EP0848397B1 - Manufacturing process of a soft magnetic iron based alloy component with nanocristalline structure - Google Patents

Abstract

The production of a magnetic component from a nanocrystalline iron based soft magnetic alloy of composition (in at. %) ≥ 60 % Fe, 0.1-3 % Cu, 0-25 % B, 0-30 (preferably ≤ 14) % Si, 0.1-30 % one or more of Nb, W, Ta, Zr, high-frequency, Ti and Mo and balance impurities, the sum of Si + B being 5-30 %, involves producing a toroidal preform by winding an amorphous strip of the alloy around a mandrel and carrying out one or more crystallisation anneal processes at 500-600 degrees C for 0.1-10 hrs. to form nanocrystals. The novelty comprises carrying out a relaxation heat treatment at below the crystallisation start temperature prior to crystallisation annealing.

Description

The present invention relates to the manufacture of magnetic components in soft magnetic alloy based on iron having a nanocrystalline structure.

Nanocrystalline magnetic materials are well known and have been described, in particular, in European patent applications EP 0 271 657 and EP 0 299 498. These are iron-based alloys, containing more than 60 at% (atoms%) of iron, copper, silicon, boron, and possibly at least one element taken among niobium, tungsten, tantalum, zirconium, hafnium, titanium and molybdenum, cast in the form of amorphous ribbons and then subjected to a treatment which causes extremely fine crystallization (the crystals have less 100 nanometers in diameter). These materials have magnetic properties particularly suitable for the manufacture of soft magnetic cores for electrotechnical devices such as earth leakage circuit breakers. In particular, they have excellent magnetic permeability and can exhibit either a cycle round hysteresis (Br / Bm ≥ 0.5), i.e. a coated hysteresis cycle (Br / Bm ≤ 0.3); Br / Bm being the ratio of remanent magnetic induction to magnetic induction Max. Round hysteresis cycles are obtained when treatment thermal consists of a simple annealing at a temperature between 500 ° C and 600 ° C. The lying hysteresis cycles are obtained when the treatment thermal includes at least one annealing under magnetic field, this annealing can be the annealing intended to cause the formation of nanocrystals.

Nanocrystalline ribbons, or more precisely, magnetic components produced with these ribbons, however, have a drawback which limits their use. This drawback is insufficient stability of the magnetic properties when the temperature rises above room temperature. This stability insufficient results in unreliability of circuit breaker operation differentials fitted with such magnetic cores.

The object of the present invention is to remedy this drawback by providing a means for manufacturing magnetic cores from material nanocrystalline having magnetic properties whose temperature stability is significantly improved.

• on fabrique avec l'alliage magnétique un ruban amorphe,
• avec le ruban on fabrique une ébauche de composant magnétique,
• et on soumet le composant magnétique à un traitement thermique de cristallisation comprenant au moins un recuit de cristallisation à une température comprise entre 500°C et 600°C pendant un temps de maintien compris entre 0,1 et 10 heures, afin de provoquer la formation de nanocristaux, et, avant d'effectuer le traitement thermique de cristallisation, on réalise un traitement thermique de relaxation à une température inférieure à la température de début de recristallisation de l'alliage amorphe.

To this end, the subject of the invention is a method for manufacturing a magnetic component made of a soft magnetic alloy based on iron having a nanocrystalline structure whose chemical composition comprises, in atoms%, Fe ≥ 60%, 0.1% ≤ Cu ≤ 3%, 0% ≤ B ≤ 25%, 0% ≤ Si ≤ 30%, and at least one element selected from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum in contents of between 0.1% and 30%, the remainder being impurities resulting from the preparation, the composition also satisfying the relationship 5% ≤ Si + B ≤ 30%, according to which:

• an amorphous ribbon is made with the magnetic alloy,
• with the ribbon we make a blank of magnetic component,
• and the magnetic component is subjected to a crystallization heat treatment comprising at least one crystallization anneal at a temperature between 500 ° C and 600 ° C for a holding time between 0.1 and 10 hours, in order to cause the formation nanocrystals, and before performing the crystallization heat treatment, a relaxation heat treatment is carried out at a temperature below the temperature at the start of recrystallization of the amorphous alloy.

The thermal relaxation treatment can be a maintenance for a time between 0.1 and 10 hours, at a temperature between 250 ° C and 480 ° C.

