FR2772181A1 - METHOD FOR MANUFACTURING A NANOCRYSTALLINE SOFT MAGNETIC ALLOY MAGNETIC CORE FOR USE IN A CLASS A DIFFERENTIAL CIRCUIT BREAKER AND MAGNETIC CORE OBTAINED - Google Patents

Abstract

Production of a nanocrystalline soft magnetic iron-silicon-boron alloy magnetic core involves crystallization heat treatment of the amorphous alloy at 250-450 degrees C in a transverse magnetic field of rectangular waveform. Production of a magnetic core of nanocrystalline soft magnetic alloy, of composition more than 60 at.% Fe, 10-20 at.% Si, 0.1-2 at.% Cu, 5-20 at.% B and 0.1-10 at.% of one or more of Ti, Nb, Zr, Hf, V, Ta, Cr, Mo, W and Mn, the sum of Si + B being less than 30 at.%, involves crystallization heat treatment of the amorphous alloy at 250-450 degrees C in a transverse magnetic field of rectangular waveform. An Independent claim is also included for a magnetic core produced by the above process and exhibiting, for a 50 Hz alternating excitation magnetic field of 10 mA/cm maximum amplitude at 25 degrees C, an impedance magnetic permeability ( mu z) of greater than 200000, a remnant induction/saturation induction (Br/Bm) ratio of less than 0.2 and DELTA Bstat and DELTA Bdyn values of greater than 0.2 T.

Description

METHOD FOR MANUFACTURING A MAGNETIC ALLOY CORE

  NANOCRYSTALLINE SOFT MAGNETIC FOR USE IN A CIRCUIT BREAKER

  CLASS A DIFFERENTIAL AND MAGNETIC CORE OBTAINED.

  The present invention relates to a magnetic core of nanocrystalline soft magnetic alloy which can be used in particular for the manufacture of a differential circuit breaker of class A. Differential circuit breakers of class A are differential circuit breakers with their own current sensitive not only to sinusoidal fault currents, but also to pulsed fault currents. These differential circuit breakers comprise 0o a magnetic core of soft magnetic alloy having a maximum magnetic permeability of impedance pz at 50 Hertz high and a Br / Bm ratio of the residual induction to the saturation induction of less than 0.2, and a good temperature stability of magnetic properties in the operating temperature range from - 25 C to + 100 C. The maximum magnetic permeability s 5 of impedance pz must be high, because the higher it is, the more it is possible to reduce the dimensions of the magnetic core and therefore to miniaturize the differential circuit breaker; the Br / Bm ratio must remain low to preserve the sensitivity of the circuit breaker to pulsed currents. In addition, the sensitivity of the circuit breaker to pulsed fault currents is all the better as the quantities ABstat and ABdylyn are higher; ABstat and ABdyn being the amplitudes of variation of the magnetic induction generated by a half wave rectified alternating excitation field

  in the first case and full wave in the second.

  Magnetic cores for class A residual current devices can be manufactured using a soft magnetic alloy of the type comprising more than 60 atoms% of iron, copper, silicon, boron and an element chosen from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese. These magnetic cores are obtained by casting the alloy in the form of an amorphous ribbon which is wound to form a torus, then subjected to a crystallization heat treatment intended to give the alloy a nanocrystalline structure, and, finally, subjected to a heat treatment under transverse magnetic field applied continuously throughout the heat treatment, the heat treatment being around 400 C. The magnetic cores

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  thus obtained have a satisfactory temperature stability and a Br / Bm ratio of less than 0.2. However, they do not make it possible to obtain a magnetic permeability of impedance pz measured at 50 Hz in a maximum excitation field of 10 mA / cm (peak value) at 25 C greater than 170,000 or values of ABstat and s ABdyn greater than 0.19 Tesla for an excitation field with a maximum amplitude of

  mA / cm, which limits the possibilities of miniaturization.

  The object of the present invention is to remedy this drawback by proposing a means for manufacturing a magnetic core usable in a class A differential circuit breaker having both a magnetic permeability 0o of impedance pz measured at 50 Hz in a field d maximum excitation of mA / cm (peak value) greater than 200,000 and values of ABstat and ABdyn greater than 0.2 Tesla for an excitation field of maximum amplitude of

mA / cm.

  To this end, the subject of the invention is a process for the manufacture of a magnetic core made of nanocrystalline soft magnetic alloy whose chemical composition comprises more than 60 atoms% of iron, from 10 to 20 atoms% of silicon, from 0, 1 to 2 atom% of copper, 5 to 20 atom% of boron, 0.1 to 10 atom% of at least one element chosen from niobium, titanium, zirconium, hafnium, vanadium, tantalum , chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the production; the sum of the silicon and boron contents being less than 30 atom%; The nanocrystalline alloy being obtained by a heat treatment of crystallization of the alloy in the amorphous state. According to this method, a thermal treatment is carried out on the magnetic core under a transverse magnetic field at a temperature between 250 ° C. and 450 ° C., the

  magnetic field being applied in the form of slots.

