Electron beam welding method for nitrogen control type low-activation steel thick plate with matched high strength and toughness

Abstract

The invention relates to the technical field of nuclear fusion, and particularly discloses a high strength and toughness matched nitrogen control type low activation steel thick plate electron beam welding method which comprises the following steps: S1, flaw detection and grinding are performed on a thick plate to be welded; s2, demagnetization and surface cleaning are carried out; s3, an arc suppression plate and an arc striking plate are machined, the arc suppression plate and the arc striking plate are fixed to the two ends of the gap formed by the thick plate to be welded, and a plate to be welded is obtained; s4, the plate to be welded is fixed to a welding tool, and the welding tool is pushed into an electron beam welding vacuum chamber; s5, the plate to be welded is sequentially subjected to symmetrical positioning welding and symmetrical filling welding, and a welded plate is obtained; and S6, postweld heat treatment is conducted. By means of the characteristics that electron beam welding is high in penetrability, high in welding speed, high in welding joint quality in the vacuum environment and the like, the welding efficiency is high, welded plates are stable in performance and have high strength and toughness matching, and the welding quality is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of nuclear fusion technology, and more particularly to an electron beam welding method for a high-strength-toughness-matched nitrogen-controlled low-activation steel thick plate. Background Art

[0002] Nuclear fusion energy is currently one of the most promising fundamental solutions to the energy crisis. The tritium blanket of a fusion reactor is a core component that enables crucial functions such as tritium breeding, energy extraction, and radiation shielding. Reduced Activation Ferritic / Martensitic Steel (RAFM) has been selected as the structural material for the International Thermonuclear Experimental Reactor (ITER-TBM) tritium breeder blanket module (TBM) due to its excellent thermophysical and thermomechanical properties, radiation resistance, low activation, mature industrial base, and good compatibility with coolant media. It is also the preferred structural material for tritium blankets in future fusion reactors.

[0003] The tritium-producing blanket components of fusion reactors are complex in structure, feature numerous components, are large in three-dimensional dimensions, and require high molding quality. The connection between structural materials is a key issue in the development of tritium-producing blankets. Traditional welding methods require high heat input and deformation, making precision difficult to guarantee. Furthermore, the tritium-producing blanket structure contains numerous welds greater than 20 mm thick, with some even exceeding 100 mm thick. High-power laser welding can achieve a maximum effective thickness of no more than 20 mm. Electron beam welding, as a high-energy beam welding method, has become the primary method for joining thick plates in fusion reactor tritium-producing blanket structures due to its advantages, including strong penetration, minimal welding deformation, virtually no contamination at the joints, and high welding efficiency.

[0004] At present, electron beam welding in the field of low-activation steel is mainly concentrated on plates with a thickness of less than or equal to 30 mm, and there is relatively little research on electron beam welding of low-activation steel thick plates (30~70 mm).

[0005] For metal materials, welds are often the weakest points, making them prone to failure and fracture under service conditions. High-energy beam welded joints in low-activation steel, the structural material for tritium-producing blankets in fusion reactors, consist of a weld and a heat-affected zone. Compared to the parent material, the weld has a coarser structure and lower dislocation density. While its strength is higher than the parent material, its impact toughness is significantly weaker. Achieving a weld joint with a good balance of strength and toughness is crucial for its overall service performance, particularly for the safety and reliability of the manufacturing quality of tritium-producing blanket components in fusion reactors. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an electron beam welding method for nitrogen-controlled low-activation steel thick plates with high strength and toughness matching; by utilizing the characteristics of electron beam welding such as strong penetration ability, fast welding speed, and high quality of welded joints under a vacuum environment, electron beam welding is performed on nitrogen-controlled low-activation steel thick plates, with high welding efficiency, stable performance of the welded plates and high strength and toughness matching, thereby ensuring welding quality.

