A method for manufacturing a tantalum sheet, a tantalum sheet, and use thereof

Abstract

This invention relates to a method for preparing tantalum sheets, a tantalum sheet, and its uses. The method for preparing the tantalum sheet includes the following steps: 1) forging a tantalum ingot to obtain a forging blank; 2) heat-treating the forging blank; and 3) rolling the tantalum forging blank obtained in step (2) to obtain a tantalum plate (the rolling rate is preferably greater than 65%, more preferably greater than 75%), and heat-treating the tantalum plate.

Description

Technical Field

[0001] This invention relates to a tantalum-based sheet and its preparation method, and more specifically to a tantalum-based sheet for superconducting wires and its preparation method. Background Technology

[0002] Niobium-tritin (Nb3Sn) superconducting wires are widely used in the winding of high-field magnets with field strengths exceeding 10T, such as magnets for magnetic confinement fusion reactors, nuclear magnetic resonance (NMR) systems, and magnets for high-energy physics. For example, Nb3Sn superconducting wires are primarily used in the toroidal field (TF) coils and central solenoids (CS) of the ITER project. Because the TF coils generate magnetic fields as high as 11.8T during operation, extremely high requirements are placed on the Nb3Sn superconducting wires, namely, moderate critical current density and sufficiently low hysteresis loss. Nb3Sn coils with even higher operating parameters are an important component of the CFETR superconducting magnet system.

[0003] During the Nb3Sn phase-forming heat treatment, Sn may diffuse and react with Nb, and may also diffuse and contaminate the external stabilizer Cu, leading to a decrease in the RRR value of the Cu matrix. To avoid this defect, a barrier layer must be used in Nb3Sn wires. The barrier layer is placed between the superconductor and the stabilizer Cu, and is generally made of Nb or Ta material. Both are further processed into the finished Nb3Sn wire as the barrier layer, with a thickness of approximately 10 μm. Tantalum sheets (also known as tantalum-based sheets or tantalum plates, which can be used interchangeably in this article, referring to tantalum metal or tantalum alloy in sheet or plate form) are frequently used as barrier layer materials in Nb3Sn superconducting wires and are an important basic material. Ideally, to ensure good mechanical properties, tantalum sheets need to meet several conditions, such as complete recrystallization, grain size in ASTM 6-9 grade (preferably 6.5-7.5 grade), hardness HV / 2.9N ≤80, preferably ≤75, and longitudinal and transverse elongation ≥40%, etc. However, conventional tantalum sheet preparation methods can no longer fully meet these requirements.

[0004] Common problems in existing technologies include:

[0005] - Tantalum sheets have poor isotropy, resulting in large deviations in plasticity and properties when processed in different directions;

[0006] - The microstructure of tantalum sheets has large deviations. After heat treatment, the local grains of tantalum sheets are coarse (ASTM 3-6 grade) and vary greatly in size (such as grain size difference of more than 3 grades), and there is banded structure, resulting in poor uniformity.

[0007] - It is difficult for tantalum sheets to achieve an elongation (both transverse and longitudinal) of more than 40%; and the deviation between the longitudinal and transverse elongation is too large, often greater than 15%.

[0008] - The hardness is not ideal, making machining (especially stretching) quite difficult. Summary of the Invention

[0009] According to a first aspect, the present invention relates to a method for preparing a tantalum-based sheet or tantalum sheet. The preparation method includes the following steps:

[0010] 1) Forging tantalum ingots to obtain forged blanks;

[0011] 2) Heat treat the forging billet;

[0012] 3) Roll the tantalum forging billet obtained in step (2) to obtain a tantalum plate, and then heat treat the tantalum plate.

[0013] The main purpose of step 1) is to fully break down the grains. The specific forging method is not limited, as long as the grains are sufficiently broken down. However, through extensive experimentation, the inventors have discovered that the following forging method yields optimized microstructure and mechanical properties. For example, from the perspective of optimizing microstructure and mechanical properties, it is preferable to heat the tantalum ingot before forging, for example, by heating it in a box-type resistance furnace. For example, it is preferable to heat it to 400-420°C. Preferably, the tantalum ingot used as raw material in step 1) is cylindrical, and the height-to-diameter ratio is not limited. However, the inventors have found that, from the perspective of ease of processing, the height-to-diameter ratio is preferably 1.8 to 2.2, more preferably 1.9 to 2.1. In a preferred embodiment, the forging in step 1) includes a first machining operation in a first direction (e.g., axial) (preferably with a machining rate of 30%-60%, more preferably 35%-50%), a second machining operation in a second direction (e.g., radial) (preferably with a machining rate of 20%-40%, more preferably 25%-35%), and a third machining operation in a third direction (e.g., radial) (preferably with a machining rate of 20-50%, more preferably 35%-45%). Preferably, the second direction is different from the third direction. More preferably, the second direction is perpendicular to the third direction. Preferably, the forging further includes a fourth machining operation, the machining rate of which is preferably greater than 50%, more preferably greater than 65%. More preferably, the direction of the fourth machining operation is the same as that of the first machining operation.

