:

26°C.min < (T - Trc).Lu/V < 160°C.min, preferably 50°C.min < (T - Trc).Lu/V < 160°C.min which is one conditions of compliance with the invention.

However, if this recrystallization may be weak, it should not be zero.

A test was also carried out (last line of Table 6) on a sample which was not completely recrystallized before LAF1 (35% recrystallization rate), under the same operating conditions, with regard to LAF1, R1, LAF2 and Rf, than for the example according to the invention which precedes it in Table 6. It is observed in this example, with respect to the example according to the invention, that the texture component {111}<112> has a much greater preponderance on the final product, and that the magnetic losses are increased, probably due to this greater anisotropy of the texturing, which the double cold rolling that the invention includes did not make it possible to correct sufficiently.

For comparison, tests were carried out on samples of alloy 2 hot rolled and cooled under the same conditions as the preceding examples, but having undergone a single sequence of cold rolling LAF causing them to pass from 2.0 to 1.0 mm, followed by a final Rf anneal under the same conditions as the preceding examples.

They present magnetic losses after the final static Rf annealing of the order of 27 W/kg, which are therefore to be considered as too high to fulfill the objectives assigned to the invention.

This shows that the double rolling LAF1+LAF2, with an intermediate annealing R1 causing a very partial recrystallization and carried out under the conditions prescribed by the invention, makes it possible to substantially improve the magnetic losses of the metal, all other things being equal. A strip which remains mainly hardened, or even restored, before the final static Rf recrystallization annealing, does not exhibit the low magnetic losses of the strips treated according to the invention, all other things being equal. Comply with the condition that 26°C.min < (T - Trc).Lu/V < 160°C.min, preferably 50°C.min < (T - Trc).Lu/V < 160°C.min , makes it possible to ensure a sufficient recrystallization rate to lower the magnetic losses to the desired level.

It is not excluded that after the static Rf annealing which constitutes the final annealing in the examples which have been described, other thermal or thermomechanical treatments are carried out with the aim, for example, of improving the cuttability of a strip obtained after the static annealing, if these treatments do not deteriorate the targeted properties that have been cited.

Indeed, as we said, the final static Rf annealing can be carried out on parts cut from the cold rolled strip (for example rotors, stators, elements of transformer cores...). However, if it turns out that the cuttability of the cold-rolled and statically annealed strip is not sufficient for the intended application, the Rf static annealing can be carried out on the coiled cold-rolled strip, then carried out on the statically annealed strip a new annealing, this time on the run, under a reducing atmosphere (preferably pure hydrogen), under conditions of running speed and length and temperature of the furnace which allow the strip to reach a temperature of between 700 and 900°C for 10 s to 1 h, preferably 10 s to 20 min. This temperature corresponds to the disordered ferritic domain, which must be reached before the start of a sufficiently rapid temperature drop. It ends with relatively rapid cooling (at least 1000°C/hour). This new annealing and the subsequent cooling make it possible to improve the cuttability of the strip, and this proves advantageous for certain applications for which the final part (or an assembly of such final parts) must be cut with great precision or in difficult conditions. They have no influence on the texture of the tape. Beyond 900°C, a phase transformation would be obtained which would degrade the properties.

This is the case, in particular, when the final parts are electrotechnical parts, formed first by the superposition of individual parts larger than the final part, each coated with an insulating varnish and assembled by gluing to form an assembly multilayer. This multilayer assembly is then cut to its precise final dimensions, which can only be done easily if the unit parts have excellent cuttability, which only the last annealing in the run and the cooling that follows provide, in some cases.