  Preferably, the heat treatment under transverse magnetic field

  is carried out at a temperature between 300 C and 400 C.

  This process applies more particularly to soft nanocrystalline magnetic alloys, the chemical composition of which comprises from 10 to 17 atom% of silicon, from 0.5 to 1.5 atom% of copper, from 5 to 14 atom% of boron and of 2 at 4% of at least one element chosen from niobium, titanium, zirconium, hafnium,

  vanadium, tantalum, chromium, molybdenum, tungsten and manganese.

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  Before carrying out the heat treatment for crystallization of the alloy in the amorphous state, it is possible to carry out on the alloy in the amorphous state a relaxation heat treatment at a temperature below the temperature at the start of crystallization of the alloy in an amorphous state. Preferably, the thermal relaxation treatment consists in maintaining a temperature of between 250 ° C. and 480 ° C. for

  a time between 0.1 and 10 hours.

  The magnetic core obtained by the method according to the invention can advantageously be used for the manufacture of a class A own current differential circuit breaker. The invention will now be described in more detail and illustrated by a

example.

  To make a magnetic core made of nanocrystalline soft magnetic alloy, the alloy is cast in the form of an amorphous ribbon, then a segment of ribbon of suitable length is wound around a mandrel so as to form a toric coil of rectangular section or square. The coil which will constitute the magnetic core is then subjected to a crystallization heat treatment intended to destabilize the amorphous structure and to cause the formation of crystals whose size is less than 100 nanometers, or even less than 20 nanometers, and, thus, obtain a structure called "nanocrystalline". This treatment is then supplemented by a heat treatment under a transverse magnetic field, that is to say, under a magnetic field parallel to the axis of the core. The alloy is of the type described in particular in European patent applications EP 0 271 657 and EP 0 299 498. It consists mainly of iron in a content greater than 60 atom%, and also contains: - from 0.1 to 2 at%, and preferably 0.5 to 1.5 at% copper; - from 10 to 20 at%, and preferably, less than 17 at% of silicon; - from 5 to 20 at%, and preferably, less than 14 at% of boron; - from 0.1 to 10 at% of at least one element taken from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten

  and manganese; preferably 2 and 4 at% niobium.

  The alloy also contains impurities resulting from the production.

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  The sum of the silicon and boron contents should preferably remain

  less than 30 at% and, better still, remain less than 25 at%.

  The crystallization annealing consists in maintaining at a temperature higher than the temperature at the start of crystallization and lower than the temperature at the start of the appearance of the secondary phases which deteriorate the magnetic properties. In general, the crystallization annealing temperature is between 500 C and 600 C, but it can be optimized for each strip, for example, by determining by tests the temperature which leads to maximum magnetic permeability. The crystallization annealing temperature can then be

  io chosen equal to this temperature.

  The heat treatment carried out under a magnetic field is carried out at a temperature between 250 C and 450 C, and preferably between 300 C and 400 C. During the temperature maintenance, the magnetic field is applied in the form of a succession of slots. A slot corresponds to a period during which the magnetic field applied is maximum, followed by a period during which it is zero or very weak (less than 10% of the maximum magnetic field reached during treatment). The magnetic field applied can be continuous or alternating, in the latter case, the intensity of the magnetic field is the peak intensity (maximum intensity reached at each half-wave). The intensity of the magnetic field can be constant during the entire period of application of the field (rectangular slots) or variable. All slots can be of the same intensity or, on the contrary, of varying intensity from one slot to another. The heat treatment can end at the end of the period of application of the magnetic field of the last slot; the main thing being that the treatment comprises at least two periods during which the magnetic field applied separated by a period during which the magnetic field is not applied. The inventors have in fact found that by doing so, the temperature stability of the magnetic properties of the magnetic core is very significantly improved. By this process, a magnetic core is obtained, the magnetic permeability of impedance pz measured at 50 Hertz in a magnetic field of maximum excitation of 10 mA / cm (peak value) at 25 C is greater than

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  000, and whose magnetic permeability varies by less than 25% over the temperature range between - 25 C and + 100 C. In addition, the Br / Bm ratio of the residual induction to the saturation induction is less than 0.2, ABstat and ABdyn

  are both greater than 0.2 Tesla, the ABstat / ABdyn ratio being close to 1.

