Process for manufacturing a nickel-based superalloy ingot

Abstract

Process for producing a nickel-based superalloy ingot. The present invention relates to a process for producing a nickel-based superalloy ingot (8). The process comprises the following steps: - preparation of a solid metallic charge (9) of a Ni-based metallic alloy composition; - introduction and melting of said charge (9) in a melting zone (20) of a cold crucible plasma arc melting furnace (12) comprising at least one plasma torch (24); - refining of the molten alloy in a refining zone (22) of the furnace comprising at least one plasma torch (26); - transfer of said refined alloy into a molding ring (14) or an ingot mold; - obtaining the ingot (8). The process further comprises injecting a reactive gas comprising dihydrogen into at least one plasma torch (24, 26) so as to obtain an ionized plasma gas comprising hydrogen. Figure for the abbreviation: Figure 1

Description

Title of the invention: Process for producing a nickel-based superalloy ingot

[0001] The present invention relates to the field of processes for the production of alloys, in particular nickel-based alloys, as well as installations for implementing such processes.

[0002] Several processes are used for the production of nickel-based alloys, which are intended, for example, for the aerospace industry. These alloys are mainly produced from virgin raw materials or by recycling scrap using a vacuum induction melting process (more commonly known as VIM for "Vacuum Induction Melting"). The alloy produced by the VIM process is then cast in the form of a cylindrical electrode, then melted and refined by a vacuum arc remelting process (more commonly known as VAR for "Vacuum Arc Remelting"): this is referred to as VIM-VAR production), or by an electro-conductive slag remelting process (more commonly known as ESR for "Electro Slag Remelting"): this is referred to as VIM-ESR production), or by a succession of ESR and VAR remeltings (this is referred to as VIM-ESR-VAR production).

[0003] Such processes, however, are not entirely satisfactory. Indeed, they do not allow for the complete elimination of oxide (e.g., SiO2, TiO2, Al2O3, and MgO) or nitride (TiN) inclusions, which can lead to the presence in the resulting products of inclusion clusters and oxide alignments, commonly called "stringers," which act as nuclei on which nitrides or carbonitrides can precipitate and concentrate. These clusters and alignments are likely to cause fatigue stress reduction, or even failure of the final parts.

[0004] Furthermore, the final VAR remelting can lead to the formation of "dirty white spots" (more commonly known as "Dirty White Spots") caused by the sloughing of solid metal associated with inclusions during remelting. A "Dirty White Spot" can also lead to fatigue stress reduction or even failure of the finished parts. The risk of "Dirty White Spots" is linked to the presence of oxide / nitride inclusions.

[0005] Alternative or complementary processes for reducing the presence of "Dirty White Spot" are known. For example, electroconductive slag remelting (ESR) processes are known. However, these processes present a higher risk of solidification defects such as positive segregation (also called "freckles") than VAR processes. These positive segregations correspond to areas enriched in alloying elements, such as C, Nb or Ti for example.

[0006] The development of superalloys by the VIM-ESR-VAR route, which is the classically used route, therefore does not give complete satisfaction.

[0007] The aim of the invention is therefore to propose a process for developing a nickel-based metal alloy that reduces the presence of undesirable inclusions such as oxides and / or nitrides, while avoiding the segregation of alloying elements.

[0008] To this end, the invention relates to a process for producing a nickel-based superalloy ingot, the process comprising the following steps:

[0009] - constitution of a solid metallic charge of a metallic alloy composition Ni-based;

[0010] - introduction and melting of said charge in a melting zone of a melting furnace by cold crucible plasma arc comprising at least one fusion plasma torch

[0011] - refining the molten alloy in a refining zone of the furnace, the refining zone including at least one plasma refining torch;

[0012] - transfer of said refined alloy into a molding ring or ingot mold;

[0013] - obtaining the ingot;

[0014] characterized in that the process further comprises injecting into at least one plasma torch a reactive gas comprising dihydrogen so as to obtain an ionized plasma gas comprising hydrogen.

