Method for producing an hshcca conductive wire, intended in particular for obtaining a hshcca coated thin wire

Abstract

The invention relates to a method for producing an HSHCCA conductive wire from an alloy consisting of chromium (0.2 to 0.6%), zirconium (0.02 to 0.06%), phosphorus (less than 0.02%) and impurities to be avoided (less than 0.1%). After melting the various components, continuous casting through a die so as to obtain a bar, followed by solidification and cooling thereof, the following steps are carried out: d) a first cold operation of reducing the cross section of the bar in order to obtain the shape and cross section of the wire; e) an under-tempering heat treatment on the wire; f) carrying out a second cold operation of reducing the cross section of the wire in order to obtain the final shape and cross section of the conductive wire.

Description

Description Title of the invention: Method for manufacturing an HSHCCA conductive wire, intended in particular for obtaining a thin HSHCCA coated wire

[0001] The present invention relates to the field of conductive wires made from a copper-based alloy.

[0002] The present invention relates more specifically to a method for manufacturing a HSHCCA conductive wire having a diameter between approximately 1 and approximately 2 mm and which has high mechanical characteristics (HS for "High Strength", i.e., high resistance), high conductivity (HC for "High Conductivity") and obtained from a copper-based alloy (CA for "Copper Alloy").

[0003] From this 1 to 2 mm wire, a fine HSHCCA coated wire with a diameter between 0.03 mm and 0.3 mm can then be manufactured, which can be used for the manufacture of very high performance electrical cables.

[0004] In the rest of the text, the expression "thin wire" or "thin conducting wire" refers to a wire between 0.03 and 0.3 mm, preferably between 0.05 and 0.3 mm.

[0005] Therefore, the HSHCCA conductive wire with a diameter between 1 and 2 mm, obtained by implementing the present process, can be described as an "intermediate" conductive wire since it can undergo further transformations.

[0006] However, the HSHCCA thread could also constitute a finished product in itself.

[0007] The present invention also relates to a method of obtaining a fine HSHCCA coated wire, with a diameter between 0.03 and 0.3 mm, from an intermediate HSHCCA conductive wire with a diameter between 1 and 2 mm.

[0008] In the state of the art, patent documents disclosing manufacturing processes for fine conductive wires that can be described as HSHCCA wires are known.

[0009] This is notably the case of the French patent published and issued under number FR 3 078 078, belonging to the same company filing the present application, which relates to a process for manufacturing a fine conductive wire, or a catenary contact wire.

[0010] This French patent describes, more specifically, a process for manufacturing a conductive wire from an alloy consisting of chromium in a proportion of between 0.1 and 0.6% by mass, zirconium in a proportion of between 0.02 and 0.06% by mass, phosphorus in a proportion of less than 0.02% by mass, the rest of the alloy being copper and unavoidable impurities in a proportion of less than 0.1% by mass.

[0011] The process covered by French patent FR 3 078 078 comprises the following steps:

[0012] a) melting of the different components of the alloy, namely copper, chromium, zirconium and phosphorus, at a temperature above 1200°C, preferably between 1200°C and 1300°C;

[0013] b) continuous casting through a cylindrical die having a diameter D less than 30 mm, allowing to obtain a bar of a diameter close to the diameter D of the die with the maintenance of the liquid metal in the casting furnace at a temperature between 1100 and 1300°C;

[0014] (c) solidification of said bar and cooling to a temperature below 100°C, the rate of cooling being at least 10°C / s until a temperature of the bar of 1060°C is reached, then at least 15°C / s between 1060 and 1040°C, then at least 20°C / s between 1040 and 1030°C, then at least 25°C / s between 1030 and 1000°C, then at least 30°C between 1000 and 900°C, then at least 20°C / s for temperatures below 900°C, until the bar is cooled to a temperature of no more than 100°C;

[0015] d) at least one drawing operation is carried out on said bar to obtain the final shape and cross-section of the wire, in particular wire drawing to obtain a fine wire of a diameter d1 between 30 µm and 3 mm, preferably between 0.08 mm and 0.3 mm;

[0016] Note here that, possibly, following this step d) of wire drawing, a step may be implemented in which a surface treatment operation is carried out by depositing a thin layer of a nickel or silver coating, preferably after surface preparation by cleaning, so as to prevent the formation of oxides during the subsequent use of the cable which would generate risks of corrosion, welding difficulties or high frequency conductivity.

[0017] e) final heat treatment, or final tempering treatment, at a temperature between 450 and 500°C for a period of between 1 h and 4 h.

[0018] The conductor wire thus obtained, following the implementation of these steps, has, on the one hand, a load resistance at break Rm greater than or equal to 414 MPa, on the other hand an electrical conductivity greater than or equal to 85% IACS (International Annealed Copper Standard), and a minimum elongation of 6 to 9% depending on the diameter of the wire.

[0019] It is also indicated that two wire drawing operations can be implemented during the manufacturing process of a conductive wire.

[0020] Thus, in this case, a first wire drawing is carried out following step c) of solidification of said bar and rapid cooling.

[0021] The second wire drawing can be carried out after the surface coating step with silver or nickel.

[0022] However, it is also possible that this second wire drawing is implemented directly after the first wire drawing step d).

[0023] Typically, good practice is to separate wire drawing into two phases, a first phase before the surface preparation and silvering operation, which allows going from the initial diameter of the bar, D0 less than 30 mm, at the exit of the solution treatment of step c), to a wire of diameter noted DA, between 30 pm and 3 mm.

[0024] On this wire with diameter DA the silvering (or nickel plating) treatment is carried out, then a second phase by drawing the silver or nickel-plated wire allows obtaining the final diameter DF, less than DA and greater than 30 pm, preferably between 80 and 300 pm.

[0025] The heat treatment is then carried out, therefore on a wire which has reached its final shape and cross-section, after coating and drawing.

[0026] Thus, the invention which is described in French patent FR 3 078 078 consists of a process which integrates the solution treatment (step c)) directly during the casting process, after complete solidification.

[0027] The process described here imposes a particular cooling kinetics (or cooling rate), which starts at 1060°C.

[0028] Such a cooling kinetic allows for maximum dissolution of the chromium and zirconium present in the starting alloy. Consequently, using the process described here, the proportion of Cr and Zr atoms outside of solution is considerably reduced. However, it is these out-of-solution atoms, which are only a few micrometers in size, that cause wire breakage during drawing, especially when the desired wire diameter is small, particularly less than 0.1 mm.

[0029] In an earlier, more traditional wire manufacturing method described in European patent EP 0 902 096, the solution treatment is carried out on a diameter of 6.35 mm or less, at a temperature between 870 and 982 °C.

[0030] Such a temperature, much lower than in the previously described French patent, does not allow the advantages highlighted in said patent, in particular limiting wire breakage during wire drawing.

[0031] However, the method of European patent EP 0 902 096 has the advantage of allowing the use of traditional means to carry out the solution treatment and quenching of the wire.

[0032] In the case of European patent EP 0 902 096, the process begins with a solution treatment between 870 and 982 °C, as mentioned above, followed by a first drawing stage to bring the wire to an intermediate diameter, between 0.762 and 3.175 mm, followed by an intermediate tempering heat treatment at a temperature between 316 and 538 °C, for a duration of between 15 min and 10 h.

[0033] After this heat treatment, a second drawing stage is carried out to bring the wire to its final diameter, less than or equal to 0.254 mm.

[0034] A final tempering treatment is then carried out, the conditions of which are defined in the same way as those implemented during the intermediate heat treatment, from 15 min to 10h, at a temperature between 316 and 538 °C.

[0035] Thus, we usually go through a wire of intermediate diameter, between the solution treatment and the final diameter of the product, before making, for example, a stranded cable by means of a plurality of wires obtained by one or the other of these processes.

