EP1629127A1

EP1629127A1 - Fe-ni alloy metal wire having a high mechanical strength and a low thermal expansion co-efficient, which is intended for high voltage cables, and production method thereof

Info

Publication number: EP1629127A1
Application number: EP04742706A
Authority: EP
Inventors: Laurent Chaput; Jacques Levigoureux; Philippe Vignier
Original assignee: Ugitech SA
Current assignee: Ugitech SA
Priority date: 2003-05-21
Filing date: 2004-05-12
Publication date: 2006-03-01
Also published as: WO2004104234A1; FR2855185B1; FR2855185A1

Abstract

The invention relates to an alloy metal wire, whereof the composition comprises in wt. %: 38 = Ni + Co + Cu = 45 %, Co = 10 %, Cu = 5 %, 0.5 % = Ti + Al = 5.5 %, Cr = 3 %, Si = 1 %, Mn = 1 %, C = 0.25 %, Nb + Ta + Mo + W + Zr + Hf + V = 6 %, Mg = 0.10 %, Ca = 0.10 %, S = 0.02 %, P = 0.04 %, B = 0.005 %, the rest being iron and possible impurities resulting from the production process. The invention also relates to the method of producing the wire and the high-voltage cable that can be produced therefrom.

Description

Metallic wire of Fe-Ni alloy having a high mechanical resistance and a low coefficient of thermal expansion, for high voltage cables, and manufacturing process.

The present invention relates to a method for manufacturing metallic wires of Fe-Ni alloy having high mechanical strength and a low coefficient of thermal expansion, more particularly intended for the manufacture of high voltage electric cables.

The first aerial high voltage electric cables were first made of steel coated with a metal or an alloy capable of transporting electrical energy, such as aluminum or zinc and their alloys, the core in steel ensuring the mechanical resistance of the assembly.

However, such cables could only carry a limited electrical power, because beyond about 70 ° C, the deflection obtained exceeded the maximum allowable, due to the too high coefficient of thermal expansion of the steel used. It was then proposed, in EP 723 025 to replace the steel core with an alloy of iron and nickel (Invar), reinforced by precipitation of different carbides, which had the advantage of having a coefficient of expansion thermal below 5.10 ^"6 / ° C between 20 and 300 ° C. However, the manufacturing process of such an alloy is complicated and delicate to implement, because it requires in particular the control of the surface ratio of precipitates at the joints of grains.

The present invention therefore aims to provide a method of manufacturing wires suitable for the manufacture of high voltage cables, which is simple to implement, unlike the methods of the prior art and which makes it possible to obtain a wire having a mechanical resistance greater than 900 MPa, and a coefficient of thermal expansion less than or equal to 6.10 ^"6 / ° C, or even 4.0 .10 ^{" 6} / ° C between 20 and 240 ° C. To this end, a first object of the present invention consists of a method of manufacturing an alloy metal wire having high mechanical strength and a low coefficient of thermal expansion, comprising the steps consisting in: - hot rolling an alloy comprising, in% by weight:

38 <Ni + Co + Cu <45%

Co <10%

Cu <5%

0.5% <Ti + Al <5.5% Cr <3%

If ≤ 1%

Mn <1%

C <0.25%

Nb + Ta + Mo + W + Zr + Hf + V <6% Mg ≤0.10%

Ca ≤O.10% S <0,02% P <0,04% B ≤ 0,005%, the complement being iron and possible impurities resulting from the elaboration, to obtain a wire rod, which is etched eventually,

- then shaping said machine wire by cold plastic deformation, in one or more passes, with or without intermediate annealing, - then annealing said shaped wire, and

- subjecting it to an aging treatment and possibly a final drawing operation, in any order.

The invention may also include the following variants, taken individually or in combination:

- the carbon content is less than or equal to 0.10%, or even less than or equal to 0.05%, the hot rolling is carried out with a reduction rate such that the wire obtained has a diameter less than or equal to 11 mm,

- shaping by cold plastic deformation is carried out with a reduction rate of between 10 and 85%, - annealing is carried out statically, at a temperature between

750 and 950 ° C, or

- the annealing is carried out on parade, at a temperature between 950 and 1150 ° C,

the method comprises an aging treatment carried out statically, at a temperature of between 600 and 750 ° C., or

the process comprises an aging treatment carried out at the parade, at a temperature of between 700 and 950 ° C.,

the method comprises an aging treatment, after the annealing of the shaped wire, the method comprises a drawing operation, following said aging treatment, or

- The process comprises, at the end of the annealing treatment, a drawing operation followed by an aging treatment.