[0014] In one exemplary embodiment, the forging process is as follows: ① first, axial upsetting with a machining rate of 30%-60%, preferably 35% to 50%; ② flattening along radial direction 1 (first time) with a machining rate of 20%-40%, preferably 25% to 35%; ③ rotating radial direction 1 by 90° and then flattening along radial direction 2 (second time) with a machining rate of 20-50%, more preferably 35% to 45%; ④ then flattening and forging again along radial direction 1 with a machining rate greater than 50%, more preferably greater than 65%. It should be understood that radial direction 1 is perpendicular to radial direction 2.

[0015] The main purpose of the heat treatment in steps 2) and 3) is to improve the internal structure, enhance the cold working plasticity and toughness of the material, thereby achieving a fine and uniform structure, clean surface, and low hardness of the tantalum sheet.

[0016] Preferably, prior to heat treatment in step 2), a pickling step is included. The preferred pickling solution is a mixture of nitric acid, hydrofluoric acid (HF), and hydrochloric acid (HCl). More preferably, the concentration of nitric acid (HNO3) is 65% to 68%; the concentration of hydrofluoric acid (HF) is 40% to 45%; and the concentration of hydrochloric acid (HCl) is 36% to 38%. Even more preferably, the volume ratio of these three acids is HNO3:HF:HCl = 3:1:2. In a preferred embodiment, prior to pickling, the forging is sawed (advantageously by means of a turning jaw) and surface defects are machined (to clean the forging surface and increase surface finish).

[0017] In a preferred embodiment, the heat treatments in steps 2) and 3) each comprise heating the tantalum forging billet to 900-1050°C (preferably 950-1000°C) and holding it at that temperature for 60-120 minutes (preferably 80-100 minutes). Preferably, each of the heat treatments in steps 2) and 3) comprises two sub-steps. The first sub-step comprises a first heating stage and a first holding stage. The second sub-step comprises a second heating stage and a second holding stage. Preferably, the heating rate of the second sub-step (e.g., 25°C-30°C / min) is greater than that of the first sub-step (e.g., 20-25°C / min). Most preferably, each of the heat treatments in steps 2) and 3) consists only of the two sub-steps, i.e., each of the heat treatments in steps 2) and 3) comprises only two heating stages and two holding stages, without further heating or holding. Those skilled in the art will readily understand that after heat treatment, the temperature generally needs to be lowered to room temperature before proceeding to the next step, such as pickling. Preferably, in this invention, furnace cooling is employed.

[0018] In a preferred embodiment, the heat treatments in steps 2) and 3) are each performed by: heating from room temperature to 600°C at a rate of 20°C / min and holding for 90 min; or heating to 1000°C at a rate of 25°C / min and holding for 90 min.

[0019] In a preferred embodiment, the rolling rate in step (3) is greater than 65%, preferably greater than 75%.

[0020] In a preferred embodiment, step 3) is repeated 2-3 times. Different process parameters can be used when repeating step 3) for the second or third time. For example, if the rolling yield of the first rolling is 80% and the heat treatment temperature is 980°C, the rolling yield of the second rolling can be 70%, and the heat treatment temperature can be 1000°C. Preferably, if multiple rolling operations are performed, the tantalum material is pickled before and / or after each rolling operation, using the acid solution from step 2).

[0021] The heat treatment process conditions in steps 2) and 3), such as the heating rate, holding temperature, and time, can be the same or different. It is preferable that they are the same, so that the furnace settings do not need to be changed, thereby simplifying the process.

[0022] Unbound by conventional theories, the inventors believe that by employing a unique forging method combined with a unique heat treatment method (especially the heat treatment after the second rolling), they ensured that the resulting tantalum sheet was essentially completely recrystallized, resulting in a significantly optimized microstructure and guaranteeing excellent mechanical properties, particularly ideal hardness and elongation, as well as minimal differences in room temperature tensile properties between the longitudinal and transverse directions. The inventors unexpectedly discovered that the heating method plays a crucial role in improving the microstructure, especially when combined with the unique forging method.