[0007] The solution adopted by the present invention to solve the technical problem is: A method for electron beam welding of a high-strength and high-toughness matched nitrogen-controlled low-activation steel thick plate, comprising the following steps: Step S1: perform flaw detection on the thick plate to be welded and polish the welded surface; Step S2: Demagnetizing on a demagnetizing machine and cleaning the surface after demagnetization; Step S3: Processing the arc-closing plate and the arc-starting plate, and fixing the arc-closing plate and the arc-starting plate to the two ends of the gap formed by the two sets of butt-jointed thick plates to be welded by manual arc welding to obtain the plates to be welded; Step S4: Fix the plate to be welded vertically on the welding fixture, and control the gap to be horizontal; push the welding fixture into the electron beam welding vacuum chamber, and evacuate the electron beam welding vacuum chamber; wherein the vacuum degree of the electron beam welding vacuum chamber is 10 -2 ~10 -3 Pa; Step S5: using a vacuum electron beam to sequentially perform symmetrical positioning welding and symmetrical filling welding on the plate to be welded in the electron beam welding vacuum chamber to obtain a welded plate; After the temperature of the welding plate is lower than 100°C, the electron beam welding vacuum chamber is vented and the welded plate is taken out; Step S6: placing the welded plate into a heat treatment furnace for post-weld heat treatment.

[0008] In some possible implementations, the thick plates to be welded include, by weight percentage: 0.015~0.040% N; 0.085~0.135% C; 0.2~0.4% V; 8.0~9.0% Cr; 0.3~0.7% Mn; 0.05~0.15% Ta; 1.3~1.7% W; 0~0.005% P; 0~0.005% S; 0~0.01% O; 0~0.05% Si; 0~0.01% Ni; 0~0.005% Mo; 0~0.01% Ti; 0~0.01% Cu; 0~0.005% Nb; 0~0.03% Al; 0~0.005% B; 0~0.005% Co; 0~0.005% Ag; As, Sn, Sb and Zr with a total content of 0-0.005%; The balance is Fe.

[0009] In some possible implementations, the thickness of the thick plate to be welded is 30 mm to 70 mm.

[0010] In some possible implementations, step S1 specifically refers to performing surface penetrant testing and overall ultrasonic testing on the thick plate to be welded; after the testing meets the requirements, mechanically polishing the welding surface of the thick plate to be welded to a surface roughness of ≤3.2 μm.

[0011] In some possible implementations, step S2 specifically includes the following steps: Step S21: Demagnetizing the thick plate to be welded using a demagnetizer; wherein the magnetic induction intensity is less than 2 Gauss, the power supply voltage of the demagnetizer is 380V ± 10%, the operating frequency is 50Hz, the maximum instantaneous demagnetization power is 152kVA, and the corresponding peak current is 400A; Step S22: After demagnetization is completed, the surface to be welded is cleaned to remove the surface oxide layer; Step S23: cleaning and removing residues on the surface to be welded.

[0012] In some possible implementations, step S3 includes the following steps: Step S31: using nitrogen-controlled low-activation ferrite martensitic steel of the same thickness as the thick plate to be welded to make the arc-ending plate and the arc-starting plate; Step S32: butting and pressing the two sets of thick plates to be welded together to form a butt joint, with a gap between the two being ≤0.15 mm; Step S33: placing an arc striking plate and an arc closing plate at the starting point and the end point of the gap respectively; Step S34: fix the arc-ending plate, arc-starting plate and the butt joint by spot welding to obtain the plate to be welded.

[0013] In some possible implementations, the symmetrical positioning welding in step S5 specifically refers to: symmetrical positioning welding of the plates to be welded with a working distance of 300-1500 mm, an electron beam power of 3-10 kW, a welding speed of 200-400 mm / min, and a rectangular scanning waveform.

[0014] In some possible embodiments, the symmetrical filling welding in step S5 refers to filling welding the plate to be welded after symmetrical positioning welding with a working distance of 300-1500 mm, an electron beam power of 20-35 kW, a welding speed of 100-300 mm / min, and a rectangular scanning waveform.

[0015] In some possible implementations, the post-weld heat treatment in step S6 specifically refers to placing the welded plate into a heat treatment furnace, heating it to 700°C to 720°C, and keeping it warm for 3h to 7h. After the insulation is completed, the plate is taken out and air-cooled; wherein the temperature of the heat treatment furnace is ≤200°C.