[0015] The process according to the invention thus makes it possible to efficiently deoxidize the molten alloy by injecting dihydrogen into the plasma, thereby promoting its chemical reactivity through ionization of hydrogen into H+ ions and enabling the removal of oxides and nitrides by chemical reaction and the formation of H2O and NH3. This chemical removal mechanism is complemented by gravitational removal of oxide and nitride aggregates with capture at the interfaces (walls and solidification zones of the alloy) during the passage of the molten alloy through the furnace before the ingot is poured

[0016] The process according to the invention thus allows the development of Ni-based superalloys exhibiting improved cleanliness, thereby minimizing the risk of failure of the parts obtained.

[0017] The method according to the invention may have one or more of the following characteristics, taken individually or in all technically possible combinations:

[0018] - the reactive gas comprises at least 5% by volume of dihydrogen, preferably at least 10% by volume of dihydrogen;

[0019] - the reactive gas is chosen from an H2 / Ar mixture, an H2 / He mixture and pure H2;

[0020] - the reactive gas comprises a water content such that the volume ratio H2 / H2O in the reactive gas is greater than 104, preferably greater than 105;

[0021] - the process includes local overheating of the molten alloy by the plasma torch at a temperature of at least 1500°C, preferably at least 1700°C, most preferably at least 2000°C;

[0022] - the alloy composition is chosen from the Inconel®718, Udimet superalloys 720, AD730® and René®65;

[0023] - the process comprises, after obtaining the ingot, a remelting step by arc under empty of said ingot;

[0024] - the process further includes a step of purifying the reactive gas previously to its injection;

[0025] - the process further includes a step of recycling the reactive gas at the outlet of the oven.

[0026] The invention also relates to an installation for producing a nickel-based superalloy ingot, the installation being suitable for implementing a production process of the type described above, the installation comprising:

[0027] - a cold crucible plasma arc melting furnace comprising a melting zone and a refining zone, with at least one plasma fusion torch being disposed in said fusion zone and at least one plasma refining torch being disposed in said refining zone;

[0028] - a molding ring or an ingot mold; and

[0029] - a device for injecting a reactive gas comprising configured dihydrogen to inject said gas into at least one plasma torch.

[0030] According to a particular embodiment, the installation further includes a vacuum arc remelting furnace for melting the ingot obtained.

[0031] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0032] [Fig-1] [Fig.1] is a schematic representation of a processing installation according to the invention;

[0033] [Fig.2] [Fig.2] is a flowchart of the production of a nickel-based alloy ingot in the installation of [Fig.1].

[0034] In this description, the terms "upstream" and "downstream" will be used in a conventional manner with reference to the direction of flow of the molten alloy in the installation.

[0035] In the present description, an alloy is said to be "nickel", "nickel base" or "nickel-based" when it comprises at least 50% by weight of Ni.

[0036] Figure 1 illustrates an installation 10 according to the invention. The installation 10 is intended for the production of a nickel-based superalloy ingot 8 from a solid metallic charge 9 of a Ni-based metallic alloy composition.

[0037] Advantageously, the ingot 8 is intended for the manufacture of at least one Ni superalloy metal part, in particular rotating engine parts intended for aircraft engines, such as turbine discs for example.

[0038] The nickel-based superalloy is preferably chosen from the following list: Inconel®718, Udimet 720, AD730® and René®65.

[0039] The installation 10 includes a furnace 12 and a molding ring 14 located downstream of the furnace 12. Alternatively, the molding ring is replaced by an ingot mold.

[0040] The furnace 12 is of the cold crucible plasma arc melting furnace type, also called a PAM-CHR furnace for "Plasma Arc Melting - Cold Hearth Refining".

[0041] The furnace 12 includes a melting zone 20 and a refining zone 22 located downstream of the melting zone 20.

[0042] Each zone 20, 22 is equipped with at least one plasma torch 24, 26. Each plasma torch 24, 26 is configured to generate a flow of ionized and excited gas, this gas flow being directed towards a free surface 27 of the molten alloy and heating said molten alloy.

[0043] The melting zone 20 is configured to melt a pre-formed solid metallic charge 9 introduced into the melting zone 20 by means of a furnace loading device 28. Said device 28 is, for example, a conveyor.

[0044] Said metallic charge 9 is in the form, for example, of solid blocks or alloy chips. Alternatively, the metallic charge 9 is in the form of alloy powders, which are, for example, loaded into the furnace in accordance with the process described in patent FR 3 123 816.

[0045] The melting zone 20 includes at least one plasma melting torch 24 intended to provide the heat necessary to melt the solid metallic charge 9 and obtain a bath 29 of molten alloy.