[0023] Preferably, the obtained tantalum sheet is substantially fully recrystallized, with a grain size of ASTM 6-9 (preferably 6.5-7.5), a hardness HV / 2.9N ≤80 (preferably ≤75), and room temperature elongation ≥40% in both the longitudinal and transverse directions. More preferably, the difference (or deviation) in room temperature elongation between the longitudinal and transverse directions of the tantalum sheet is ≤15%. The tantalum sheet can be used in superconducting wires and / or fusion engineering test reactors.

[0024] The term "substantially complete recrystallization" in this article means that more than 80% of the grains are recrystallized, preferably more than 85%, more preferably more than 90%, even more preferably more than 95%, and most preferably no unrecrystallized grains can be detected.

[0025] The term "longitudinal and lateral deviation" and similar terms "longitudinal and lateral elongation deviation" in this article refer to: (longitudinal value - lateral value) ÷ lateral value × 100%.

[0026] In this article, "min" and minutes can be used interchangeably.

[0027] According to a second aspect, the present invention relates to a tantalum-based sheet or tantalum plate. Preferably, the tantalum-based sheet can be used in Nb3Sn superconducting wires. Preferably, the tantalum plate is fully recrystallized with a grain size of ASTM 6-9 (preferably 6.5-7.5), a hardness HV / 2.9N ≤ 75, and a room temperature elongation ≥ 40% (longitudinal and / or transverse). More preferably, the difference in room temperature elongation between the longitudinal and transverse directions of the tantalum plate is ≤ 15%. The tantalum plate can be used in superconducting wires and / or fusion engineering test reactors.

[0028] According to a third aspect, the present invention also relates to the use of the tantalum-based sheet or tantalum sheet in superconducting wires and / or fusion engineering test reactors.

[0029] According to the present invention, one or more of the following advantages can be obtained:

[0030] ① The tantalum sheet has fully broken and refined grains, resulting in improved deformation superplasticity;

[0031] ②This makes the hardness of tantalum sheets more controllable and makes it easier to achieve lower hardness in tantalum sheets;

[0032] ③ It is easier to achieve surface treatment and purification of tantalum sheets.

[0033] To obtain tantalum sheets with a grain size of ASTM 6-9 (preferably 6.5-7.5), a hardness of HV / 2.9N ≤80, preferably ≤75, and a room temperature elongation ≥40% (longitudinal and / or transverse). Attached Figure Description

[0034] Figure 1 These are optical microscope images of the microstructures of tantalum ingots obtained according to embodiments and comparative examples of the present invention, wherein (a) is the microstructure of Example 1, (b) is the microstructure of Example 2, (c) is the microstructure of Example 3, (d) is the microstructure of Comparative Example 1, (e) is the microstructure of Comparative Example 2, and (f) is the microstructure of Comparative Example 3.

[0035] Figure 2 These are bar charts showing the mechanical properties of tantalum ingots obtained from various embodiments and comparative examples, where a) represents the yield strength (σ). 0.2 ) and tensile strength (σ b (a) is a bar chart of the elongation rate, and (b) is a bar chart of the elongation rate.

[0036] Figure 3 This is a bar chart showing the hardness of the tantalum sheets obtained in Examples 1-3.

[0037] Figure 4 This is a schematic diagram of the specific forging process of step 1) of an exemplary embodiment of the first aspect of the present invention.

[0038] To further understand the present invention, the preparation method of tantalum-based sheet provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0039] These descriptions are merely for further illustrating the features and advantages of the invention, and not for limiting the invention. Unless otherwise specified in the embodiments, conventional conditions were followed. Reagents, raw materials, or instruments used, unless otherwise specified, are all commercially available conventional products.

[0040] For the purposes of this specification, all figures indicating amounts of ingredients, reaction conditions, etc., in the specification and claims shall in all cases be understood to be modified by the term "about," unless otherwise specified. Accordingly, the numerical parameters given in the following specification and appended claims are approximate values, which may vary according to the desired properties sought to be obtained according to the invention, unless indicated to the contrary. At least, and without limitation, the application of the doctrine of equivalence to the scope of the claims is intended, each numerical parameter shall be interpreted at least according to the number of significant figures reported and in accordance with ordinary rounding techniques.

[0041] Example 1:

[0042] The 190mm tantalum ingot is first axially upset with a machining rate of 35%; then flattened along radial direction 1 (first time) with a machining rate of 25%; then rotated 90° along radial direction 1 and flattened along radial direction 2 (second time) with a machining rate of 35%; finally flattened and forged along radial direction 1 with a machining rate of 70%.