[0016] In some possible implementations, the following further comprises: Step S7: performing nondestructive testing on the welded plate after heat treatment; Step S8: Perform microstructure and mechanical property testing on the weld area of ​​the welded plate after passing the flaw detection.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention can effectively stabilize the welding between two sets of thick plates to be welded, realize single-sided welding and double-sided forming, and obtain an I-type butt weld with the advantages of full penetration, no cracks, good back forming, and no undercut. The results of non-destructive testing show that the weld quality meets the Class B requirements of ISO13919 standard. The results of mechanical property tests show that the room temperature and high temperature tensile strength of the weld is higher than that of the parent material, and the impact performance is equivalent to that of the parent material. The weld side bending test meets the specified requirements, and a high strength and toughness match is obtained. The metallographic structure after heat treatment shows fully tempered martensite, without micro defects such as cracks and holes. At the same time, it has the advantages of simple process, easy implementation, and high efficiency. The present invention provides technical support for the development of tritium-producing blanket components for fusion reactors, and can also be extended to vacuum electron beam welding of thick plates of other types of structural materials for other fusion reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a macroscopic morphology diagram of a cross section of an electron beam weld in an embodiment of the present invention; Figure 2 This is a metallographic diagram of the electron beam weld structure in Example 3 of the present invention; Figure 3 are the tensile strength and yield strength test results in Example 3 of the present invention; Figure 4 These are the test results of elongation after fracture and reduction of area in Example 3 of the present invention; Figure 5 is the impact test result in Example 3 of the present invention; DETAILED DESCRIPTION In this application, unless otherwise specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integration; they can refer to direct connections or indirect connections through an intermediary; they can refer to internal communication between two components or interactions between two components. The terms "first," "second," and similar terms mentioned in this application do not denote any order, quantity, or importance; they are simply used to distinguish between different components. Similarly, terms such as "one" or "a" do not indicate a quantitative limitation; rather, they indicate the presence of at least one. In the implementation of this application, "and / or" describes an association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. In the description of the embodiments of this application, unless otherwise specified, "plurality" means two or more. For example, "plurality" refers to two or more positioning posts. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0019] The present invention is described in detail below.

[0020] A method for electron beam welding of a high-strength and high-toughness matched nitrogen-controlled low-activation steel thick plate, wherein the thickness of the nitrogen-controlled low-activation steel thick plate is 30 mm to 70 mm; The thick plate to be welded, calculated by weight percentage, includes: 0.015~0.040% N; 0.085~0.135% C; 0.2~0.4% V; 8.0~9.0% Cr; 0.3~0.7% Mn; 0.05~0.15% Ta; 1.3~1.7% W; 0~0.005% P; 0~0.005% S; 0~0.01% O; 0~0.05% Si; 0~0.01% Ni; 0~0.005% Mo; 0~0.01% Ti; 0~0.01% Cu; 0~0.005% Nb; 0~0.03% Al; 0~0.005% B; 0~0.005% Co; 0~0.005% Ag; As, Sn, Sb and Zr with a total content of 0-0.005%; The balance is Fe; Compared with the low-activation ferrite / martensitic steel in the technology, the nitrogen-controlled low-activation ferrite-martensitic steel can obtain the precipitation of nitride / carbonitride dispersed phase with higher stability by adding nitrogen element, thereby significantly improving the high-temperature performance of RAFM steel.

[0021] The welding method specifically includes the following steps: Step S1: performing flaw detection on the thick plate to be welded and polishing the welded surface; Step S1 specifically refers to performing surface penetrant flaw detection and overall ultrasonic flaw detection on the thick plate to be welded; after the flaw detection meets the requirements, mechanically polishing the welded surface of the thick plate to a surface roughness of ≤3.2μm; Specifically, when performing flaw detection on thick plates to be welded, the results of penetrant testing and ultrasonic testing should meet the requirements of EJ / T 20242 standard.

[0022] Step S2: Demagnetizing on a demagnetizing machine and cleaning the surface after demagnetization; Step S2 specifically includes the following steps: Step S21: Demagnetizing the thick plate to be welded using a demagnetizer; wherein the magnetic induction intensity is less than 2 Gauss, the power supply voltage of the demagnetizer is 380V ± 10%, the operating frequency is 50Hz, the maximum instantaneous demagnetization power is 152kVA, and the corresponding peak current is 400A; Step S22: After demagnetization is completed, the surface to be welded is cleaned to remove the surface oxide layer; Step S23: cleaning and removing residues on the surface to be welded.

[0023] Step S3: Processing the arc-closing plate and the arc-starting plate, and fixing the arc-closing plate and the arc-starting plate to the two ends of the gap formed by the two sets of butt-jointed thick plates to be welded by manual arc welding to obtain the plates to be welded; specifically, the following steps are included: Step S31: using nitrogen-controlled low-activation ferrite martensitic steel of the same thickness as the thick plate to be welded to make the arc-ending plate and the arc-starting plate; Step S32: butting and pressing the two sets of thick plates to be welded together to form a butt joint, with a gap between the two being ≤0.15 mm; Step S33: placing an arc striking plate and an arc closing plate at the starting point and the end point of the gap respectively; Step S34: fix the arc-ending plate, arc-starting plate and the butt joint by spot welding to obtain the plate to be welded.