[0046] Preferably, the molten alloy in the melting zone 20 is maintained at a temperature above the alloy's melting temperature. Here, the temperature of the molten alloy bath 29 is considered to be at the core of the bath. The power of the melting torch 24 is advantageously chosen to achieve a target melting rate.

[0047] Each plasma fusion torch 24 is preferably configured to allow local heating, at a superheat zone, of the molten alloy to a temperature of at least 1500°C, preferably at least 1700°C, and most preferably at least 2000°C. This local superheating, to a temperature of at least 100°C above the melting temperature of the metal, preferably at minus 150°C above said temperature, facilitates the reduction of oxides present in the bath, as well as denitriding.

[0048] The melting zone 20 further comprises at least one crucible 30 containing the molten alloy bath 29. The crucible 30 is typically cooled by circulating a heat transfer fluid through the walls of said crucible.

[0049] As a result of said cooling, the metal alloy contained in the crucible 30 forms a skin 31 in contact with the cooled surface of the crucible. The skin is in solid, pasty, or even thick liquid form. The heavy inclusions that settle in the molten alloy are trapped in said skin.

[0050] Preferably, the molten alloy passes from the melting zone 20 to the refining zone 22 by overflow.

[0051] The refining zone 22 is configured to dissolve and / or eliminate impurities that may exist in the molten alloy from the melting zone 20. Part of the impurities, also called inclusions, are dissolved, that is to say, are gradually put into solution under the effect of heating the molten alloy and bringing it into chemical equilibrium.

[0052] Another part of the inclusions is eliminated by gravity by decantation or by flotation and captured at the interfaces (walls and solidification zones of the alloy) during the passage of the molten alloy in the furnace before the casting of the ingot.

[0053] The refining zone 22 includes at least one refining plasma torch 26 intended to maintain the molten alloy at temperature, and to allow the dissolution or gravity separation of inclusions.

[0054] Each refining plasma torch 26 is preferably configured to allow local heating, at the level of a superheating zone 32, of the molten alloy to a temperature of at least 1500°C, preferably at least 1700°C, most preferably at least 2000°C. This local superheating, to a temperature of at least 100°C above the melting temperature of the metal, preferably at least 150°C above said temperature, facilitates the reduction of oxides present in the bath, as well as denitriding.

[0055] The refining zone 22 comprises at least one crucible 34 containing the molten alloy bath 29. The crucible 34 is typically cooled by circulating a heat transfer fluid through the walls of said crucible. As a result of said cooling, the metallic alloy contained in the crucible 34 also forms a skin 31 in contact with the cooled surface of the crucible.

[0056] According to an embodiment not shown, the refining zone 22 is divided into several crucibles, the molten alloy passing successively from one crucible to another, for example by overflow.

[0057] Preferably, the molten alloy passes from the refining zone 22 to the molding ring 14 by overflow.

[0058] The molding ring 14 is intended for shaping the ingot 8.

[0059] As shown in [Fig. 1], the molding ring 14 typically comprises a cylindrical crucible 36, with a vertical central axis and extending between an alloy inlet end 360 and an alloy outlet end 362.

[0060] The crucible 36 is cooled by a heat transfer fluid circulating in the wall of the crucible 36.

[0061] The molding ring 14 further includes a plasma torch 38 disposed above the inlet end 360 of the crucible and intended to heat the free surface 27 of the molten alloy bath.

[0062] The installation 10 further includes a drawing device (not shown) comprising a plate and an actuator arranged to move the plate vertically relative to the cylindrical crucible 36, in order to allow the solidification of the molten alloy and the drawing of the ingot 8 at the alloy outlet end 362.

[0063] The installation 10 further includes a reactive gas injection device 40 configured to inject said gas into at least one plasma torch 24, 26.

[0064] For example, as shown in the embodiment of [Fig.1], the injection device 40 is configured to inject said gas into at least one refining plasma torch 26.

[0065] Preferably, when the installation 10 includes several refining plasma torches 26, the installation 10 includes one or more reactive gas injection devices 40 configured to inject said gas into each refining plasma torch 26.

[0066] The reactive gas comprises dihydrogen such that the resulting ionized plasma gas comprises hydrogen in the form of H+ ions. Preferably, the reactive gas comprises at least 5% dihydrogen by volume, and very preferably at least 10% dihydrogen by volume.

