Uniform-structure pure niobium bar and extrusion preparation method thereof

Abstract

The invention discloses a pure niobium bar with a uniform structure and an extrusion preparation method thereof. The extrusion preparation method comprises the following steps: step 1, selecting a pure niobium cast ingot, coating a copper sheath in a vacuum environment, and welding; 2, the coating material is heated, subjected to heat preservation and then extruded into a primary blank; 3, the primary blank is straightened, and then surface copper sheets and surface oxidation are removed; 4, the primary blank is coated with a copper sheath in a vacuum environment and welded; 5, the coating material is heated, subjected to heat preservation and then extruded into a secondary blank; and 6, the secondary blank is subjected to recrystallization heat treatment, and then is straightened, ground and polished to obtain a pure niobium finished product bar. According to the invention, a blank is prepared by a method of coating a copper sheath in a vacuum environment and heating and extruding, and finally, the small-specification pure niobium bar with yield strength of 73MPa, tensile strength of 125MPa, elongation of 25%, reduction of area of 90%, no obvious streamline at low power and high-power grain range of less than level 2 is obtained by recrystallization annealing.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal material processing, and specifically relates to a method for preparing a pure niobium rod with uniform structure by extrusion. The invention also relates to a pure niobium rod with uniform structure prepared by the extrusion preparation method. Background Art

[0002] Large-scale scientific facilities such as the International Thermonuclear Experimental Reactor and the China Fusion Engineering Experimental Reactor use a large number of Nb3Sn superconducting wires and magnets. Pure niobium rods are an important raw material for the preparation of Nb3Sn superconducting wires, and more than 99.99% of the tensile deformation is completed during the wire processing. Because the deformation is very large, abnormalities in the structure, performance or surface quality of the original rods will cause non-uniform deformation during the plastic deformation process, resulting in local stress concentration, which will cause the superconducting wire to break during the stretching process, and the wire will be scrapped, causing significant economic losses and time cost losses.

[0003] In order to ensure that there are no abnormalities during the wire drawing process, the organization, performance uniformity and surface quality of the raw materials of pure niobium bars need to be strictly controlled. Pure niobium itself has low soft strength, and it is easy to produce non-uniform deformation during conventional forging and rolling plastic deformation, resulting in uneven organization. At the same time, Nb is very easy to oxidize during hot working. Therefore, uniform deformation should be used for processing, while reducing oxidation loss during processing and improving the surface quality of the finished product. Summary of the invention

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

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

[0006] The technical solution adopted by the present invention is: a pure niobium rod with uniform structure and an extrusion preparation method thereof, comprising the following steps: Step 1: Select pure niobium ingot, coat it with copper sleeve and weld it in vacuum welding box; Step 2, placing the coated material obtained in step 1 in a box-type resistance furnace for heating and heat preservation, and then using an extruder to extrude into a primary billet; Step 3, straightening the primary blank obtained in step 2 by using a straightening machine, and then removing the surface copper skin and surface oxidation by machining; Step 4, the primary blank obtained in step 3 is coated with a copper sheath in a vacuum welding box and welded; Step 5, placing the coated material obtained in step 4 in a box-type resistance furnace for heating and heat preservation, and then using an extruder to extrude into a secondary billet; Step 6: The secondary billet obtained in step 5 is subjected to recrystallization heat treatment in a vacuum furnace, and then straightened, ground and polished to obtain a pure niobium finished bar.

[0007] The present invention is also characterized in that: The specification of the pure niobium ingot selected in step 1 is Φ150mm~Φ350mm.

[0008] The heating temperature in step 2 is 500°C to 850°C.

[0009] In step 2, the extrusion ratio of the primary billet extruded by the extruder is 4.0 to 10.0.

[0010] The heating temperature in step 5 is 500°C to 850°C.

[0011] In step 5, the extrusion ratio of the secondary billet extruded by the extruder is 10.0 to 25.0.

[0012] In step 6, the holding temperature of the vacuum furnace recrystallization heat treatment is 700°C to 1100°C, the vacuum degree during the holding stage is ≤10-2Pa, and the holding time is 120min to 240min.