  Such a magnetic core can be used in a class A differential circuit breaker. Due to its magnetic properties, at equal sensitivity of the circuit breaker, the section of the core can be reduced significantly compared to the section of a core

magnetic according to the prior art.

  In addition to the heat treatments which have just been described, it is possible, 0 ° before the crystallization heat treatment, to carry out a relaxation heat treatment on the core at a temperature below the temperature at the start of crystallization of the amorphous band, and, preferably between 250 ° C. and 480 ° C. This relaxation annealing has the advantage of further reducing the sensitivity of the magnetic properties of the cores to temperature, of reducing the dispersion of the magnetic properties of cores produced in series and of reducing the sensitivity of the

  magnetic properties under stress.

  For example, from a Fe73.5Si13.5B9Cu1Nb3 alloy ribbon (73.5 at% iron, 13.5 at% silicon, etc.), 20 μm thick and 10 mm in width obtained by direct quenching on a cooled wheel, two series A and B of magnetic cores were manufactured, which were both subjected to a 1 hour crystallization treatment at 530 ° C. (without relaxation treatment). By way of comparison, the first series A of cores was subjected to a 1 hour heat treatment at 350 ° C. under a transverse magnetic field applied continuously. In accordance with the invention, the other series, B, was subjected to a heat treatment of 1 hour at 350 under transverse magnetic field applied in the form of slots of 5 min under magnetic field separated by periods of 15 min without magnetic field . For one of the series, the quantities pz, ABstat and ABdyn were measured at C for a magnetic field of alternating excitation at 50 Hertz with a maximum amplitude of 10 mA / cm; the Br / Bm ratio was also measured. The results were as follows:

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  series || p (10 mA / cm ABstat (T) ABdyn (T) [ABstat / ABdyn Br / Bm A compare 153,000 0.172 0.169 1.017 0.05 B invention 230,000 0.240 0.234 1.025 0.1 These examples clearly show l improvement of magnetic properties provided by the process according to the invention: pz greater than 200,000, ABstat and ABdyn

  greater than 0.2 Tesla, with ABstat / ABdyn close to 1 and Br / Bm less than 0.2.

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Claims (7)

  1 - Process for the manufacture of a magnetic core of soft nanocrystalline magnetic alloy whose chemical composition comprises more than 60 atoms% of iron, from 10 to 20 atoms% of silicon, from 0.1 to 2 atoms% of copper, 5 to 20 atom% of boron, from 0.1 to 10 atom% of at least one element chosen from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the production, the sum of the silicon and boron contents being less than 30 atom%, the nanocrystalline alloy being obtained by a heat treatment of crystallization of the alloy in the state amorphous, characterized in that a thermal treatment is carried out on the magnetic core under a transverse magnetic field at a temperature between 250 C and 450 C, the magnetic field being applied in the form of slots.   2 - Method according to claim 1 characterized in that the heat treatment under transverse magnetic field is carried out at a temperature between 300 C and 400 C.   3 - Process according to claim 1 or claim 2 characterized in that the chemical composition of the nanocrystalline soft magnetic alloy comprises from 10 to 17 atoms% of silicon, from 0.5 to 1.5 atoms% of copper, of 5 with 14 atom% boron and from 2 to 4% of at least one element chosen from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese.   4 - Method according to any one of claims 1 to 3 characterized in that   that, before carrying out the thermal treatment for crystallization of the alloy in the amorphous state, a thermal relaxation treatment is carried out on the alloy in the amorphous state at a temperature below the temperature at the start of crystallization of the alloy in the amorphous state.   5 - Method according to claim 4 characterized in that the thermal relaxation treatment consists of maintaining at a temperature between   250 C and 480 C for a time between 0.1 and 10 hours. 8 2772181   6 - Magnetic core made of nanocrystalline soft magnetic alloy whose chemical composition includes more than 60 atoms% of iron, 10 to 20 atoms% of silicon, 0.1 to 2 atoms% of copper, 5 to 20 atoms% of boron , from 0.1 to atom% of at least one element taken from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the preparation, the sum of the silicon and boron contents being less than 30 atom%, the nanocrystalline alloy being obtained by a heat treatment of crystallization of the alloy in the amorphous state, characterized in that, for an alternating excitation magnetic field at 50 Hertz with a maximum amplitude of 10 mA / cm, at 25 C, the magnetic permeability of impedance pz is greater than 200,000, the Br / Bm ratio of the remanent induction Br to l induction at saturation Bm less than 0.2 and the quantities ABstat and ABdyn s have greater than 0.2 Tesla.   7 - Use of a magnetic core according to claim 6 for the manufacture of a class A own current differential circuit breaker.