[0036] In prior art patents, the characteristics of the finished HSHCCA fine wire, after the final tempering heat treatment, are defined by ASTM B624 with a tensile strength Rm greater than or equal to 414 MPa, an electrical conductivity greater than or equal to 85% IACS, and a minimum elongation of 6 to 9%, depending on the wire diameter.

[0037] In the present invention, it was sought to use the intermediate step, during which the wire is brought to an intermediate diameter, before the final diameter, this step being generally necessary, in order to design an innovative HSHCCA conductive wire, in particular whose flexibility is improved and optimal compared to wires known in the prior art.

[0038] Such an HSHCCA conductor wire will, on the one hand, facilitate the implementation of subsequent complementary steps, in particular to avoid breakage during subsequent wire drawing and to facilitate the coating of said innovative conductor wire, which can then be described as "intermediate", with silver or nickel, and, on the other hand, improve the mechanical characteristics of the coated conductor wire, or HSHCCA coated wire, obtained from this intermediate HSHCCA conductor wire, and also, finally, improve the characteristics of a conductor cable made from a plurality of such HSHCCA coated wires.

[0039] In an inventive approach, the inventors conceived of first implementing the initial steps of the manufacturing process for a conductive wire as described in the previous patent FR 3 078 078, and then defining a specific wire diameter Di, between the diameter De of the bar following casting, and the diameter DF of the finished fine conductive wire, on which wire of diameter Di will be implemented, in combination, an intermediate and original heat treatment process, corresponding to an under-tempering treatment and different from the final heat treatment, then an additional operation of reducing the cross-section, particularly limited, of the wire to a wire diameter noted, in the rest of the application, DA.

[0040] Next, to produce the HSHCCA coated fine conductive wire, it will be necessary to start with this innovative HSHCCA conductive wire and implement the following steps:

[0041] - silver and nickel plating treatment;

[0042] - section reduction or final wire drawing;

[0043] - final heat treatment.

[0044] By combining, in the end, a plurality of fine HSHCCA coated conductive wires, in particular between 2 and 400 wires, in stranding or braiding operations, the conductive cable intended for commercialization is finally obtained.

[0045] To this end, the invention relates to a method for manufacturing a flexible HSHCCA conductive wire (for "High Strength High Conductivity Copper Alloy," i.e., a copper-based alloy with high strength and high conductivity), intended for the subsequent manufacture of a thin HSHCCA-coated conductive wire, from an alloy consisting of chromium in a proportion of between 0.2 and 0.6% by mass, zirconium in a proportion of between 0.02 and 0.06% by mass, phosphorus in a proportion of less than 0.02% by mass, the remainder of the alloy being copper and impurities to be avoided, the sum of whose proportions does not exceed 0.1% by mass, said method comprising at least the following steps:

[0046] - melting of the different components of the alloy, namely copper, chromium, zirconium and phosphorus, at a temperature above 1200 °C, preferably between 1200 °C and 1300 °C;

[0047] - continuous casting through a cylindrical die with a diameter D less than 30 mm, allowing the production of a bar with a diameter DC close to the diameter D of the die with the maintenance of the liquid metal in the casting furnace at a temperature between 1100 and 1300 °C;

[0048] - solidification of said bar and cooling to a temperature below 100 °C, the cooling rate being at least 10 °C / s until a temperature of the bar of 1060 °C is reached, then at least 15 °C / s between 1060 and 1040 °C, then at least 20 °C / s between 1040 and 1030 °C, then at least 25 °C / s between 1030 and 1000 °C, then at least 30 °C between 1000 and 900 °C, then at least 20 °C / s for temperatures below 900 °C, until the bar is cooled to a temperature of no more than 100 °C;

[0049] - said process being characterized in that it comprises, following this solidification step, the following steps, taken in order:

[0050] - first cold reduction operation of greater than 99% of said bar to obtain the shape and cross-section of the wire before heat treatment, with a diameter Di between Dimin equal to 1 mm and Dimax equal to 2 mm, the cross-section reduction rate being calculated using the following mathematical formula: (From 2 - Di 2 ) / Dc 2 , the section reduction rate being expressed as a percentage;

[0051] - heat treatment of under-tempered wire with a diameter D1 at a temperature between a temperature Tmin equal to 440°C and a temperature Tmax equal to 460°C, for a holding time between 3 and 9 hours at Tmin and between 1 and 3 hours at Tmax, or for a holding time proportionate to an intermediate temperature between Tmin and Tmax;

[0052] - carrying out at least one second cold reduction operation of 5 to 20% on said wire with a diameter Di to obtain the shape and cross-section of the flexible HSHCCA conductor wire with a diameter denoted DA, the cross-section reduction rate being calculated using the following mathematical formula: (D1 2 - DA 2 ) / DI 2 , the section reduction rate being expressed as a percentage;

[0053] said HSHCCA conductor wire having a minimum break load resistance Rm greater than or equal to 500 MPa, and an electrical conductivity between 83 and 90% IACS (International Annealed Copper Standard) and an elongation of less than 6%.

[0054] Note that the mechanical characteristics of the HSHCCA conductor wire according to the present invention are measured, with respect to Rm, Rp, and elongation A%, using a tensile test carried out in accordance with EN ISO 6892-1 (2019). Regarding conductivity (%IACS), a resistivity measurement (pohm-cm) is performed according to ASTM B 63 (2018), the result then being converted into conductivity using the following calculation: Conductivity (%IACS) = (1.724 / resistivity) x 100, the resistivity being expressed in pohm-cm.

[0055] According to specific methods of implementing the process:

[0056] - the heat treatment of under-revenue from step e) is carried out at a temperature of 460 °C, for a period of between 1 h and 3 h, more preferably for a period of 2 h;

[0057] - the heat treatment of under-revenue from step e) is carried out at a temperature of 440 °C, for a period of between 3 h and 9 h, more preferably for a period of 6 h;

[0058] - said HSHCCA conductor wire has a diameter DA between DAmin equal to 0.89 mm and ÜAmax equal to 1.95 mm, depending on the starting diameter D1 and the applied section reduction rate;

[0059] - the implementation of step f) on a wire of diameter D1, obtained following step e), in combination with step e), is capable of reducing the electrical conductivity by at least 2% IACS, and of reducing the elongation of said wire by at least 40% of its initial value at the end of step e), and of increasing the value of the load resistance at break Rm by at least 8%; It is therefore possible to implement a control step to confirm the effects of step f) on a wire of diameter Di, obtained following step e), in combination with step e), step f) resulting in a decrease in electrical conductivity of at least 2% IACS, and a decrease in the elongation of said wire of at least 40% of its initial value at the end of step e), and an increase in the value of the load resistance at break Rm of at least 8% of its initial value at the end of step e);

[0060] - step f) of cold section reduction of 5 to 20% is followed by a step f1) of conditioning the HSHCCA conductor wire by bending into a drum or by winding onto a reel or drum;

[0061] The present invention also relates to a method for manufacturing a thin HSHCCA coated conductive wire from the HSHCCA conductive wire obtained according to the detailed process above, in which, after step f) of cross-section reduction, the following steps are carried out: • Silver plating or nickel plating treatment on the HSHCCA conductor wire with a diameter noted DA; • Third cold cross-section reduction operation on said coated HSHCCA conductor wire to obtain the final shape and cross-section of the coated HSHCCA fine conductor wire, with a diameter noted DF; • Final heat treatment to obtain the HSHCCA coated fine conductor wire.

[0062] Preferably, in this process:

[0063] - the third cold section reduction operation consists of wire drawing to go from DA to DF, with DF between 0.05 mm and 0.3 mm;

[0064] - the final heat treatment is carried out at a temperature between 450 °C and 550 °C, with a holding time between 1 h and 3 h;

[0065] - said HSHCCA coated fine conductor wire has a breaking load resistance Rm greater than 450 MPa, an electrical conductivity greater than 90% IACS and an elongation A greater than 6%.