A second object of the invention consists of a metal wire, the composition of which comprises in% by weight:

38 <Ni + Co + Cu <45% Co <10% Cu <5% 0.5% <Ti + Al <5.5%

Cr <3%

If ≤ 1%

Mn ≤ 1%

C <0.25% Nb + Ta + Mo + W + Zr + Hf + V <6%

Mg <0.10% Ca <0.10% S <0.02% P <0.04% B <0.005%, the balance being iron and possible impurities resulting from the production.

In a preferred embodiment, the average grain size in the transverse direction of the wire is between 5 and 160 μm, particularly preferably, between 10 and 80 μm, and more particularly preferably, between 20 and 40 .mu.m.

In another preferred embodiment, the coefficient of thermal expansion of the alloy between 20 and 240 ° C is less than or equal to 6.10 ^"δ / ° C, preferably less than or equal to 4.0.10 ^{" 6} / ° C.

Finally, the third object of the invention is an electric cable for a high-voltage line comprising a metal wire according to the invention, said wire having been coated with a metal coating capable of transporting electrical energy, such as than preferably aluminum, zinc or copper, or one of their alloys.

Cables with a breaking strength greater than or equal to 900 MPa, or even greater than or equal to 1100 MPa, or even greater than or equal to 1200 MPa are preferred. The invention will now be described in more detail, but without limitation, and illustrated by the examples which follow.

To make a thin drawn wire with a diameter less than or equal to 2 mm, a wire rod with a diameter greater than or equal to 5 mm is used made of Fe-Ni alloy, which comprises the following elements:

- nickel with a content of between 38 and 45%, optionally substituted by cobalt and / or copper up to a height of 10%, preferably 5%, and more preferably less than 0.5% for cobalt because of its cost, and 5% for copper. Respecting the range of these elements conventionally makes it possible to obtain a low coefficient of thermal expansion. - titanium and / or aluminum in a cumulative content of 0.5 to 5.5%.

One or the other of these elements, combined with nickel, makes it possible to obtain the formation of a γ 'type hardening phase of formula Ni ₃ (Ti, AI), which makes it possible to obtain good resistance characteristics. mechanical. It is preferred that the titanium content is less than or equal to 3.5% and the aluminum content less than 1%. In another preferred embodiment, the titanium content is greater than or equal to 0.5%.

- niobium and / or tantalum and / or molybdenum, and / or tungsten, and / or zirconium, and or hafnium and / or vanadium, in a maximum cumulative content of 6%. These elements allow the alloy matrix to harden, but tend to increase the coefficient of thermal expansion, hence the limitation of their content. The same applies to chromium, which also plays a hardening role.

- carbon with a maximum content of 0.25%. This element is used as a deoxidizer, but its content is limited because it makes the alloy fragile. This is why it is preferable to limit its content to 0.1%, or even to

0.05%.

- silicon and / or manganese, used as deoxidizers. Their content is limited to 1% by weight, because they tend to increase the coefficient of thermal expansion. The manganese content is preferably less than 0.5% for the same reason.

The other elements mentioned, such as Mg, Ca, S, P and B, are considered as impurities.

The wire according to the invention can be manufactured by any suitable process. By way of illustration, a possible manufacturing method will be described, described for information but not limiting. With the steel which has just been defined, a wire rod with a diameter generally less than or equal to 11 mm is first manufactured, by a conventional hot rolling operation.

The wire rod is then pickled, then shaped by cold plastic deformation to a diameter generally less than or equal to 6 mm, in one or more stages of several passes each, with or without intermediate heat treatment. The purpose of cold plastic deformation is, in particular, to reduce the cross-section and, possibly, to give the cross-section of the wire the desired shape (round, square, triangle, etc.). This plastic deformation can be carried out by drawing, by rolling or by any other method of manufacturing a wire by cold plastic deformation. However, it is preferred to shape by drawing.

Before the last wire drawing to reach the final diameter, which is generally less than or equal to 3 mm, the wire is subjected to a softening annealing, in order to restore its deformation capacity after the hardening undergone. This annealing can be done in static, as in the parade.

This drawing operation can be carried out in one or more passes and remains optional, the final diameter of the wire having been obtained previously during the cold shaping carried out following hot rolling.

To obtain the desired mechanical properties, it is necessary to carry out an aging heat treatment, which makes it possible to precipitate the hardening phase of type γ 'of formula Ni ₃ (Ti, AI). This aging treatment can consist of heating for a time between 1 min and 3 hours, at a temperature between 600 and 750 ° C in static or at the parade at a temperature of 700-950 ° C.

