Niobium-zirconium alloy dense circumferential weld vacuum electron beam welding method

Abstract

The invention provides a niobium-zirconium alloy dense circumferential weld vacuum electron beam welding method. The niobium-zirconium alloy dense circumferential weld vacuum electron beam welding method comprises the following steps that S1, surface oxidation film removal treatment is conducted on an Nb-1Zr alloy sheet workpiece to be welded; s2, the to-be-welded workpiece treated in the step S1 is placed in ultrapure water to be stored, and follow-up welding is completed within preset time; s3, the to-be-welded workpiece is taken out of the ultrapure water, dried and then clamped into a vacuum chamber of an electron beam welding system, and vacuumizing is conducted till the vacuum degree meets the welding requirement; s4, vacuum electron beams are adopted for conducting double-circle welding on the dense circumferential welds, and the double-circle welding sequentially comprises first-circle first current preheating welding and second-circle second current scanning welding; and S5, after welding is completed, the to-be-welded part is cooled to be below the preset temperature, and then the to-be-welded part is taken out of the vacuum chamber. According to the method, the double-circle welding process is adopted, gas in the welding seam is promoted to fully escape, the problem that welding air holes are prone to being caused by poor liquidity of Nb-1Zr alloy liquid metal is solved, and the thin-wall niobium-zirconium alloy dense circumferential welding seam is good in forming and free of air holes.

Description

Technical Field

[0001] This invention relates to the field of vacuum electron beam welding technology, specifically to a vacuum electron beam welding method for dense circumferential welds of niobium-zirconium alloys. More particularly, it relates to a vacuum electron beam welding method for achieving porosity-free dense circumferential welds of niobium-zirconium alloys. Background Technology

[0002] Niobium-zirconium alloy (Nb-1Zr) is a high-temperature resistant and corrosion-resistant material with niobium as the matrix and zirconium as the main alloying element. Niobium, as its main component, is a refractory metal with a high melting point, high strength, and excellent corrosion resistance. The addition of zirconium further refines the grain size, improving the material's machinability and fatigue strength. Through special alloying processes and precision heat treatment technology, Nb-1Zr alloy achieves a balance between strength and toughness, maintaining stable mechanical properties over a wide temperature range of -253℃ to 2000℃. Therefore, it has broad application prospects in the aerospace and nuclear industries. In the aerospace field, it can be used to manufacture high-temperature components such as rocket engine nozzles and satellite structural parts to withstand extreme temperatures and severe thermal shocks. In the nuclear industry, due to its extremely low neutron absorption cross section, it can be used to manufacture key devices such as nuclear fuel cladding and pressure vessels, effectively reducing neutron loss and improving nuclear reaction efficiency. As a "safety barrier" for the reactor core of nuclear power plants, it can operate stably for long periods under strong radiation and high-pressure water environments.

[0003] In engineering applications, the welding of Nb-1Zr alloys presents significant technical challenges. Firstly, the alloy readily oxidizes at high temperatures to form zirconium oxide (ZrO2). Zirconia exhibits a high oxygen ion diffusion rate at high temperatures, creating oxygen diffusion channels that accelerate oxygen diffusion into the alloy, further intensifying the oxidation process. Secondly, Nb-1Zr alloys have extremely high melting points (close to niobium's melting point of 2468℃), resulting in poor fluidity of the liquid metal during welding. When using vacuum electron beam welding, the large weld depth-to-width ratio and rapid cooling rate make it difficult for gases inside the weld to escape, easily leading to dense porosity defects.

[0004] From the current state of technological research, current research on Nb-1Zr alloy mainly focuses on the field of material preparation. There are few relevant documents and patents on the welding technology of this alloy. Moreover, existing welding research focuses on the vacuum electron beam welding of Nb-1Zr alloy with other dissimilar metals. No relevant documents or patents on vacuum electron beam butt welding of Nb-1Zr alloy thin plates have been found, which cannot meet the technical requirements of dense circumferential welds of Nb-1Zr alloy thin plates in engineering.

