EP0921541B1 - Fabrication process of a soft nanocrystalline magnetic core for 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 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

The present invention relates to a magnetic core of magnetic alloy soft nanocrystalline usable in particular for the manufacture of a circuit breaker Class A differential.

Class A RCDs are self-contained RCDs sensitive not only to sinusoidal fault currents, but also to pulsed fault currents. These differential circuit breakers comprise a magnetic core of soft magnetic alloy having a maximum magnetic permeability of impedance μ _z at 50 Hertz high and a Br / Bm ratio of the residual induction to the induction at saturation 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 of impedance µ _z 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 residual current device; ; 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 magnitudes ΔB _stat and ΔB _dyn are higher; ΔB _stat and ΔB _dyn 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 selected 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 magnetic field parallel to the axis of the core applied continuously throughout the heat treatment, the heat treatment taking place at around 400 ° C. The magnetic cores 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 µ _z impedance measured at 50 Hz in a maximum excitation field of 10 mA / cm (peak value) at 25 ° C greater than 170,000 nor values of ΔB _stat and ΔB _dyn greater than 0.19 Tesla for an excitation field with a maximum amplitude of 10 mA / cm, which limits the possibilities of miniaturization.

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

The aim of the present invention is to remedy this drawback in The aim 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 magnetic permeability impedance µ _z measured at 50 Hz in a maximum excitation field of 10 mA / cm (peak value) greater than 200,000 and values of ΔB _stat and ΔB _dyn greater than 0.2 Tesla for a field of maximum amplitude excitation of 10 mA / cm.

To this end, the invention relates to a process for the manufacture of a core magnetic nanocrystalline soft magnetic alloy with a chemical composition contains more than 60 atom% of iron, from 10 to 20 atom% of silicon, from 0.1 to 2 atom% of copper, 5 to 20 atom% of boron, 0.1 to 10 atom% of at least minus one element taken from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, as well only impurities resulting from processing; the sum of the silicon and boron being less than 30 atom%; the nanocrystalline alloy being obtained by a heat treatment for crystallization of the alloy in an amorphous state. According to this process, a thermal treatment is carried out on the magnetic core magnetic parallel to the axis of the core at a temperature between 250 ° C and 450 ° C, the magnetic field being applied in the form of slots.

Preferably, the heat treatment under magnetic field parallel to the axis of the core is carried out at a temperature between 300 ° C and 400 ° C.

This process applies more particularly to soft magnetic alloys nanocrystalline whose chemical composition contains from 10 to 17 atom% of silicon, from 0.5 to 1.5 atom% of copper, from 5 to 14 atom% of boron and from 2 to 4% at least one element taken from niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese.

Before carrying out the heat treatment of crystallization of the alloy in the state amorphous, one can carry out on the alloy in the amorphous state a heat treatment of relaxation at a temperature below the temperature at the start of crystallization of the alloy in the amorphous state. Preferably, 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.

The magnetic core obtained by the process according to the invention can be used advantageously for the manufacture of a differential circuit breaker with its own current class A.

The invention will now be described in more detail and illustrated by a example.

• 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 niobium, le titane, 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 .

L'alliage contient également des impuretés résultant de l'élaboraton. 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 magnetic field parallel to the axis of the core, 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:

• 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% silicon;
• from 5 to 20 at%, and preferably less than 14 at% boron;
• from 0.1 to 10 at% of at least one element chosen 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.

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 of maintaining at a temperature higher than the start of crystallization temperature and lower than the temperature from the onset of secondary phases which deteriorate the properties magnetic. In general, the crystallization annealing temperature is understood between 500 ° C and 600 ° C, but it can be optimized for each ribbon, by example, by determining by tests the temperature which leads to permeability maximum magnetic. The crystallization annealing temperature can then be chosen equal to this temperature.

