EP0293286A1 - Method and device for manufacturing articles for magnetic use - Google Patents

Abstract

Method and device for manufacturing articles for magnetic use which are composed of a metal alloy taking the form of a continuous strip (3) from which the articles (33) are cut out, the alloy being subjected to a heat treatment comprising at least one annealing operation carried out in the presence of a magnetic field. <??>The annealing operation is divided into at least two successive phases, respectively a first initiation phase in the presence of a magnetic field, carried out on the move on the alloy in the form of a continuous strip (3), and a second ageing phase carried out on the separate articles (33) obtained from the strip (3) which has undergone the first initiation phase. <??>The invention makes it possible to produce articles in particular for the electrotechnical industry. <IMAGE>

Description

The subject of the invention is a method and an installation for producing metal parts for magnetic use and also covers the products obtained by the method and used for the production of such parts.

Various alloys are known having particular magnetic properties and used for the manufacture of usable parts, thanks to their magnetic properties, in the electrotechnical or electronic industry, for example for the manufacture of relays, counters, transducers, etc.

In particular, quaternary alloys based on Iron, Aluminum, Nickel, Cobalt are commonly used which have advantageous magnetic properties but which are advantageously replaced, in certain cases, by ternary alloys based on Iron, Cobalt, Chromium . Such alloys in fact have the advantage of being able to be shaped by cutting or stamping the alloy which is in the form of elongated products such as continuous strips or wires, sheets or bars.

The magnetic properties of the alloys can be adjusted as required by playing on the one hand on the composition of the alloy and on the other hand on the heat treatments to which it is subjected. In particular, the Fe, Co, Cr alloys comprising 26 to 32% of chromium and 9 to 25% of cobalt have the advantage of developing magnetic properties close to the quaternary alloys Fe, Al, Ni, Co and which can also be cut. and shaped, for example by stamping or forging. This is why we can call them formable magnets.

The heat treatments capable of developing the desired properties are quite complicated and include various heating, temperature maintenance or cooling operations with determined rates of temperature variation. However, for some time it has been found to be interesting to penny put the magnetic alloy in an annealing operation carried out for example around 650 ° C. and in the presence of a high magnetic field, greater than 160,000 A / m) (2000 Oe).

This annealing operation in the presence of a magnetic field gives very interesting results but has the drawback of requiring the use of an electromagnet or any similar device for the production of such a strong magnetic field. Therefore, the installation is quite expensive and difficult to use.

The subject of the invention is a new method of carrying out annealing under a magnetic field, making it possible in particular to avoid the use of an electromagnet because the magnetic field used is much weaker than in the methods known before.

According to the invention, the annealing operation is divided into at least two successive phases, respectively a first initiation phase, in the presence of a magnetic field, carried out on the elongated product before cutting the parts and a second phase of maturation carried out on the separate parts obtained from the product having undergone the first phase.

In the case where the elongated product is a strip or a continuous wire capable of being unwound from a reel, the first initiation phase is carried out continuously by passing the strip or wire inside. a tubular furnace provided with means for producing a magnetic field preferably made up of a solenoid supplied with electric current and incorporated in the tubular furnace.

In another embodiment of the invention, applicable both to continuous strips or wires and to products in the form of sheets or bars, it is parked in a tubular oven provided with means for producing a magnetic field at least a part of the product of length corresponding to that of the oven, during the time necessary for carrying out the first phase of the treatment.

According to another advantageous characteristic, the strip is put under tension during the first initiation phase in the presence of a magnetic field.

Particularly advantageously, the magnetic field applied during the first initiation phase can be less than 80,000 A / m (1000 Oe).

The invention also covers the installation for carrying out the method comprising a tubular furnace associated with means for producing a magnetic field and means for controlling the movement of the strip of alloy inside the furnace.

When all the treatment and preparation of the parts is carried out at the same place, the installation comprises two separate ovens, respectively a tubular furnace for carrying out the first phase of initiation on the continuously moving strip and a furnace for carrying out of the second maturation phase on the cut pieces, the cutting and possibly forming installation for the pieces being placed between the two ovens.

However, it is also possible to separate the two phases of the annealing treatment and the invention covers the product consisting of a continuous strip of alloy having undergone the first phase of initiation of the annealing operation and which can subsequently be cut into separate pieces, these being finally subjected to the second maturation phase.

• La Figure 1 représente très schématiquement et à titre d'exemple une installation pour la mise en oeuvre du procédé selon l'invention.
• La Figure 2 est un diagramme des températures du traitement thermique.

The invention will be better understood from the detailed description of an embodiment of magnetic parts by the method of the invention, with reference to the accompanying drawings.

• Figure 1 shows very schematically and by way of example an installation for implementing the method according to the invention.
• Figure 2 is a diagram of the temperatures of the heat treatment.