[0043] The obtained forging billet is sawed and machined to remove surface defects, and then pickled. The pickling solution is a mixture of HF:HCl:HNO3 = 1:2:3 (volume ratio, HNO3 concentration 65%; HF concentration 40%; HCl concentration 36%). Pickling further removes surface impurities; pickling is performed until a tantalum metallic luster is visible to the naked eye. Then, the pickled tantalum forging billet is heat-treated. Specifically, the temperature is increased to 600℃ at a rate of 20℃ / min and held for 90 min; then increased to 1000℃ at a rate of 25℃ / min and held for 90 min. It is then cooled to room temperature.

[0044] The aforementioned tantalum forging billet is subjected to a first rolling process (also known as roughing rolling). Specifically, it is rolled from a thickness of δ = 50 mm to δ = 6.5 mm; then it is pickled with the same pickling solution to remove surface impurities until a tantalum metallic luster is visible to the naked eye; the pickled billet is then heat-treated, specifically by heating at 20°C / min to 600°C and holding at that temperature for 90 min; then heating at 25°C / min to 1000°C and holding at that temperature for 90 min. Finally, it is cooled to room temperature to obtain a tantalum slab.

[0045] The tantalum slab is then subjected to a second rolling process. Specifically, it is rolled from δ = 6.5 mm to δ = 0.6 mm. It is then pickled using the same pickling solution to remove surface impurities until a visible tantalum metallic luster is observed. The pickled slab is then heat-treated, specifically by heating at 20°C / min to 600°C and holding for 90 min; then heating at 25°C / min to 1000°C and holding for 90 min. Finally, it is cooled to room temperature to obtain the finished tantalum slab.

[0046] Example 2:

[0047] The 190mm tantalum ingot is first axially upset with a machining rate of 45%; then flattened along radial direction 1 (first time) with a machining rate of 30%; then rotated 90° along radial direction 1 and flattened along radial direction 2 (second time) with a machining rate of 40%; finally flattened and forged along radial direction 1 with a machining rate of 70%.

[0048] The obtained forging billet is sawed and machined to remove surface defects, and then pickled. The pickling solution is a mixed acid of HF:HCl:HNO3 = 1:2:3 (volume ratio, HNO3 concentration 65%; HF concentration 40%; HCl concentration 36%), used to remove surface impurities until a tantalum metallic luster is visible to the naked eye. The pickled tantalum forging billet is then heat-treated, specifically by heating at 20℃ / min to 600℃ and holding for 90 min; then heating at 25℃ / min to 1000℃ and holding for 90 min. It is then cooled to room temperature.

[0049] The aforementioned tantalum forging billet is subjected to a first rolling process. Specifically, it is rolled from a thickness of δ = 50 mm to δ = 6.5 mm; then, it is pickled using the same pickling solution to remove surface impurities until a tantalum metallic luster is visible to the naked eye; the pickled billet is then subjected to heat treatment, specifically by heating at 20°C / min to 600°C and holding at that temperature for 90 min; then heating at 25°C / min to 1000°C and holding at that temperature for 90 min. Finally, it is cooled to room temperature.

[0050] The tantalum slab is then subjected to a second rolling process. Specifically, it is rolled from δ = 6.5 mm to δ = 0.6 mm. It is then pickled using the same pickling solution to remove surface impurities until a visible tantalum metallic luster is observed. The pickled slab is then heat-treated, specifically by heating at 20°C / min to 600°C and holding for 90 min (then heating at 25°C / min to 950°C and holding for 90 min). Finally, it is cooled to room temperature to obtain the finished tantalum plate.

[0051] Example 3:

[0052] The 190mm tantalum ingot is first axially upset with a machining rate of 50%; then flattened along radial direction 1 (first time) with a machining rate of 35%; then rotated 90° along radial direction 1 and flattened along radial direction 2 (second time) with a machining rate of 45%; finally flattened and forged along radial direction 1 with a machining rate of 70%.

[0053] The obtained forging billet is sawed and machined to remove surface defects, and then pickled. The pickling solution is a mixed acid of HF:HCl:HNO3 = 1:2:3 (volume ratio, HNO3 concentration 65%; HF concentration 40%; HCl concentration 36%), to further remove surface impurities until a tantalum metallic luster is visible to the naked eye. The pickled tantalum forging billet is then heat-treated. Specifically, the temperature is increased to 600℃ at a rate of 20℃ / min and held for 90min; then increased to 1000℃ at a rate of 25℃ / min and held for 90min. Finally, it is cooled to room temperature.

