EP0921540B1 - Fabrication process of a magnetic core of a soft magnetic nanocrystalline alloy and use in a differential circuit breaker - Google Patents

Abstract

Production of a nanocrystalline soft magnetic iron-silicon-boron alloy magnetic core involves crystallization heat treatment of the amorphous alloy at 150-400 degrees C in a transverse magnetic field of rectangular waveform. Production of a magnetic core of nanocrystalline soft magnetic alloy, containing 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 to obtain a core having a maximum impedance magnetic permeability ( mu z) with a value of 350000 at 50 Hz and 25 degrees C and with a variation of less than 25% over the -25 to +100 degrees C range. The novelty is that the core is heat treated at 150-400 degrees C in a transverse magnetic field of rectangular waveform.

Description

The present invention relates to a magnetic core made of nanocrystalline soft magnetic alloy that can be used, in particular, for the manufacture of a differential breaker of class AC.

AC class differential circuit breakers are differential circuit breakers sensitive to sinusoidal fault currents. They comprise in particular a magnetic core of soft magnetic alloy for which one seeks both a high magnetic permeability μ and a very good temperature stability of this magnetic permeability. Given a given magnetic core size, the sensitivity of the differential circuit breaker is all the better as the magnetic permeability is high; this permeability must be stable in the operating temperature range of the GFCI (generally from -25 ° C to + 100 ° C) so as to obtain good operational safety.

The magnetic cores for AC class AC circuit breakers are made of a soft magnetic alloy of the type Fe-Ni 20-80, stabilized by annealing. This technique has the disadvantage of not making it possible to reliably obtain magnetic maximum impedance permeabilities μ _z substantially greater than 300 000, which limits the possibilities of reducing the size of the magnetic cores, and therefore, of the dimension of the differential circuit breakers.

Nano-crystalline soft magnetic alloys of the type comprising more than 60% iron, copper, silicon, boron and one of titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, the molybdenum, tungsten and manganese have the advantage of allowing to obtain maximum impedance magnetic permeabilities μ _z greater than 300 OOC, which would make it possible to manufacture magnetic cores for circuit breakers of the AC class of substantially reduced size. . These magnetic cores are obtained by casting the alloy in the form of an amorphous ribbon, which is wound to form a torus, and then subjected to a crystallization heat treatment intended to give the alloy a nanocrystalline structure. However, magnetic cores of this type have insufficient temperature stability: at 100 ° C. permeability magnetic is less than 40% lower than the magnetic permeability at 25 ° C; they can not therefore be used for the manufacture of miniaturized differential circuit breakers.

EP 0563606 discloses a current transformer for differential circuit breaker of the kind comprising a magnetic core toroid can be made of a soft magnetic iron-based alloy composed more than 50% of fine crystal grains less than 100 nm in size and comprising, in addition to an iron content of greater than 60% (at), 0.5 to 2% of copper, at least 2% to 5% of one of the following metals niobium, tungsten, tantalum, zirconium, hafnium , titanium and / or molybdenum, 5 to 14% boron and 14 to 17% silicon

WO 96/33595 discloses an intensity transformer, in particular for a pulsed current sensitive fault current differential tripping device, of the type comprising a magnetic core toroid which can be made of a soft magnetic iron-based alloy composed of more than 50 % of fine-crystal grains less than 100 nm in size and comprising, in addition to an iron content of greater than 60% (at), 0.5 to 2% of copper, at least 2 to 5% of one of the following metals niobium, tungsten, tantalum, zirconium, hafnium, titanium and / or molybdenum, 5 to 14% boron and 14 to 17% silicon.

DE 4,019,636 describes a method for improving the magnetic properties of amorphous ferromagnetic materials by continuously subjecting them to an alternating magnetic field whose frequency is between 50 and 50 kHz, sinusoidal, at right angles or triangular and whose the current density is between 10 and 500 A / cm ² .

The object of the present invention is to overcome this disadvantage by proposing a means for manufacturing a magnetic core used in a differential circuit breaker of the AC class of reduced dimensions.