The invention results from a study carried out on ternary alloys, Iron, Chromium, Cobalt, produced in a vacuum furnace in which carbon deoxidation of a mixture of iron and cobalt is carried out successively, the addition of chromium and then manganese, the shading, and the falling cast. The ingots obtained undergo several hot transformation operations for the production of bars which, after cooling, are peeled. A hot rolling of the bars is then carried out in order to obtain dishes or wires which are finally subjected to water quenching and, optionally to a work hardening operation.

The heat treatment to which the alloy is subjected can be defined as a phase transformation leading to magnetic hardening by spinodal decomposition of the α phase into two phases α₁ rich in cobalt and highly magnetic and α₂, rich in chromium and little or not magnetic.

To obtain the maximum α phase, the spinodal decomposition treatment is preferably preceded by a short-term recrystallization treatment carried out at around 900-950 ° C. The alloy is then subjected to an annealing operation at around 600-650 ° C. which allows the spinodal decomposition to be carried out. However, it has been observed that this treatment can be carried out in two phases separated from each other, respectively an initiation phase during which it is advantageous to apply to the alloy a magnetic field and a maturation phase which, on the other hand, does not require the application of the magnetic field. We can think that the initiation phase makes it possible to conduct a localized demixing leading to a periodic variation of the composition whose period is precisely regulated to have precipitates from the α₁ phase in the α₂ phase, the maturation phase making it possible to cause a concentration difference between the phases as high as possible.

This maturation treatment requires a fairly long temperature maintenance time, of the order of 10 to 20 hours, at a temperature lower than the initiation treatment temperature, while the first initiation phase can be carried out more quickly.

In addition, it was found that the cutting and forming operations of the parts could be carried out after the first initiation phase.

It is therefore possible, according to the essential characteristic of the process, to subject the alloy to the first initiation phase when it is in the form of a continuous strip, then to cut the parts and finally to subject them to the second maturation phase.

As shown diagrammatically in FIG. 1, an installation for implementing the method will therefore comprise at least two separate heating chambers, respectively a first oven 1 for carrying out the first initiation phase and a second oven 2 for carrying out the maturation phase. The alloy is in the form of a strip 3 which is unwound from a coil 31 to be wound on the drum 32. The strip 3 thus travels in a longitudinal direction inside the furnace 1 of tubular shape . This is preferably preceded by an oven 11 inside which the recrystallization treatment is carried out at around 950 ° C.

At the outlet of the oven 1 is placed a cutting device 4 which makes it possible to obtain, from the strip 3, separate pieces 33 having the desired shape and which, optionally after cooling, are directed to the oven 2 to undergo the treatment there. of maturation.

The tubular furnace 11 delimits an elongated internal space 12 in which the strip 3 is passed. On the other hand, the furnace 1 is provided with means for producing a magnetic field, for example a solenoid 13 connected to a current source. electric 14 and which is incorporated into the wall of the furnace 1 so as to completely surround the central space 12 inside which the magnetic field is thus produced by current flow.

According to an essential advantage of the invention, since the magnetic field is applied to a product of very great length compared to its thickness and consequently having a weak demagnetizing field, it is not necessary to produce in the oven 1 a very high magnetizing field to develop the desired magnetic properties. In practice, it has been found that the necessary magnetizing field which depends on the desired result and on the composition of the alloy, could even be less than 80,000 A / m (1000 Oe), whereas until now it was necessary to use a field of at least 16,000 A / m (2000 Oe for small parts. This avoids the use of an always expensive electromagnet. At the exit of the tubular furnace 1, the strip 3 passes in the cutting device 4, the cutting operation does not modify the developed magnetic structure.

A temperature cycle has been shown by way of example in FIG. 2 which is a diagram indicating the treatment temperature as a function of time.

The strip which is at room temperature and is unwound from the reel 31 first passes through the furnace 11 where its temperature rises to around 900 ° C, according to the OAB trace. From point B, the strip passes through the tubular furnace 1 in which its temperature drops to a temperature of the order of 630 ° C following the line BC which is therefore carried out in part in the presence of the magnetic field produced by the solenoid 13. the strip is then cooled rapidly according to the layout CD. Preferably, the parts 33 are cut cold. The pieces 33 are then directed into the furnace 2 where their temperature is maintained for the necessary time, for example from 10 to 20 hours, at a temperature decreasing regularly, preferably from 610 to 520 ° C.

Since, preferably, the strip is sou put in the parade, firstly to the recrystallization treatment then to the initiation phase, the duration of the temperature maintenance will be adjusted by acting on the scrolling speed and as a function of the relative lengths of the tubular furnace 1 and the recrystallization furnace 11, the recrystallization treatment being applied normally for 1/2 hour to 1 hour.