[0013] The beneficial effects of the present invention are as follows: the pure niobium rod with uniform structure and the extrusion preparation method thereof of the present invention, the pure niobium ingot is coated with a copper sheath in a vacuum welding box, oxidation of the Nb material can be prevented at high temperature, and primary and secondary extrusion are performed at a hot working temperature of 500°C to 850°C, the copper sheath can play a lubricating role during extrusion to avoid scratches on the surface of the material, and finally a pure niobium rod with a yield strength of 73MPa, a tensile strength of 125MPa, an elongation of 25%, a cross-sectional reduction of 90%, good structural uniformity, no obvious streamlines at low magnification, and a high magnification grain range of less than 2 levels is obtained through recrystallization heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a low-power image of the transverse structure of a Φ19.4 mm pure niobium rod prepared by the extrusion preparation method of a pure niobium rod with uniform structure of the present invention; Figure 2 This is a high-magnification image of the transverse edge structure of a Φ19.4 mm pure niobium rod prepared by the extrusion preparation method of a pure niobium rod with uniform structure of the present invention; Figure 3 This is a high-magnification image of the transverse core structure of a Φ19.4 mm pure niobium rod prepared by the extrusion preparation method of a pure niobium rod with uniform structure of the present invention; Figure 4 The room temperature mechanical properties of the pure niobium rod in the annealed state prepared by the extrusion preparation method of the pure niobium rod with uniform structure of the present invention. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] The present invention provides a method for preparing a pure niobium rod with uniform structure by extrusion, which is specifically implemented according to the following steps: Step 1: Vacuum cladding of ingot with copper cladding Select Φ150mm~Φ350mm pure niobium ingots, assemble and coat them with copper sleeves in a vacuum welding box, and complete the coating material welding; Step 2: Heating and extruding the coating material The cladding material after vacuum assembly and cladding welding in step 1 is placed in a box-type resistance furnace for heating at a temperature of 500° C. to 850° C., and extruded into a primary billet using an extruder at an extrusion ratio of 4.0 to 10.0, and the specifications after extrusion are Φ47.4 mm to Φ175 mm; Step 3, one-time blank straightening machine The primary blank prepared in step 2 is straightened by a straightening machine, and then the surface copper skin and surface oxidation are removed by machining; Step 4: vacuum cladding of copper sleeve on primary blank The primary blank prepared in step 3 is assembled and coated with a copper sheath in a vacuum welding box and welded; Step 5: Heating and extruding the primary blank coating material The primary blank coated material after vacuum assembly and coating welding in step 4 is placed in a box-type resistance heating temperature of 500°C to 850°C, and extruded into a secondary blank using an extruder, with an extrusion ratio of 10.0 to 25.0, and the specifications after extrusion are Φ9.5mm to Φ55.3mm; Step 6: Finished product recrystallization straightening and grinding The billet extruded in step 5 is subjected to recrystallization heat treatment in a vacuum furnace, the holding temperature of the recrystallization heat treatment is 700°C to 1100°C, the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 120min to 240min; and the billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0017] Example 1 Step 1, select a Φ150mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 500° C., and extruding it into a primary billet using an extruder after heating at an extrusion ratio of 4.0, and a specification of Φ75 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating at a temperature of 850° C., and extruding it into a secondary blank using an extruder, with an extrusion ratio of 15.0, and a specification of Φ19.4 mm after extrusion; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature of the recrystallization heat treatment is 1100° C., the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 120 minutes, and the billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0018] Example 2 Step 1, select a Φ150mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 850° C., and extruding it into a primary billet using an extruder after heating, with an extrusion ratio of 10.0 and a specification of Φ47.4 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating temperature of 500° C., using an extruder to extrude into a secondary blank, the extrusion ratio is 25.0, and the specification after extrusion is Φ9.5 mm; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature of the recrystallization heat treatment is 700° C., the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 240min. The billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0019] Example 3 Step 1, select a Φ350mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 850° C., and extruding it into a primary billet using an extruder after heating, with an extrusion ratio of 10.0 and a specification of Φ110.7 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating temperature of 700° C., using an extruder to extrude into a secondary blank, the extrusion ratio is 20.0, and the specification after extrusion is Φ24.8 mm; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature of the recrystallization heat treatment is 950° C., the vacuum degree of the holding stage is ≤10-2Pa, the holding time is 180min, and the billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0020] Example 4 Step 1, select a Φ350mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 600° C., and extruding it into a primary billet using an extruder after heating, with an extrusion ratio of 4.0 and a specification of Φ175 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating temperature of 600° C., using an extruder to extrude into a secondary blank, the extrusion ratio is 10.0, and the specification after extrusion is Φ55.3 mm; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature of the recrystallization heat treatment is 1000° C., the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 120 minutes, and the billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0021] Example 5 Step 1, select a Φ250mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 700° C., and extruding it into a primary billet using an extruder after heating, with an extrusion ratio of 6.0 and a specification of Φ102.1 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating temperature of 750° C., using an extruder to extrude into a secondary blank, the extrusion ratio is 15.0, and the specification after extrusion is Φ26.3 mm; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature of the recrystallization heat treatment is 900° C., the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 240min. The billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0022] Example 6 Step 1, select a Φ300mm pure niobium ingot, assemble and coat it with a copper sleeve in a vacuum welding box and complete welding; Step 2, placing the cladding material after vacuum assembly and cladding welding in step 1 in a box-type resistance furnace for heating at a temperature of 800° C., and extruding it into a primary billet using an extruder after heating, with an extrusion ratio of 8.0 and a specification of Φ106 mm after extrusion; Step 3, straightening the primary blank prepared in step 2 by using a straightening machine, and then removing the surface copper scale and surface oxidation by machining; Step 4, assembling and coating the primary blank prepared in step 3 with a copper sheath in a vacuum welding box and completing welding; Step 5, placing the primary blank coated material after vacuum assembly, coating and welding in step 4 in a box-type resistance heating at a temperature of 550° C., and extruding it into a secondary blank using an extruder, with an extrusion ratio of 12.5, and a specification of Φ30 mm after extrusion; Step 6, subjecting the billet extruded in step 5 to recrystallization heat treatment in a vacuum furnace, wherein the holding temperature for the recrystallization heat treatment is 1050° C., the vacuum degree in the holding stage is ≤10-2Pa, and the holding time is 180 minutes, and the billet is straightened, ground and polished to obtain a pure niobium finished bar.