[0067] The injection of dihydrogen, and more particularly into the plasma, allows the reduction of oxides present in the bath, by formation of H2O, as well as the elimination of nitrides by formation of NH3.

[0068] Preferably, the reactive gas is chosen from an H2 / Ar mixture, an H2 / He mixture and pure H2.

[0069] Preferably, the water content in the reactant gas is such that the H2 / H2O volume ratio is greater than 104, preferably greater than 105. A low H2O content thus allows maximizing the reduction of oxides and denitriding.

[0070] For example, for a reactive gas having 10% by volume of dihydrogen, the reactive gas preferably comprises less than 0.001% water, advantageously less than 0.0001% water.

[0071] The injection device 40 includes, for example, an injection system 42 configured to inject the reactive gas into the plasma torch 26 upstream of the electric arc formed in said torch, so as to obtain an ionized plasma gas comprising hydrogen in the form of H+ ions. For example, the injection system 42 includes an injection tube.

[0072] Preferably, the installation 10 further comprises a purification device (not shown) adapted to purify the reactive gas prior to its injection into the plasma torch. In particular, the purification device is adapted to remove traces of H2O present, so as to advantageously obtain an H2 / H2O volume ratio of at least 10⁴, preferably at least 10⁵. Advantageously, the purification device is also adapted to recycle the furnace outlet gas, for example, for reinjection into the furnace. For example, the purification device is adapted to reduce the H2O content of the gas. Preferably, the purification device is also adapted to reduce the NH3 content of the gas, so as to facilitate denitriding by shifting the chemical equilibrium.

[0073] The injection of the reactive gas containing dihydrogen allows the removal of oxides and nitrides present in the molten alloy bath, such as SiO2, TiO2, MgO, Al2O3 and TiN. The injection of dihydrogen into the plasma thus makes the gas more reactive and therefore the oxide reduction and denitriding reactions more efficient.

[0074] The use of a PAM-CHR type furnace 12 allows for the separation of the melting and refining of the alloy, unlike other melting or remelting furnaces. This makes it possible to have a low melting and pouring rate, which limits the formation of segregations during the solidification of the alloy in the mold ring. This eliminates the need for subsequent remelting in a VAR furnace, thus preventing the formation of white spots.

[0075] According to one embodiment, the installation 10 is devoid of a vacuum arc reflow furnace.

[0076] Such a furnace may, however, be present. Indeed, the use of a PAM-CHR furnace according to the invention upstream of the VAR furnace makes it possible to limit or even eliminate the presence of oxide / nitride inclusions, and therefore the risk of formation of dirty white spots.

[0077] According to another embodiment, the installation 10 thus comprises a vacuum arc remelting furnace (not shown), said furnace being intended for remelting the ingot 8 after its drawing.

[0078] This additional remelting makes it possible to improve the inclusion cleanliness of the alloy and to better control the solidification conditions, minimizing the risk of segregation of alloying elements.

[0079] According to an unrepresented variant, the injection device 40 is configured to inject the reactive gas into at least one fusion plasma torch 24, preferably into each fusion plasma torch 24.

[0080] According to an alternative not shown, the installation 10 includes one or more reactive gas injection devices 40 configured to inject said gas into at least one plasma torch 24 for melting and into at least one plasma torch 26 for refining. For example, the installation 10 includes one or more injection devices 40 configured to inject said gas into each plasma torch 24, 26 of the furnace.

[0081] The injection device(s) 40 are, for example, configured to inject a reactive gas having the same dihydrogen and / or water content for all the plasma torches 24, 26 concerned. This facilitates the management of the installation 10, and in particular the recycling of the gas used in the furnace.

[0082] According to one variant, the injection device(s) 40 are configured to inject a reactive gas having a different dihydrogen and / or water content depending on the plasma torch 24, 26 concerned.

[0083] For example, the hydrogen content of the reactive gas injected into the plasma torches 24, 26 increases from upstream to downstream, with the hydrogen content of the reactive gas injected into the first upstream melting plasma torch 24 being lower than that in the last downstream refining plasma torch 26. Alternatively, the water content of the reactive gas injected into the plasma torches 24, 26 decreases from upstream to downstream, with the water content of the reactive gas injected into the first melting plasma torch 24 being higher than that in the last downstream refining plasma torch 26. The deoxidation and denitriding conditions thus improve from upstream to downstream. Optionally, the power of the plasma torches 24, 26 increases from upstream to downstream, further promoting deoxidation and denitriding as the alloy progresses through the furnace.