[0066] The present invention also relates to a method of manufacturing a conductive cable from a plurality of identical HSHCCA coated fine conductive wires, obtained according to the method, assembled by a stranding operation to obtain said conductive cable.

[0067] Other objects and advantages of the present invention will become apparent during the following description relating to embodiments which are given only as indicative and non-limiting examples.

[0068] Understanding this description will be facilitated by referring to the attached drawings, in which:

[0069] [Fig.1 A] and [Fig.1 B] correspond to two graphs; the first, in figure [Fig.1 A] showing the effect of work hardening, by a reduction of section, for different reductions of section from 10 to 75% on copper, and of the annealing temperature (on the x-axis, in degrees Celsius °C), on the Vickers hardness (HV, on the y-axis) of copper Cu-a1, for an annealing of one hour; the second graph in figure [Fig.1 B] represents the variation of the tensile strength (*1000 psi) as a function of temperature for different concentrations of Zr in the alloy;

[0070] [Fig.2A] and [Fig.2B] correspond to two graphs, from chapter 3 "structural hardening" publication CICLA (Centre d'information du Cuivre, Laitons et Alliages), the first, in figure [Fig.2A], illustrates the variation of the hardness (Brinell hardness on the ordinate) of a copper with 0.6% chromium quenched (at 1030°C / 10 min / water), as a function of the duration (min then hours, on the abscissa) and of different tempering temperatures between 350 and 550 °C; on figure [Fig.2B] is illustrated the variation of the electrical conductivity (IACS %) of a copper with 0.6% chromium quenched (at 1030°C / 10 min / water), as a function of the duration (min then hours, on the abscissa) and of different tempering temperatures between 350 and 550 °C;

[0071] [Fig.3] corresponds to a scatter plot illustrating, for an imposed section reduction of 7%, followed by an intermediate heat treatment, under different time and temperature conditions, namely 480°C for 2h, or 500°C for 3h, or 460°C for 2h, the elastic limit values ​​(Rp, in MPa, on the ordinate), and IACS conductivity (on the abscissa, in % IACS) of the HSHCCA conducting wire obtained, in order to demonstrate the interest and effect of the process of the invention;

[0072] [Fig. 4] corresponds to a graph in the form of two histograms illustrating the dispersion of elongation values ​​(A in %) according to the conditions implemented during the intermediate heat treatment step, namely 460°C for 2 hours for the histogram in grey, located on the left of the figure, and at 440°C for a holding time of 2h as well, with regard to the histogram shown in black color, on the right.

[0073] [Fig. 5] corresponds to a graph with two curves representing the evolution of the IACS conductivity (in %) on the one hand, and of the elongation (in %) on the other hand, as a function of the rate of section reduction imposed during step f) of section reduction, after a heat treatment at 460 °C for a duration of 2h.

[0074] The present invention relates to a method for manufacturing a HSHCCA conductive wire, that is to say having a diameter, noted DA, preferably between about 1 mm and about 2 mm.

[0075] Such a conductive wire can, in the present invention, be described as an "intermediate" wire because it is capable of being used for the subsequent manufacture of a thin HSHCCA coated conductive wire.

[0076] In other words, the HSHCCA conductor wire, at the end of the process according to the present invention, can be intended to undergo a plurality of further steps, which will be detailed later in this description, before resulting in the HSHCCA coated fine conductor wire.

[0077] The combination of a multitude of fine coated HSHCCA conductive wires, in particular between 2 and 400 fine coated conductive wires, by braiding or stranding, allows the manufacture of a conductive cable which can ultimately be marketed.

[0078] That being said, the HSHCCA connecting wire from the process of the invention could also constitute a finished product.

[0079] Returning to the HSHCCA conductor wire according to the present invention, this wire is, more particularly, manufactured from an alloy initially composed of, as a percentage by mass relative to the total mass of the alloy:

[0080] - chromium (Cr) in a proportion of between 0.2 and 0.6% by mass,

[0081] - zirconium (Zr) in a proportion between 0.02 and 0.06% by mass,

[0082] - of phosphorus (P) in a proportion of less than 0.02% by mass,

[0083] the remainder of the alloy being copper (Cu) and unavoidable impurities in a proportion of less than 0.1% by mass, in other words impurities to be avoided whose sum of proportions cannot exceed 0.1%.

[0084] The process for manufacturing an HSHCCA conductive wire according to the present invention comprises a succession of steps, namely at least the steps which will be described in detail, and in order, in the continuation of the description.

[0085] In the first stage of the process, stage a), the different components of the alloy, which have been detailed previously, namely Cu, Cr, Zr and P, are melted at a temperature greater than or equal to 1200 °C.

[0086] Preferably, the melting of the alloy constituents is carried out at a temperature between 1200 °C and 1300 °C.

[0087] Following the melting of the different constituent elements of the alloy, a step b) of continuous casting is implemented, through a cylindrical die having a diameter D less than or equal to 30 mm.

[0088] During this stage, the liquid metal is maintained in the casting furnace at a temperature between 1100 and 1300 °C.

[0089] Step b) of the process of the invention makes it possible to obtain a bar of a diameter denoted De, close to the diameter D of the die, and less than 30 mm.

[0090] Step c) of the process consists of solidifying said bar of diameter De and cooling it down to a temperature below 100 °C.

[0091] During this stage, the cooling rate is at least 10 °C / s until the bar reaches a temperature of 1060 °C, then at least 15 °C / s for a bar temperature between 1060 and 1040 °C, then at least 20 °C / s between 1040 and 1030 °C, then at least 25 °C / s between 1030 and 1000 °C, then at least 30 °C / s between 1000 and 900 °C, then at least 20 °C / s for temperatures below 900 °C, until the bar is cooled to a temperature of no more than 100 °C.

[0092] It should be noted here that steps a), b) and c) of the present process are similar to the steps implemented in the known prior art process described in French patent FR 3 078 078.

[0093] The cooling rate during step c) can be measured and / or controlled as follows: - Computer-aided design (CAD) of the tooling (die), from the liquid metal inlet zone at the pouring temperature, to the bar outlet; - Integration of all tooling components, in dimensions and physical characteristics, as a function of the temperature of the material constituting the different tooling components (Young's modulus, Poisson's ratio, material density, thermal expansion, thermal conductivity); - Integration of the physical characteristics of the metal constituting the casting bar, from the casting temperature to the exit temperature of the bar tooling; - Definition of contact conditions: tooling component / tooling component and tooling component / metal constituting the bar; - Definitions of boundary conditions, inlet temperature for water, liquid metal and starter bar, heat flux conditions (thermal resistance or heat transfer coefficient) for the surfaces of the different tooling components, and evolution of conductivity of the insulation in the cape by deliquescence; - For each test configuration, record the initial and performance conditions given by the measuring instruments; - Performing a numerical simulation (execution type "Nonlinear coupled thermomechanical analysis (transient with elapsed time 30s)", Hypermesh 2012 software; post-processing and pre-processing with Mentat 2012 and Marc 2012 solver); - Calibration of the model based on experimental results; - Reaching steady state; definition of the steady-state product temperature value at each point in 1 mm increments over 1000 mm, from the tooling inlet to the tooling outlet, along the bar axis and along a bar generatrix - Calculation of the cooling rate at each point: - For each point on the bar, association of temperature and cooling rate.

[0094] Following the implementation of step c) of solidification and cooling, we therefore have a bar, with a diameter noted De, less than or equal to 30 mm, which has undergone a particular solution treatment.

[0095] The said bar of diameter De has a particularly large length, so that it can be wound into a coil by bending before the implementation of the following steps of the manufacturing process of the HSHCCA conductor wire according to the invention.

