EP0784100B1 - Iron-cobalt alloy, manufacturing process for strips made from iron-cobalt alloy and product obtained - Google Patents

Abstract

Iron-cobalt alloy contains (in wt.%): 5-40 Co; 0-5 Si, 0.2-5 Al; 0.5-5 Si+Al; Fe and usual production impurities.

Description

The present invention relates to an Iron-Cobalt alloy for the manufacture of magnetic circuits for electrotechnical machines.

electrotechnical machines such as electric motors, transformers or relays have built-in magnetic circuits of stacks of parts cut from alloy strips, the magnetic properties are suitable. These properties should be all the more better than machines with high specific energy, which is the case, for example, for machines on board vehicles such as planes or high speed trains. Indeed, for these applications it is necessary to minimize the weight of the equipment, which involves an increase in specific energy, i.e. power per unit massive.

The magnetic circuits of machines with high specific energy are often made of Iron-Cobalt alloy whose chemical composition includes, by weight, about 50% cobalt and 2% vanadium, the balance being iron and impurities. But these alloys have several disadvantages because that they all have an α / γ phase transformation which limits very notably the possibilities of action on the magnetic properties by heat treatment. In addition, these alloys generally have a resistivity electric too weak and are too expensive.

It has been proposed, in particular in DE - C - 705 516 to use alloys iron-cobalt-silicon containing from 2% to 18% of cobalt and from 1% to 6% of silicon. However, these alloys do not provide a satisfactory solution to the problem stated above. Indeed, to obtain magnetic properties satisfactory, it is necessary that the alloy contains more than 3% of silicon, it then becomes very fragile and can no longer be cold rolled in satisfactory conditions, we can no longer obtain the small thicknesses desirable to reduce eddy current losses in circuits magnetic.

The object of the present invention is to remedy these drawbacks by proposing an alloy of the Iron-Cobalt type having magnetic properties close to those of known alloys, but with a higher cobalt content low, so as to be less expensive than existing alloys, and which can be cold rolled.

5 % ≤ Co ≤ 40 %

0 % ≤ Si ≤ 4 %

0,2 % ≤ Al ≤ 5 %

0,5 % ≤ Si + Al ≤ 5 %

le reste étant du fer et des impuretés résultant de l'élaboration.To this end, the subject of the invention is an Iron-Cobalt alloy, the chemical composition of which comprises by weight:

5% ≤ Co ≤ 40%

0% ≤ If ≤ 4%

0.2% ≤ Al ≤ 5%

0.5% ≤ Si + Al ≤ 5%

the remainder being iron and impurities resulting from processing.

The impurities resulting from the preparation can be, in particular, elements such as chromium, titanium, germanium, vanadium and molybdenum, and elements like carbon, oxygen, nitrogen, sulfur and phosphorus.

C ≤ 0,03 %

O ≤ 0,005 %

N ≤ 0,003 %

S ≤ 0,003 %

P ≤ 0,003 %

et la somme des teneurs en chrome, titane, germanium, vanadium et molybdène doit être inférieure à 0,5%.Preferably, the impurities resulting from the production, which are carbon, oxygen, nitrogen, sulfur and phosphorus, have contents lower than the following values:

C ≤ 0.03%

O ≤ 0.005%

N ≤ 0.003%

S ≤ 0.003%

P ≤ 0.003%

and the sum of the contents of chromium, titanium, germanium, vanadium and molybdenum must be less than 0.5%.

Preferably also, the chemical composition checks one or more more than one of the following relationships: 10% ≤ Co ≤ 35%, Si ≥ 2.5% or Al ≥ 1.5% or Si + Al ≥ 1.5%.

• on élabore l'alliage soit sous vide soit au four à arc suivi d'une opération de métallurgie en poche et, éventuellement, après une première solidification, on le refond sous vide ou sous laitier électroconducteur pour obtenir un demi produit,
• on lamine à chaud le demi-produit pour obtenir une bande à chaud dont l'épaisseur est comprise entre 1 et 6 mm,
• on décape la bande à chaud et on la lamine après l'avoir éventuellement réchauffée entre 200°C et 600°C pour obtenir une bande à froid d'épaisseur comprise entre 0,05 mm et 0,5 mm,
• on effectue un traitement thermique entre 850 °C et 1200 °C pendant 1 à 10 heures et un revêtement par une couche électriquement isolante.