[0024] Step S4: Fix the plate to be welded vertically on the welding fixture, and control the gap to be horizontal; push the welding fixture into the electron beam welding vacuum chamber, and evacuate the electron beam welding vacuum chamber; wherein the vacuum degree of the electron beam welding vacuum chamber is 10 -2 ~10 -3 Pa; Step S5: using a vacuum electron beam to sequentially perform symmetrical positioning welding and symmetrical filling welding on the plate to be welded in the electron beam welding vacuum chamber to obtain a welded plate; single-sided welding is used during welding to achieve single-sided welding and double-sided forming; specifically, an electron beam horizontal gun is used for welding; After the temperature of the welding plate is lower than 100°C, the electron beam welding vacuum chamber is vented and the welded plate is taken out; Specifically, during welding, first, the working distance is 300-1500 mm, the electron beam power is 3-10 kW, the welding speed is 200-400 mm / min, and the scanning waveform is rectangular, and the plates to be welded are symmetrically positioned and welded; Then, the working distance is 300~1500mm, the electron beam power is 20~35kW, the welding speed is 100~300mm / min, and the scanning waveform is rectangular, and the plates to be welded after symmetrical positioning welding are filled with welding.

[0025] Step S6: placing the welded plate into a heat treatment furnace for post-weld heat treatment to eliminate residual stress; the post-weld heat treatment in step S6 specifically refers to placing the welded plate into a heat treatment furnace, heating it to 700°C to 720°C, and keeping it warm for 3h to 7h. After the insulation is completed, the plate is taken out and air-cooled; wherein the temperature of the heat treatment furnace is ≤200°C.

[0026] Step S7: performing nondestructive testing on the welded plate after heat treatment; Non-destructive testing, specifically: 100% ultrasonic testing shall be performed on welded joints, and the quality of welded joints shall meet the requirements of ISO 13919 Class B; or 100% radiographic testing shall be performed on welded joints, and the quality of welded joints shall meet the requirements of ISO 13919 Class B. Only one of the ultrasonic testing and radiographic testing is required for welded joints, and radiographic testing is preferred.

[0027] 100% surface penetration testing is performed on welded joints, and the quality of welded joints should meet the requirements of ISO 13919 Class B.

[0028] Step S8: Perform microstructure and mechanical property testing on the weld area of ​​the welded plate after passing the flaw detection.

[0029] Microstructure and mechanical properties evaluation, specific indicators are: At room temperature and 550°C, the tensile strength of the weld is greater than that of the thick plate to be welded; The average room temperature impact value of the weld and heat-affected zone is ≥160J. In each group of specimens, only one specimen is allowed to have an impact value lower than the average value and ≥112J. The average impact energy of the weld and heat-affected zone at -20°C is ≥80J. In each group of specimens, only one specimen is allowed to have an impact value lower than the average value and ≥56J; In the bending test, there shall be no single open defect with a length greater than 3mm in any direction on the weld and the tensile surface of the heat-affected zone; The weld microstructure is fully tempered martensite.

[0030] Example 1: A method for electron beam welding of a nitrogen-controlled low-activation steel thick plate with high strength and toughness matching, wherein the specifications of the nitrogen-controlled low-activation steel thick plate (the thick plate to be welded) are 300 mm (length) × 150 mm (width) × 30 mm (thickness), specifically comprising the following steps: (1) The surface to be welded of the thick plate to be welded is smoothed, and the roughness of the surface to be welded is 3.2μm. The surface to be welded is subjected to penetrant testing and ultrasonic testing, and the testing results meet the requirements of EJ / T20242 standard; (2) Use a demagnetizer to demagnetize the magnetic induction intensity of the thick plate to be welded to 1 Gauss; after demagnetization, use a stainless steel brush to clean the surface to be welded to remove the surface oxide scale, and then use acetone to clean the surface of the test plate to remove oil, water and other residues to ensure the cleanliness of the surface to be welded; (3) The thick plates to be welded are butted and pressed together to form a butt joint with a gap, and an arc-starting plate and an arc-ending plate are placed at the starting and ending positions of the gap, respectively; wherein the arc-starting plate and the arc-ending plate are made of the same material as the thick plates to be welded, and then the arc-starting plate, the arc-ending plate and the butt joint are fixed by manual arc welding to obtain the plates to be welded; (4) The vacuum in the electron beam welding vacuum chamber was evacuated to 0.05 Pa, and then the plates to be welded in the electron beam welding vacuum chamber were symmetrically positioned and welded at a working distance of 300 mm, an electron beam power of 3 kW, a welding speed of 400 mm / min, and a rectangular scanning waveform; (5) After symmetrical positioning welding, symmetrical filling welding is performed on the plate to be welded in the electron beam welding vacuum chamber at a working distance of 300 mm, an electron beam power of 20 kW, a welding speed of 200 mm / min, and a rectangular scanning waveform; (6) Place the welded plate taken out of the electron beam welding vacuum chamber into a heat treatment furnace, heat it up to 700°C, and keep it warm for 3 hours. After the end of the heat preservation, air cool it. The welded plates after air cooling are subjected to non-destructive testing, microstructure and mechanical property testing. The testing methods are: radiographic testing and surface penetrant testing, room temperature and high temperature tensile testing, V-notch impact testing, bending testing, and microstructure testing.