To this end, the subject of the invention is a process for the manufacture of a magnetic core made of nanocrystalline soft magnetic alloy, the chemical composition of which comprises more than 60% iron atoms, from 10 to 20% silicon atoms, and 1 to 2 atoms% copper, 5 to 20 atoms% boron, 0.1 to 10 atoms% of at least one element selected from titanium, niobium, zirconium, hafnium, vanadium, tantalum chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the elaboration; the sum of the silicon and boron contents being less than 30% atoms; the nanocrystalline alloy being obtained by a crystallization heat treatment of the alloy in the amorphous state; the magnetic core having a maximum impedance magnetic permeability μ _z at 50 Hertz, at 25 ° C, greater than 350,000, this maximum magnetic permeability impedance μ _z varying by less than 25% over the temperature range between - 25 ° C and + 100 ° C. According to this method, a magnetic heat treatment is carried out on the magnetic core in a magnetic field parallel to the axis of the core at a temperature of between 150 ° C. and 400 ° C., the magnetic field being applied in the form of crenellations.

Preferably, the heat treatment in a magnetic field parallel to the axis of the core is carried out at a temperature between 200 ° C and 350 ° C.

Also preferably, 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, from 5 to 14 atoms of boron and from 2 to 4 % of at least one of titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese.

Before carrying out the crystallization heat treatment 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 crystallization start temperature of the alloy in the amorphous state. For example, the relaxation heat treatment can consist in maintaining at a temperature between 250 ° C and 480 ° C for a time between 0.1 and 10 hours.

The magnetic core obtained by this method can advantageously be used for the manufacture of a current-class differential circuit breaker of the AC class.

The invention will now be described more precisely, but not limitatively, and illustrated by examples.

• de 0,1 à 2 at %, et de préférence, de 0,5 à 1,5 at % de cuivre ;
• de 10 à 20 at %, et de préférence, moins de 17 at % de silicium ;
• de 5 à 20 at %, et de préférence, moins de 14 at % de bore ;
• de 0,1 à 10 at % d'au moins un élément pris parmi le titane, le niobium, le zirconium, le hafnium, le vanadium, le tantale, le chrome, le molybdène, le tungstène et le manganèse ; de préférence de 2 et 4 at % de niobium.

To fabricate a nanocrystalline soft magnetic alloy magnetic core, the alloy is cast as an amorphous ribbon, and then a ribbon segment of appropriate length is wound around a mandrel to form a rectangular section toroidal coil or square. The coil that 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 to obtain a structure called "nanocrystalline". This treatment is then supplemented by a heat treatment in a magnetic field parallel to the axis of the core. The alloy is of the type described in particular in the European patent applications EP 0 271 657 and EP 0 299 498. It consists mainly of iron in a content greater than 60 atoms%, and further contains:

• from 0.1 to 2 at%, and preferably from 0.5 to 1.5 at% copper;
• from 10 to 20 at%, and preferably less than 17 at% silicon;
• from 5 to 20 at%, and preferably less than 14 at% boron;
• from 0.1 to 10 at% of at least one of titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese; preferably 2 and 4 at% niobium.

The sum of the silicon and boron contents should preferably be less than 30 at% and more preferably less than 25 at%.

Crystallization annealing consists of maintaining at a temperature above the crystallization start temperature and lower than the onset temperature 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 ribbon, for example, by determining by testing the temperature that leads to the maximum magnetic permeability.

The heat treatment carried out under a magnetic field is carried out at a temperature of between 150 ° C. and 400 ° C., and preferably between 200 ° C. and 300 ° C. During the maintenance of temperature, the magnetic field is applied in the form of a succession of slots. A slot corresponds to a period during which the applied magnetic field is maximal, followed by a period during which it is null or very weak (less than 10% of the maximum magnetic field reached during the treatment). The magnetic field applies during a period may be continuous or alternating, in the latter case the intensity of the magnetic field is the peak intensity (maximum intensity reached at each alteremance). The intensity of the magnetic field can be constant during the whole period of application of the field (rectangular crenels) or variable. All the slots can be of the same intensity or on the contrary of variable intensity from one niche to another. The heat treatment may end at the end of the period of application of the magnetic field of the last slot; the essential point being that the treatment comprises at least two periods during which the magnetic field is applied separated by a period during which the magnetic field is not applied. The inventors have indeed found that by doing so, the temperature stability of the magnetic properties of the magnetic core were very substantially improved.

By this method there is obtained a magnetic core whose maximum magnetic impedance permeability μ _z at 50 Hertz, for an alternating excitation magnetic field of 8 mA / cm (peak value), at 25 ° C is greater than 350 000 or 400,000, this magnetic permeability varying from less than 25% between -25 ° C and + 100 ° C. Such a magnetic core can be used in a class AC differential circuit breaker. Because of its high magnetic permeability, at equal sensitivity of the circuit breaker, the core section can be substantially reduced with respect to the section of a Fe-Ni alloy magnetic core according to the prior art.