The invention also relates to a method of manufacturing a strip of an alloy in accordance with the invention, according to which:

• the alloy is produced either under vacuum or in an arc furnace followed by a ladle metallurgy operation and, possibly, after a first solidification, it is remelted under vacuum or under electroconductive slag to obtain a semi-finished product,
• the semi-finished product is hot rolled to obtain a hot strip whose thickness is between 1 and 6 mm,
• the strip is stripped hot and it is laminated after having optionally reheated it between 200 ° C and 600 ° C to obtain a cold strip of thickness between 0.05 mm and 0.5 mm,
• heat treatment is carried out between 850 ° C and 1200 ° C for 1 to 10 hours and coating with an electrically insulating layer.

The coating with an insulating layer can be obtained by covering the strip, or, after the heat treatment, of at least one layer of varnish mineral or organic, i.e., before the heat treatment, at least one layer of magnesium methylate.

When the silicon content of the alloy is greater than 2%, the coating with an insulating layer can be obtained by applying to the band a milk of magnesia, before the heat treatment.

Finally, the invention relates to a strip of an alloy according to the invention, coated with at least one electrically insulating layer, preferably having a cubic texture (100) [001] or a texture (110) [001], as well as its use for manufacturing a magnetic circuit of a machine electrical engineering.

The invention will now be described in more detail, but not limiting.

The inventors have found in a new way that by adding aluminum to an Iron-Cobalt alloy possibly containing silicon, we significantly increased the resistivity of the alloy without dropping too much the saturation magnetization, and, that by choosing the content of this element taking into account the possible silicon content, we could remove the α / γ phase transformation while obtaining a material sufficiently ductile to be suitable for cold rolling. This provides a strip whose magnetic properties can be improved by a heat treatment and by obtaining a favorable texture.

• de 5% à 40% et de préférence de 10% à 35% de cobalt qui est le seul élément connu améliorant l'aimantation à saturation du fer; le cobalt étant un élément très coûteux sa teneur est ajustée, pour chaque application particulière, à la teneur juste nécessaire pour obtenir les caractéristiques magnétiques souhaitées pour l'application;
• de 0,2 % à 5 % d'aluminium et de 0% à 5% de silicium pour réduire l'étendue du domaine d'existence de la phase γ ; l'aluminium présente l'avantage supplémentaire d'augmenter la résistivité électrique et de ne pas détériorer la ductilité à froid ; le silicium qui réduit également le domaine d'existence de la phase γ, présente cependant l'inconvénient de rendre difficile les opérations de laminage à froid ; de préférence, soit la teneur en aluminium est supérieure ou égale à 1,5%, soit la teneur en silicium est supérieure ou égale à 2,5%, soit la somme des teneurs en silicium et aluminium est supérieure ou égale à 1,5%, car au delà de ces valeurs, la phase γ n'existe plus, ce qui permet des traitements thermiques à haute température pour faire grossir le grain et développer une texture favorable, et ainsi, améliorer les propriétés magnétiques;

In addition to the iron and the impurities resulting from the production, the chemical composition of the alloy according to the invention comprises by weight:

• from 5% to 40% and preferably from 10% to 35% of cobalt which is the only known element improving the saturation magnetization of iron; cobalt being a very expensive element, its content is adjusted, for each particular application, to the content just necessary to obtain the magnetic characteristics desired for the application;
• from 0.2% to 5% of aluminum and from 0% to 5% of silicon to reduce the extent of the domain of existence of the γ phase; aluminum has the additional advantage of increasing the electrical resistivity and of not deteriorating the ductility when cold; silicon which also reduces the domain of existence of the γ phase, however has the drawback of making cold rolling operations difficult; preferably, either the aluminum content is greater than or equal to 1.5%, or the silicon content is greater than or equal to 2.5%, or the sum of the silicon and aluminum contents is greater than or equal to 1.5 %, because beyond these values, the γ phase no longer exists, which allows heat treatments at high temperature to make the grain coarser and develop a favorable texture, and thus, improve the magnetic properties;

