WO2021088608A1 - Smelting method for preparing fine crystalline pure niobium ingot - Google Patents

Abstract

Disclosed is a smelting method for preparing a fine crystalline pure niobium ingot. In the method, a vacuum electron beam cold bed furnace is used for carrying out smelting to prepare a pure niobium ingot; and during the smelting, 0.01-0.06 wt% of the element yttrium is added. A pure niobium ingot material prepared by using the method has the characteristics of fine crystal grains and a good uniformity of structure, and a uniform and equiaxed finished ingot with a crystal grain size of 5-15 mm and a residual resistance ratio (RRR) value > 300 can be obtained.

Description

Smelting method for preparing fine-crystalline pure niobium ingot Technical field

The invention belongs to the technical field of non-ferrous metal smelting, and relates to a method for preparing fine-crystalline pure niobium ingots by adding fine-crystalline nucleation elements.

Background technique

Disclosure of the background information is only intended to increase the understanding of the overall background of the present invention, and is not necessarily regarded as an acknowledgement or any form of suggestion that the information constitutes the prior art known to those of ordinary skill in the art.

Fine-grained pure niobium ingots are the raw materials required to produce high-quality pure niobium products. In recent years, the global energy crisis has become more and more serious. The development of a new generation of nuclear energy conversion devices has become more and more urgent to meet development needs. High-purity niobium rods and cavities are important basic materials for the development of new superconducting magnets and accelerator devices. According to incomplete statistics, the global demand for such pure niobium ingots exceeded 1,000 tons in 2008, and this demand has shown an upward trend year by year. Such special-purpose pure niobium products have extremely high requirements for the smelting process and the quality of the ingot: first, the ingot must have high purity to ensure the residual resistance ratio (RRR value> 300) to meet the requirements of superconductivity (references) : Ren Junshuai, Zhang Yingming, Guo Xuepeng, Xi Enping, Wang Juan. Preparation of high-purity niobium materials for radio frequency superconducting cavity, Rare Metal Materials and Engineering, 48(2), 2019, 688-692). Thirdly, the grain size of the pure niobium ingot should be small and relatively uniform, which is conducive to its subsequent plastic forming to ensure that a pure niobium product with uniform microstructure and excellent mechanical properties is obtained. At present, the ingots produced by the electron beam cooling bed smelting method generally have the problems of coarse crystal grains, large differences in the edge and center, insufficient purity of the niobium ingot, and small residual resistance ratio. It is difficult to balance the performance of the two aspects.

Summary of the invention

In order to overcome the above-mentioned problems, the present invention provides a smelting method for preparing fine-crystalline pure niobium ingots, which solves the existing smelting technology that has large as-cast crystal grains, large differences in edge and center, insufficient purity of niobium ingots, and residual resistance ratio. Minor problem.

In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

A smelting method for preparing fine-crystalline pure niobium ingots, using vacuum electron beam cooling bed furnace smelting to prepare pure niobium ingots;

During the smelting process, 0.01-0.06% by weight of yttrium element is added.

In order to make the ingot not only have high purity to ensure the residual resistance ratio (RRR value> 300) to meet the requirements of superconductivity, but also have fine and uniform grain size to facilitate subsequent plastic forming to obtain uniform microstructure and excellent mechanical properties Of pure niobium products. Through systematic research and experimentation, this application found that during the process of preparing pure niobium ingots by smelting in a vacuum electron beam cooling bed furnace, adding trace metal yttrium can not only control the as-cast crystal grain size, but also limit the impurity content to ensure the RRR of the final pure niobium product The value meets the requirements, achieving a balance of two aspects of performance.

In some embodiments, the yttrium element is metal yttrium powder dissolved in an organic solvent. The purpose of the present invention is to solve the problem of refining the structure of the pure Nb alloy ingot by adding Y element. Too little addition can not achieve the refining effect, and too much addition will reduce the RRR value.

In this application, the organic solvent for dissolving yttrium is not particularly limited. In some embodiments, the organic solvent is CCl ₄ or toluene to dissolve yttrium and make it more uniformly distributed on the pure niobium electrode.

The research of this application found that the different ways of adding yttrium powder will affect the as-cast crystal grain size and morphology. Therefore, in some embodiments, the method for adding the yttrium powder is: coating an organic solvent containing yttrium on a pure niobium electrode for smelting and drying;

Or the pure niobium electrode is surrounded by multiple circles of metal yttrium wire, and the obtained pure niobium ingot material has fine grained pure niobium ingots with fine grains, good structure uniformity, and an RRR value (>300).

The drying temperature is too low and the solvent evaporates slowly; the drying temperature is too high, and the yttrium is unevenly distributed on the niobium electrode. Therefore, in some embodiments, the drying conditions are 60-65°C for 25-30 minutes, In order to ensure the uniform distribution of yttrium on the niobium electrode, the drying efficiency is improved.