[0084] The process for producing an ingot 8 according to the invention will now be described, with reference to [Fig.2].

[0085] The process is advantageously carried out in an installation 10 as described above.

[0086] The process includes an initial step 110 of constituting a solid metallic charge 9 of a Ni-based metallic alloy composition.

[0087] Said metallic charge 9 is in the form of solid blocks, chips or alloy powders.

[0088] During an introduction step 112, the metal charge is then introduced into the furnace 12, more particularly into the melting zone 20 of the furnace 12, for example by means of the loading device 28.

[0089] The process then includes a step 114 of melting said charge in the melting zone 20, by means of the fusion plasma torch(s) 24.

[0090] The charge 9 thus forms a bath 29 of molten alloy.

[0091] The molten alloy bath 29 present in the melting zone 20 is maintained at a temperature above the melting temperature of the alloy.

[0092] The molten alloy then passes from the melting zone 20 to the refining zone 22, for example by overflow.

[0093] During a refining step 116, the molten alloy is refined in the refining zone 22 of the furnace 12 by means of at least one refining plasma torch 26.

[0094] During this step, the oxides, as well as the alignments of oxides and nitrides, rise to the surface of the metal bath by gravity separation, their density being lower than that of the rest of the liquid alloy. This maximizes the possibility of removing said oxides and nitrides, which are then subjected to the direct impact of the plasma torches 26 at the level of the free surface 27 of the molten alloy, and are repelled and then captured in the skin 31.

[0095] Concurrently, the process includes a step 118 of injecting reactive gas comprising dihydrogen into at least one plasma torch 24, 26 so as to obtain an ionized plasma gas comprising hydrogen. Preferably, the reactive gas comprises at least 5% dihydrogen by volume, most preferably at least 10% dihydrogen by volume.

[0096] In the embodiment of [Fig.2], the injection step 118 includes the injection into the at least one refining plasma torch 26 of the reactive gas comprising dihydrogen so as to obtain an ionized plasma gas.

[0097] Thus, the plasma gas used for refining step 116 includes hydrogen in the form of H+ ions.

[0098] Preferably, prior to its injection, the reactive gas has been subjected to a purification step 119, so that the injected dihydrogen has less than 0.001% water, preferably less than 0.0001% water.

[0099] The injection of dihydrogen allows the deoxidation and denitrification of the alloy bath, by facilitating the elimination of oxides and nitrides present in the bath thanks to the H+ ions obtained by ionization of dihydrogen.

[0100] Preferably, during the refining step 116, the refining plasma torch(s) 26 locally heats the molten alloy bath to a temperature of at least 1500°C, preferably at least 1700°C, and most preferably at least 2000°C. This local overheating promotes the reduction of oxides present in the bath.

[0101] For the reduction of SiO2 and TiO2 oxides, local overheating of the bath to at least 1500°C is preferred when the reactive gas used for refining step 116 comprises 10% by volume of dihydrogen with an initial H2 purity of at least 99.999%, corresponding to an H2 / H2O ratio of at least 104.

[0102] For the reduction of MgO and Al₂O₃ oxides, local overheating of the bath to at least 2000°C is preferred when the reactive gas used for refining step 116 comprises 10% by volume of dihydrogen with an initial H₂ purity of at least 99.999%. When the reactive gas used for refining step 116 comprises 10% by volume of dihydrogen with an initial H₂ purity of at least 99.9999%, corresponding to an H₂ / H₂O ratio of at least 10⁵, local overheating of the bath to at least 1700°C is sufficient.

[0103] Since the oxides act as germs for the precipitation of nitrides, their elimination minimizes the risk of formation of "stringer" type agglomerates.

[0104] The use of a PAM-CHR type furnace makes it possible to separate the melting step 114 from the refining step 116, unlike other melting or remelting furnaces. This allows the molten alloy to be refined at high temperatures under the refining plasma torch(s) 26, while maintaining a low melting rate by controlling the metal feed.

[0105] The refining of the alloy, the deoxidation and the denitriding of the bath are thus improved.