[0096] Step d) of the present process consists of a first cold operation, in particular a drawing or wire drawing of the bar, this operation being more specifically defined by a reduction in cross-section of more than 99% of said bar to obtain the shape and cross-section of the wire before the implementation of a heat treatment step of under-tempering.

[0097] In a manner that is entirely preferable to the process of the present invention, step d) of the process allows the initial diameter De of the bar (less than 30 mm) to be moved to a diameter Di between Dimin, which is equal to 1 mm, and Dimax, which is equal to 2 mm.

[0098] Such a selected diameter helps to avoid the risks of wire breakage, which are higher as the wire diameter decreases, while also preventing excessive reduction in cross-section during a final drawing stage that could damage a previously applied coating.

[0099] Furthermore, applying the intermediate heat treatment of under-tempered wire with a diameter Di between 1 and 2 mm notably improves the breaking strength Rm, which contributes to the improvement of the flexibility of the wire obtained after step f) of cold cross-section reduction.

[0100] The cross-section reduction ratio applied during a cold operation to reduce the diameter of a bar or wire, and in this case from an initial casting diameter De to a diameter smaller than the initial diameter, namely Di, is calculated using the following mathematical formula: (De 2 - Di 2 ) / Dc 2 the section reduction rate being expressed as a percentage.

[0101] It was determined by the inventors that, following this first step d) of section reduction, the characteristics of the wire obtained, in terms of electrical conductivity, tensile strength Rm and elongation, are as follows: % IACS > 45; Rm > 430 MPa and A% > 0.5%.

[0102] However, such characteristics may not be optimal, and their dispersion may be detrimental, to the conduct of the subsequent steps usually implemented following the first phase of section reduction, namely surface preparation and silvering or nickel plating, followed by the second phase of wire drawing.

[0103] In particular, the flexibility of the wire following this first phase of section reduction is likely to be insufficient, and can therefore lead to risks of breakage at the final wire drawing stages, as well as brittleness and adhesion defects of the coating (Ag or Ni), also during the final wire drawing.

[0104] On the contrary, in the process of the invention, following the first phase of section reduction, during the subsequent heat treatment steps e) and conditioning by section reduction f) which are implemented, and which are specific to the present process of manufacturing a conductive wire of the invention, these three characteristics (% IACS, Rm and A%) will evolve, in particular as a function of the adjustment parameters of the heat treatment and the rate of section reduction applied, so as to reach particularly optimal values ​​for obtaining an HSHCCA conductive wire with improved performance.

[0105] In particular, the HSHCCA conducting wire obtained following the implementation, in combination, of steps e) and f) of the process of the invention, exhibits particularly high flexibility, this being characterized, - at least, by a load resistance at break Rm greater than or equal to 490 MPa, preferably greater than or equal to 491 MPa, preferably even greater than 495 MPa and, even more preferably, greater than or equal to 500 MPa; - preferably, in addition, by a proportionality limit (elastic limit) Rp, with (Rm - Rp) less than or equal to 35 MPa, preferably less than 25 MPa.

[0106] Indeed, a wire is considered flexible if, once bent and displaced under the effect of a force, it regains its properties when the force is removed. A flexible wire must therefore have both a high Rp value and not operate within the plastic range; consequently, its variability (Rm - Rp) is preferably between 25 and 35 MPa, to prevent the wire from deforming plastically (with a stress greater than Rp) without breaking (with a stress remaining below Rm).

[0107] Indeed, it is possible to have low Rp values ​​with a high Rm value. The relationship between the two quantities can be established as follows:

[0108] - If Rp = 350 MPa, then Rm = 450 MPa;

[0109] - If Rp = 400 MPa, then Rm = 470 MPa;

[0110] - If Rp = 450 MPa then Rm = 485 MPa;

[0111] - If Rp = 500 MPa then Rm = 525 MPa;

[0112] - If Rp = 550 MPa then Rm = 565 MPa.

[0113] Thus, typically, a wire whose Rm has a value of 470 MPa, which is traditionally considered a high value of breaking strength, has an Rp value of 400 MPa considered too low to characterize optimal flexibility, because the wire is then likely to deform plastically.

[0114] Since the breaking strength of the load Rm is greater than 490 MPa, preferably greater than 500 MPa, the value of Rp used to characterize the optimal flexibility of the HSHCCA wire of the invention is deduced by reducing this Rm value of 25 to 35 MPa, which results in a minimum Rp value between 455 and 465 MPa.

[0115] In summary, step d) defines a critical diameter range to achieve the required characteristics after the under-revenue treatment of step e).

[0116] Step f) allows the yarn to be given the necessary flexibility conditions for subsequent operations, in particular surface coating, and as will be described later, step f) also allows the equilibrium state of the chromium to be obtained after step e).

[0117] On this HSHCCA wire, exhibiting significant flexibility, it will then be particularly easy to implement further treatments to obtain a fine conductive wire coated with HSHCCA, compared with existing processes in the state of the art, which do not implement these steps e) and f) combined.

[0118] Thus, step e) of the present process consists of a heat treatment of under-tempered wire having diameter Di.

[0119] This heat treatment, which can be described as intermediate because it is carried out between two section reduction steps, is preferably carried out between a minimum temperature Tmin equal to 440°C and a maximum temperature Tmax equal to 460°C, knowing that the holding time at temperature Tmax must be between 1 h and 3 h maximum while the holding time at Tmin must be increased and between 3 h and 9 h.

[0120] In a particularly preferential manner, such an intermediate heat treatment is carried out either at a temperature equal to or about equal to 460 °C for a holding period equal to, or about equal to, 2 hours.

[0121] The term "temperature approximately equal" to a given temperature refers to a temperature varying by plus or minus 5°C, preferably plus or minus 2°C, from that given temperature. The heat treatment can therefore be carried out between 455 and 465°C, preferably between 458 and 462°C.

[0122] Similarly, "holding time approximately equal" to a given duration is understood to mean a duration varying by plus or minus 10 minutes, preferably plus or minus 5 minutes, relative to said given duration. The heat treatment can thus be implemented (at the aforementioned temperatures) between 1 h50 min (110 min) and 2 h 10 min (130 min), preferably between 1 h55 min (115 min) and 2 h05 min (125 min).

[0123] Indeed, such conditions make it possible to obtain, in the end, after the implementation of step f) which will be described below, an HSHCCA conductor wire with characteristics, in terms of Rm, A% and %IACS, which are particularly high and interesting for the following operations and the production of a thin coated HSHCCA conductor wire, and then of a conductor cable with improved performance.

[0124] The results and methods of conducting comparative tests, illustrating this improvement in characteristics, will be given below, as non-limiting examples.

[0125] However, it is also conceivable that the intermediate heat treatment of step e) of the present process may be carried out at a temperature below 460°C, in particular at a temperature of 440°C (or about 440°C), by increasing the holding time, in particular for a period of between 3 h and 9 h and, more particularly, for a period of 6 h.

[0126] It was thus determined that the under-revenue treatment in step e) is optimized between a minimum temperature Tmin of 440°C and a maximum temperature Tmax of 460°C. The minimum holding time is 1 hour at 460°C and 3 hours at 440°C, and the holding time can be adjusted proportionally for an intermediate temperature between Tmin and Tmax.

[0127] The maximum holding time is 3 hours at 460°C and 9 hours at 440°C and it can, again, be defined proportionally for an intermediate temperature between Tmin and Tmax.

[0128] Thus, for example, at an intermediate temperature of 450 °C, the holding time can advantageously be between 2 h and 6 h.

[0129] It is recalled here that a commonly applied income treatment, following a section reduction, will have two effects:

[0130] - The release of mechanical stresses accumulated by work hardening of the material during the first cold deformation;

[0131] - The diffusion of chromium and zirconium atoms put into solution during step a) through the crystal lattice.

[0132] Regarding the first effect of stress release, the greater the reduction in cross-section during cold deformation, the lower the annealing temperature.