The relaxation heat treatment can also consist of a progressive heating from room temperature to a temperature greater than 450 ° C, at a heating rate between 30 ° C / hour and 300 ° C / hour between 250 ° C and 450 ° C.

According to the desired magnetic properties, in particular according to the shape desired for the hysteresis cycle, and in accordance with the state of the art, at least one annealing constituting the heat treatment can be carried out under magnetic field.

This process applies more particularly to soft magnetic alloys with iron base having a nanocrystalline structure, the chemical composition of which is such that Si ≤ 14%.

The invention will now be described in more detail, but not in detail. limiting and illustrated by examples.

• de 0,1 à 3 at %, et de préférence, de 0,5 à 1,5 at % de cuivre ;
• de 0,1 à 30 at %, et, de préférence, de 2 à 5 at % d'au moins un élément pris parmi le niobium, le tungstène, le tantale, le zirconium, le hafnium, le titane, et le molybdène ; de préférence, la teneur en niobium est comprise entre 2 et 4 at % ;
• du silicium et du bore, la somme des teneurs en ces éléments étant comprise entre 5 et 30 at %, et, de préférence, entre 15 et 25 at % ; la teneur en bore pouvant aller jusqu'à 25 at %, et, de préférence, étant comprise entre 5 et 14 at % ; la teneur en silicium pouvant atteindre 30 at %, et, de préférence, étant comprise entre 12 et 17 at %.

To mass produce magnetic components, for example magnetic cores for differential circuit breaker of class AC (sensitive to alternating fault currents), a ribbon of soft magnetic alloy having an amorphous structure is used, capable of acquiring a nanocrystalline structure, consisting mainly iron in a content greater than 60 atom%, and also containing:

• 0.1 to 3 at%, and preferably 0.5 to 1.5 at% copper;
• from 0.1 to 30 at%, and preferably from 2 to 5 at% of at least one element chosen from niobium, tungsten, tantalum, zirconium, hafnium, titanium, and molybdenum; preferably, the niobium content is between 2 and 4 at%;
• silicon and boron, the sum of the contents of these elements being between 5 and 30 at%, and preferably between 15 and 25 at%; the boron content which can range up to 25 at%, and preferably being between 5 and 14 at%; the silicon content being able to reach 30 at%, and preferably being between 12 and 17 at%.

In addition to these elements, the alloy may have low levels of impurities provided by raw materials or resulting from production.

The amorphous ribbon is obtained in a manner known per se by solidification very fast liquid alloy, poured, for example, on a cooled wheel.

The magnetic core blanks are also manufactured known in itself, by winding the ribbon on a mandrel, cutting it and fixing its end by a welding point, in order to obtain small toroids of rectangular section.

To give the blanks their final magnetic properties, they are first subjected to a so-called "relaxation" annealing, at a temperature below the temperature of onset of crystallization of the amorphous strip, and preferably between 250 ° C and 480 ° C, then an annealing of crystallization which may or may not be carried out under magnetic field, and possibly be followed by annealing at lowest temperature under magnetic field. The inventors have, in effect, noticed in a completely unexpected way, that this annealing of relaxation had for advantage of significantly reducing the sensitivity of magnetic properties nuclei at temperature. The inventors have also found that the annealing of relaxation prior to crystallization annealing had the added benefit of reduce the dispersion of the magnetic properties of the nuclei observed on mass production.

The crystallization annealing is intended to precipitate in the matrix amorphous nanocrystals of size less than 100 nanometers, preferably between 10 and 20 nanometers. This very fine crystallization makes it possible to obtain the desired magnetic properties. The crystallization annealing consists of a maintaining at a temperature higher than the temperature at the start of crystallization and lower than the onset temperature of the secondary phases which deteriorate the magnetic properties. In general, the annealing temperature of crystallization is between 500 ° C and 600 ° C, but it can be optimized for each ribbon, for example, by determining by tests the temperature which leads to maximum magnetic permeability. The annealing temperature of crystallization can then be chosen equal to this temperature, or, better, be chosen to be about 30 ° C higher.

In order to modify the shape of the hysteresis cycle what is necessary for Class A residual current devices (sensitive to polarized fault currents), crystallization annealing can be carried out under a transverse magnetic field. The crystallization treatment can also be supplemented by annealing at a temperature below the crystallization start temperature, for example towards 400 ° C, carried out under transverse magnetic field.