Claims

1.- Process for manufacturing a strip or cold-rolled sheet of substantially equiatomic FeCo alloy, characterized in that:

- a hot-rolled sheet or strip is prepared with a thickness (e _H R) of between 1.5 and 2.5 mm, and whose composition consists, in weight percentages, of:

* 47.0% < Co < 51.0%; preferably 47.0% < Co < 49.5%;

* traces < V + W < 3.0%; preferably 0.5%<V+W<2.5%;

* traces < Ta + Zr < 0.5%;

* traces <Nb<0.5%, preferably traces <Nb<0.1%;

* traces < B < 0.05%; preferably traces <B<0.005%;

* traces < Si < 3.0%;

* trace < Cr < 3.0%;

* trace < Ni < 5.0%; preferably traces <Ni<0.1%;

* trace < Mn < 2.0%; preferably traces < Mn < 0.1%;

* traces < C < 0.02%; preferably traces <C<0.01%;

* traces < O < 0.03%; preferably traces <0 <0.01%;

* traces < N < 0.03%; preferably traces <N<0.01%;

* traces < S < 0.005%; preferably traces <S<0.002%;

*traces < P < 0.015; preferably traces <P<0.007%;

* traces < MB < 0.3%; preferably traces < Mo < 0.1%;

* traces < Cu < 0.5%; preferably traces <Cu<0.1%;

* traces < Al < 0.01%; preferably traces < Al < 0.002%;

* traces < Ti < 0.01%; preferably traces <Ti <0.002%;

* traces < Ca + Mg < 0.05%; preferably traces <Ca + Mg <0.001%;

* traces < rare earths < 500 ppm;

* the rest being iron and impurities resulting from processing;

- then an intermediate annealing (R1) is carried out as the strip or sheet passes through an annealing furnace, leading to partial recrystallization of the strip or sheet, said strip or sheet passing through said annealing furnace at one speed (V), the rate of partial recrystallization being 10 to 50%, preferably 15 to 40%, more preferably 15 to 30%, and where the temperature of the strip or sheet, in the useful zone of the furnace having a useful length (Lu), is comprised between Trc and 900°C, preferably between 700 and 880°C, the strip or sheet remaining in this useful zone (Lu) for 15 s to 5 min at a temperature (T) such as 26°C.min < ( T - Trc).Lu/V < 160°C.min, preferably 50°C.min

< (T - Trc).Lu/V < 160°C.min, with T and Trc in °C, Lu in m, V in m/min, and the strip or sheet is cooled on leaving the furnace at a rate at least 600° C./hour, preferably at least 1000° C./hour, better still at least 2000° C./hour, up to a temperature less than or equal to 200° C.;

2. A method according to claim 1, characterized in that (V + W) / 2 + (Ta + Zr) / 0.2> 0.8%, preferably> 1.0%.

3.- Method according to claim 1 or 2, characterized in that traces <Si <0.1%.

4.- Method according to one of claims 1 to 3, characterized in that traces < Cr

< 0.1%.

5.- Method according to one of claims 1 to 4, characterized in that, before said first cold rolling step (LAF1) is carried out at least one additional cold rolling cycle (LAFi) + intermediate annealing (Ri ) to bring the cold rolled strip or sheet to a thickness between its thickness after hot rolling (6HR) and the entry thickness of the first cold rolling (LAF1), the passage time of the strip in the zone useful temperature of the furnace, situated between Trc and 900°C, during each additional annealing (Ri), leading to total recrystallization of the strip or of the sheet, the intermediate annealings (Ri) having a residence time in the length zone Read from the oven, where the temperature of the strip is between Trc and 900° C., from 10 s to 10 min, and preferably between 15 s and 5 min, better still between 30 s and 5 min, and being followed by cooling of the strip or the sheet on leaving the oven at a rate of at least 600° C./hour, preferably at least 1000° C./hour, better still at least 2000° C./hour, down to a temperature less than or equal to 200° C., the strip or sheet having a 100% recrystallized microstructure after the last of said additional annealings (Ri).

6.- Method according to one of claims 1 to 5, characterized in that after the hot rolling and before the first cold rolling (LAF1) one proceeds to an annealing of the strip or hot rolled sheet, by cooling hot-rolled strip or sheet from a temperature between 800 and 1000°C at a speed of at least 600°C/s, preferably at least 1000°C/second, better still at least 2000°C /second, down to room temperature.