In some embodiments, the yttrium element is a metal yttrium wire welded on the surface of a pure niobium electrode, so that the metal yttrium wire is uniformly and stably distributed on the niobium electrode.

In some embodiments, the diameter of the added yttrium wire is 0.75 mm, and it is welded by argon arc welding. When the amount of yttrium added is as small as possible, the crystal grains are refined and the uniformity of the structure is improved.

In some embodiments, the specific steps of smelting include:

Put the electrode into the electron beam cooling bed furnace, vacuum, when the vacuum degree ≤ 10 ^-3 Pa, start smelting;

During the smelting process, keep the vacuum degree ≤10 ^-2 Pa. After the solution enters the cooling bed, keep it for 10-600S before pouring.

In some embodiments, the melting rate is selected to be 25-40 kg/h, and the cooling water pressure of the crystallizer should be greater than 0.35 MPa. The use of a smaller smelting speed and larger water pressure is beneficial to speed up the cooling rate of the molten pool, control the depth of the molten pool, and limit the diffusion distance of metal elements during solidification, thereby improving the uniformity of the crystal grains in the pure niobium ingot.

In some embodiments, the power of the electron gun (ie, the melting power) is 100 kW to 150 kW. The voltage is 20000～30000V, and the melting current is about 5A. The electrode Z-direction travel speed (that is, the pulling speed) is 6-10mm/min.

The invention also provides a fine-crystalline pure niobium ingot prepared by any of the above methods.

The invention also provides the application of the above-mentioned fine-crystalline pure niobium ingot in the preparation of superconducting materials, atomic energy structure materials and super heat-resistant alloys.

The beneficial effects of the present invention are:

(1) The pure niobium ingot prepared by this application has the characteristics of fine grains, good uniformity of the structure, and high residual resistance ratio (RRR value> 300), and uniformly equiaxed with an average grain size of 5-15 mm can be obtained Finished ingots. In the melting process, 0.01-0.06% by weight of yttrium element is added. During the electron beam cooling bed melting process, the solution is kept in the cooling bed for 10-600S, and the electron beam is continuously stirred. Then, it is poured into a mold to obtain a fully equiaxed finished ingot with as-cast grain size of 4-10mm.

(2) The operation method of this application is simple, low cost, universal, and easy to scale production.

Description of the drawings

The drawings of the specification forming a part of the application are used to provide a further understanding of the application, and the exemplary embodiments and descriptions of the application are used to explain the application and do not constitute an improper limitation of the application.

Figure 1 shows the structure of a pure niobium ingot with no element yttrium added, and the maximum grain size is about 40mm.

Figure 2 shows the pure niobium ingot structure with sprayed yttrium powder and 0.01wt% element yttrium. The maximum grain size is about 20mm, and the average grain size is about 15mm.

Figure 3 is a schematic diagram of adding metal yttrium wire by argon arc welding.

Figure 4 shows the structure of a pure niobium ingot with a welded yttrium wire and 0.01wt% element yttrium. The ingot grain size distribution is uneven, the average grain size at the edge is 10mm, and the maximum grain size at the core is about 30mm.

Figure 5 shows the pure niobium ingot structure with sprayed yttrium powder and 0.04wt% element yttrium. The maximum grain size is about 12mm, and the average grain size is 10mm.

Figure 6 shows the pure niobium ingot structure with sprayed yttrium powder and 0.06wt% element yttrium. The maximum grain size is about 8mm, and the average grain size is 5mm.

Detailed ways

It should be pointed out that the following detailed descriptions are all illustrative and are intended to provide further explanations for the application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

It should be noted that the terms used here are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprising" and/or "including" are used in this specification, they indicate There are features, steps, operations, devices, components, and/or combinations thereof.

As described in the background art, the current ingots produced by the electron beam cooling bed melting method generally have the problems of coarse crystal grains and large differences between the edges and the center. Therefore, the present invention proposes a smelting method for fine-crystalline pure niobium ingots, which specifically includes the following process:

(1) After dissolving 0.01-0.06% of metal yttrium powder calculated according to the proportion in _{solvents such as CCl 4} or toluene, it is evenly coated on the pure niobium electrode for smelting. Then put the electrode in an oven and dry it at 40-100°C for 20-60min, check the adhesion of the metal yttrium powder on the electrode, and then put it into an electron beam cooling bed furnace to prepare for smelting.

⑵ Put the prepared electrode into the electron beam cooling bed furnace and vacuum, when the vacuum degree ≤ 10 ^-3 Pa, start smelting.