The aging treatment can be carried out either directly after the annealing preceding the possible last wire drawing, or after having carried out this last wire drawing.

By way of example, two drawn wire A and B of 3 mm were produced, in accordance with the invention, starting from a machine wire of 11 mm in diameter, consisting of an alloy whose chemical composition was as follows, in% by weight:

Wire A was pickled and drawn in 6 passes until it reached a diameter of 3.0 mm, then annealed at 1125 ° C in the process and aged in a static oven at 730 ° C.

Wire B was pickled and then drawn in 2 passes until it reached a diameter of 6.5 mm, annealed in the oven at a temperature of 1125 ° C, drawn up to 5.0 mm, annealed in the process at a temperature of 1125 ° C and aged in static oven at a temperature of 730 ° C, then drawn in 6 passes to 3.0 mm.

The mechanical and dilatometric characteristics obtained are collated in the following table:

Claims

1. A method of manufacturing an alloy metal wire having high mechanical strength and a low coefficient of thermal expansion, comprising the steps consisting in:

hot rolling an alloy comprising, in% by weight:

38 <Ni + Co + Cu <45% Co <10% Cu <5% 0.5% <Ti + Al <5.5%

Cr <3%

If ≤ 1%

Mn ≤ 1%

C <0.25% Nb + Ta + Mo + W + Zr + Hf + V <6%

Mg <0.10% Ca <0.10% S <0.02% P <0.04% B <0.005%, the remainder being iron and possible impurities resulting from the production, to obtain a wire rod , which we possibly strip,

then shaping said wire rod by cold plastic deformation, in one or more passes, with or without intermediate annealing,

- then annealing said shaped wire, and

2. The method of claim 1, further characterized in that the carbon content is less than or equal to 0.10%.

3. The method of claim 2, further characterized in that the carbon content is less than or equal to 0.05%.

4. Method according to any one of claims 1 to 3, further characterized in that said shaping by cold plastic deformation, is carried out with a reduction rate of between 10 and 85%.

5. Method according to any one of claims 1 to 4, further characterized in that said annealing is carried out statically, at a temperature between 750 and 950 ° C.

6. Method according to any one of claims 1 to 4, further characterized in that said annealing is carried out in the process, at a temperature between 950 and 1150 ° C.

7. Method according to any one of claims 1 to 6, further characterized in that it comprises an aging treatment carried out statically, at a temperature between 600 and 750 ° C.

8. Method according to any one of claims 1 to 6, further characterized in that it comprises an aging treatment carried out at the parade, at a temperature between 700 and 950 ° C.

9. Method according to any one of claims 1 to 8, further characterized in that it comprises an aging treatment, after the annealing of the work hardened wire.

10. The method of claim 9, further characterized in that it comprises a drawing operation, following said aging treatment.

1 1. Method according to any one of claims 1 to 8, further characterized in that it comprises, after the annealing treatment, a drawing operation followed by an aging treatment.

12. Alloy metal wire, the composition of which comprises in% by weight:

38 <Ni + Co + Cu ≤ 45%

Co <10%

Cu <5%

0.5% <Ti + Al <5.5% Cr <3%

If ≤ 1%

Mn ≤ 1%

C <0.25%

Nb + Ta + Mo + W + Zr + Hf + V <6% Mg <0.10%

Ca <0.10%

S <0.02%

P <0.04%

B <0.005%, the remainder being iron and any impurities resulting from the preparation.

13. A wire according to claim 12, further characterized in that the average grain size in the transverse direction of said wire is between 5 and 160 microns.

14. The wire according to claim 13, further characterized in that said grain size is between 10 and 80 microns.

15. The wire of claim 14, further characterized in that said grain size is between 20 and 40 microns.

16. Wire according to any one of claims 12 to 15, further characterized in that the coefficient of expansion of the alloy between 20 and 40 ° C is less than or equal to 6.10 ^"6 / ° C.

17. The wire of claim 16, further characterized in that the coefficient of expansion of the alloy between 20 and 40 ° C is less than or equal to 4.0.10 ^"6 / ° C.

18. Electric cable for high-voltage line comprising a metal wire according to any one of claims 12 to 17, or obtained by the method according to any one of claims 1 to 11, said wire having been coated using '' a metallic coating capable of transporting electrical energy.

19. The cable of claim 18, further characterized in that its breaking strength is greater than or equal to 900 MPa.

20. The cable of claim 19, further characterized in that its breaking strength is greater than or equal to 1100 MPa.

21. The cable of claim 20, further characterized in that its breaking strength is greater than or equal to 1200 MPa.