The impurities resulting from processing are, in particular, elements such as chromium, titanium, germanium, vanadium and molybdenum which can be tolerated provided the sum of their contents remains less than 0.5%. Impurities are also elements such as carbon, oxygen, nitrogen, sulfur and phosphorus whose contents must be as low as possible and preferably such that: C ≤ 0.03%, O ≤ 0.005 %, N ≤ 0.003%, S ≤ 0.003%, P ≤ 0.003%.

In order to obtain a sufficient level of purity, the alloy can be produced using vacuum oven or arc furnace followed by a vacuum bag treatment then cast as a semi-finished product. Advantageously, the alloy can be remelted under vacuum or under electroconductive slag. In this case, after preparation under vacuum or after the vacuum bag processing operation, the alloy is cast in the form of a reflow electrode which is remelted under vacuum or under electroconductive slag to obtain the semi-finished product.

The semi-finished product is placed still hot in a reheating oven to be brought to rolling temperature, then hot rolled to obtain a hot strip of thickness between approximately 1 mm and approximately 6 mm. The hot strip is then pickled and, if necessary, stretched by heating between 200 ° C and 600 ° C and finally, cold rolled (or warm when the strip is stretched) in several passes with, possibly annealing intermediate between 700 ° C and 1100 ° C, to obtain a cold strip generally between 0.05 mm and 0.5 mm thick.

In some cases, the succession of cold rolling and annealing intermediaries to obtain a cubic texture (100) [001] or a texture (110) [001] very favorable for obtaining good magnetic properties. In order to avoid oxidation of aluminum or silicon, intermediate annealing should preferably be made under an atmosphere of pure and dry hydrogen.

The cold strip is then subjected to a heat treatment by heating and maintaining temperature between 850 ° C and 1200 ° C for a time between 1 hour and 10 hours and coated with at least one insulating layer electrically. The heat treatment which is done under atmosphere pure and dry hydrogen makes it possible to enlarge the grain which improves the magnetic properties.

At least one electrically insulating layer may consist of a mineral or organic varnish deposited after heat treatment, or magnesium methylate deposited before heat treatment.

When the silicon content of the alloy is sufficient, i.e. greater than 2%, at least one electrically insulating layer can be obtained by applying to the strip, before the heat treatment, a milk of magnesia. During the heat treatment, the silicon located on the surface of the tape reacts with magnesia to form an insulating glass.

The strips thus obtained can be cut to obtain parts which, after stacking, form magnetic circuits for transformers, electric motors, relays or any other electrotechnical machine.

These bands have a weak coercive field (Hc <0.55 Oe; 1 Oe = 79.577 A / m) and a high electrical resistivity (ρ> 33 µ.Ω.cm), which makes them particularly suitable for the manufacture of magnetic circuits for high specific energy electrotechnical machines intended in particular for equip vehicles such as high-speed trains or aircraft.

For example, alloys C to D were manufactured (chemical composition by weight in%): alloy Fe Co Yes Al VS NOT O S VS ball 15 - 1.54 0.016 0.0008 0.001 0.0005 D ball 15 - 2.4 0.027 0.0005 0.001 0.0005 E ball 15 - 3.1 0.011 0.0005 0.001 0.0005 F ball 15 0.98 1.55 0.011 0.0012 0.0013 0.0005

All these alloys were produced in a vacuum oven, hot rolled then cold rolled to obtain strips of 0.2 mm thick. The strips were subjected to a heat treatment under hydrogen. The heat treatment conditions and the magnetic characteristics obtained were: alloy Θ ° C t (hours) ρ (µ.Ω.cm) B to 600Oe (G) Hc (Oe) VS 900 4 35 22100 0.5 VS 1050 4 35 22100 0.53 D 900 4 38 21200 0.53 D 1150 4 38 21200 0.4 E 900 4 40 21000 0.43 E 1150 4 40 21000 0.4 F 900 4 39.5 21500 0.4 F 1000 4 39.5 21500 0.32