However, instead of carrying out the treatment continuously in the tubular furnace, it is also possible to advance the strip at regular intervals by making part of the strip of corresponding length park in the furnace for the necessary time. We could also proceed in the same way on an elongated product in the form of sheets or separate bars but having a fairly large length relative to their transverse dimensions so that the magnetic treatment can be carried out under a relatively weak field. The sheets or bars would then follow one another in the oven, stationing there the time necessary for the first phase of the treatment, the pieces then being cut to undergo the second phase.

Depending on the properties that one wishes to develop and the composition of the alloy, the magnetic field created by the solenoid 13 inside the furnace 1 will be between 8000 and 12,000 A / m (100 to 1500 Oe). example 4800 A / m (600 Oe).

The magnetic structure obtained after the first initiation phase is permanent and, therefore, the cutting operation and the second maturing phase of the treatment can be performed some time after the completion of the first phase. It is therefore possible to first treat the alloy strip by subjecting it to the first initiation phase possibly preceded by a recrystallization treatment and to deliver it to the user who will cut the parts and submit them to a second maturation phase, this for vant to be carried out in a fairly simple way since it is applied to parts of small sizes and without magnetic field.

As a simple example, the invention has been implemented as follows:

EXAMPLE 1

An ingot of composition by weight Co 10.2%, Cr 28%, Mn 0.5%, Fe remains, and the usual impurities due to the manufacturing processes are prepared by conventional methods of production and casting under vacuum. The ingot is then hot rolled around 1200 - 1250 ° C and rapidly cooled. A strip 0.75 mm thick is produced with the hot-rolled product by cold rolling.

The cold-rolled strip is then treated on passing through the system of ovens shown in FIG. 1, so that in the first oven 11 the temperature of the strip reaches 950 ° C. for approximately 30 minutes. The distance between the furnace 11 and the furnace 1 as well as the thermal insulation are such that from approximately 700 ° C. the strip cools to approximately 100 ° C./h and enters the furnace 1 in which a magnetic field is applied to at least 650 ° C. The temperature of oven 1 is adjusted to 630 ° C and the axial magnetic field is 800 Oe (48000 Am⁻¹) the running time in oven 1 is at least 30 min. At the outlet of the oven 1 the strip is rapidly cooled and wound up.

On the previously treated strip, parts are cut to make the measurements and for use: for example drilled discs used in automobile counters. These parts are then treated in an ordinary oven, the temperature of which gradually drops from 620 ° C to 520 ° C in 20 hours, for example oven 2.

The magnetic properties obtained are as follows and illustrate the advantage of the process.

EXAMPLE 2

The same strip is used as in Example No. 1 but before proceeding to the process at the parade in the ovens 11 and 1, this strip is subjected to a treatment at 950 ° C. for one hour under hydrogen and rapidly cooled at the end. of treatment.

This pretreated strip is then treated in the process in the ovens shown in Figure 1. During this process in the process the strip is subjected to uniaxial traction in the direction of the length of about 10 kg mm⁻².

The temperature of the oven 11 is 700 ° C. and the strip enters the oven 1 at 650 ° C. The temperature of oven 1 is set at 630 ° C and the axial magnetic field is 800 Oe. The running time in the oven 1 is 40 min. At the outlet of the furnace 1 the strip is rapidly cooled and wound up.

Pieces are cut from the strip thus treated under magnetic field and under tension. These parts then undergo the maturation treatment in a conventional oven where the temperature gradually drops from 620 ° C to 500 ° C in 20 hours. A complementary treatment at 500 ° C for 24 hours is beneficial. The properties obtained are as follows:

EXAMPLE NO.3

An alloy with Co = 12%, Cr = 28%, Mn = 0.5% by weight, the balance being iron and the usual impurities, is produced under vacuum and poured into ingots. The ingots are then hot rolled into 5 mm strips, then cold rolled into 1 mm thick strips.

The strip is then subjected to a 1/2 hour treatment at 1050 ° C. under hydrogen. This treatment ends with rapid cooling.

The strip is then sheared to the width necessary for the application and cut into sections of 1.5 meters. These sections are then assembled into bundles of small diameter and placed in the furnace 1.

The temperature of oven 1 is brought quickly to 700 ° C and then allowed to cool to 620 ° C at a speed of about 100 ° C / h. From 650 ° C the magnetic field of 800 Oe is applied. The duration of maintenance at 620 ° C is one hour. At the end of this treatment at 620 ° C. the bundles of strips are rapidly cooled.

The pieces for measurement and use are cut from the strips and then treated in an oven whose temperature drops from 620 ° C to 520 ° C in 20 hours. A further 24 hour treatment at 500 ° C further improves the magnetic properties.