[0054] The aforementioned tantalum forging billet is subjected to a first rolling process (i.e., initial rolling). Specifically, it is rolled from a thickness of δ = 50 mm to δ = 6.5 mm. Then, it is pickled with the same solution to remove surface impurities until a tantalum metallic luster is visible to the naked eye. The pickled billet is then heat-treated, specifically by heating at 20°C / min to 600°C and holding at that temperature for 90 min; then heating at 25°C / min to 950°C and holding at that temperature for 90 min. Finally, it is cooled to room temperature.

[0055] The tantalum slab is then subjected to a second rolling process. Specifically, it is rolled from δ = 6.5 mm to δ = 0.6 mm. Next, it is pickled using the same solution to remove surface impurities until a visible tantalum metallic luster is observed. The pickled slab is then heat-treated, specifically by heating at 20°C / min to 600°C and holding for 90 min; then heating at 25°C / min to 950°C and holding for 90 min. Finally, it is cooled to room temperature to obtain the finished tantalum plate.

[0056] Comparative Example 1:

[0057] Other conditions are the same as in Example 1.

[0058] The difference is only

[0059] The specific heating regime for heat treatment of the tantalum forging billet after the second rolling is as follows: heat from room temperature to 500℃ at a heating rate of 10℃ / min and hold for 30 min; then heat to 800℃ at a rate of 10℃ / min and hold for 30 min; then heat to 1000℃ at a rate of 10℃ / min and hold for 90 min. Then cool to room temperature to obtain the tantalum plate product.

[0060] Comparative Example 2:

[0061] Other conditions are the same as in Example 1.

[0062] The difference is only

[0063] The specific heating regime for heat treatment of the tantalum forging billet after the first rolling is as follows: heat from room temperature to 500℃ at a heating rate of 10℃ / min and hold for 30min; then heat to 800℃ at a rate of 10℃ / min and hold for 30min; then heat to 1050℃ at a rate of 10℃ / min and hold for 90min.

[0064] The specific heating regime for heat treatment of the tantalum forging billet after the second rolling is as follows: heat from room temperature to 500℃ at a heating rate of 10℃ / min and hold for 30 min; then heat to 800℃ at a rate of 10℃ / min and hold for 30 min; then heat to 1000℃ at a rate of 10℃ / min and hold for 90 min. Then cool to room temperature to obtain the tantalum plate product.

[0065] Comparative Example 3:

[0066] Other conditions are the same as in Example 1.

[0067] The only difference lies in the specific heating regime during the heat treatment of the tantalum forging billet after the second rolling: the temperature is increased from room temperature to 500℃ at a heating rate of 10℃ / min and held for 30min; then the temperature is increased to 1000℃ at a rate of 25℃ / min and held for 90min. Finally, it is cooled to room temperature to obtain the tantalum plate product.

[0068] The test methods and results for grain size, room temperature tensile properties, and hardness of the tantalum plates in the examples and comparative examples are summarized below:

[0069] 1. The microstructure of the rolled surface of the tantalum materials in Examples 1-3 and Comparative Examples 1-3 was observed using an optical microscope, and the results are as follows: Figure 1 As shown. According to the "Method for Determination of Average Grain Size of Metals" (GB / T6394-2017), the average grain size of the tantalum plates in Examples 1-3 was statistically analyzed from... Figure 1 The grain size in the samples is: (a) 6.5 grade, (b) 7.0 grade, (c) 7.0 grade; the average grain size of the tantalum plates in Comparative Examples 1-3 is (d) 3.0 grade, (e) 3.0 grade, (f) 4.0 grade.

[0070] 2. The room temperature tensile properties of the tantalum plates in Examples 1-3 and Comparative Examples 1-3 were tested according to the standard GB / T228.1-2021, "Metallic Materials - Tensile Testing: Room Temperature Test Method". Figure 2 ).

[0071] In Example 1, the longitudinal tensile strength of the tantalum plate is 254.4 MPa, the yield strength is 143.7 MPa, and the elongation after fracture is 56.8%; the transverse tensile strength is 256.3 MPa, the yield strength is 148.7 MPa, and the elongation after fracture is 51.2%; the difference between the longitudinal and transverse elongation is 10.93%.