[0031] The test results show that: radiographic inspection and surface penetrant inspection results show that the weld quality meets the ISO13919-1B requirements; the tensile specimen breaks at the base metal, that is, the tensile strength of the weld joint is higher than that of the base metal; the impact performance is equivalent to that of the base metal; the weld joint has no cracks when bent 180° at room temperature; and the weld microstructure is fully tempered martensite.

[0032] Example 2: A method for electron beam welding of nitrogen-controlled low-activation steel thick plates with high strength and toughness matching, wherein the specifications of the nitrogen-controlled low-activation thick plates (thick plates to be welded) are 1500 mm (length) × 150 mm (width) × 50 mm (thickness), comprising the following steps: (1) The surface to be welded with the thick plate to be welded is processed to be flat and the surface roughness is ≤1.6μm. The surface to be welded is subjected to penetrant testing and ultrasonic testing. The testing results meet the requirements of EJ / T 20242 standard; (2) Use a demagnetizer to demagnetize the magnetic induction intensity of the thick plate to be welded to 1 Gauss; after demagnetization, use a stainless steel brush to clean the surface to be welded to remove the surface oxide scale, and then use acetone to clean the surface of the test plate to remove oil, water and other residues to ensure the cleanliness of the surface to be welded; (3) Butt and press the thick plates to be welded together to form a butt joint with a gap. Place an arc-starting plate and an arc-ending plate at the starting and ending positions of the gap between the butt joints, respectively. The arc-ending plate and the arc-starting plate are made of the same material as the thick plates to be welded. Then, manual arc welding is used to fix the arc-starting plate, the arc-ending plate and the butt joint to obtain the plate to be welded. (4) The vacuum in the electron beam welding vacuum chamber was evacuated to 0.05 Pa, and then the plates to be welded in the electron beam welding vacuum chamber were symmetrically positioned and welded at a working distance of 1500 mm, an electron beam power of 6 kW, a welding speed of 300 mm / min, and a rectangular scanning waveform; (5) After symmetrical positioning welding, symmetrical filling welding is performed on the plate to be welded in the electron beam welding vacuum chamber at a working distance of 1500 mm, an electron beam power of 30 kW, a welding speed of 100 mm / min, and a rectangular scanning waveform; (6) Place the welded plate taken out of the electron beam welding vacuum chamber into a heat treatment furnace, heat it up to 710°C, and keep it warm for 5 hours. After the insulation is completed, air cool it. The welded plates after air cooling are subjected to non-destructive testing, microstructure and mechanical property testing. The testing methods are: radiographic testing and surface penetrant testing, room temperature and high temperature tensile testing, V-notch impact testing, bending testing, and microstructure testing.

[0033] The test results show that: radiographic inspection and surface penetrant inspection results show that the weld quality meets the ISO13919-1B requirements; the tensile specimen breaks at the base metal, that is, the tensile strength of the weld joint is higher than that of the base metal; the impact performance is equivalent to that of the base metal; the weld joint has no cracks when bent 180° at room temperature; and the weld microstructure is fully tempered martensite.

