Preparation method of small and medium-sized pure niobium rod with uniform structure

Abstract

The present application belongs to the technical field of non-ferrous metal material processing, and particularly relates to a preparation method of a medium-small size pure niobium bar with uniform structure, which comprises the following steps: step one, open-die forging: 1-2 times of open-die forging of pure niobium ingot at room temperature, the open-die forging mode being upsetting and drawing; step two, intermediate forging: 3-5 times of repeated upsetting and drawing of the intermediate blank after step one at room temperature; step three, finished product forging: 2-4 times of elongation deformation of the intermediate blank after step two at room temperature, and finally forging to finished product bar blank; step four, recrystallization annealing of finished product bar blank: annealing of the bar blank after step three by using a vacuum annealing furnace, and grinding of the annealed bar blank to finished product pure niobium bar. The present application can obtain medium-small size pure niobium bar with uniform high and low magnification structure by using only simple free forging processing mode, can improve deformation uniformity and yield, is simple in process, and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal material processing technology, specifically relating to a method for preparing small- to medium-sized pure niobium rods with uniform microstructure. Background Technology

[0002] Pure niobium rods are an important raw material for the preparation of low-temperature superconducting wires. In the preparation of superconducting wires, pure niobium rods need to be continuously extruded and drawn to micrometer-level diameters. The rods undergo significant deformation, and to minimize wire breakage during deformation, the uniformity of the microstructure is crucial. Superconducting pure niobium rods have low impurity content and extremely high purity requirements, resulting in lower material strength and hardness. During deformation, they are prone to instability and uneven deformation, ultimately leading to inhomogeneous microstructure in different parts of the rod, severely affecting the processing and performance of the superconducting wires. Furthermore, niobium readily reacts with oxygen, and high-temperature environments or the deformation heat caused by intense deformation can easily lead to the formation of a severe oxide layer on the material surface, hindering plastic deformation. Therefore, a suitable processing method is essential for obtaining pure niobium rods with uniform microstructure.

[0003] Currently, the main manufacturing processes for niobium rods used in superconducting applications are extrusion and drawing. However, these methods have the following limitations: 1) Extrusion requires high precision in the extrusion dies and lubrication system, limiting the processed products to small-sized parts; 2) Drawing is suitable for producing wires or rods with small cross-sections, but it requires surface oxide coating, making the process complex and costly. These methods are generally used to prepare small-diameter pure niobium rods, tubes, and wires; no reports have been made for producing highly uniform small- to medium-sized pure niobium rods. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing small- to medium-sized pure niobium rods with uniform microstructure. This invention employs only a simple free forging process, which can obtain small- to medium-sized pure niobium rods with uniform microstructure at both high and low magnification levels. This improves deformation uniformity and yield, and the process is simple and suitable for industrial production.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing small- to medium-sized pure niobium rods with uniform microstructure includes the following steps:

[0007] Step 1, billet forging: The pure niobium ingot is subjected to 1 to 2 forgings at room temperature, and the forging method is upsetting and drawing;

[0008] Step 2, intermediate forging: The intermediate billet after step 1 forging is repeatedly upsetting and drawing 3 to 5 times at room temperature;

[0009] Step 3, finished product forging: The intermediate billet after step 2 forging is subjected to 2 to 4 drawing deformations at room temperature, and finally forged into finished bar billets;

[0010] Step 4, recrystallization annealing of finished billet: The billet forged in step 3 is annealed in a vacuum annealing furnace, and then ground to produce pure niobium finished billet.

[0011] Preferably, in step one, the pure niobium ingot has a size of Φ240mm~Φ300mm.

[0012] Preferably, in step one, the upsetting-drawing-forging ratio is controlled between 1.6 and 2.1.

[0013] Preferably, in step two, the upsetting-drawing-forging ratio is controlled between 1.5 and 1.9.

[0014] Preferably, in step three, the upsetting-drawing-forging ratio is controlled between 1.8 and 2.4.

[0015] Preferably, in step four, the annealing and holding temperature is set to 900℃~1200℃, the holding time is 2h~8h, and the vacuum degree during the holding stage is no greater than 10. -2 Pa, the cooling method is furnace cooling.

[0016] Preferably, in steps one and two, the cross-section of the forged billet is square with a side length of 240mm to 280mm.

[0017] Preferably, in steps one, two, and three, the forging rate is 10 mm / s to 50 mm / s.

[0018] Preferably, in step four, the specifications of the pure niobium finished bar are Φ60mm~Φ150mm.

[0019] Preferably, in steps one, two, and three, air cooling is performed after forging.