The properties obtained following this set of treatment are as follows:

Of course, the invention is not limited to the details of the embodiment which has just been described and which could be subject to variants without departing from the protective framework defined by the claims. In particular, the processing temperatures have been indicated for an alloy comprising substantially 10% of cobalt but could be modified according to the desired properties and the composition of the alloy. Moreover, it would be possible to carry out more complex heat treatments including in particular different temperature stages possibly separated by more or less rapid cooling phases. In fact, even when the treatment is carried out on the alloy in the form of a strip, the ovens can be placed one after the other, separating them by heat-insulated zones to achieve the various desired temperatures.

Of course, if the term "strip" has been used in the text, the invention also covers the use of any elongated product, such as a continuous wire or sheets or bars, the product being able, in section transverse, be adapted to the shape of the parts. Similarly, after their cutting, they can undergo various shaping operations, for example by forging.

Furthermore, it could be interesting, by adjusting the relative speeds of unwinding and winding of the strip or else by means of a device associated with the oven, to exert a certain traction on the product so as to combine the action of this with that of temperature and magnetic field. The latter can also be created by various known means, using a direct current or an alternating current and, by adapting the circuit, the electric current could moreover simultaneously produce the magnetic field and the heating of the furnace.

Claims (16)

1. Method for producing parts for magnetic use made of a metal alloy in the form of an elongated product (3) from which the parts (33) are cut, the alloy being subjected to a heat treatment comprising at least an annealing operation carried out in the presence of a magnetic field, characterized in that the annealing operation is divided into at least two successive phases, respectively a first initiation phase in the presence of a magnetic field, carried out on the elongated product (3) before cutting the pieces and a second maturation phase carried out on the separate pieces (33) obtained from the product (3) having undergone the first initiation phase. 2. Method according to claim 1, in which the elongated product (3) is a continuous strip or wire capable of being unwound from a reel, characterized in that the first initiation phase is carried out continuously by scrolling the strip or wire (3) along a tubular oven (4) provided with means (13) for producing a magnetic field. 3. Method according to claim 1, characterized in that the first initiation phase is carried out in a tubular oven (4) of great length, provided with means (13) for producing a magnetic field, in which one makes park at least a part of the corresponding length of the product for the time necessary to carry out the first phase of the treatment. 4. Method according to one of claims 2 and 3, characterized in that the magnetic field is produced by passing an electric current through a conductor (13) incorporated in the tubular furnace (1). 5. Method according to claim 1, characterized in that, during the application of the initiation phase under magnetic field, the strip (3) is put under voltage. 6. Method according to one of the preceding claims, characterized in that the metal alloy is a magnetic alloy based on Iron, Cobalt and Chromium. 7. Method according to one of the preceding claims, characterized in that the magnetic field applied during the first phase of initiation of the treatment can be less than 80,000 A / m (1000 Oe). 8. Method according to claim 6, characterized in that the first initiation phase is carried out at a temperature between 600 and 650 ° C and that the second maturation phase is carried out at a temperature between 500 and 600 ° C . 9. Method according to one of the preceding claims, characterized in that before being subjected to the first phase of initiation under magnetic field, the alloy strip (3) is subjected to a recrystallization treatment at a temperature between 900 and 950 ° C for a time of 1/2 to 1 h. 10. Product for the production of parts (33) for magnetic use, characterized in that it consists of a strip or an elongated metal wire (3) having undergone the first phase of initiation of the method according to the 'One of the preceding claims and in which parts (33) can subsequently be cut and subjected to the second maturation phase. 11. Installation for producing parts for magnetic use from an elongated product (3), a metal alloy from which the parts are cut, said alloy undergoing a heat treatment carried out in the presence of a magnetic field, characterized by the fact that it comprises a tubular oven (1) associated with means (13) for producing a magnetic field and with means (31, 32) for controlling the passage of the product (3) in the tubular oven (1), the latter being associated with means for adjusting the time of passage of the product, of the temperature and of the magnetic field so as to carry out a first phase of initiation of the treatment during the running of the strip of alloy, the heat treatment comprising a second phase of maturation carried out without magnetic field on the pieces cut from the strip after the first initiation phase. 12. Installation according to claim 11, characterized in that it comprises two separate ovens (1) and (2) for carrying out the two phases of the treatment respectively on the elongated product (3) and on the cut pieces (33) and a device (4) for cutting the parts (33) placed between the two ovens (1) and (2). 13. Installation according to claim 11, characterized in that the means for producing the magnetic field consist of a solenoid (13) incorporated in the wall of the tubular furnace (1) and supplied with electric current. 14. Installation according to claim 12, characterized in that the solenoid (13) is supplied with alternating current. 15. Installation according to one of claims 11 to 14, characterized in that, the elongated product (3) consisting of a strip or a continuous wire wound on a coil (31) the installation comprises means for controlling the unwinding of the coil (31) and the movement of the product (3) inside the oven. 16. Installation according to one of claims 11 and 15, characterized in that the oven is associated with means for tensioning the product (3) inside the oven.

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