Preparation method of niobium alloy thin-walled tube used at high temperature

Abstract

The invention discloses a preparation method of a niobium alloy thin-walled tube used at high temperature. The method comprises the following steps: 1, extruding a niobium alloy ingot to obtain an extruded bar, and processing the extruded bar into a hollow round ingot; 2, putting the hollow round ingot into an anti-oxidation sheath, sealing and welding, and extruding to obtain an extruded pipe; thirdly, the extruded pipe is subjected to surface treatment and annealing and then subjected to cogging rolling, and a rough pipe blank is obtained; fourthly, the rough pipe blank is rolled after being cleaned and annealed, and a niobium alloy pipe semi-finished product is obtained; and fifthly, the niobium alloy pipe semi-finished product is annealed after being cleaned, and the niobium alloy thin-walled pipe is obtained. According to the preparation method, the process of two-time extrusion and large-deformation rolling is adopted, grains in niobium alloy ingots are effectively broken, strict control rolling and heat treatment processes are combined, the niobium alloy thin-walled tube with fine grains and good plasticity is obtained, the machining efficiency and the yield of the niobium alloy thin-walled tube are improved, the preparation period is shortened, and the niobium alloy thin-walled tube is suitable for a cladding material for a high-temperature-resistant environment.

Description

Technical Field

[0001] The invention belongs to the technical field of preparation of refractory metal material pipes, and particularly relates to a method for preparing a niobium alloy thin-walled pipe for high temperature use. Background Art

[0002] Niobium-tungsten alloys are corrosion-resistant and offer excellent high-temperature performance, with a tensile strength of 60 MPa at 1650°C. They are widely used as thermal protection and structural materials in aerospace and aviation. Chinese patent CN108213109A reports a method for preparing niobium-zirconium alloy tubes, which are produced through a single extrusion and rolling process. This method is suitable for preparing niobium alloys with relatively low tensile strength (200 MPa at room temperature). However, for medium-strength niobium-tungsten alloys (450 MPa at room temperature), the deformation resistance is too high when directly extruding them into tubes, resulting in a low yield. While Chinese patent CN109226326 B reports a method for preparing ultra-thin-walled niobium-tungsten alloy tubes, this method can only produce niobium alloy tubes with a length of no more than 300 mm and a wall thickness of 0.1 mm to 0.2 mm, which is not suitable for preparing long niobium alloy tubes. Summary of the Invention

[0003] The present invention addresses the shortcomings of the prior art by providing a method for preparing thin-walled niobium alloy tubes for high-temperature use. This method utilizes extrusion into rods followed by tubes, reducing the deformation resistance of direct tube extrusion and improving the yield rate of extruded tubes. Combined with high-deformation rolling, this method shortens the rolling cycle and improves processing efficiency, ultimately producing long, thin-walled niobium alloy tubes that meet the requirements. This method addresses the long production cycle and low yield rate associated with existing niobium alloy thin-wall tubes.

[0004] To solve the above technical problems, the present invention adopts a technical solution: a method for preparing a niobium alloy thin-walled tube for high temperature use, characterized in that the method comprises the following steps: Step 1: Extruding a niobium alloy ingot to obtain an extruded rod, and then processing the extruded rod into a hollow round ingot; the niobium alloy ingot is a Nb5W-2 alloy ingot prepared by two electron beam melting processes and two arc melting processes; the extrusion temperature is 1200° C. to 1300° C., and the extrusion speed is 300 mm / s; Step 2: Place the hollow round ingot prepared in step 1 into an anti-oxidation sheath, seal and weld it, and then extrude it to obtain an extruded tube; the extrusion temperature is 1200° C. to 1300° C., and the extrusion speed is 200 mm / s; Step 3: The extruded tube obtained in step 2 is subjected to surface treatment and annealing to obtain a tube billet to be rolled, and then the tube billet to be rolled is placed in a two-roll rolling mill for blanking to obtain a rough tube billet; the blanking rolling has a pass reduction rate of 50% to 70% and a rolling speed of 60 times / min to 80 times / min; Step 4: Cleaning and annealing the rough tube obtained in step 3, and then rolling it in a three-roll mill to obtain a niobium alloy tube semi-finished product; the rolling speed is 30 times / min to 40 times / min; Step 5: After cleaning the semi-finished niobium alloy tube obtained in step 4, place it in a vacuum annealing furnace for annealing to obtain a niobium alloy thin-walled tube; the vacuum degree of the vacuum annealing furnace is 10 -2 Pa or above, the annealing system is 1200℃~1300℃ for 1h; the outer diameter of the niobium alloy thin-walled tube is 10mm~20mm, the wall thickness is 0.5mm~1mm, and the length is 1000mm~6000mm.