7.- Method according to claim 6, characterized in that said annealing takes place directly after hot rolling, without intermediate reheating.

8.- Method according to one of claims 1 to 7, characterized in that the atmospheres of the annealing furnaces are reducing atmospheres, preferably pure hydrogen.

9.- Method according to one of claims 5 to 8, characterized in that the at least one additional intermediate annealing is a scroll annealing of the strip or sheet, in an annealing furnace where the temperature of the strip or sheet , in the useful zone of the oven, is between Trc and 900° C., the strip remaining in this useful zone for 15 s to 5 min, and in that the strip or sheet is cooled at the outlet of the oven at a speed d at least 600° C./hour, preferably at least 1000° C./hour, better still at least 2000° C./hour, up to a temperature less than or equal to 200° C., and in that the at least one Additional cold rolling (LAFi) is performed in one or more passes, with an overall reduction rate of at least 40%.

10 - Method according to one of claims 1 to 9, characterized in that after the final static annealing (Rf), an additional annealing is carried out on the parade of the strip or sheet, so that the metal reaches at least 700 °C and at most 900°C, for at least 10 seconds and at most 1 h, preferably 10 s to 20 min, followed by cooling at a rate of at least 1000°C/hour.

11.- Substantially equiatomic FeCo alloy, characterized in that:

- its composition consists of, in weight percentages:

* 47.0% < Co < 51.0%; preferably 47.0% < Co < 49.5%;

* traces < V + W < 3.0%; preferably 0.5%<V+W<2.5%;

* traces < Ta + Zr < 0.5%;

* traces <Nb<0.5%, preferably traces <Nb<0.1%;

* traces < B <0.05%; preferably traces <B<0.005%; * traces < Si <3.0%; traces < Cr <3.0%; trace < Ni <5.0%; preferably traces <Ni<0.1%; trace < Mn <2.0%; preferably traces < Mn <0.1%; traces < C <0.02%; preferably traces <C<0.01%; traces < 0 <0.03%; preferably traces <0 <0.01%; traces < N <0.03%; preferably traces <N<0.01%; traces < S <0.005%; preferably traces <S<0.002%; trace < P <0.015; preferably traces <P<0.007%; traces < Mo <0.3%; preferably traces < Mo <0.1%; traces < Cu <0.5%; preferably traces <Cu<0.1%; traces < Al <0.01%; preferably traces < Al <0.002%; traces < Ti <0.01%; preferably traces <Ti <0.002%; traces < Ca + Mg <0.05%; preferably traces <Ca + Mg <0.001%; traces < rare earths < 500 ppm; the remainder being iron and impurities resulting from the elaboration; in that the microstructure of the alloy is completely recrystallized; and in that the texture of said alloy is as follows:

* 5 to 15%, preferably 6 to 11%, by surface or by volume, of {111}<110> component disoriented at a maximum of 15°;

* the rest of the material being made up of other texture components, disoriented by at most 15°, each representing a maximum of 15% in surface area or in volume, the covering of said other texture components with any of the components {001} <110>, {111}<112> and

{111}<110> not exceeding 10% in area and volume.

12.- Alloy according to claim 11, characterized in that (V + W) / 2 + (Ta + Zr) / 0.2> 0.8%, preferably> 1.0%.

13.- Alloy according to claim 11 or 12, characterized in that traces <Si <0.1%.

14.- Alloy according to one of claims 11 to 13, characterized in that traces <Cr <0.1%.

15.- Magnetic part cut from a substantially equiatomic FeCo alloy, characterized in that it results from the cutting of a strip or a sheet of alloy according to one of claims 11 to 14.

16.- Magnetic core in a substantially equiatomic FeCo alloy, characterized in that it is made from magnetic parts cut according to claim

15.