[0023] The pure niobium finished rod obtained in the embodiment of the present invention was tested. The yield strength and tensile strength of the finished rod were tested by strength testing equipment. The elongation and cross-sectional expansion ratio were tested by an elongation tester. The metallographic microscope was used to analyze the metallographic structure of Example 1. The low-magnification image of the transverse structure is shown in FIG. Figure 1 As shown, the high-power image of the transverse edge structure is as follows Figure 2 As shown, the high-magnification image of the transverse heart tissue is as follows Figure 3 As shown, the room temperature mechanical properties of the annealed state of Examples 1 to 5 were tested. Figure 4 shown.

[0024] By metallographic Figures 1 to 3 It can be seen that the lateral structure of pure niobium rod is uniform; the test results Figure 4It is shown that the yield strength of the pure niobium rod produced by the present invention reaches 73MPa, the tensile strength reaches 125MPa, and the elongation reaches 25%, which meets the requirements of ASTM B392 standard. At the same time, the cross-sectional reduction rate reaches 90%, there is no obvious streamline at low magnification, and the grain range at high magnification is less than 2 levels, which has good batch stability.

[0025] Through the above-mentioned method, the present invention prepares the blank by a method of vacuum environment copper coating and heating extrusion, and finally obtains a small-sized pure niobium rod with a yield strength of 73MPa, a tensile strength of 125MPa, an elongation of 25%, a cross-sectional reduction of 90%, no obvious streamlines at low magnification, and a high-magnification grain range of less than 2 levels through recrystallization annealing, and has good batch consistency and stability and good use effect.

Claims

1. A method for preparing pure niobium rods with uniform structure by extrusion, characterized in that: The following steps are involved: Step 1: Select pure niobium ingot, coat it with copper sleeve and weld it in vacuum welding box; Step 2, placing the coated material obtained in step 1 in a box-type resistance furnace for heating and heat preservation, and then using an extruder to extrude into a primary billet; Step 3, straightening the primary blank obtained in step 2 by using a straightening machine, and then removing the surface copper skin and surface oxidation by machining; Step 4, the primary blank obtained in step 3 is coated with a copper sheath in a vacuum welding box and welded; Step 5, placing the coated material obtained in step 4 in a box-type resistance furnace for heating and heat preservation, and then using an extruder to extrude into a secondary billet; Step 6: The secondary billet obtained in step 5 is subjected to recrystallization heat treatment in a vacuum furnace, and then straightened, ground and polished to obtain a pure niobium finished bar.

2. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: The specification of the pure niobium ingot selected in step 1 is Φ150mm-Φ350mm.

3. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: The heating temperature in step 2 is 500°C to 850°C.

4. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: In the step 2, the extrusion ratio of the primary billet extruded by the extruder is 4.0 to 10.

0.

5. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: The heating temperature in step 5 is 500°C to 850°C.

6. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: In the step 5, the extrusion ratio of the extruder used to extrude the secondary billet is 10.0 to 25.

0.

7. The method for preparing pure niobium rods with uniform structure by extrusion according to claim 1, characterized in that: In step 6, the holding temperature of the vacuum furnace recrystallization heat treatment is 700° C. to 1100° C., the vacuum degree during the holding stage is ≤10-2Pa, and the holding time is 120min to 240min.

8. A pure niobium rod with uniform structure obtained by the extrusion preparation method according to claim 1.

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