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  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
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  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/84—Controlled slow cooling
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  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/007—Heat treatment of ferrous alloys containing Co
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  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
  • C21D8/1266—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest between cold rolling steps
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  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
  • C21D8/1272—Final recrystallisation annealing
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  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
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  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/02—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working in inert or controlled atmosphere or vacuum
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
  • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
  • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
  • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
  • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
  • H01F1/16—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys in the form of sheets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
  • H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
  • H01F41/0206—Manufacturing of magnetic cores by mechanical means
  • H01F41/0233—Manufacturing of magnetic circuits made from sheets
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  • C21D2201/00—Treatment for obtaining particular effects
  • C21D2201/05—Grain orientation
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  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
  • C21D8/1222—Hot rolling
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  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Definitions

• 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.
• 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.
• VIM Vacuum Induction melting
• VIM vacuum arc remelting
• VAR Vauum Arc Remelting
• 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.
• 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.
• 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.
• Table 2 Coercive field and magnetic loss measurements performed on the reference samples in Table 1
• 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.
• 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:
• LAF1 cold rolling
• TR1 overall reduction rate
• an intermediate annealing 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
• 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;
• 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.
• 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
• 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 %.
• LAFi additional cold rolling
• 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:
• composition consists of, in weight percentages:
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• traces 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%.
• 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).
• 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.
• 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.
• the Nb content is between traces and 0.5%, preferably between traces and 0.1%.
• 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.
• 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.
• 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).
• 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.
• 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.
• 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.
• 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.
• 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).
• 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).
• VI M vacuum melting of the raw materials
• VAR vacuum remelting
• ESR under slag
• 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
• VAR, ESR Remelting operations
• 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.
• 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.
• 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).
• t u 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.
• Trc critical recrystallization temperature Trc, from which the material begins its recrystallization
• Trc 600°C.
• 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.
• 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.
• 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;
• 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-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.
• 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.
• 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.
• 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
• 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.
• 900°C 900°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.
• 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.
• 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.
• the speed For an industrial furnace of the order of one meter in length, the speed must be greater than 0.1 m/min.
• 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.
• the processing furnace on the parade used can be of any type.
• 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.
• the strip On leaving the oven, the strip must be cooled at a sufficiently high rate to avoid a total order-disorder transformation during cooling.
• 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 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.
• 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.
• 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:
• 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%.
• 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.
• 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.
• 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.
• 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:
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• component ⁇ 001 ⁇ 110> disoriented at a maximum of 15° (component A 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.
• 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],
• 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:
• 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.
• 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).
• 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.
• 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.
• 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).
• 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.

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