[0020] The beneficial effects of this invention are as follows:

[0021] This process utilizes free forging pressure processing to produce small- to medium-sized pure niobium rods with uniform microstructure. Upsetting and drawing forging are employed to uniformly deform the ingot, effectively breaking down the coarse microstructure in the as-cast state. The billet is then further forged using upsetting and drawing techniques. By controlling the pressing rate and deformation method, the uniformity of deformation in different parts of the billet is effectively improved, while avoiding surface oxidation due to material temperature rise and reducing material loss. The billet undergoes drawing deformation forging, resulting in a billet with good surface quality and high dimensional accuracy. Vacuum annealing then yields small- to medium-sized pure niobium rods with uniform microstructure at both high and low magnification levels, and a high-magnification grain size difference of no more than 3 levels between the edge and core. Attached Figure Description

[0022] Figure 1 This is a low-magnification image of the transverse microstructure of a Φ80mm pure niobium rod prepared according to Example 1 of the method of the present invention.

[0023] Figure 2 This is a high-magnification image of the transverse edge microstructure of pure niobium with a diameter of Φ80mm prepared according to Example 1 of the method of the present invention.

[0024] Figure 3 This is a high-magnification image of the transverse core tissue of pure niobium with a diameter of Φ80mm prepared according to Example 1 of the method of the present invention.

[0025] Figure 4 This is a low-magnification image of the transverse microstructure of a Φ95mm pure niobium rod prepared according to Example 2 of the method of the present invention.

[0026] Figure 5 This is a high-magnification image of the transverse edge tissue of pure niobium with a diameter of Φ95mm, prepared according to Example 2 of the method of the present invention.

[0027] Figure 6 This is a high-magnification image of the transverse core tissue of pure niobium with a diameter of Φ95mm, prepared according to Example 2 of the method of the present invention.

[0028] Figure 7 This is a flowchart of the method of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments.

[0030] like Figure 7 As shown, a method for preparing small- to medium-sized pure niobium rods with uniform microstructure includes the following steps:

[0031] Step 1, billet forging: The pure niobium ingot is forged in 1 to 2 heats at room temperature. The billet forging method is upsetting and drawing.

[0032] Pure niobium ingots are Φ240mm~Φ300mm in size, with an upsetting-drawing ratio controlled at 1.6~2.1 to fully break down coarse grains in the as-cast state. The forged billet has a square cross-section with a side length of 240mm~280mm. When the intermediate billet is forged into a square billet under a flat anvil, the forging rate is 10mm / s~50mm / s, and it is air-cooled after forging.

[0033] Step 2, intermediate forging: The intermediate billet after step 1 forging is repeatedly upsetting and drawing 3 to 5 times at room temperature.

[0034] The upsetting-drawing ratio is controlled between 1.5 and 1.9. The cross-section of the forged billet is square with a side length of 240 mm to 280 mm. When the intermediate billet is forged into a square billet under a flat anvil, the forging rate is 10 mm / s to 50 mm / s, and it is air-cooled after forging.

[0035] Step 3, finished product forging: The intermediate billet after step 2 forging is subjected to 2 to 4 drawing deformations at room temperature, and finally forged into finished bar billets.

[0036] The upsetting-drawing ratio is controlled between 1.8 and 2.4. When the intermediate billet is forged into a small cross-section billet, the forging rate is 10 mm / s to 50 mm / s, and it is air-cooled after forging.

[0037] Step 4, recrystallization annealing of finished billet: The billet forged in step 3 is annealed in a vacuum annealing furnace, and then ground to produce pure niobium finished billet.

[0038] The annealing and holding temperature is set to 900℃~1200℃, the holding time is 2h~8h, and the vacuum degree during the holding stage is no greater than 10. -2 Pa, cooling method is furnace cooling. After annealing, the billets are ground to pure niobium finished bars with a diameter of Φ60mm~Φ150mm.

[0039] This invention employs a free forging method, which reduces surface damage to materials and avoids oxidation caused by temperature rise by selecting deformation temperature, deformation method, deformation rate, and cooling method. This improves the yield and produces small to medium-sized pure niobium rods with uniform high and low magnification structures and a high-magnification grain size difference of no more than 3 levels between the edges and the core. Furthermore, the rods exhibit good batch consistency and stability, making them suitable for industrial production.

[0040] Example 1:

[0041] Step 1, Forging the billet:

[0042] Pure niobium ingots with dimensions of Φ240~Φ300mm were subjected to a single-fire forging process at room temperature. The forging method was upsetting and drawing, with the upsetting-drawing ratio controlled at 1.7 to fully break down the coarse grains in the as-cast state. The cross-section of the forged billet was square with a side length of 260mm. When the intermediate billet was forged into a square billet under a flat anvil, the forging rate was 20mm / s~40mm / s, and it was air-cooled after forging.

[0043] Step 2, intermediate forging:

[0044] The intermediate billet after step one forging is subjected to three upsetting and drawing forgings at room temperature, with the upsetting-drawing ratio controlled at 1.7. The cross-section of the forged billet is square with a side length of 260mm. When the intermediate billet is forged into a square billet under a flat anvil, the forging rate is 20mm / s to 40mm / s, and it is air-cooled after forging.