In addition to the thermal treatments which have just been described, it is possible, before the crystallization heat treatment, to carry out on the core a heat treatment for relaxation at a temperature below the crystallization start temperature of the amorphous strip, and preference; 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, reducing the dispersion of the magnetic properties of series-produced cores and reducing the sensitivity of the cores. magnetic properties to constraints.

By way of example, from a ribbon of Fe _73.5 Si _13.5 BgCu ₁ Nb ₃ alloy, (73.5 at% iron, 13.5 at% silicon, etc.), 20 Thickness and width of 10 mm obtained by direct quenching on a cooled wheel, three magnetic reactor series A, B, C were produced which were subjected to a 3-hour crystallization treatment at 530 ° C. (without relaxation treatment). By way of comparison, the first series A of cores was not subjected to heat treatment in a magnetic field parallel to the axis of the core. According to the invention, the other two series B and C were subjected to a heat treatment in a magnetic field parallel to the axis of the core applied in the form of slots: 3 periods of 5 minutes in a magnetic field separated from one of the other by periods of 15 minutes without magnetic field. For one series, B, the treatment temperature was 200 ° C, and for the other, C, the treatment temperature was 300 ° C. Of the three series of magnetic cores, the maximum impedance magnetic permeability μ _z measured at 50 Hz was measured in a maximum excitation field of 8 mA / cm (peak value) at 25 ° C, at -25 ° C , at + 80 ° C and + 100 ° C, the ratio Δμ / μ representing the variations of μ _z with respect to its value at 25 ° C. The results were as follows: series μ (25 ° C: 8 mA / cm) Δμ / μ -25 ° C (%) Δμ / μ +80 ° C (%) Δμ / μ +100 ° C (%) A (comparison) 700,000 - 20% - 30 % - 45% B 555,000 - 12% - 8% - 15% VS 380000 - 5% - 5% - 8%

These examples show that if the series A has excellent magnetic permeability, its temperature stability is insufficient. By contrast, Examples B and C have lower permeability, but nevertheless very satisfactory, and exhibit good temperature stability of the magnetic permeability.

Claims (7)

1. Process for manufacturing a magnetic core made of a nanocrystalline soft magnetic alloy, the chemical composition of which comprises more than 60 at% iron, 10 to 20 at% silicon, 0.1 to 2 at% copper, 5 to 20 at% boron and 0.1 to 10 at% of at least one element taken from titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, and also impurities resulting from the smelting, the sum of the silicon and boron contents being less than 30 at%, the nanocrystalline alloy being obtained by a crystallization heat treatment of the alloy in the amorphous state, characterized in that the magnetic core has a maximum impedance permeability µ_z at 50 hertz, at 25°C, of greater than 350 000, this maximum impedance permeability µ_z varying by at least 25% over the temperature range between -25°C and +100°C, and in that a heat treatment in a magnetic field is carried out on the magnetic core at a temperature between 150°C and 400°C, the magnetic field being applied in the form of pulses.
2. Process according to Claim 1, characterized in that the heat treatment in a magnetic field is carried out at a temperature between 200°C and 350°C.
3. Process according to Claim 1 or Claim 2, characterized in that the chemical composition of the nanocrystalline soft magnetic alloy comprises 10 to 17 at% silicon, 0.5 to 1.5 at% copper, 5 to 14 at% boron and 2 to 4% of at least one element taken from titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese.
4. Process according to any one of Claims 1 to 3, characterized in that, before the crystallization heat treatment of the alloy in the amorphous state is carried out, a relaxation heat treatment is carried out on the alloy in the amorphous state at a temperature below the crystallization onset temperature of the alloy in the amorphous state.
5. Process according to Claim 4, characterized in that the relaxation heat treatment consists of a soak at a temperature between 250°C and 480°C for a time of between 0.1 and 10 hours.
6. Magnetic core made of a nanocrystalline soft magnetic alloy, the chemical composition of which comprises more than 60 at% iron, 10 to 20 at% silicon, 0.1 to 2 at% copper, 5 to 20 at% boron and 0.1 to 10 at% of at least one element taken from titanium, niobium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, and also impurities resulting from the smelting, the sum of the silicon and boron contents being less than 30 at%, the nanocrystalline alloy being obtained by a crystallization heat treatment of the alloy in the amorphous state, characterized in that the magnetic core has a maximum impedance permeability µ_z at 50 hertz, at 25°C, of greater than 350 000, this permeability varying by at least 25% over the temperature range between -25°C and +100°C.
7. Use of a magnetic core according to Claim 6 for the manufacture of a Class AC residual current circuit breaker.