[0005] Patent document CN121061274A discloses a vacuum brazing process and parts for niobium-zirconium alloy and nickel-based alloy. The process includes the following steps: S1, assembling a welded assembly structure formed by niobium-zirconium alloy parts and nickel-based alloy parts, wherein BNi-2 brazing filler metal is provided at the mating positions of the welded assembly structure; S2, performing staged heating on the welded assembly structure under a preset vacuum degree in a vacuum brazing furnace. This solution can effectively control defects in the welded joints of niobium-zirconium alloy and nickel-based alloy, and ensure the strength and sealing of the welded joints. The drawback of patent document CN121061274A is that it only addresses the welding of dissimilar metals of niobium-zirconium alloy and nickel-based alloy, and does not involve any technical solutions for butt welding of Nb-1Zr alloy thin plates with the same metal, thus failing to address the welding needs of dense circumferential welds on Nb-1Zr alloy thin plates in engineering applications. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a vacuum electron beam welding method for dense niobium-zirconium alloy circumferential welds.

[0007] A vacuum electron beam welding method for dense circumferential weld seams of niobium-zirconium alloys according to the present invention includes the following steps: S1: Remove the surface oxide film from the Nb-1Zr alloy thin plate workpiece to be welded; S2: Place the workpiece to be welded after step S1 in ultrapure water for storage, and complete the subsequent welding within a preset time. S3: After removing the workpiece from the ultrapure water and drying it, clamp it into the vacuum chamber of the electron beam welding system and evacuate it to the vacuum level required for welding. S4: Vacuum electron beam is used to perform double-ring welding on dense circumferential welds, which includes the first ring of preheating welding with first current and the second ring of scanning welding with second current. S5: After welding is completed, wait for the welded parts to cool to below the preset temperature before taking them out of the vacuum chamber.

[0008] Preferably, in step S1, the surface oxide film removal treatment is an acid pickling treatment, and the pickling solution used is a mixed acid solution of hydrofluoric acid and nitric acid.

[0009] Preferably, in the mixed acid solution, the concentration range of hydrofluoric acid is 2% to 4%, and the concentration range of nitric acid is 5% to 10%.

[0010] Preferably, in step S2, the preset time is less than 8 hours.

[0011] Preferably, in step S3, the vacuum level required to meet the welding requirements is less than 5 × 10⁻⁶. -5 mbar.

[0012] Preferably, in step S4, before performing double-ring welding, a vacuum electron beam spot welding positioning step is also included: within the circumference to be welded, welding points are set at preset angles, and the spot welding process adopts a surface focusing defocusing mode.

[0013] Preferably, the preset angle is 90°, and the spot welding process parameters are: voltage 60-80KV, current 16-20mA.

[0014] Preferably, in step S4, both the first round of first current preheating welding and the second round of second current scanning welding include an arc-starting segment, a full arc segment, and an arc-extinguishing segment. The arc-starting segment corresponds to an angle range of 0° to 30°, the full arc segment corresponds to an angle range of 30° to 390°, and the arc-extinguishing segment corresponds to an angle range of 390° to 420°.

[0015] Preferably, the full arc segment process parameters for the first round of first current preheating welding are: voltage 60-80KV, current 16-20mA, welding speed 400-600mm / min, and surface focusing using upper decoking. The full arc segment process parameters for the second round of second current scanning welding are: voltage 70-90KV, current 18-24mA, welding speed 500-700mm / min, surface focusing using upper defocusing, scanning frequency 250-350Hz, and scanning swing amplitude 1-2mm.

