Pure niobium rod with uniform structure and extrusion method thereof

Abstract

This invention discloses a method for preparing uniformly structured pure niobium rods and their extrusion, comprising the following steps: Step 1, selecting a pure niobium ingot, encasing it in a copper cladding in a vacuum environment and welding it; Step 2, heating and holding the cladding material and then extruding it into a primary billet; Step 3, straightening the primary billet and removing the surface copper foil and surface oxide; Step 4, encasing the primary billet in a copper cladding in a vacuum environment and welding it; Step 5, heating and holding the cladding material and then extruding it into a secondary billet; Step 6, recrystallizing and heat-treating the secondary billet, followed by straightening, grinding, and polishing to obtain a finished pure niobium rod. This invention prepares billets by encasing them in a copper cladding in a vacuum environment and by heating and extruding, ultimately obtaining small-sized pure niobium rods with a yield strength of 73 MPa, a tensile strength of 125 MPa, an elongation of 25%, a reduction of area of ​​90%, no obvious flow lines at low magnification, and a grain size difference of less than 2 at high magnification through recrystallization annealing.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal material processing technology, specifically relating to a method for extruding pure niobium rods with uniform microstructure. This invention also relates to pure niobium rods with uniform microstructure obtained by the extrusion method. Background Technology

[0002] Large-scale scientific facilities such as the International Thermonuclear Experimental Reactor (ITER) and the China Fusion Engineering Experimental Reactor (CFE) utilize a large amount of Nb3Sn superconducting wires and magnets. Pure niobium rods, as an important raw material for preparing Nb3Sn superconducting wires, undergo over 99.99% tensile deformation during wire processing. Due to the extremely large deformation, abnormalities in the original rod's microstructure, properties, or surface quality can lead to non-uniform deformation during plastic deformation, resulting in localized stress concentrations. This can cause wire breakage during the stretching process, rendering the wire unusable and causing significant economic losses and time costs.

[0003] To ensure a smooth wire drawing process, strict control must be exercised over the microstructure, property uniformity, and surface quality of the pure niobium bar raw materials. Pure niobium itself has low softness and strength, and is prone to non-uniform deformation during conventional forging and rolling plastic deformation, resulting in uneven microstructure. Furthermore, Nb is highly susceptible to oxidation during hot working. Therefore, uniform deformation methods should be employed during processing to minimize oxidation losses and improve the surface quality of the finished product. Summary of the Invention

[0004] The purpose of this invention is to provide a method for extruding pure niobium rods with uniform structure, which solves the problem of non-uniform deformation that is easily generated in existing processing methods.

[0005] Another object of the present invention is to provide a pure niobium rod with uniform structure obtained by an extrusion preparation method.

[0006] The technical solution adopted in this invention is: a pure niobium rod with uniform structure and its extrusion preparation method, comprising the following steps:

[0007] Step 1: Select a pure niobium ingot, cover it with a copper sleeve in a vacuum welding box and weld it.

[0008] Step 2: Place the coating material obtained in Step 1 in a box-type resistance furnace for heating and heat preservation, and then use an extruder to extrude it into a primary billet;

[0009] Step 3: The blank obtained in Step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0010] Step 4: Wrap the primary blank obtained in Step 3 with a copper sleeve and weld it in a vacuum welding box;

[0011] Step 5: Place the coating material obtained in Step 4 in a box-type resistance furnace for heating and heat preservation, and then use an extruder to extrude it into a secondary billet.

[0012] Step 6: The secondary billet obtained in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace, followed by straightening, grinding, and polishing to produce pure niobium finished bars.

[0013] The invention is further characterized in that,

[0014] The pure niobium ingots selected in step 1 have a size of Φ150mm~Φ350mm.

[0015] The heating temperature in step 2 is 500℃~850℃.

[0016] In step 2, the extrusion ratio of the blank is 4.0 to 10.0 when the blank is extruded using an extruder.

[0017] The heating temperature in step 5 is 500℃~850℃.

[0018] In step 5, the extrusion ratio of the secondary billet extruded using an extruder is 10.0 to 25.0.

[0019] In step 6, the holding temperature for recrystallization heat treatment in a vacuum furnace is 700℃~1100℃, the vacuum degree during the holding stage is ≤10-2Pa, and the holding time is 120min~240min.

[0020] The beneficial effects of this invention are as follows: The pure niobium rod with uniform microstructure and its extrusion preparation method involve covering the pure niobium ingot with a copper sheath in a vacuum welding box, which can prevent the oxidation of Nb material at high temperatures. The rod is then subjected to primary and secondary extrusion at a hot working temperature of 500℃~850℃. During extrusion, the copper sheath acts as a lubricant, preventing scratches on the material surface. Finally, through recrystallization heat treatment, a pure niobium rod with a yield strength of 73MPa, a tensile strength of 125MPa, an elongation of 25%, a reduction of area of ​​90%, good microstructure uniformity, no obvious flow lines at low magnification, and a grain size difference of less than grade 2 at high magnification is obtained. Attached Figure Description

[0021] Figure 1 This is a low-magnification image of the transverse microstructure of a Φ19.4mm pure niobium rod prepared by the extrusion method of the present invention for producing pure niobium rods with uniform microstructure;