[0133] Figure 1A attached shows the effect of work hardening by reducing the cross-section from 10% to 75% on copper, and the influence of annealing temperature and work hardening rate on the hardness of copper for one hour annealing.

[0134] It can be deduced that, for a section reduction rate greater than 99%, the first effect will be complete for tempering temperatures above 200°C.

[0135] As shown in Figure 1B, zirconium acts inversely to the cold reduction rate on the work hardening retention of the material.

[0136] In the case of a cold reduction greater than 70%, softening starts at a temperature of 300 to 400 °C.

[0137] From a concentration of 0.019% of Zr, a hardening "bump" appears due to the effect of precipitation (effect 2 above), clearly visible for a Zr concentration of 0.07%, which corresponds to a value slightly higher than the maximum concentration of 0.06% of Zr possible in the alloy on which the process of the present invention is implemented.

[0138] The alloying elements can delay the release of stresses introduced during the cold drawing of the wire, such as Zr which acts on the retention of work hardening up to temperatures of 300 to 400 °C.

[0139] In summary, the first effect will be complete at a temperature level lower than the temperature of step e) of the process of the invention.

[0140] Referring now to Figures 2A and 2B of the attached drawings, concerning the second diffusion effect of Cr and Zr atoms through the crystal lattice, during temperature increase, the Cr and Zr atoms accumulate in GP zones (or Guinier-Preston zones, < 10 nm) and form a structure semi-coherent with the matrix. These constitute a very important disturbance of the network, which manifests itself by a significant hardening, and consequently an increase in the load resistance at break Rm.

[0141] Over time, and especially under the effect of temperature, the Cr and Zr atoms gradually organize themselves inside the GP zones until the atoms are transformed into precipitates, with a structure that is inconsistent with the structure of the copper matrix.

[0142] By continuing to increase the time and temperature of tempering, the precipitates coalesce together, the treatment is then described as "over-tempering", and the softening of the material accelerates.

[0143] The tempering time to reach maximum resistance (Figure 2A) is lower the higher the temperature, and the tempering time to reach maximum conductivity is lower the higher the temperature.

[0144] Thus, for the conditions of a final temper, a maximum of mechanical resistance and electrical conductivity will be sought here, which leads to starting the transformation of the GP zones into precipitates, with an incoherent own structure, without however reaching over-tempering, which would result in the very rapid coalescence of the precipitates to dimensions of several microns, leading, on the one hand, to a decrease in mechanical resistance, difficulties in carrying out the subsequent wire drawing, and, on the other hand, to the prevention of sufficient hardening during the final tempering heat treatment.

[0145] Note that the transformation of GP zones into incoherent precipitates is irreversible, except by carrying out a new solution treatment, which should be avoided for a wire diameter like that of the wire which constitutes the present invention.

[0146] It is understood that implementing a heat treatment step at this stage of the manufacturing process of a fine wire is particularly delicate, and it could be considered not to carry out such a heat treatment, after the first wire drawing stage, just as in the usual processes of the state of the art, before carrying out the silver or nickel coating stage.

[0147] In particular, the process covered by patent FR 3 078 078 does not include a heat treatment step for the production of the wire on which the silvering or nickel plating treatment is then carried out.

[0148] However, it is worth noting here that such an option presents the following difficulties:

[0149] - risk of wire breakage during the final drawing stages;

[0150] - fragility and poor adhesion of the silver or nickel plating, as the case may be, during the second phase of wire drawing;

[0151] - mechanical characteristics conform, but very close to the requirements of the ASTM B624 standard mentioned above, in other words without significant improvement in characteristics.

[0152] The present invention therefore consists of carrying out an under-tempering treatment, with a determined duration and temperature, as already defined above, and combining this under-tempering treatment with a wire drawing step with a low cross-section reduction ratio, so as to allow the characterization of an intermediate wire state, which will facilitate the subsequent manufacturing steps for obtaining the coated fine conductive wire, and will improve the performance of said wire, as well as that of a cable made from a plurality of such wires.

[0153] Thus, in step f) subsequent to the under-income treatment e), implemented in the present process, a second cold operation is carried out.

[0154] During this step f), a limited section reduction, with a rate between 5 and 20%, is implemented on said wire with an initial diameter Di, to obtain the final shape and section of the HSHCCA conductor wire, with a diameter noted DA.

[0155] Thus, considering a wire, obtained following the first drawing step d), and having a diameter Dimin equal to 1 mm, on which is applied during step f) a section reduction rate of 5% to 20%, a conductive wire HSHCCA of diameter DA between 0.97 mm and 0.89 mm (DAmin) is finally obtained.

[0156] If we now consider a wire with a diameter Dimax equal to 2 mm, on which a cross-section reduction ratio is applied during step f) of 5% to 20%, a HSHCCA conductive wire with a diameter DA between 1.95 mm (ÜAmax) and 1.79 mm is finally obtained.

[0157] Consequently, at the end of the process of the invention, we obtain a conductive wire HSHCCA having a diameter between about 1 mm (minimum diameter DAmin of 0.89 mm) and about 2 mm (maximum diameter ÜAmax of 1.95 mm).

[0158] The inventors have been able to demonstrate that the implementation of step f) on a wire of diameter Di, obtained following step e), in combination with step e), is capable of reducing the electrical conductivity by at least 2% IACS, and of reducing the elongation of said wire by at least 40% of its initial value at the end of step e).

[0159] In addition, the limited section reduction of step f) results in an increase in the value of the load resistance at break Rm of at least 8%.

[0160] Therefore, after implementation of the process of the invention, said HSHCCA conducting wire has the following characteristics:

[0161] - a minimum breaking load resistance Rm greater than or equal to 490 MPa, and more preferably greater than 500 MPa;

[0162] - an electrical conductivity of between 83 and 92% IACS (International Annealed Copper Standard), preferably between 83 and 91% IACS, preferably between 83 and 90% IACS, and

[0163] - an elongation of less than 6%, which results from the cold section reduction, between 5 and 20% of step f), applied after the under-tempering treatment of step e).

[0164] Preferably, the value of the elongation after the implementation of the steps of the process of the invention, in particular after step f), is between 2.5 and 5%, and, more advantageously still, between 4 and 5%.

[0165] Note that, in one alternative embodiment, step f) of cold drawing could potentially have a cross-sectional reduction ratio greater than 20%; however, in this event, this drawing necessarily requires passing through an intermediate stage which corresponds to a cross-sectional reduction ratio between 5 and 20%, so that, in this intermediate state, the resulting yarn has the same characteristics as those mentioned above.

[0166] Similarly, it could be considered to implement a cold wire drawing step with a section reduction rate of less than 5%, but which would in this case necessarily be followed by wire drawing with a section reduction rate between 5 and 20% to obtain the desired characteristics.

[0167] Advantageously, for the implementation of steps e) and f), coils of wire, with a mass of 500 to 1000 kg, can be placed in a static tempering furnace, under atmosphere.

[0168] From each coil, the HSHCCA conductor wire is produced by applying the limited section reduction between 5 and 20%, then it can be conditioned, in a step f1), by bending into a drum or by winding onto a reel or drum, with a quantity of wire from 110 to 260 kg, on average 200 kg.

[0169] Note that, in the case of drum packaging, the HSHCCA conductive wire coils are positioned flat and the wire must not turn around in the drum, in order to ensure subsequent correct unwinding of the wire.

[0170] The limited section reduction, with a rate between 5 and 20%, greatly facilitates the proper conditioning of the wire, while the quality of its surface is very favorable for subsequent silver or nickel coating treatment, while maintaining optimal wire flexibility.