[0016] Preferably, in step S5, the preset temperature is 60°C; after welding is completed, the step of performing a sealing test on the weld is also included, wherein the sealing test includes at least one of liquid penetration test, gas pressure test and helium leak detection.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention employs a double-ring welding process, which involves preheating welding with a first current in the first ring and scanning welding with a second current in the second ring. This process promotes the full escape of gas from the weld seam, improves the welding porosity problem caused by the poor fluidity of Nb-1Zr alloy liquid metal, and achieves good formation of dense circumferential weld seams in thin-walled niobium-zirconium alloy without producing porosity. 2. This invention fills the gap in the existing technology for this type of welding by designing a complete welding process and clear process parameters specifically for dense circumferential welds of Nb-1Zr alloy thin plates, and provides a feasible solution for welding Nb-1Zr alloy thin plate components in aerospace, nuclear industry and other fields. 3. Through process optimization, this invention enables the weld to pass rigorous quality inspections. Specifically, the liquid penetration test results meet the requirements, the pressure test shows no pressure drop after 30 minutes, and the helium leak detection rate meets the requirements. Attached Figure Description

[0018] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating the vacuum electron beam welding method for dense circumferential weld seams of niobium-zirconium alloys, which is the main feature of this invention. Detailed Implementation

[0019] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0020] Example 1 The first step is to remove the surface oxide film from the Nb-1Zr alloy thin plate workpiece to be welded. In this embodiment, pickling is used to remove the oxide film on the surface of the niobium-zirconium alloy. The pickling solution used is a mixed acid solution of hydrofluoric acid (HF) and nitric acid (HNO3), with a concentration range of 2% to 4% for hydrofluoric acid and 5% to 10% for nitric acid. The composition of Nb-1Zr material is shown in Table 1.

[0021] Table 1 Chemical composition of Nb-1Zr alloy

[0022] The second step involves placing the workpiece to be welded, after the first step, in ultrapure water for preservation, and then completing the subsequent welding within a preset time, which should be less than 8 hours. In this embodiment, the workpiece is preserved in ultrapure water for 4 hours.

[0023] The third step involves removing the workpiece from the ultrapure water, drying it, and then clamping it into the vacuum chamber of the electron beam welding system. The vacuum level is then evacuated to meet the welding requirements; in this embodiment, the vacuum level is below 5 × 10⁻⁶. -5 mbar.

[0024] The fourth step, before performing double-ring welding, involves a vacuum electron beam spot welding positioning step. Welding points are set at preset angles within the circumference to be welded; in this embodiment, the preset angle is 90°. The spot welding process uses a surface focusing defocusing mode, with specific process parameters of 60KV voltage and 18mA current.

[0025] The fifth step involves preheating welding with the first current for the first round of double-round welding using a vacuum electron beam: corresponding to an arc-starting angle range of 0°–30°, a full-arc angle range of 30°–390°, and an arc-extinguishing angle range of 390°–420°. The full-arc process parameters are: voltage 60–80KV, current 16–20mA, welding speed 400–600mm / min, and upper decoking for surface focusing. In this embodiment, a voltage of 60KV, a current of 18mA, and a welding speed of 500mm / min are used.

[0026] Step 6: Perform the second current scan welding of the second round of double-round welding using a vacuum electron beam: corresponding to the arc initiation angle range of 0–30°, the full arc angle range of 30–390°, and the arc extinguishing angle range of 390–420°. The full arc process parameters are: voltage 70–90KV, current 18–24mA, welding speed 500–700mm / min, surface focusing using upper defocusing, scanning frequency 250–350Hz, and scanning amplitude 1–2mm. In this embodiment, the voltage is 80KV, the current is 22mA, the welding speed is 600mm / min, the scanning frequency is 300Hz, and the scanning amplitude is 1.5mm.

[0027] Step 7: After welding is completed, wait for the welded parts to cool to below the preset temperature before taking them out of the vacuum chamber. In this embodiment, the preset temperature is 60°C, specifically, it is taken out after cooling to below 55°C.

[0028] Step 8: Perform a sealing test on the weld. The sealing test includes at least one of the following: liquid penetration test, gas pressure test, and helium leak detection. In this embodiment, the following tests are performed in sequence: liquid penetration test, the result meets the requirements; gas pressure test at 0.28 MPa, pressure holding time of 30 minutes with no pressure drop, the result meets the requirements; helium leak detection, the leakage rate is 4.1 × 10⁻⁶. -7 Pa·m³ / s, the result meets the requirements.