[0005] The above-mentioned method for preparing a niobium alloy thin-walled tube for high temperature use is characterized in that, in step one, the extruded rod is processed into a hollow round ingot by a wire cutting method. Niobium tungsten alloy sticks to the knife and is not easy to remove chips, and the difficulty of surface turning is higher than that of general titanium alloys and steel. Therefore, niobium tungsten alloy is more difficult to cut using conventional drilling methods. The drill bit shakes severely during cutting, which can easily cause eccentricity. In response to this, the present invention uses a wire cutting method to make up for the shortcomings of drilling, and has better concentricity; at the same time, the wire cutting method is used to reuse the removed center rod instead of machining it into waste chips, thereby improving the utilization rate of the material.

[0006] The aforementioned method for preparing a thin-walled niobium alloy tube for high-temperature use is characterized in that the anti-oxidation sheath in step 2 is made of stainless steel. Typically, the extrusion temperature after sealing welding in the present invention is 1200°C to 1300°C. Therefore, stainless steel with a melting point of approximately 1400°C is used as the anti-oxidation sheath. This means it will not melt at the extrusion temperature, effectively protecting the niobium alloy. Furthermore, stainless steel is inexpensive and readily available.

[0007] The aforementioned method for preparing a thin-walled niobium alloy tube for high-temperature use is characterized in that the roughness of the extruded tube after surface treatment in step 3 is Ra ≤ 6.3 μm. Because the inner and outer surfaces of the extruded tube have numerous grooves and occasional stainless steel inlays, surface treatment such as conventional machining can easily achieve a roughness Ra ≤ 6.3 μm. This not only meets the requirements for tube surface inspection (tube defect inspection is a crucial step, and ultrasonic inspection of tubes can detect defects at this roughness), but also ensures the surface quality of the rough tube obtained through subsequent rolling.

[0008] The aforementioned method for preparing a thin-walled niobium alloy tube for high-temperature use is characterized in that, during the cogging rolling process in step 3, the outer wall of the tube to be rolled is coated with a lubricant prepared from graphite emulsion and machine oil in a volume ratio of 1:80. Since the two-roll mill used in cogging rolling produces significant deformation per rolling pass, the lubricant with excellent lubricity and fluidity is used to ensure a smooth cogging rolling process.

[0009] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts a method of first extruding into rods and then extruding into tubes. Compared with single-stage extrusion into tubes, this method reduces the deformation resistance of direct extrusion into tubes and improves the yield rate of extruded tubes. Combined with the use of large-deformation rolling, the rolling cycle is shortened and processing efficiency is improved. Ultimately, a long, thin-walled niobium alloy tube that meets the requirements is obtained, solving the problems of long production cycles and low yield rates of existing niobium alloy thin-walled tubes.

[0010] 2. The present invention adopts a method of extruding into rods first and then into tubes. Compared with hot forging, the high-temperature, short-time extrusion method reduces the high-temperature oxidation of the niobium alloy ingot during the extrusion process, ensuring the surface quality of the extruded tube. In addition, the material is subjected to three-dimensional forces during extrusion, which improves the formability of the extruded tube. At the same time, compared with a single pressurization method, the double extrusion method reduces the deformation resistance of the direct extrusion method, making it easier, improving the yield rate of the extruded tube, and ensuring the smooth progress of subsequent processing.

[0011] 3. The present invention crushes the niobium alloy ingot grains by double extrusion, laying the foundation for large-deformation rolling using a two-roll mill. This facilitates effective grain crushing during large-deformation rolling, shortens the rolling cycle, and improves the processing efficiency of niobium alloy thin-walled tubes, ultimately obtaining long, thin-walled niobium alloy tubes that meet the requirements.

[0012] 4. The present invention combines two extrusion processes with a large deformation rolling process, which is simple in process, can shorten the processing cycle, improve the utilization rate of niobium alloy materials, and ultimately successfully produce niobium alloy long thin-walled tubes. It is suitable for promotion and application in the preparation of other difficult-to-process tubes.