^{⑶Keep the vacuum degree ≤10 -2} Pa during the smelting process, after the solution enters the cooling bed, keep it for 10-600S before pouring. Stir continuously during the pouring process to refine the crystal grains.

⑷The smelting speed should be 25-40kg/h, and the cooling water pressure of the crystallizer should be greater than 0.35MPa.

The present invention will be further described in detail below in conjunction with specific embodiments. It should be pointed out that the specific embodiments are for explaining rather than limiting the present invention.

Example 1

A Φ100mm pure niobium electrode (it has been purified and smelted twice to effectively remove O, N and other magazine elements, and the electrode purity is ≥99.90%), put into a vacuum electron beam cooling bed furnace, evacuated to 10 ^-3 Pa, then start smelting , The smelting power is increased to 150kW at a rate of 20kW/min, the voltage is 30000V, and the smelting current is about 5A. During the smelting process, keep the vacuum degree ≤10 ^-2 Pa, the electrode Z-direction travel speed (that is, the ingot drawing speed) 6～10mm/min, and the smelting speed is basically maintained at about 30kg/h. After the solution enters the cooling bed, keep it for 10-600S before pouring Put it into a Ф120mm round water-cooled copper crucible, the pressure of the cooling water in the crystallizer (water-cooled copper crucible) is kept greater than 0.35MPa, and it is continuously stirred during the pouring process. The maximum grain size of the prepared Ф120mm pure niobium ingot is about 40mm, see attached figure 1. For the three parts of the ingot head, middle and tail, the sampled and tested RRR values are 401, 399 and 404 respectively, which are all> 300.

Example 2

A Φ100mm pure niobium electrode (it has been purified and smelted twice to effectively remove O, N and other magazine elements, and the electrode purity is ≥99.90%). Use industrial spraying equipment to evenly coat the surface of the electrode with metal yttrium powder with a ratio of 0.01wt% Put the solution in an oven and dry at 60°C for 30 minutes. The pure niobium electrode that has been added with metal yttrium powder is put into a vacuum electron beam cooling bed furnace, and after evacuating to 10 ^-3 Pa, smelting is started. The smelting power is increased to 150kW at a rate of 20kW/min, and the voltage is 30000V. The current is about 5A. During the smelting process, keep the vacuum degree ≤10 ^-2 Pa, the electrode Z-direction travel speed (that is, the ingot drawing speed) 6～10mm/min, and the smelting speed is basically maintained at about 30kg/h. After the solution enters the cooling bed, keep it for 10-600S before pouring Put it into a Ф120mm round water-cooled copper crucible, the pressure of the cooling water in the crystallizer (water-cooled copper crucible) is kept greater than 0.35MPa, and it is continuously stirred during the pouring process. The maximum grain size of the prepared Ф120mm pure niobium ingot is about 20mm, and the average grain size is about 15mm. See attached figure 2. For the three parts of the ingot head, middle and tail, the RRR values were 374, 369 and 374, all of which were >300.

Example 3

A Φ100mm pure niobium electrode (it has been purified and smelted twice to effectively remove O, N and other magazine elements, and the electrode purity is ≥99.90%), add element yttrium by welding the yttrium wire on the electrode circumference with argon arc welding, as shown in the picture 3 The metal yttrium wire is spirally wound in the axial direction and welded and fixed on the surface of the pure niobium electrode. The diameter of the metal yttrium wire is 0.75mm, and the proportion of added element yttrium is 0.01wt%. Put the pure niobium electrode which has been added with metal yttrium wire into a vacuum electron beam cooling bed furnace, evacuate to 10 ^-3 Pa, and start smelting. The smelting power is increased to 150kW at a rate of 20kW/min, and the voltage is 30000V. The current is about 5A. During the smelting process, keep the vacuum degree ≤10 ^-2 Pa, the electrode Z-direction travel speed (that is, the ingot drawing speed) 6～10mm/min, and the smelting speed is basically maintained at about 30kg/h. After the solution enters the cooling bed, keep it for 10-600S before pouring Put it into a Ф120mm round water-cooled copper crucible, the pressure of the cooling water in the crystallizer (water-cooled copper crucible) is kept greater than 0.35MPa, and it is continuously stirred during the pouring process. For the three parts of the ingot head, middle, and tail, the RRR values are 390, 385 and 384 respectively, all of which are greater than 300. The maximum grain size of the prepared Ф120mm pure niobium ingot is about 30mm. The largest grain appears in the center of the ingot, and the edge grain size is small (average 10mm). It can be seen that the addition of yttrium is adopted to make the ingot grain size. Uneven distribution. See attached figure 4.