[0072] In Example 2, the longitudinal tensile strength of the rolled tantalum plate is 254.0 MPa, the yield strength is 168.5 MPa, and the elongation after fracture is 60.4%; the transverse tensile strength is 256.6 MPa, the yield strength is 179.0 MPa, and the elongation after fracture is 54.8%; the deviation between the longitudinal and transverse elongation is 10.22%.

[0073] In Example 3, the longitudinal tensile strength of the tantalum plate is 248.7 MPa, the yield strength is 170.1 MPa, and the elongation after fracture is 55.6%; the transverse tensile strength is 252.2 MPa, the yield strength is 169.5 MPa, and the elongation after fracture is 49.6%; the deviation between the longitudinal and transverse elongation is 12.10%.

[0074] In Comparative Example 1, the longitudinal tensile strength of the tantalum plate is 235.4 MPa, the yield strength is 146.3 MPa, and the elongation after fracture is 35.1% in the longitudinal direction; the transverse tensile strength is 237.4 MPa, the yield strength is 144.3 MPa, and the elongation after fracture is 29.2%; the deviation between the longitudinal and transverse elongation is 20.21%.

[0075] In Comparative Example 2, the longitudinal tensile strength of the tantalum plate is 242.4 MPa, the yield strength is 156.1 MPa, and the elongation after fracture is 34.9%; the transverse tensile strength is 233.0 MPa, the yield strength is 148.6 MPa, and the elongation after fracture is 28.8%; the deviation between the longitudinal and transverse elongation is 21.18%.

[0076] In Comparative Example 3, the longitudinal tensile strength of the tantalum plate is 261.3 MPa, the yield strength is 167.2 MPa, and the elongation after fracture is 42.3%; the transverse tensile strength is 257.4 MPa, the yield strength is 162.4 MPa, and the elongation after fracture is 35.4%; the deviation between the longitudinal and transverse elongation is 19.49%.

[0077] As can be seen from these embodiments and comparative examples, the mechanical properties of the embodiments of the present invention are significantly superior to those of the comparative examples. In particular, the longitudinal and transverse elongation after fracture of the comparative examples are inferior to those of the embodiments, and the deviation between the longitudinal and transverse elongation after fracture is significantly greater than that of the embodiments, which cannot meet the high requirements in the industry.

[0078] 3. The Vickers hardness of the tantalum plates in Examples 1-3 was tested according to "Metallic Materials - Vickers Hardness Test - Part 1: Test Method" (GB / T4340.1-2009); achieving a hardness HV / 2.9N (2.9N load) ≤ 75; see [link to relevant documentation]. Figure 3 ( Figure 3 Points 1, 2, and 3 of HV2.9 indicate three different regions on the surface of the sample being tested.

[0079] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a tantalum sheet, comprising the following steps: 1) forging a tantalum ingot to obtain a forged blank; 2) heat treating the forged blank; 3) rolling the tantalum forged blank obtained in step (2) to obtain a tantalum sheet and heat treating the tantalum sheet, wherein the heat treating in steps 2) and 3) is each accomplished by heating from room temperature to 600°C at 20°C / min, then holding for 90 min; then heating to 1000°C at 25°C / min and holding for 90 min, then decreasing to room temperature, wherein the forging in step 1) comprises a first pass in a first direction, a second pass in a second direction and a third pass in a third direction.

2. The method according to claim 1, wherein in step 1) the tantalum ingot is heated before forging.

3. The method according to claim 2, wherein the heating is performed by a box-type resistance furnace.

4. The method according to claim 2, wherein the heating is to 400-420°C.

5. The method according to any one of claims 1-4, further comprising a fourth pass.

6. The method according to claim 5, wherein the fourth pass is in the same direction as the first pass.

7. The method according to claim 5, wherein the first pass has a reduction of 30-60%; the second pass has a reduction of 20-40%; the third pass has a reduction of 20-50%; and the fourth pass has a reduction of more than 50%.

8. The method according to claim 7, wherein the first pass has a reduction of 35-50%; the second pass has a reduction of 25-35%; the third pass has a reduction of 35-45%; and the fourth pass has a reduction of more than 65%.

9. The method according to any one of claims 1-4 and 6-8, wherein step 3) is repeated 2-3 times.

10. The method according to claim 9, wherein the tantalum material is pickled before and / or after each rolling, and the pickling solution is a mixture of nitric acid, hydrofluoric acid (HF) and hydrochloric acid (HCI).

11. The method according to any one of claims 1-4 and 6-8, wherein the rolling in step 3) has a reduction of more than 65%.

12. The method according to claim 11, wherein the rolling in step 3) has a reduction of more than 75%.

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