[0013] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram showing the organizational structure of the niobium alloy long thin-walled tube prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0015] Example 1 This embodiment includes the following steps: Step 1: A Nb5W-2 alloy ingot with a diameter of Φ220 mm, prepared by two electron beam melting processes and two arc melting processes, is kept at 1250°C for 1 hour and extruded at an extrusion speed of 300 mm / s to obtain an extruded rod with a diameter of Φ100 mm. The extruded rod is then cut into a central round rod with a diameter of Φ33 mm by a warp cut, and then processed into a hollow round ingot with a diameter × wall thickness of Φ89 mm × 28 mm. Step 2: Place the hollow round ingot prepared in step 1 into a stainless steel anti-oxidation sheath and seal it with welding, then keep it at 1250°C for 1 hour and extrude it at an extrusion speed of 200 mm / s to obtain an extruded tube with a diameter of Φ53 mm and a wall thickness of Φ15 mm. Step 3: The extruded tube obtained in Step 2 is surface treated to an inner and outer surface roughness of Ra ≤ 6.3 μm, and then annealed after cleaning to obtain a tube blank to be rolled with a diameter × wall thickness of Φ39 mm × 7 mm. The annealing system is 1250° C. and heat preservation for 1 hour. The tube blank to be rolled is then placed in a two-roll rolling mill for open-rolling cold rolling at a rolling speed of 80 times / min to obtain a rough tube blank with a diameter × wall thickness of Φ25 mm × 3 mm. The pass thinning rate of the open-rolling cold rolling is 70%. During the open-rolling cold rolling, the outer wall of the tube blank to be rolled is coated with a lubricant prepared by graphite emulsion and engine oil at a ratio of 1:80; Step 4: The rough tube obtained in step 3 is cleaned and annealed at 1250° C. for 1 hour, and then placed in a three-roll mill for multiple rolling at a rolling speed of 30 times / minute to obtain a niobium alloy tube semi-finished product with an outer diameter of Φ16 mm, a wall thickness of Φ0.8 mm, and a length of 6000 mm. Step 5: After cleaning the semi-finished niobium alloy tube obtained in step 4, place it in a vacuum annealing furnace for annealing. The vacuum degree of the vacuum annealing furnace is 10 -2 Pa, and the annealing system is 1250℃ for 1h to obtain a niobium alloy long thin-walled tube.

[0016] The room temperature tensile properties of the niobium alloy long thin-walled tube prepared in this example were tested, as shown in Table 1 below: Table 1 Room temperature tensile properties of the niobium alloy thin-walled tube prepared in Example 1

[0017] It can be seen from Table 1 that the niobium alloy long thin-walled tube prepared in this embodiment maintains relatively high strength and good plasticity at room temperature.

[0018] Example 2 This embodiment includes the following steps: Step 1: A Nb5W-2 alloy ingot with a diameter of Φ220 mm, prepared by two electron beam melting processes and two arc melting processes, was kept at 1200°C for 1 hour and extruded at an extrusion speed of 300 mm / s to obtain an extruded rod with a diameter of Φ110 mm. The extruded rod was then cut into a central round rod with a diameter of Φ40 mm by a warp cut, and then processed into a hollow round ingot with a diameter × wall thickness of Φ100 mm × 30 mm; Step 2: Place the hollow round ingot prepared in step 1 into a stainless steel anti-oxidation sheath and seal it with welding, then keep it at 1200°C for 1 hour and extrude it at an extrusion speed of 200 mm / s to obtain an extruded tube with a diameter of Φ56 mm and a wall thickness of Φ17 mm. Step 3: The extruded tube obtained in Step 2 is surface treated to an inner and outer surface roughness of Ra ≤ 6.3 μm, and then annealed after cleaning to obtain a tube blank to be rolled with a diameter × wall thickness of Φ46 mm × 7 mm. The annealing system is 1200° C. and holding for 1 hour. The tube blank to be rolled is then placed in a two-roll rolling mill for open-roll cold rolling at a rolling speed of 60 times / min to obtain a rough tube blank with a diameter × wall thickness of Φ32 mm × 3 mm. The pass thinning rate of the open-roll cold rolling is 68%. During the open-roll cold rolling, the outer wall of the tube blank to be rolled is coated with a lubricant prepared by graphite emulsion and engine oil at a ratio of 1:80; Step 4: The rough tube obtained in step 3 is cleaned and annealed at 1200° C. for 1 hour, and then placed in a three-roll mill for multiple rolling at a rolling speed of 40 times / minute to obtain a niobium alloy tube semi-finished product with an outer diameter × wall thickness × length of Φ10 mm × 0.5 mm × 4000 mm. Step 5: After cleaning the semi-finished niobium alloy tube obtained in step 4, place it in a vacuum annealing furnace for annealing. The vacuum degree of the vacuum annealing furnace is 10 -2 Pa, and the annealing system is 1200℃ for 1h to obtain a niobium alloy long thin-walled tube.

[0019] Figure 1 This is the organizational structure diagram of the niobium alloy long thin-walled tube prepared in this embodiment. Figure 1 It can be seen that the grains of the niobium alloy long thin-walled tube are uniform, fine and equiaxed.