Example 4

A Φ100mm pure niobium electrode (it has been purified and smelted twice to effectively remove O, N and other magazine elements, and the electrode purity is ≥99.90%), and the surface of the electrode is uniformly coated with metal yttrium powder with an addition ratio of 0.04wt% with industrial spraying equipment Put the solution in an oven and dry at 60°C for 30 minutes. The pure niobium electrode that has been added with metal yttrium powder is put into a vacuum electron beam cooling bed furnace, and after evacuating to 10 ^-3 Pa, smelting is started. The smelting power is increased to 150kW at a rate of 20kW/min, and the voltage is 30000V. The current is about 5A. During the smelting process, keep the vacuum degree ≤10 ^-2 Pa, the electrode Z-direction travel speed (that is, the ingot drawing speed) 6～10mm/min, and the smelting speed is basically maintained at about 30kg/h. After the solution enters the cooling bed, keep it for 10-600S before pouring Put it into a Ф120mm round water-cooled copper crucible, the pressure of the cooling water in the crystallizer (water-cooled copper crucible) is kept greater than 0.35MPa, and it is continuously stirred during the pouring process. The maximum grain size of the prepared Ф120mm pure niobium ingot is about 12mm, and the average grain size is 10mm, see Figure 5. For the three parts of the ingot head, middle, and tail, the measured RRR values are 353, 367, and 362, respectively, which are all> 300.

Example 5

A Φ100mm pure niobium electrode (it has been purified and smelted twice to effectively remove O, N and other magazine elements, and the electrode purity is ≥99.90%). Use industrial spraying equipment to uniformly coat the surface of the electrode with metal yttrium powder with a ratio of 0.06wt% Put the solution in an oven and dry at 60°C for 30 minutes. The pure niobium electrode that has been added with metal yttrium powder is put into a vacuum electron beam cooling bed furnace, and after evacuating to 10 ^-3 Pa, smelting is started. The smelting power is increased to 150kW at a rate of 20kW/min, and the voltage is 30000V. The current is about 5A. During the smelting process, keep the vacuum degree ≤10 ^-2 Pa, the electrode Z-direction travel speed (that is, the ingot drawing speed) 6～10mm/min, and the smelting speed is basically maintained at about 30kg/h. After the solution enters the cooling bed, keep it for 10-600S before pouring Put it into a Ф120mm round water-cooled copper crucible, the pressure of the cooling water in the crystallizer (water-cooled copper crucible) is kept greater than 0.35MPa, and it is continuously stirred during the pouring process. The maximum grain size of the prepared Ф120mm pure niobium ingot is about 8mm, and the average grain size is 5mm, see Figure 6. For the three parts of the ingot head, middle and tail, the sampled and tested RRR values were 342, 341 and 358, all of which were greater than 300.

Finally, it should be noted that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, it is still for those skilled in the art. The technical solutions described in the foregoing embodiments may be modified, or some of them may be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, they do not limit the scope of protection of the present invention. Those skilled in the art should understand that on the basis of the technical solutions of the present invention, those skilled in the art do not need to make creative efforts. Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (10)

1. A smelting method for preparing fine-crystalline pure niobium ingots, which is characterized in that the pure niobium ingots are prepared by smelting in a vacuum electron beam cooling bed furnace;

   During the smelting process, 0.01-0.06% by weight of yttrium element is added.
2. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 1, wherein the yttrium element is metal yttrium powder dissolved in an organic solvent.
3. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 2, wherein the organic solvent is CCl ₄ or toluene.
4. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 1, wherein the method of adding yttrium element is: coating an organic solvent containing yttrium on a pure niobium electrode for smelting, and drying ；

   Or the pure niobium electrode is surrounded by multiple circles of yttrium wire.
5. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 4, wherein the drying conditions are 40-100°C for 20-60 minutes.
6. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 1, wherein the specific steps of smelting include:

   Put the electrode into the electron beam cooling bed furnace, vacuum, when the vacuum degree ≤ 10 ^-3 Pa, start smelting;

   During the smelting process, keep the vacuum degree ≤10 ^-2 Pa. After the solution enters the cooling bed, keep it for 10-600S before pouring.
7. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 1, wherein the smelting speed is selected to be 25-40 kg/h, and the cooling water pressure of the crystallizer should be greater than 0.35 MPa.
8. The smelting method for preparing fine-crystalline pure niobium ingots according to claim 1, wherein the smelting speed is selected to be 25-40 kg/h, the cooling water pressure of the crystallizer should be greater than 0.35 MPa, and the power of the electron gun is 100 kW to 150 kW. The voltage is 20000～30000V, and the melting current is about 5A. The electrode Z-direction travel speed is 6-10mm/min.
9. A fine-crystalline pure niobium ingot prepared by the method of any one of claims 1-8.
10. The application of the fine-crystalline pure niobium ingot of claim 9 in the preparation of superconducting materials, atomic energy structure materials and super heat-resistant alloys.

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