[0045] Step 3, Finished Product Forging:

[0046] The intermediate billet after step two forging is subjected to three-stage drawing deformation at room temperature to finally forge into a finished bar billet, with the upsetting-drawing ratio controlled at 1.7 to 1.9. When the intermediate billet is forged into a small cross-section billet, the forging rate is 20 mm / s to 40 mm / s, and it is air-cooled after forging.

[0047] Step 4: Recrystallization annealing of the finished billet:

[0048] The forged billet from step three is then annealed in a vacuum annealing furnace. The annealing holding temperature is set at 1180℃ for 6 hours, and the vacuum degree during the holding stage is no greater than 10. -2 Pa, cooling method is furnace cooling. After annealing, the billet is ground to a finished bar with a diameter of Φ=80mm.

[0049] High and low magnification microstructures of finished bars, such as Figures 1-3 As shown, the bar has a uniform microstructure at low magnification, and a uniform microstructure at high magnification at the edges and center. The grain size difference between the edges and center at high magnification is no more than 3 levels, indicating that the bar has undergone sufficient and uniform deformation at all locations.

[0050] Example 2:

[0051] Step 1, Forging the billet:

[0052] Pure niobium ingots with dimensions of Φ240~Φ300mm were subjected to two-stage forging at room temperature. The forging method was upsetting and drawing, with the upsetting-drawing ratio controlled at 1.9 to fully break down the coarse grains in the as-cast state. The cross-section of the forged billet was square with a side length of 260mm. When the intermediate billet was forged into a square billet under a flat anvil, the forging rate was 20mm / s~40mm / s, and it was air-cooled after forging.

[0053] Step 2, intermediate forging:

[0054] The intermediate billet after step one forging is subjected to five upsetting and drawing forgings at room temperature, with the upsetting-drawing ratio controlled at 1.9. The cross-section of the forged billet is square with a side length of 260mm. When the intermediate billet is forged into a square billet under a flat anvil, the forging rate is 20mm / s to 40mm / s, and it is air-cooled after forging.

[0055] Step 3, Finished Product Forging:

[0056] The intermediate billet after step two forging is subjected to three-stage drawing deformation at room temperature to finally forge into a finished bar billet, with the forging ratio controlled between 1.9 and 2.2. When the intermediate billet is forged into a small cross-section billet, the forging rate is 20 mm / s to 40 mm / s, and it is air-cooled after forging.

[0057] Step 4: Recrystallization annealing of the finished billet:

[0058] The forged billet from step three is then annealed in a vacuum annealing furnace. The annealing holding temperature is set at 1080℃ for 5 hours, and the vacuum degree during the holding stage is no greater than 10. -2 Pa, cooled by furnace cooling. After annealing, it is ground to a finished bar stock with a diameter of Φ=95mm.

[0059] High and low magnification microstructures of bar stock, such as Figures 4-6 As shown, the bar has a uniform microstructure at low magnification, and a uniform microstructure at high magnification at the edges and center. The grain size difference between the edges and center at high magnification is no more than 3 levels, indicating that the bar has undergone sufficient and uniform deformation at all locations.

Claims

1. A method for preparing small- to medium-sized pure niobium rods with uniform microstructure, characterized in that, Includes the following steps: Step 1, billet forging: The pure niobium ingot is subjected to 1 to 2 forgings at room temperature, and the forging method is upsetting and drawing; In step one, the upsetting-drawing-forging ratio is controlled between 1.6 and 2.1; Step 2, intermediate forging: The intermediate billet after step 1 forging is repeatedly upsetting and drawing 3 to 5 times at room temperature; In step two, the upsetting-drawing-forging ratio is controlled at 1.5~1.9; Step 3, finished product forging: The intermediate billet after step 2 forging is subjected to 2 to 4 drawing deformations at room temperature, and finally forged into finished bar billets; In step three, the upsetting-drawing-forging ratio is controlled between 1.8 and 2.

4. Step 4, recrystallization annealing of finished billet: The billet forged in step 3 is annealed in a vacuum annealing furnace, and then ground to obtain pure niobium finished billet. In step four, the annealing and holding temperature is set to 900℃~1200℃, the holding time is 2h~8h, and the vacuum degree during the holding stage is no greater than 10. -2 Pa, the cooling method is furnace cooling; In steps one, two, and three, the forging rate is 10 mm / s to 50 mm / s.

2. The method for preparing uniformly structured small-to-medium-sized pure niobium rods according to claim 1, characterized in that, In step one, the pure niobium ingot has a size of Φ240mm~Φ300mm.

3. The method for preparing uniformly structured small-to-medium-sized pure niobium rods according to claim 1, characterized in that, In steps one and two, the cross-section of the forged billet is square with a side length of 240mm to 280mm.

4. The method for preparing uniformly structured small-to-medium-sized pure niobium rods according to claim 1, characterized in that, In step four, the specifications of the finished pure niobium rods are Φ60mm~Φ150mm.

5. The method for preparing uniformly structured small-to-medium-sized pure niobium rods according to claim 1, characterized in that, In steps one, two, and three, air cooling is performed after forging.

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