[0171] Indeed, from the HSHCCA conductive wire obtained by implementing the steps of the process of the present invention, detailed above, it is then possible to obtain a thin HSHCCA coated conductive wire, by implementing the following steps, following step f) of limited cross-section reduction between 5 and 20% and allowing to obtain said HSHCCA wire of diameter DA substantially between about 1 and about 2 mm (more precisely between DAmin of 0.89 mm and ÜAmax of 1.95 mm):

[0172] g) silver plating or nickel plating treatment on the HSHCCA conductor wire with a diameter noted DA, which can then be described as intermediate;

[0173] (h) third cold cross-section reduction operation on said HSHCCA intermediate conductor wire to obtain the final shape and cross-section of the HSHCCA coated fine conductor wire, with a diameter denoted DF, between 0.03 and 0.3 mm;

[0174] i) final heat treatment to obtain the HSHCCA coated fine conductor wire.

[0175] Preferably, the third cold section reduction operation of the aforementioned step h) consists of wire drawing to go from a diameter DA (between, for the record, DAmin equal to 0.89 mm and DAmax equal to 1.95 mm) to a final diameter noted DF, with DF between DFmin equal to 0.05 mm and ÜFmax equal to 0.3 mm.

[0176] Thus, we understand that the final section reduction of step h) is carried out according to a section reduction rate of between 88.6 and 99.9%, following a section reduction of 5% to 20% during step f) carried out on a wire with a diameter of between 1 and 2 mm.

[0177] Advantageously, the final heat treatment is carried out at a temperature between 450 °C and 550 °C, with a holding time at this temperature of between 1 h and 3 h.

[0178] The implementation of these final steps makes it possible to obtain a thin HSHCCA coated conductor wire which has particularly interesting characteristics, namely a load resistance at break Rm greater than 450 MPa, an electrical conductivity greater than 90% IACS and an elongation A greater than 6%.

[0179] Consequently, the finished cable, obtained by assembling a plurality of such thin conducting wires, will perform better than state-of-the-art cables.

[0180] If we now summarize the entire process leading to the manufacture of a thin HSHCCA coated conductor wire, it therefore presents the following steps, taken in order:

[0181] a) melting of the different components of the alloy, namely copper (remaining), chromium (between 0.2 and 0.6%), zirconium (between 0.02 and 0.06%), phosphorus (less than 0.02%), at a temperature above 1200 °C, preferably between 1200 °C and 1300 °C;

[0182] b) continuous casting through a cylindrical die having a diameter D less than 30 mm, allowing to obtain a bar of a diameter De close to the diameter D of the die with the maintenance of the liquid metal in the casting furnace at a temperature between 1100 and 1300 °C;

[0183] (c) solidification of said bar and cooling to a temperature below 100 °C, the rate of cooling being at least 10 °C / s until a temperature of the bar of 1060 °C is reached, then at least 15 °C / s between 1060 and 1040 °C, then at least 20 °C / s between 1040 and 1030 °C, then at least 25 °C / s between 1030 and 1000 °C, then at least 30 °C between 1000 and 900 °C, then at least 20 °C / s for temperatures below 900 °C, until the bar is cooled to a temperature not exceeding 100 °C;

[0184] d) first cold reduction operation of cross-section greater than 99% of said bar to obtain the shape and cross-section of the wire before heat treatment, with a diameter Di between Dimin equal to 1 mm and Dimax equal to 2 mm;

[0185] e) heat treatment of under-tempered on said wire with a diameter Di either at a temperature less than or equal to 460 °C for a holding time of between 1 and 3 h, or at a temperature less than 460 °C and greater than or equal to 440 °C by increasing the holding time between 3 and 9 hours, preferably at 460 °C for 2 h or 440 °C for 6 h;

[0186] f) carrying out at least one second cold reduction operation of 5 to 20% on said wire with a diameter Di to obtain the final shape and section of the HSHCCA conductor wire, with a diameter noted DA, between DAmin equal to 0.89 mm and ÜAmax equal to 1.95 mm, depending on the starting diameter Di and the applied section reduction rate;

[0187] g) silver plating or nickel plating treatment on the HSHCCA conductor wire with a diameter noted DA between DAmin equal to 0.89 mm and ÜAmax equal to 1.95 mm;

[0188] (h) third cold cross-section reduction operation on said HSHCCA coated conductor wire to obtain the final shape and cross-section of the HSHCCA coated fine conductor wire, with a diameter denoted DF, preferably between DFmin equal to 0.05 mm and ÜFmax equal to 0.3 mm.

[0189] i) final heat treatment to obtain the finished HSHCCA coated fine conductor wire, or HSHCCA coated wire, advantageously carried out at a temperature between 450 and 550 °C for 1 to 3 h.

[0190] The interest and effects of implementing the combined steps e) and f) in the process of the present invention for manufacturing an HSHCCA conductive wire, on the mechanical and electrical conductivity characteristics of a fine conductive wire will now be illustrated through the example below, given by way of non-limiting example.

[0191] Example: Measurement of the mechanical and electrical conductivity characteristics of thin wires after application of different heat treatments

[0192] During the tests carried out, the following steps were implemented for the manufacture of the yarns:

[0193] a) melting of the different components of the alloy, namely copper (remaining), chromium (0.2 to 0.6%), zirconium (0.02 to 0.06%) and phosphorus (< 0.02%), possibly with impurities to be avoided, the sum of whose proportions must not exceed 0.1%, the melting being carried out at a temperature of 1350 °C;

[0194] b) continuous casting through a cylindrical die having a diameter D allowing to obtain a bar of a diameter De equal to 28 mm with the maintenance of the liquid metal in the casting furnace at a temperature of 1250 to 1300 °C;

[0195] (c) solidification of said bar and cooling to a temperature below 100 °C, the rate of cooling being at least 10 °C / s until a temperature of the bar of 1060 °C is reached, then at least 15 °C / s between 1060 and 1040 °C, then at least 20 °C / s between 1040 and 1030 °C, then at least 25 °C / s between 1030 and 1000 °C, then at least 30 °C between 1000 and 900 °C, then at least 20 °C / s for temperatures below 900 °C, until the bar is cooled to a temperature not exceeding 100 °C;

[0196] d) first cold reduction operation of greater than 99% of said bar to obtain the shape and cross-section of the wire before heat treatment, with a diameter Di between 1 and 2 mm, more particularly equal to 1.5 mm; and

[0197] Following this cold drawing operation, various tempering heat treatments were implemented, namely:

[0198] - application of a temperature of 460 °C for a holding time of 2 h (conditions of the manufacturing process according to the present invention);

[0199] - application of a temperature of 480 °C for a holding time of 2 h;

[0200] - application of a temperature of 500 °C for a holding time of 3 hours.

[0201] For each of these three different heat treatments, at each conditioning, three samples are taken, and the measurements of mechanical resistance (Rp expressed in MPa) and electrical conductivity (% IACS) are carried out.

[0202] Recall here that the quantity Rp corresponds to the proportionality limit, which is considered equivalent to the elastic limit. The elastic limit is calculated over a specimen length of 100 mm, and for an elongation of 0.2%.

[0203] Regarding the resistance Rm, this corresponds to the maximum load before breakage.

[0204] Therefore, Rm is greater than Rp, statistically based on the transmitted results, and the relationship between the two quantities can be established as follows, and as already indicated above:

[0205] - If Rp = 450 MPa then Rm = 485 MPa;

[0206] - If Rp = 500 MPa then Rm = 525 MPa;

[0207] - If Rp = 550 MPa then Rm = 565 MPa.

[0208] The results in terms of mechanical resistance (Rp in MPa) and electrical conductivity (% IACS) are illustrated in the graph in the attached figure 3, for an imposed section reduction of 7% in step f) of the process, following the heat treatment.

[0209] On this graph, a point is defined on the x-axis by the average conductivity and on the y-axis by the average mechanical resistance.