[0106] Then, during a transfer step 120, the refined alloy is transferred into the molding ring 14 or the ingot mold. For example, a stream of refined alloy is poured into the molding ring 14 by overflow.

[0107] An ingot 8 is then obtained, for example by drawing, in a step 122 of obtaining the ingot.

[0108] According to one embodiment, the process does not include a subsequent remelting step.

[0109] Alternatively, the process includes a subsequent step 123 of remelting the ingot by vacuum arc (more commonly known as VAR for "Vacuum Arc Remelting" in English).

[0110] Advantageously, the process includes a step of recycling the reactive gas at the outlet of the furnace 12, for example with a view to reinjecting it into the furnace 12.

[0111] In an alternative (not shown), the injection step includes the injection into at least one fusion plasma torch 24 of the reactive gas.

[0112] In an alternative (not shown), the process comprises a first step of injecting the reactive gas into at least one fusion plasma torch 24 and a second step injection of the reactive gas into at least one refining plasma torch 26. The dihydrogen and / or water content of the reactive gas and / or the power of the plasma torches 24, 26 vary optionally depending on the position of the torch concerned.

[0113] The process and installation 10 according to the invention make it possible to obtain an ingot 8 in Ni-based superalloy exhibiting improved inclusion cleanliness, thanks to better elimination of oxides and nitrides present in the alloy bath.

[0114] The use of a PAM-CHR type process makes it possible to separate the melting step from the alloy refining step, unlike a VAR remelting process, which is beneficial for refining the liquid alloy. Indeed, it is thus possible to maximize both the residence time of the liquid metal in the refining zone by reducing the pouring speed and the overheating of the liquid metal by increasing torch power, which promotes the chemical and gravitational removal of inclusions.

Claims

Demands

1. A process for producing a nickel-based superalloy ingot (8), the process comprising the following steps: • forming a solid metal charge (9) of a Ni-based metal alloy composition; • introducing and melting said charge (9) in a melting zone (20) of a cold crucible plasma arc melting furnace (12) comprising at least one plasma melting torch (24); • refining the molten alloy in a refining zone (22) of the furnace, the refining zone (22) comprising at least one plasma refining torch (26); • transferring said refined alloy into a molding ring (14) or an ingot mold; • obtaining the ingot (8); characterized in that the process further comprises injecting a reactive gas comprising dihydrogen into at least one plasma torch (24, 26) so as to obtain an ionized plasma gas comprising hydrogen.

2. A process according to claim 1, wherein the reactive gas comprises at least 5% by volume of dihydrogen, preferably at least 10% by volume of dihydrogen.

3. A method according to claim 1 or 2, wherein the reactive gas is selected from an H2 / Ar mixture, an H2 / He mixture and pure H2.

4. A process according to any one of the preceding claims, wherein the reactive gas comprises a water content such that the H2 / H2O volume ratio in the reactive gas is greater than 104, preferably greater than 105.

5. A method according to any one of the preceding claims, comprising local overheating of the molten alloy by the plasma torch (24, 26) to a temperature of at least 1500°C, preferably of at least 1700°C, most preferably of at least 2000°C.

6. A process according to any one of the preceding claims, wherein the alloy composition is selected from the superalloys Inconel®718, Udimet 720, AD730® and René®65.

7. A method according to any one of the preceding claims, comprising, after obtaining the ingot (8), a vacuum arc remelting step of said ingot (8).

8. A method according to any one of the preceding claims, further comprising a step of purifying the reactive gas prior to its injection.

9. A method according to any one of the preceding claims, further comprising a step of recycling the reactive gas at the outlet of the furnace (12).

10. Installation (10) for producing a nickel-based superalloy ingot, the installation (10) being adapted to carry out a production process according to any one of claims 1 to 9, the installation (10) comprising: • a cold crucible plasma arc melting furnace (12) comprising a melting zone (20) and a refining zone (22), at least one plasma melting torch (24) being disposed in said melting zone (20) and at least one plasma refining torch (26) being disposed in said refining zone (22); • a molding ring (14) or an ingot mold; and • a reactive gas injection device comprising dihydrogen configured to inject said gas into the at least one plasma torch (24, 26).

11. Installation (10) according to claim 10, further comprising a vacuum arc remelting furnace for melting the ingot (8) obtained.

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