By way of comparison, a strip of Fer-Cobalt alloy was manufactured according to the prior art (marked A), the chemical composition of which was: alloy Fe Co Yes Al VS NOT O S AT ball 15 0.98 - 0.01 0.0014 0.0027 0.0005

After heat treatment at 900 ° C and 1000 ° C, their characteristics were: alloy Θ ° C t (hours) ρ (µ.Ω.cm) B to 600Oe (G) Hc (Oe) AT 900 4 30 22500 0.58 AT 1000 4 30 22500 0.71 It can be seen that the alloys according to the invention have a higher resistivity, a lower coercive field and a magnetization comparable to that of alloy A.

In general, the iron-cobalt alloys according to the prior art contain more than 15% of cobalt and the characteristics of the bands in these alloys are typically: Co% ρ (µ.Ω.cm) B to 600 Oe (G) Hc (Oe) 50 40 22500 1 25 22 22500 1.5

It is found that the alloys according to the invention have a resistivity comparable electric power, a significantly weaker coercive field and a fairly close magnetization despite a very appreciably higher cobalt content low. These results show some of the advantages of the alloy according to the invention.

Claims (13)

1. Iron-cobalt alloy, characterized in that its chemical composition comprises, by weight:

   5% ≤ Co ≤ 40%

   0% ≤ Si ≤ 5%

   0.2% ≤ Al ≤ 5%

   0.5% ≤ Si + Al ≤ 5%

   the balance being iron and impurities resulting from the smelting.
2. Alloy according to Claim 1, characterized in that the carbon, oxygen, nitrogen, sulphur and phosphorus impurities resulting from smelting have contents less than the following values:

   C ≤ 0.03%

   O ≤ 0.005%

   N ≤ 0.003%

   S ≤ 0.003%

   P ≤ 0.003%.
3. Alloy according to Claim 1 or Claim 2, characterized in that the chromium, titanium, germanium, vanadium and molybdenum impurities resulting from smelting have contents whose sum is less than 0.5%.
4. Alloy according to any one of Claims 1 to 3, characterized in that:
      10% ≤ Co ≤ 35%
5. Alloy according to any one of Claims 1 to 4, characterized in that:
      Si ≥ 2.5%
6. Alloy according to any one of Claims 1 to 4, characterized in that:
      Al ≥ 1.5%
7. Alloy according to any one of Claims 1 to 4, characterized in that:
      Si + Al ≥ 1.5%
8. Process for manufacturing a strip made of an alloy according to any one of Claims 1 to 5, characterized in that:

   the alloy is smelted either under vacuum or in an arc furnace followed by an in-ladle metallurgy operation and, optionally, after a first solidification, the alloy is remelted under vacuum or under an electrically conductive slag, in order to obtain an intermediate product;

   the intermediate product is hot-rolled in order to obtain a hot-rolled strip whose thickness is between 1 and 6 mm;

   the hot-rolled strip is pickled, optionally reheated between 200°C and 600°C and rolled in order to obtain a cold-rolled strip having a thickness of between 0.05 mm and 0.5 mm;

   a heat treatment between 850°C and 1200°C for 1 to 10 hours is carried out and a coating, with an insulating layer, is applied.
9. Process according to Claim 8, characterized in that the coating with an insulating layer is obtained by covering the strip either, after the heat treatment, with at least one layer of inorganic or organic varnish, or, before the heat treatment, with at least one layer of magnesium methoxide.
10. Process according to Claim 8, characterized in that, when the silicon content of the alloy is greater than 2%, the coating with an insulating layer is obtained by applying a milk of magnesia to the strip before the heat treatment.
11. Strip made of an alloy according to any one of Claims 1 to 7.
12. Strip according to Claim 11, characterized in that it has a (100)[001] cubic texture or a (110) [001] texture.
13. Strip according to Claim 11 or Claim 12, characterized in that it is coated with at least one electrically insulating layer.