[0210] The proportionality limit values ​​Rp shown in Figure 3 are translated using the quartile method in the table below (IQR corresponds to the interquartile range):

[0211] We observe:

[0212] - The mechanical resistance dispersion of the points is low for the treatment of 460 °C for 2 h (IQR equal to 31);

[0213] - The dispersion of mechanical strength increases with increasing temperature from 480 °C (2 h) to 500 °C (3 h); for these two heat treatment temperatures, the median value of Rp is virtually identical (443 MPa and 442 MPa respectively), but the interquartile range (IQR) being 59 and 152 respectively, it increases with increasing temperature.

[0214] - Maximum mechanical resistance is obtained after a treatment at 460 °C;

[0215] - The higher the heat treatment temperature above 460 °C, the more the extreme positions correspond to high conductivity and low mechanical resistance.

[0216] Of the three treatments that were tested, only the treatment at 460 °C, under-tempered, for 2 h, allows a minimum Rp value of 456 MPa to be reached, which corresponds to an Rm value equal to (456 + 35) or 491 MPa, after step f) of section reduction.

[0217] Furthermore, only one value was measured at this minimum, and all other measured Rp values ​​are greater than 465, or even 470 MPa, which leads to An Rm value exceeding 500 MPa was observed for almost all measured values. The results presented below further illustrate that the average Rm value is over 535 MPa. The same applies to conductivity values, which are concentrated between 83% and 90% IACS, although a small number of points were measured slightly above 90% IACS, and in all cases below 92% IACS.

[0218] Regarding treatments at 480 °C for 2 h and 500 °C for 3 h, 50% of the test results show an Rp value below 443 MPa (the median value for the 500 °C / 3 h conditions being 442 MPa, while the median for the 480 °C / 2 h conditions was 443 MPa), which corresponds to an Rm value below 443 + 35, or less than 478 MPa. Furthermore, minimum Rp values ​​of 350 MPa were measured for the 480 °C / 2 h conditions, and even significantly lower for 550 °C / 3 h, which is insufficient, in particular, to achieve the optimal flexibility required for the HSHCCA wire within the scope of the present invention.

[0219] Thus, the under-tempering treatment of step e) according to the process of the present invention is particularly optimized, as it allows a reduction in the dispersion of mechanical characteristics, avoiding high electrical conductivity values, which are characteristic of an over-tempering treatment.

[0220] The diagram in Figure 4 illustrates that lowering the under-tempering temperature to 440 °C, maintained for a period of 2 h, shows a lowering and greater dispersion of the after-tempering elongation value, compared with under-tempering at a temperature of 460 °C for a period of 2 h.

[0221] Indeed, for an under-temperature treatment of 440 °C for 2 h, the elongation values ​​are between 2.5 and 5% while, for the same duration and an under-temperature of 460 °C, the elongation values ​​obtained are grouped between 4 and 5%.

[0222] However, such a reduction, as well as a greater dispersion, of the elongation value after tempering leads to a reduction in the wire's flexibility, then that optimal flexibility is required for conducting subsequent conditioning and silver or nickel plating operations on the wire.

[0223] However, with regard to the other characteristics for applying a tempering treatment in step e) at a temperature of 440 °C for 2 h, the inventors have determined that:

[0224] - the electrical conductivity values ​​in % IACS are lower than those obtained for treatment at a temperature of 460 °C for a duration of 2 h, but they remain close;

[0225] - the values ​​obtained in terms of mechanical resistance are particularly high, and systematically greater than 510 MPa, or even greater than 520 MPa.

[0226] The results obtained are not included in this description.

[0227] These results, and in particular the fact that the electrical conductivity is lower, demonstrate that, for an intermediate heat treatment temperature of 440 °C, for a holding time of 2 h, the precipitation treatment of the GP zones, accumulating Cr and Zr atoms, is not completed.

[0228] Thus, it can be deduced that, at a temperature of 440 °C, an adjustment, by increasing the tempering time, as previously indicated, to a duration between 3 h and 9 h, will allow an increase in the value of the electrical conductivity, while recovering optimal elongation characteristics, similar to those obtained for treatment at a temperature of 460 °C for 2 h, and sufficiently grouped, to allow good conduct of subsequent treatment operations on the fine conductive wire, when the process is intended for the production of an intermediate wire.

[0229] Furthermore, in all cases, when the temperature is increased beyond 460 °C, particularly to a temperature of 480 °C or 500 °C, whether for 2 h or 3 h, the value of the mechanical resistance Rp decreases, and the dispersion of the results increases, so that the temperature of 460 °C, associated with a duration of 2 h or 3 h, is a maximum.

[0230] The table below compares the results in terms of mechanical characteristics, namely the tensile strength Rm (in MPa) and elongation (A%), and in terms of electrical conductivity, under the following conditions:

[0231] - after a heat treatment of under-tempered in accordance with step e) of the present invention, at a temperature of 460 °C for a holding time of 2 h;

[0232] - after a heat treatment of over-tempered at a temperature of 500 °C for a holding period of 3 h.

[0233] This table also gives the mechanical and electrical conductivity characteristics after the conditioning stage, i.e. after the application of the limited section reduction between 5 and 20% of step f) of the process of the present invention.

[0234] In this case, a 7% reduction in the wire diameter was imposed.

[0235] The measurements of the characteristics (IACS, Rm and A%) are therefore carried out after heating and after conditioning.

[0236] The under-temperature, implemented in the present process, compared to the over-temperature at 500 °C, is characterized by:

[0237] - a lower average conductivity value after tempering, namely 87% compared to almost 97%, and after conditioning, namely 85% compared to almost 96%;

[0238] - a greater increase in the average value of mechanical properties after conditioning; indeed, the Rm increases by 8% after conditioning under under-temper conditions, rising from an average of 497.4 MPa to 535.7 MPa, while the Rm only increases by 4% after the conditioning, with the conditions of over-income, increasing from 448.0 MPa to 469.4 MPa.

[0239] - a lower average residual lengthening value after conditioning, namely 4.6% against 8.6%, which corresponds to a decrease in lengthening value between after income and after final conditioning of more than 6% (from an lengthening of 11 to 4.6) i.e. a decrease of more than 40% of its initial value, more precisely a decrease equal to 58% of the initial value ((11 -4.6) / 11).

[0240] On the contrary, for a heating at 500 °C for a period of 3 h, the decrease in elongation is only around 5%, going from 9.1% after heating to 8.6% after conditioning ((9.1 -8.6) / 9.1).

[0241] The essential result that can be achieved by combining steps e) of under-tempering and f) of limited section reduction, specific to the process of the invention, is the guarantee of obtaining reproducible and homogeneous characteristics on different batches of wire, and regardless of the position of the wire coil in the furnace at the time of step e).

[0242] The cause of the dispersion of the characteristic values ​​is the transition to over-tempering during heat treatment, which manifests itself by an increase in IACS conductivity values ​​beyond 90%; it is necessary to avoid complete precipitation of chromium and maintain post-conditioning conductivity between 83 and 91% IACS, preferably between 83 and 90% IACS.

[0243] The inventors believe that step e) of under-tempering in the process of the present invention promotes the resuspension of the finest chromium precipitates by cold working, which is a highly original effect. Resuspension is characterized by a decrease in conductivity (compared to the over-tempering treatment), and it can be observed, from the results presented above, in a novel and previously undocumented manner, that the decrease in conductivity is accompanied by a substantial loss of elongation, reflecting, according to a hypothesis formulated by the inventors, the retention of very fine (nanometric) chromium precipitates.

[0244] Therefore, a shift in equilibrium occurs between precipitated chromium and chromium in solution, possible only in the presence of nanoprecipitates of chrome from steps b) and c) of the process of the invention. This concomitant decrease in conductivity and elongation for a relatively small reduction in cross-section during step f) is the way to characterize the chromium precipitates of the material of the invention associated with a sub-temperature within the limits of step e).