[0034] Example 3: A method for electron beam welding of a nitrogen-controlled low-activation steel thick plate with high strength and toughness matching, wherein the specifications of the nitrogen-controlled low-activation steel thick plate (the thick plate to be welded) are 1000 mm (length) × 150 mm (width) × 70 mm (thickness), comprising the following steps: (1) The surface to be welded with the thick plate to be welded is processed to be flat and the surface roughness is ≤1.6μm. The surface to be welded is subjected to penetrant testing and ultrasonic testing. The testing results meet the requirements of EJ / T 20242 standard; (2) Use a demagnetizer to demagnetize the magnetic induction intensity of the thick plate to be welded to 1 Gauss; after demagnetization, use a stainless steel brush to clean the surface to be welded to remove the surface oxide scale, and then use acetone to clean the surface of the test plate to remove oil, water and other residues to ensure the cleanliness of the surface to be welded; (3) Butt and press two sets of thick plates to be welded together to form a butt joint with a gap. Place an arc-starting plate and an arc-ending plate at the starting and ending positions of the gap between the butt joints, respectively. The arc-ending plate and the arc-starting plate are made of the same material as the thick plates to be welded. Then, manual arc welding is used to fix the arc-starting plate, the arc-ending plate and the butt joint to obtain the plates to be welded. (4) The vacuum in the electron beam welding vacuum chamber was evacuated to 0.05 Pa, and then the plates to be welded in the electron beam welding vacuum chamber were symmetrically positioned and welded at a working distance of 1000 mm, an electron beam power of 10 kW, a welding speed of 300 mm / min, and a rectangular scanning waveform; (5) After symmetrical positioning welding, the plate to be welded in the electron beam welding vacuum chamber is symmetrically filled with welding at a working distance of 1000 mm, an electron beam power of 35 kW, a welding speed of 200 mm / min, and a rectangular scanning waveform to obtain a welded plate; (6) Place the welded plate taken out of the electron beam welding vacuum chamber into a heat treatment furnace, heat it up to 720°C, and keep it warm for 7 hours. After the insulation is completed, air cool it. The welded plates after air cooling are subjected to nondestructive testing, microstructure and mechanical property testing. The testing methods are: radiographic testing and surface penetrant testing, room temperature and high temperature tensile testing, V-notch impact testing, bending testing, microstructure testing, such as Figure 1-Figure 5 shown.

[0035] The test results show that the weld quality meets the requirements of ISO 13919-1 Class B by radiographic inspection and surface penetrant testing; the tensile specimen breaks at the base metal, indicating that the tensile strength of the weld joint is higher than that of the base metal; the impact performance is comparable to that of the base metal; the weld joint exhibits no cracks when bent 180° at room temperature; and the weld microstructure is fully tempered martensite.

[0036] Comparative Example 1: A method for electron beam welding of a nitrogen-controlled low-activation steel thick plate with high strength and toughness matching, wherein the specifications of the nitrogen-controlled low-activation steel thick plate (the thick plate to be welded) are 1500 mm (length) × 150 mm (width) × 50 mm (thickness), comprising the following steps: (1) The surface to be welded of the thick plate to be welded is processed flat and the surface roughness is ≤1.6μm. The surface to be welded is subjected to penetrant testing and ultrasonic testing. The testing results meet the requirements of EJ / T 20242 standard; (2) Use a demagnetizer to demagnetize the magnetic induction intensity of the thick plate to be welded to 1 Gauss; after demagnetization, use a stainless steel brush to clean the surface to be welded to remove the surface oxide scale, and then use acetone to clean the surface of the test plate to remove oil, water and other residues to ensure the cleanliness of the surface to be welded; (3) Butt and press the thick plates to be welded together to form a butt joint with a gap. Place an arc-starting plate and an arc-ending plate at the starting and ending positions of the gap between the butt joints, respectively. The arc-ending plate and the arc-starting plate are made of the same material as the thick plates to be welded. Then, manual arc welding is used to fix the arc-starting plate, the arc-ending plate and the butt joint to obtain the plates to be welded. (4) The vacuum in the electron beam welding vacuum chamber was evacuated to 0.05 Pa, and then the plates to be welded in the electron beam welding vacuum chamber were symmetrically positioned and welded at a working distance of 1500 mm, an electron beam power of 2 kW, a welding speed of 100 mm / min, and a rectangular scanning waveform; (5) Perform symmetrical fill welding on the plate to be welded in the electron beam welding vacuum chamber at a working distance of 1500 mm, an electron beam power of 15 kW, a welding speed of 80 mm / min, and a rectangular scanning waveform; (6) Place the welded plate taken out of the electron beam welding vacuum chamber into a heat treatment furnace, heat it up to 710°C, and keep it warm for 5 hours. After the insulation is completed, air cool it. After air cooling, the welded plates were subjected to nondestructive testing, microstructure, and mechanical property testing using radiographic and surface penetrant testing, as well as room- and high-temperature tensile, V-notch impact, and bend tests. The test results showed that the weld quality did not meet ISO 13919-1 Class B requirements; the tensile specimen broke at the weld, indicating that the tensile strength of the weld joint was lower than that of the parent material; the impact performance was significantly lower than that of the parent material (the room-temperature impact energy of the weld was 100 J, 157 J, and 80 J, while the low-temperature impact energy at -20°C was 8 J, 28 J, and 29 J); cracks appeared in the weld joint after 180° lateral bending at room temperature; and although the weld microstructure was fully tempered martensite, defects such as pores and cracks were present.