The heat treatment carried out under magnetic field is carried out at a temperature between 250 ° C and 450 ° C, and preferably between 300 ° C and 400 ° C. During temperature maintenance, 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 maximum, followed by a period during which it is zero or very weak (less than 10% of the magnetic field reached during treatment). The magnetic field applied for a period can be continuous or alternating, in the latter case, the intensity of the magnetic field is peak intensity (maximum intensity reached at each alternation). The intensity of magnetic field can be constant during the entire period of application of the field (rectangular slots) or variable. All slots can be from same intensity or on the contrary of variable intensity from one niche to another. The heat treatment can end at the end of the field application period magnetic of the last slot; the main thing is that the treatment involves at least two periods during which the applied magnetic field separated by a period during which the magnetic field is not applied. The the inventors have in fact found that by doing so, the temperature stability magnetic properties of the magnetic core were very noticeably improved.

By this process, a magnetic core is obtained, the magnetic permeability of impedance µ _z measured at 50 Hertz in a magnetic field of maximum excitation of 10 mA / cm (peak value) at 25 ° C is greater than 200,000, 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, ΔB _stat and ΔB _dyn are both greater than 0.2 Tesla, the ΔB _stat / ΔB _dyn 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, before the crystallization heat treatment, carry out a treatment on the core thermal relaxation at a temperature below the start temperature 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 magnetic properties of cores at temperature, reduce the dispersion of magnetic properties of mass-produced cores and reduce the sensitivity of magnetic properties under stress.

For example, from a strip of Fe _73.5 Si _13.5 B ₉ Cu ₁ Nb ₃ alloy (73.5 at% iron, 13.5 at% silicon, etc.), 20 µm thick and 10 mm wide obtained by direct quenching on a cooled wheel, two series A and B of magnetic cores were produced, 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 heat treatment for 1 hour at 350 ° C. under a magnetic field parallel to the axis of the core applied continuously. In accordance with the invention, the other series, B, was subjected to a heat treatment of 1 hour at 350 under magnetic field parallel to the axis of the core applied in the form of slots of 5 min under magnetic field separated by periods 15 min without magnetic field. For one of the series, the magnitudes µ _z , ΔB _stat and ΔB _dyn were measured at 25 ° C for an alternating magnetic excitation field at 50 Hertz with a maximum amplitude of 10 mA / cm; the Br / Bm ratio was also measured. The results were as follows: series µ (10 mA / cm ° ΔB _stat (T) ΔB _dyn (T) ΔB _stat / ΔB _dyn Br / Bm To 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 the improvement in magnetic properties provided by the method according to the invention: μ _z greater than 200,000, ΔB _stat and ΔB _dyn greater than 0.2 Tesla, with ΔB _stat / ΔB _dyn close to 1 and Br / Bm less than 0.2.

Claims (7)

1. Process for manufacturing a magnetic core from a nanocrystalline soft magnetic alloy, the chemical composition of which comprises more than 60 at% iron, 10-20 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 niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the smelting, the sum of the silicon and boron contents being less than 30AT% and the nanocrystalline alloy being obtained by a crystallization heat treatment of the alloy in the amorphous state, characterized in that a heat treatment is carried out on the magnetic core in a magnetic field parallel to the axis of the core at a temperature between 250°C and 450°C, the magnetic field being applied in the form of square pulses.
2. Process according to Claim 1, characterized in that the heat treatment in a magnetic field parallel to the axis of the core 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 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 niobium, titanium, 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 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, 10-20 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 niobium, titanium, zirconium, hafnium, vanadium, tantalum, chromium, molybdenum, tungsten and manganese, as well as impurities resulting from the smelting, the sum of the silicon and boron contents being less than 30 at%, it being possible to obtain the nanocrystalline alloy by a crystallization heat treatment of the alloy in the amorphous state in a field parallel to the axis of the core, characterized in that, for a 50 Hz AC excitation magnetic field with a maximum amplitude of 10 mA/cm, at 25°C, the impedance magnetic permeability µ_z is greater than 200 000, the ratio B_r/B_m of the remnant induction B_r to the saturation induction B_m is less than 0.2 and the quantities ΔB_stat and ΔB_dyn are greater than 0.2 tesla.
7. Use of a magnetic core according to Claim 6 for the manufacture of a Class A residual-current circuit breaker.