[0245] Such conditions implemented in the process of the invention thus also make it possible to achieve values ​​of breaking load of the fine conducting wire after step f) of the present process substantially greater, on average, than 500 MPa, the minimum values ​​measured being, in all cases, greater than 490 MPa, more particularly greater than or equal to 491 MPa.

[0246] Such results were obtained when a 7% reduction in cross-section was applied during step f). It can be deduced that the characteristics will change as the cross-section reduction increases up to a maximum of 20%.

[0247] Indeed, the values ​​of electrical conductivity and elongation will decrease, increasing the reduction in cross-section, as illustrated in the attached figure 5, while the tensile strength will increase.

[0248] However, the change is dampened with increasing section reduction (see figure 5), and beyond 20% section reduction, the values ​​of electrical conductivity and elongation decrease too significantly.

[0249] In general, in view of the foregoing, and without being limited to the example described here, it is conceivable in the process of the invention to control the equilibrium of chromium precipitation obtained at the end of step e) of the process of the invention, between the chromium nanoprecipitates and the residual chromium in solution, from steps b) and c) of the process.

[0250] This control is advantageously carried out following step f), during a step f1 '). It is carried out by measuring the effect of step f), on the evolution of the final characteristics after step f), symbolized by (**), compared to the characteristics initially reached after step e), symbolized by (*).

[0251] This control allows for verification and confirmation that, simultaneously: - for electrical conductivity %IACS* - %IACS** is greater than or equal to 2%; - for the elongation, (A%* - A%**) / A%* is greater than or equal to 0.4 x A%*.

[0252] The conductivity characteristics % IACS and elongation A % are therefore measured after step e) and after step f), in order to be able to carry out this control step f1 ').

[0253] For the record, the standards used to measure these characteristics are EN ISO 6892-1 (2019) for elongation, as well as for Rm and Rp, and ASTM B63 (2018) for the measurement of resistivity, from which conductivity is deduced by the formula: electrical conductivity (% IACS) = 1.7241 / resistivity (pohm-cm) x 100).

Claims

Demands

1. A method for manufacturing a flexible and conductive HSHCCA wire, for "High Strength High Conductivity Copper Alloy", i.e., a copper-based alloy with high strength and high conductivity, intended in particular for the subsequent manufacture of a thin coated HSHCCA conductive wire, from an alloy consisting of chromium in a proportion of between 0.2 and 0.6% by mass, zirconium in a proportion of between 0.02 and 0.06% by mass, phosphorus in a proportion of less than 0.02% by mass, the remainder of the alloy being copper and impurities to be avoided, the sum of whose proportions does not exceed 0.1% by mass, said method comprising at least the following steps: a) melting the different components of the alloy, namely copper, chromium, zirconium and phosphorus, at a temperature above 1200 °C, preferably between 1200 °C and 1300 °C;b) continuous casting through a cylindrical die having a diameter D less than 30 mm, allowing a bar of a diameter De close to the diameter D of the die to be obtained with the liquid metal maintained in the casting furnace at a temperature between 1100 and 1300 °C; c) solidification of said bar and cooling to a temperature below 100 °C, the cooling rate being at least equal to 10 °C / s until a bar temperature of 1060 °C is reached, then at least equal to 15 °C / s between 1060 and 1040 °C, then at least equal to; 20 °C / s between 1040 and 1030 °C, then at least 25 °C / s between 1030 and 1000 °C, then at least 30 °C between 1000 and 900 °C, then at least 20 °C / s for temperatures below 900 °C, until the bar is cooled to a temperature of no more than 100 °C; said process being characterized in that it comprises, following this solidification step, the following steps, taken in order: d) first cold reduction operation of greater than 99% of said bar to obtain the shape and cross-section of the wire before heat treatment, with a diameter Di between Dimin equal to 1 mm and Dimax equal to 2 mm, the cross-section reduction rate being calculated using the The following mathematical formula: (From 2 - Di 2 ) / Dc 2, the cross-section reduction rate being expressed as a percentage; e) heat treatment of under-tempered said wire with a diameter Di at a temperature between a temperature Tmin equal to 440°C and a temperature Tmax equal to 460°C, for a holding time of between 3 and 9 hours at Tmin and between 1 and 3 hours at Tmax, or for a holding time proportionate to an intermediate temperature between Tmin and Tmax; f) carrying out at least one second cold operation of cross-section reduction of 5 to 20% on said wire with a diameter Di to obtain the shape and cross-section of the flexible HSHCCA conductor wire, with a diameter denoted DA, the cross-section reduction rate being calculated using the following mathematical formula: (D1 2 - DA 2 ) / DI 2, the section reduction rate being expressed in %; said HSHCCA conductor wire having, after step f), a breaking load resistance Rm greater than or equal to 500 MPa, and an electrical conductivity between 83 and 90% IACS, for International Annealed Copper Standard, and an elongation of less than 6%.

2. A method for manufacturing an HSHCCA conductive wire according to claim 1 characterized in that the heat treatment of the under-tempered wire of step e) is carried out at a temperature of 460 °C, for a period of between 1 h and 3 h, more preferably for a period of 2 h.

3. A method for manufacturing an HSHCCA conductive wire according to claim 1 characterized in that the heat treatment of the under-tempered wire of step e) is carried out at a temperature of 440 °C, for a period of between 3 h and 9 h, more preferably for a period of 6 h.

4. A method for manufacturing an HSHCCA conductive wire according to any one of the preceding claims characterized in that said HSHCCA conductive wire has a diameter DA between DAmin equal to 0.89 mm and ÜAmax equal to 1.95 mm, depending on the starting diameter Di and the applied section reduction rate.

5. A method for manufacturing a HSHCCA conductive wire according to any one of the preceding claims, wherein a control operation f1') is applied, measuring the effects of step f) on a wire of diameter Di, obtained following step e), in combination with step e), step f) resulting in a decrease in the electrical conductivity of at least 2% IACS, and a decrease in the elongation of said wire of at least 40% of its initial value at the end of step e), and an increase in the value of the load resistance at break Rm of at least 8% of its initial value at the end of step e).

6. A method for manufacturing an HSHCCA conductive wire according to any one of the preceding claims, characterized in that step f) of cold cross-section reduction from 5 to 20%, the cross-section reduction rate being calculated using the following mathematical formula: (D1 2 - DA 2 ) / DI 2 , the section reduction rate being expressed in %, is followed by a step f1 ) of conditioning the HSHCCA conductor wire by bending into a drum or by winding onto a reel or drum.

7. A method for manufacturing a fine HSHCCA-coated conductive wire from the HSHCCA conductive wire obtained according to any one of the preceding claims, characterized in that, after step f) of cross-section reduction, the following steps are carried out: g) Silver plating or nickel plating of the HSHCCA conductive wire with a diameter denoted DA; h) A third cold cross-section reduction operation on said conductive wire HSHCCA coated to obtain the final shape and section of the HSHCCA coated fine conductor wire, with a diameter noted DF; i) Final heat treatment to obtain the HSHCCA coated fine conductor wire.

8. A method for manufacturing a fine HSHCCA coated conductive wire according to the preceding claim, characterized in that the third cold cross-section reduction operation consists of drawing to go from DA to DF, with DF between 0.05 mm and 0.3 mm.

9. A method for manufacturing a fine HSHCCA coated conductive wire according to any one of claims 7 or 8 characterized in that the final heat treatment is carried out at a temperature between 450 °C and 550 °C, with a holding time between 1 h and 3 h.

10. A method for manufacturing a HSHCCA coated fine conductive wire according to any one of claims 7 to 9 characterized in that said HSHCCA coated fine conductive wire has a breaking load resistance Rm greater than 450 MPa, an electrical conductivity greater than 90% IACS and an elongation A greater than 6%.

11. Method of manufacturing a conductive cable from a plurality of identical HSHCCA coated fine conductive wires, obtained according to any one of claims 7 to 10, assembled by a stranding operation to obtain said conductive cable.

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