[0022] Figure 2 This is a high-magnification image of the transverse edge microstructure of a Φ19.4mm pure niobium rod prepared by the extrusion method of the present invention for producing pure niobium rods with uniform microstructure;

[0023] Figure 3 This is a high-magnification image of the transverse core structure of a Φ19.4mm pure niobium rod prepared by the extrusion method of the present invention for producing pure niobium rods with uniform structure;

[0024] Figure 4 The present invention describes the room temperature mechanical properties of pure niobium rods prepared by the extrusion method for producing pure niobium rods with uniform microstructure. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] This invention provides a method for extruding pure niobium rods with uniform microstructure, specifically implemented according to the following steps:

[0027] Step 1, Vacuum-coating copper sleeve for ingot casting

[0028] Select pure niobium ingots with diameters of 150mm to 350mm, assemble and coat them with copper sleeves in a vacuum welding box, and complete the welding of the cladding material.

[0029] Step 2, heating and extruding the coating material.

[0030] The cladding material that has undergone vacuum assembly and welding in step 1 is placed in a box-type resistance furnace and heated to a temperature of 500℃~850℃. It is then extruded into a single billet using an extruder with an extrusion ratio of 4.0~10.0. The extruded dimensions are Φ47.4mm~Φ175mm.

[0031] Step 3, one-time billet straightening machine

[0032] The primary blank prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0033] Step 4, Vacuum-coating copper sleeve onto billet in one step

[0034] The primary blank prepared in step 3 is assembled and coated with a copper sleeve in a vacuum welding box and then welded.

[0035] Step 5, heating and extruding the billet coating material.

[0036] The primary blank material that has undergone vacuum assembly and welding in step 4 is placed in a box-type resistance heating system at a temperature of 500℃~850℃ and extruded into a secondary blank using an extrusion press with an extrusion ratio of 10.0~25.0. The extruded material has a size of Φ9.5mm~Φ55.3mm.

[0037] Step 6, Recrystallization, Straightening, and Grinding of the Finished Product

[0038] The billet after extrusion in step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The holding temperature during recrystallization heat treatment is 700℃~1100℃, the vacuum degree during the holding stage is ≤10-2Pa, and the holding time is 120min~240min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0039] Example 1

[0040] Step 1: Select a Φ150mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0041] Step 2: The coating material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 500℃. After heating, it is extruded into a primary blank using an extruder with an extrusion ratio of 4.0. The extruded specification is Φ75mm.

[0042] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0043] Step 4: The primary blank prepared in step 3 is assembled and coated with a copper sleeve in a vacuum welding box and then welded.

[0044] Step 5: The primary blank material that has undergone vacuum assembly and welding in Step 4 is placed in a box-type resistance heating system at 850℃ and extruded into a secondary blank using an extrusion press. The extrusion ratio is 15.0, and the extruded size is Φ19.4mm.

[0045] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 1100℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 120min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0046] Example 2

[0047] Step 1: Select a Φ150mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0048] Step 2: The coating material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 850℃. After heating, it is extruded into a single billet using an extruder with an extrusion ratio of 10.0. The extruded specification is Φ47.4mm.

[0049] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0050] Step 4: The primary blank prepared in step 3 is assembled and covered with a copper sleeve in a vacuum welding box and then welded.

[0051] Step 5: Place the primary blank coated material that has undergone vacuum assembly and welding in Step 4 into a box-type resistance heating system at a temperature of 500℃, and extrude it into a secondary blank using an extrusion press with an extrusion ratio of 25.0. The extruded material has a specification of Φ9.5mm.

[0052] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 700℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 240min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0053] Example 3

[0054] Step 1: Select a Φ350mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0055] Step 2: The coating material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 850℃. After heating, it is extruded into a single billet using an extruder with an extrusion ratio of 10.0. The extruded specification is Φ110.7mm.

[0056] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0057] Step 4: The primary blank prepared in step 3 is assembled and covered with a copper sleeve in a vacuum welding box and then welded.

[0058] Step 5: Place the primary blank coated material that has undergone vacuum assembly and welding in Step 4 into a box-type resistance heating system at a temperature of 700℃, and extrude it into a secondary blank using an extrusion press with an extrusion ratio of 20.0. The extruded material has a specification of Φ24.8mm.

[0059] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 950℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 180min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0060] Example 4

[0061] Step 1: Select a Φ350mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0062] Step 2: The coating material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 600℃. After heating, it is extruded into a single billet using an extruder with an extrusion ratio of 4.0. The extruded specification is Φ175mm.

[0063] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0064] Step 4: The primary blank prepared in step 3 is assembled and covered with a copper sleeve in a vacuum welding box and then welded.

[0065] Step 5: The primary blank material that has undergone vacuum assembly and welding in Step 4 is placed in a box-type resistance heating system at a temperature of 600℃ and extruded into a secondary blank using an extrusion press with an extrusion ratio of 10.0. The extruded material has a diameter of Φ55.3mm.