More generally, the heat treatment of the blanks magnetic component include a relaxation annealing, a crystallization possibly carried out under magnetic field, and, possibly, an additional annealing carried out under magnetic field.

The relaxation annealing which precedes the crystallization annealing, and which can be performed both on the amorphous tape itself and on the component blank magnetic, can consist in maintaining a constant temperature during a time which preferably should be between 0.1 and 10 hours. This annealing can also consist of a gradual rise in temperature, which precedes, by example, crystallization annealing, and which must be done at a rate of rise in temperature between 30 ° C / h and 300 ° C / h, at least between 250 ° C and 450 ° C; preferably the rate of temperature rise should be around 100 ° C / h.

In all cases, it is preferable to carry out heat treatments in ovens with controlled, neutral or reducing atmosphere.

For example, two strips of Fe ₇₃ Si ₁₅ B ₈ Cu ₁ Nb ₃ alloy (73 at% iron, 15 at% silicon, etc.), 20 μm thick and 10 mm thick, were produced. width obtained by direct quenching on a cooled wheel. With each of the ribbons, two series of blanks of magnetic cores were made, labeled A1 and A2 respectively (for the first ribbon) and B1 and B2 (for the second ribbon). The series of blanks of magnetic cores A1 and B1 were subjected to a heat treatment in accordance with the invention and consisting of a relaxation annealing of 3 hours at 400 ° C followed by a crystallization annealing of 3 hours at 530 ° vs. The series of blanks of magnetic cores A2 and B2 have, for comparison, been treated in accordance with the prior art by a single crystallization annealing for 3 hours at 530 ° C. On the four series of blanks of magnetic cores, the maximum magnetic permeability at 50 Hz was measured at different temperatures between - 25 ° C and + 100 ° C, and it was expressed as a% of the maximum magnetic permeability at 50 Hz at 20 ° C. The results are as follows: sample - 25 ° C - 5 ° C 20 ° C 80 ° C 100 ° C A1 (inv) 100% 102% 100% 93% 86% A2 (comp) 102% 103% 100% 87% 78% B1 (inv) 97% 98% 100% 88% 78% B2 (comp) 98% 99% 100% 75% 60%

These results must be interpreted by examining separately the case of samples A1 and A2 on the one hand, and samples B1 and B2 on the other. Indeed, although the alloy making up all the samples is the same, two ribbons produced separately and which therefore have slightly different properties.

This remark made, we can see that, as well for the group A1, A2 that for group B1, B2, the degradation of the magnetic permeability generated by heating to 80 ° C or 100 ° C, is much lower for samples in accordance with the invention only for samples given as comparison. At 100 ° C, for example, the loss of magnetic permeability is, for the samples according to the invention, about half of what it is for them samples made in accordance with the prior art.

Besides the effect obtained on the temperature stability of the properties magnetic, the inventors have found that the invention improves reproducibility magnetic properties of mass-produced cores. This favorable effect will now be illustrated by the following two examples.

The first example relates to toroidal magnetic cores produced from ribbons 20 µm thick and 10 mm wide obtained by direct quenching on a cooled wheel, of an alloy of composition (in at%) Fe _73.5 Si _13.5 B ₉ Cu ₁ Nb ₃ . After quenching on a wheel, it was checked by X-ray that the ribbon was completely amorphous. The ribbon was then separated into three sections, one, A, remained as it was, the other two, B and C, were subjected to relaxation annealing, for one, B, 1 hour at 400 ° C, for the other, C, 1 hour at 450 ° C. The coercive field was measured, the minimum and maximum values of which were, in mOe (1 mOe = 0.079577 A / m): A from 80 to 200 mOe, B and C from 25 to 35 mOe. These results show the effect of the relaxation treatment which not only reduces the dispersion of the coercive field, but also very significantly reduces its value.

The three portions of ribbon were then used to form sketches of toric magnetic nuclei and these nuclei were first annealed with 1 hour crystallization at 530 ° C to obtain a round hysteresis cycle, then at a annealing under transverse magnetic field for 1 hour at 400 ° C to obtain a cycle lying hysteresis. Coercive field values, maximum permeability at 50 Hz, and, for the coated cycles only, the Br / Bm ratio (remanent induction on saturation induction) have been determined.