[0029] This patent addresses the welding of dense circumferential welds on thin-walled (3-4 mm thick) Nb-1Zr alloy components. Through a combination of pickling and passivation of the workpiece, first-round vacuum electron beam welding with first current (without scanning), and second-round welding with second current scanning, it achieves well-formed dense circumferential welds on thin-walled niobium-zirconium alloy components without porosity. Liquid penetration testing of the welds yielded satisfactory results; a pressure test of 0.2-0.3 MPa was conducted, with no pressure drop after 30 minutes, also meeting requirements; and helium leak detection showed a leakage rate below 5 × 10⁻⁶. -7 Pa·m³ / s, the result meets the requirements.

[0030] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0031] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A vacuum electron beam welding method for a Nb-Zr alloy close-circled weld, characterized by, The method comprises the following steps: S1: removing surface oxide film of Nb-1Zr alloy sheet to be welded; S2: placing the sheet to be welded after step S1 in ultrapure water for storage, and completing subsequent welding within a preset time; S3: taking the sheet to be welded out of the ultrapure water, drying, clamping to a vacuum chamber of an electron beam welding system, and vacuumizing to a vacuum degree meeting the welding requirement; S4: double-circle welding of the dense girth weld by using a vacuum electron beam, comprising first-circle first-current preheating welding and second-circle second-current scanning welding in sequence; S5: after the welding, cooling the welded piece to below a preset temperature, and taking the welded piece out of the vacuum chamber.

2. The vacuum electron beam welding method of the Nb-Zr alloy close- up ring weld according to claim 1, characterized by, In step S1, the surface oxide film removal treatment is acid pickling treatment, and a mixed acid solution of hydrofluoric acid and nitric acid is used.

3. The vacuum electron beam welding method of a Nb-Zr alloy close- up ring weld joint as claimed in claim 2, wherein In the mixed acid solution, the concentration of hydrofluoric acid ranges from 2% to 4%, and the concentration of nitric acid ranges from 5% to 10%.

4. The Nb-Zr alloy close-encircled weld vacuum electron beam welding method according to claim 1, characterized by, In step S2, the preset time is less than 8 hours.

5. The Nb-Zr alloy close-encircled weld vacuum electron beam welding method according to claim 1, characterized by, In step S3, the vacuum level satisfying the welding requirement is lower than 5x10 -5 mbar.

6. The Nb-Zr alloy close-encircled weld vacuum electron beam welding method according to claim 1, characterized by, In step S4, before the double-circle welding, a step of vacuum electron beam spot welding positioning is further included, that is, welding spots are arranged at intervals of a preset angle within the welding circumference range, and the spot welding process adopts a surface focusing and upper defocusing mode.

7. The Nb-Zr alloy close-encircled weld vacuum electron beam welding method according to claim 6, characterized by, The preset angle is 90°, and the spot welding process parameters are: voltage 60-80KV and current 16-20mA.

8. The Nb-Zr alloy close- spaced ring weld vacuum electron beam welding method of claim 1 wherein, In step S4, the first-circle first-current preheating welding and the second-circle second-current scanning welding each comprise an arc striking section, a full-arc section and an arc extinguishing section, the arc striking section corresponds to an angle range of 0°-30°, the full-arc section corresponds to an angle range of 30°-390°, and the arc extinguishing section corresponds to an angle range of 390°-420°.

9. The vacuum electron beam welding method of a niobium-zirconium alloy close- up ring weld according to claim 8, characterized by, The full-arc section process parameters of the first-circle first-current preheating welding are: voltage 60-80KV, current 16-20mA, welding speed 400-600mm / min, and surface focusing by upper defocusing; The full-arc section process parameters of the second-circle second-current scanning welding are: voltage 70-90KV, current 18-24mA, welding speed 500-700mm / min, surface focusing by upper defocusing, scanning frequency 250-350Hz, and scanning swing 1-2mm.

10. The Nb-Zr alloy close-encircled weld vacuum electron beam welding method according to claim 1, characterized by, In step S5, the preset temperature is 60℃, and after the welding, a step of quality detection of the weld is further included, and the weld quality detection comprises three kinds of liquid penetration detection, gas pressure test and helium leak detection.

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