[0037] Comparative Example 2: A method for electron beam welding of a nitrogen-controlled low-activation steel thick plate with high strength and toughness matching, wherein the specifications of the nitrogen-controlled low-activation steel thick plate (the thick plate to be welded) are 1000 mm (length) × 150 mm (width) × 70 mm (thickness), comprising the following steps: (1) The surface to be welded of the thick plate to be welded is processed flat and the surface roughness is ≤1.6μm. The surface to be welded is subjected to penetrant testing and ultrasonic testing. The testing results meet the requirements of EJ / T 20242 standard; (2) Use a demagnetizer to demagnetize the magnetic induction intensity of the thick plate to be welded to 1 Gauss; after demagnetization, use a stainless steel brush to clean the surface to be welded to remove the surface oxide scale, and then use acetone to clean the surface of the test plate to remove oil, water and other residues to ensure the cleanliness of the surface to be welded; (3) Butt and press the thick plates to be welded together to form a butt joint with a gap. Place an arc-starting plate and an arc-ending plate at the starting and ending positions of the gap between the butt joints, respectively. The arc-ending plate and the arc-starting plate are made of the same material as the thick plates to be welded. Then, manual arc welding is used to fix the arc-starting plate, the arc-ending plate and the butt joint to obtain the plate to be welded. (4) The vacuum in the electron beam welding vacuum chamber was evacuated to 0.05 Pa, and then symmetrical positioning welding was performed on 70 mm thick nitrogen-controlled low-activation steel at a working distance of 1000 mm, an electron beam power of 12 kW, a welding speed of 350 mm / min, and a rectangular scanning waveform; (5) Symmetrical fill welding of 70 mm thick nitrogen-controlled low-activation steel was performed with a working distance of 1000 mm, an electron beam power of 37 kW, a welding speed of 350 mm / min, and a rectangular scanning waveform; (6) Place the welded plate taken out of the electron beam welding vacuum chamber into a heat treatment furnace, heat it up to 720°C, and keep it warm for 7 hours. After the insulation is completed, air cool it. After air cooling, the welded plates were subjected to nondestructive testing, microstructure, and mechanical property testing using radiographic and surface penetrant testing, as well as room-temperature and elevated-temperature tensile, V-notch impact, and bend tests. The test results showed that the weld quality did not meet ISO 13919-1 Class B requirements; the tensile specimen broke at the weld, indicating that the tensile strength of the weld joint was lower than that of the parent material; the impact properties were significantly lower than those of the parent material (the room-temperature impact energy of the weld was 265J, 280J, and 40J, while the low-temperature impact energy at -20°C was 4.5J, 28J, and 52J); cracks appeared in the weld joint upon 180° lateral bending at room temperature; and although the weld microstructure was fully tempered martensite, defects such as cracks and pores were present.

[0038] The test results of Example 2 and Comparative Example 1, and Example 3 and Comparative Example 2 indicate that welding using the present invention can achieve an I-type butt weld with the advantages of full penetration, no cracks, good back forming, and no undercut. The nondestructive testing results show that the weld quality meets the Class B requirements of the ISO 13919 standard. The mechanical property test results show that the room temperature and high temperature tensile strengths of the weld are higher than those of the base material, and the impact performance is equivalent to that of the base material. The weld side bend test meets the specified requirements, achieving a high strength and toughness match. The metallographic structure after heat treatment presents fully tempered martensite, without microscopic defects such as cracks and holes.