The results were as follows

a) round cycles:

sample relaxation treatment coercive field (mOe) max permeability at 50 Hz AT without 6.1 650,000 B 1 h at 400 ° C 5.2 690,000 VS 1 h at 450 ° C 5.1 760,000

b) recumbent cycles:

sample Relaxed trait ch coercive (mOe) Br / Bm perm max at 50 Hz AT without 5 0.12 200,000 B 1 h at 400 ° C 3.8 0.08 215,000 VS 1 h at 450 ° C 3.4 0.07 205,000

These results clearly show the improvement in magnetic properties generated by the relaxation treatment: reduction of the coercive field, increased maximum permeability, and greater ease in obtaining recumbent cycles.

The second example relates to toroidal magnetic cores produced from ribbons 20 µm thick and 10 mm wide obtained by direct quenching on a cooled wheel, of an alloy of composition (in at%) Fe ₇₃ Si ₁₅ B ₈ Cu ₁ Nb ₃ . With the ribbon, two batches of 300 toroids with an internal diameter of 11 mm and an external diameter of 15 mm were produced using automatic winding machines. The batches were then treated in ovens with neutral atmosphere. A control batch A was only subjected to a 1 hour crystallization annealing at 530 ° C. The second batch was treated in accordance with the invention: a relaxation annealing of 1 hour at 400 ° C. was first carried out, then a crystallization annealing of 1 hour at 530 ° C. The toroids were put in a box and wedged with a foam washer. For each lot, the mean and standard deviation of the maximum permeability at 50 Hz were determined.

The results were as follows: treatment max permeability at 50 Hz average max permeability at 50 Hz standard deviation without relaxation (lot A) 585,000 28,000 with relaxation (lot B) 615,000 20,000

They show the effect of relaxation annealing which, on the one hand, improves the value average maximum permeability, and, on the other hand, reduces dispersion.

The two batches were then treated for 1 hour at 400 ° C. under a transverse magnetic field in order to obtain coated hysteresis cycles. The coercive field, the Br / Bm ratio and the permeability at 5 mOe at 50 Hz were measured. The results were as follows: Treatment ch coercive (mOe) Br / Bm perm at 5mOe at 50 Hz without relaxation (lot A) 5.2 0.08 117,000 with relaxation (lot B) 4.3 0.06 124,000

These results clearly show the improvement in magnetic properties generated by the relaxation treatment: reduction of the coercive field, increased permeability in 5 mOe at 50 Hz, and greater ease for get recumbent cycles.

Claims (6)

1. Process for manufacturing a magnetic component made of an iron-based soft magnetic alloy having a nanocrystalline structure, the chemical composition of which is, in at.%, Fe ≥ 60%, 0.1% ≤ Cu ≤ 3%, 0% ≤ B ≤ 25%, 0% ≤ Si ≤ 30%, and at least one element selected from niobium, tungsten, tantalum, zirconium, hafnium, titanium and molybdenum in proportions of between 0.1% and 30%, the balance being impurities resulting from the smelting, the composition furthermore satisfying the relationship 5% ≤ Si + B ≤ 30%, according to which:

   an amorphous ribbon is manufactured from the magnetic alloy,

   a blank for a magnetic component is manufactured from the ribbon by winding the magnetic ribbon around a mandrel in such a manner as to form a forum,

   and the magnetic component is subjected to a crystallization heat treatment comprising at least one annealing step at a temperature of between 500°C and 600°C for a temperature hold time of between 0.1 and 10 hours so as to cause nanocrystals to form, characterized in that, before the crystallization heat treatment, a relaxation heat treatment is carried out at a temperature below the temperature for the onset of recrystallization of the amorphous alloy.
2. Process according to Claim 1, characterized in that the relaxation heat treatment is a temperature hold for a time of between 0.1 and 10 hours at a temperature of between 250°C and 480°C.
3. Process according to Claim 1, characterized in that the relaxation heat treatment consists of a gradual heating from ambient temperature up to a temperature above 450°C, at a heating rate of between 30°C/hour and 300°C/hour between 250°C and 450°C.
4. Process according to any one of Claims 1 to 3, characterized in that the crystallization annealing is carried out in a magnetic field.
5. Process according to any one of Claims 1 to 4, characterized in that a complementary annealing step is carried out in a magnetic field at a temperature below the crystallization on set temperature.
6. Process according to any one of Claims 1 to 5, characterized in that the chemical composition of the alloy is such that Si ≤ 14 %.