[0066] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 1000℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 120min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0067] Example 5

[0068] Step 1: Select a Φ250mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0069] Step 2: The cladding material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 700℃. After heating, it is extruded into a single billet using an extruder with an extrusion ratio of 6.0. The extruded size is Φ102.1mm.

[0070] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0071] Step 4: The primary blank prepared in step 3 is assembled and covered with a copper sleeve in a vacuum welding box and then welded.

[0072] Step 5: Place the primary blank coated material that has undergone vacuum assembly and welding in Step 4 into a box-type resistance heating system at a temperature of 750℃, and extrude it into a secondary blank using an extrusion press. The extrusion ratio is 15.0, and the extruded material has a specification of Φ26.3mm.

[0073] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 900℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 240min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0074] Example 6

[0075] Step 1: Select a Φ300mm pure niobium ingot, assemble and cover it with a copper sleeve in a vacuum welding box, and complete the welding.

[0076] Step 2: The coating material that has been vacuum assembled and welded in Step 1 is placed in a box-type resistance furnace and heated to 800℃. After heating, it is extruded into a primary billet using an extruder with an extrusion ratio of 8.0. The extruded specification is Φ106mm.

[0077] Step 3: The primary billet prepared in step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining.

[0078] Step 4: The primary blank prepared in step 3 is assembled and covered with a copper sleeve in a vacuum welding box and then welded.

[0079] Step 5: Place the primary blank material that has undergone vacuum assembly and welding in Step 4 into a box-type resistance heating system at a temperature of 550℃, and extrude it into a secondary blank using an extrusion press with an extrusion ratio of 12.5. The extruded material has a specification of Φ30mm.

[0080] Step 6: The billet extruded in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace. The recrystallization heat treatment temperature is 1050℃, the vacuum degree during the heat treatment stage is ≤10-2Pa, and the heat treatment time is 180min. The billet is then straightened, ground, and polished to produce pure niobium finished bars.

[0081] The pure niobium finished bars obtained in the embodiments of the present invention were tested. The yield strength and tensile strength of the finished bars were tested using a strength testing device. The elongation and cross-sectional expansion rate were tested using an elongation meter. The metallographic structure of Example 1 was analyzed using a metallographic microscope. The low-magnification image of its transverse structure is shown below. Figure 1 As shown, the high-magnification image of the transverse edge tissue is as follows: Figure 2 As shown, a high-magnification image of the transverse cardiac tissue is as follows. Figure 3 As shown, the room temperature mechanical properties of the annealed states in Examples 1-5 were tested, as follows. Figure 4 As shown.

[0082] Metallography Figures 1-3 It can be seen that the transverse microstructure of pure niobium rods is uniform; test results Figure 4 The results show that the pure niobium rods prepared by this invention have a yield strength of 73 MPa, a tensile strength of 125 MPa, and an elongation of 25%, meeting the requirements of ASTM B392 standard. At the same time, the reduction of area reaches 90%, there are no obvious streamlines at low magnification, and the grain size difference is less than 2 at high magnification, exhibiting good batch stability.

[0083] Through the above methods, the present invention prepares billets by vacuum-encapsulating copper sheaths and heating and extruding them. Finally, through recrystallization annealing, small-sized pure niobium rods with a yield strength of 73 MPa, a tensile strength of 125 MPa, an elongation of 25%, a reduction of area of ​​90%, no obvious flow lines at low magnification, and a grain size difference of less than 2 at high magnification are obtained. Furthermore, the batches exhibit good consistency and stability, and the performance in use is excellent.

Claims

1. A method for extruding pure niobium rods with uniform microstructure, characterized in that, Includes the following steps: Step 1: Select a pure niobium ingot, cover it with a copper sleeve in a vacuum welding box and weld it. Step 2: Place the coating material obtained in Step 1 in a box-type resistance furnace and heat it at a temperature of 500℃~850℃. Then, use an extruder to extrude it into a primary billet with an extrusion ratio of 4.0~10.

0. Step 3: The blank obtained in Step 2 is straightened using a straightening machine, and then the surface copper foil and surface oxide are removed by machining. Step 4: Wrap the primary blank obtained in Step 3 with a copper sleeve and weld it in a vacuum welding box; Step 5: Place the coating material obtained in Step 4 into a box-type resistance furnace and heat it at a temperature of 500℃~850℃. Then, use an extruder to extrude it into a secondary billet with an extrusion ratio of 10.0~25.

0. Step 6: The secondary billet obtained in Step 5 is subjected to recrystallization heat treatment in a vacuum furnace, followed by straightening, grinding, and polishing to produce pure niobium finished bars.

2. The method for preparing uniformly structured pure niobium rods by extrusion as described in claim 1, characterized in that, The pure niobium ingots selected in step 1 have a size of Φ150mm~Φ350mm.

3. The method for preparing uniformly structured pure niobium rods by extrusion as described in claim 1, characterized in that, In step 6, the holding temperature for recrystallization heat treatment in a vacuum furnace is 700℃~1100℃, and the vacuum degree during the holding stage is ≤10. -2 Pa, the heat preservation time is 120min~240min.

4. Pure niobium rods with uniform microstructure obtained by the extrusion preparation method as described in claim 1.

Images