[0039] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for electron beam welding of high strength and toughness matching nitrogen-controlled low-activation steel thick plates, characterized in that: The specific steps include: Step S1: perform flaw detection on the thick plate to be welded and polish the welded surface; Step S2: Demagnetizing on a demagnetizing machine and cleaning the surface after demagnetization; Step S3: Processing the arc-closing plate and the arc-starting plate, and fixing the arc-closing plate and the arc-starting plate to the two ends of the gap formed by the two sets of butt-jointed thick plates to be welded by manual arc welding to obtain the plates to be welded; Step S4: Fix the plate to be welded vertically on the welding fixture, and control the gap to be horizontal; push the welding fixture into the electron beam welding vacuum chamber, and evacuate the electron beam welding vacuum chamber; wherein the vacuum degree of the electron beam welding vacuum chamber is 10 -2 ~10 -3 Pa; Step S5: using a vacuum electron beam to sequentially perform symmetrical positioning welding and symmetrical filling welding on the plate to be welded in the electron beam welding vacuum chamber to obtain a welded plate; After the temperature of the welding plate is lower than 100°C, the electron beam welding vacuum chamber is vented and the welded plate is taken out; Step S6: placing the welded plate into a heat treatment furnace for post-weld heat treatment.

2. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The thick plate to be welded comprises, by weight percentage, 0.015-0.040% N; 0.085-0.135% C; 0.2-0.4% V; 8.0-9.0% Cr; 0.3-0.7% Mn; 0.05-0.15% Ta; 1.3-1.7% W; 0-0.005% P; 0-0.005% S; 0-0.01% O; 0 ~0.05% Si; 0~0.01% Ni; 0~0.005% Mo; 0~0.01% Ti; 0~0.01% Cu; 0~0.005% Nb; 0~0.03% Al; 0~0.005% B; 0~0.005% Co; 0~0.005% Ag; the total of As, Sn, Sb and Zr is 0~0.005%; the balance is Fe.

3. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The thickness of the thick plate to be welded is 30 mm to 70 mm.

4. The method for electron beam welding of high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The step S1 specifically refers to performing surface penetrant testing and overall ultrasonic testing on the thick plate to be welded; after the testing meets the requirements, mechanically grinding the welding surface of the thick plate to be welded to a surface roughness of ≤3.2μm.

5. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The step S2 specifically includes the following steps: Step S21: Demagnetizing the thick plate to be welded using a demagnetizer; wherein the magnetic induction intensity is less than 2 Gauss, the power supply voltage of the demagnetizer is 380V ± 10%, the operating frequency is 50Hz, the maximum instantaneous demagnetization power is 152kVA, and the corresponding peak current is 400A; Step S22: After demagnetization is completed, the surface to be welded is cleaned to remove the surface oxide layer; Step S23: cleaning and removing residues on the surface to be welded.

6. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The step S3 comprises the following steps: Step S31: using nitrogen-controlled low-activation ferrite / martensitic steel of the same thickness as the thick plate to be welded to make the arc-ending plate and the arc-starting plate; Step S32: butting and pressing the two sets of thick plates to be welded together to form a butt joint, with a gap between the two being ≤0.15 mm; Step S33: placing an arc striking plate and an arc closing plate at the starting point and the end point of the gap respectively; Step S34: fix the arc-ending plate, arc-starting plate and the butt joint by spot welding to obtain the plate to be welded.

7. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The symmetrical positioning welding in step S5 specifically refers to: performing symmetrical positioning welding on the plates to be welded with a working distance of 300-1500 mm, an electron beam power of 3-10 kW, a welding speed of 200-400 mm / min, and a rectangular scanning waveform.

8. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The symmetrical filling welding in step S5 refers to performing filling welding on the plates to be welded after symmetrical positioning welding at a working distance of 300-1500 mm, an electron beam power of 20-35 kW, a welding speed of 100-300 mm / min, and a rectangular scanning waveform.

9. The method for electron beam welding of high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: The post-weld heat treatment in step S6 specifically refers to placing the welded plate into a heat treatment furnace, heating it to 700°C-720°C, and keeping it warm for 3h-7h. After the insulation is completed, the plate is taken out and air-cooled; wherein the temperature of the heat treatment furnace is ≤200°C.

10. The electron beam welding method for high strength and toughness matching nitrogen-controlled low-activation steel thick plates according to claim 1, characterized in that: Also includes: Step S7: performing nondestructive testing on the welded plate after heat treatment; Step S8: Perform microstructure and mechanical property testing on the weld area of ​​the welded plate after passing the flaw detection.

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