[0020] Example 3 This embodiment includes the following steps: Step 1: A Nb5W-2 alloy ingot with a diameter of Φ220 mm, prepared by two electron beam melting processes and two arc melting processes, was kept at 1300°C for 1 hour and extruded at an extrusion speed of 300 mm / s to obtain an extruded rod with a diameter of Φ100 mm. The extruded rod was then cut into a central round rod with a diameter of Φ36 mm by a warp cut, and then processed into a hollow round ingot with a diameter × wall thickness of Φ90 mm × 27 mm; Step 2: Place the hollow round ingot prepared in step 1 into a stainless steel anti-oxidation sheath and seal it with welding, then heat-hold it at 1300°C for 1 hour and extrude it at an extrusion speed of 200 mm / s to obtain an extruded tube with a diameter of Φ56 mm and a wall thickness of Φ17 mm. Step 3: The extruded tube obtained in Step 2 is surface treated to an inner and outer surface roughness of Ra ≤ 6.3 μm. After cleaning, the tube is annealed to obtain a tube blank to be rolled with a diameter of Φ46 mm and a wall thickness of Φ7 mm. The annealing process is 1300° C. and a holding temperature of 1 h. The tube blank to be rolled is then placed in a two-roll mill for open-roll cold rolling at a rolling speed of 70 times / min to obtain a rough tube blank with a diameter of Φ32 mm and a wall thickness of Φ5 mm. The pass reduction rate of the open-roll cold rolling is 50%. During the open-roll cold rolling, the outer wall of the tube blank is coated with a lubricant prepared by mixing graphite emulsion and engine oil at a ratio of 1:80. Step 4: The rough tube obtained in step 3 is cleaned and annealed at 1300° C. for 1 hour, and then placed in a three-roll mill for multiple rolling at a rolling speed of 35 times / minute to obtain a niobium alloy tube semi-finished product with an outer diameter of Φ20 mm, a wall thickness of Φ1 mm, and a length of 1000 mm. Step 5: After cleaning the semi-finished niobium alloy tube obtained in step 4, place it in a vacuum annealing furnace for annealing. The vacuum degree of the vacuum annealing furnace is 10 -2 Pa, and the annealing system is 1300℃ for 1h to obtain a niobium alloy long thin-walled tube.

[0021] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a niobium alloy thin-walled tube for high temperature use, characterized in that: The method comprises the following steps: Step 1: Extruding a niobium alloy ingot to obtain an extruded rod, and then processing the extruded rod into a hollow round ingot; the niobium alloy ingot is a Nb5W-2 alloy ingot prepared by two electron beam melting processes and two arc melting processes; the extrusion temperature is 1200° C. to 1300° C., and the extrusion speed is 300 mm / s; Step 2: Place the hollow round ingot prepared in step 1 into an anti-oxidation sheath, seal and weld it, and then extrude it to obtain an extruded tube; the extrusion temperature is 1200° C. to 1300° C., and the extrusion speed is 200 mm / s; Step 3: The extruded tube obtained in step 2 is subjected to surface treatment and annealing to obtain a tube billet to be rolled, and then the tube billet to be rolled is placed in a two-roll rolling mill for blanking to obtain a rough tube billet; the blanking rolling has a pass reduction rate of 50% to 70% and a rolling speed of 60 times / min to 80 times / min; Step 4: Cleaning and annealing the rough tube obtained in step 3, and then rolling it in a three-roll mill to obtain a niobium alloy tube semi-finished product; the rolling speed is 30 times / min to 40 times / min; Step 5: After cleaning the semi-finished niobium alloy tube obtained in step 4, place it in a vacuum annealing furnace for annealing to obtain a niobium alloy thin-walled tube; the vacuum degree of the vacuum annealing furnace is 10 -2 Pa or above, the annealing system is 1200℃~1300℃ for 1h; the outer diameter of the niobium alloy thin-walled tube is 10mm~20mm, the wall thickness is 0.5mm~1mm, and the length is 1000mm~6000mm.

2. The method for preparing a niobium alloy thin-walled tube for high temperature use according to claim 1, characterized in that: In step 1, the extruded rod is processed into a hollow ingot by using a wire cutting method.

3. The method for preparing a niobium alloy thin-walled tube for high temperature use according to claim 1, characterized in that: The material of the anti-oxidation sheath in step 2 is stainless steel.

4. The method for preparing a niobium alloy thin-walled tube for high temperature use according to claim 1, characterized in that: The roughness of the extruded tube after surface treatment in step 3 is Ra≤6.3μm.

5. The method for preparing a niobium alloy thin-walled tube for high temperature use according to claim 1, characterized in that: During the blank rolling in step 3, the outer wall of the tube blank to be rolled is coated with lubricating oil prepared by graphite emulsion and engine oil in a volume ratio of 1:80.

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