A welding method for low magnetic stainless steel structure of a Tokamak device

Abstract

The present invention relates to the technical field of manufacturing a Tokamak device for controlled nuclear fusion, and in particular to a welding method for a low-magnetic stainless steel structure of a Tokamak device. A welding method for a low-magnetic stainless steel structure of a Tokamak device comprises the following steps: Step 1, grinding and cleaning the groove surface to be welded and the parent material within 20 mm of the groove surface to be welded before welding; Step 2, adopting multi-layer and multi-pass welding technology for welding; Step 3, after welding, adopting an aging treatment method to release internal stress. The beneficial effects of the present invention are: it can effectively prevent thermal cracks, reduce stress and avoid cracking; the metal arc gas shielded welding and tungsten arc argon welding use special shielding gas plus conventional welding materials to achieve the control of the relative magnetic permeability of the weld, which has high economic benefits. The relative magnetic permeability of the weld can be controlled without post-weld heat treatment, which solves the problem that large components or on-site components cannot be heat treated.

Description

Technical Field

[0001] The invention relates to the technical field of manufacturing a Tokamak device for controlled nuclear fusion, in particular to a welding method for a low-magnetic stainless steel structure of a Tokamak device. Background Art

[0002] The main constraint of the Tokamak device is magnetic constraint, so the relative magnetic permeability of the product is required to be less than 1.2, otherwise it will affect the magnetic field distribution in its working conditions. Conventional welding generally uses 308 series welding materials for welding, and welding is carried out in a protective gas atmosphere of pure argon or argon plus oxygen. Under this process condition, the relative magnetic permeability of the welding exceeds the standard and cannot meet the requirement of relative magnetic permeability of the product of μ < 1.2.

[0003] According to the analysis of welding mechanism, the increase of magnetic permeability of pure austenite structure after welding is mainly due to the generation of δ ferrite phase during the solidification of welding pool. δ ferrite phase has magnetism, which leads to the excessive relative magnetic permeability of weld. Therefore, the welding process that suppresses the generation of δ ferrite phase can meet the low magnetic requirements of Tokamak device. At the same time, pure austenite structure is prone to thermal cracks, so the welding process needs to consider measures to prevent thermal cracks.

[0004] The Chinese patent document with application number CN111702296B discloses a multi-layer and multi-pass welding process for a non-magnetic stainless steel support seat of a Tokamak device, but it only includes metal-electrode gas shielded welding, and special welding materials are used in the process, resulting in high welding costs. At the same time, this technology requires heat treatment after welding, which is not conducive to the manufacture of large structural parts and on-site product manufacturing. Summary of the invention

[0005] The object of the present invention is to provide a welding method for a low magnetic stainless steel structure of a Tokamak device to solve the problems mentioned in the background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for welding a low magnetic stainless steel structure of a Tokamak device, comprising the following steps:

[0008] Step 1: Grind and clean the groove surface to be welded and the parent material within 20mm of the groove surface to be welded before welding. Check the roughness of the surface to be welded before welding, and the roughness is required to be no greater than Ra3.2;

[0009] Step 2: Multi-layer and multi-pass welding technology is used for welding. During the welding process, a symmetrical and uniform segmented de-welding method is used to control welding stress and welding deformation;

[0010] Step 3, after welding is completed, internal stress is released by aging treatment, wherein a plurality of sleepers are used to support the welded component, and the plurality of sleepers are evenly arranged in the circumferential direction to divide the welded component into a plurality of equal areas; an exciter is used to sequentially perform multi-order vibration aging treatment on the plurality of equal areas to eliminate internal stress;

[0011] When the weld seam between layers is poorly formed during welding, the weld seam is ground or an additional tungsten inert gas arc welding pass is added to avoid interlayer unfusion. Ultrasonic testing is used to determine whether there are welding defects during welding. For welds with a thickness of more than 40 mm, ultrasonic testing is performed once when the cladding metal reaches 10 mm, when the cladding metal reaches 50% of the total thickness, and when welding is completed. If welding defects are found during ultrasonic testing, they are repaired. After the defects are repaired, the original non-destructive process is used for secondary testing.

[0012] In the process of multi-layer welding, the arc is not started and extinguished at the same place, and the distance between the arc extinguishing point and the arc starting point is more than 200mm; the arc is closed by the circle arc closing method until the arc pit is filled and then the arc is cut off to ensure that no arc pit cracks are generated;

[0013] During the welding process, a humidified towel is used on the back to ensure that the weld can be cooled quickly, and the interlayer temperature is controlled to be ≤150°C, avoiding the occurrence of welding thermal cracks while preventing the appearance of coarse single-phase grain structure, thereby improving the comprehensive mechanical properties of the weld.

[0014] As a further solution of the present invention: for all vacuum welds and non-vacuum welds in the Tokamak device, if they bear the load of the main structure, tungsten inert gas arc welding shall be adopted for welds with a thickness of no more than 20 mm, and tungsten inert gas arc welding shall be adopted for welds with a thickness of more than 20 mm, with tungsten inert gas arc welding for the base and arc welding for the filling and covering; for non-vacuum welds and welds that do not bear the load of the main structure, gas metal arc welding shall be adopted for welding.

[0015] As a further solution of the present invention: for tungsten inert gas welding, ER308L welding material is used for welding, and the shielding gas is 96% Ar + 4% N2, and the proportion deviation of N2 does not exceed ±0.25%;

[0016] For stick arc welding, E310Mo welding consumables are used for welding;

[0017] For metal-electrode gas shielded welding, ER308L welding material is used for welding, and the shielding gas is 91%Ar+2%C02+7%N2, and the deviation of the proportion of N2 does not exceed ±0.25%.

[0018] As a further solution of the present invention: the raw material of the Tokamak device is solid solution 06Cr19Ni10 or 022Cr19Ni10 stainless steel.

[0019] As a further solution of the present invention: when grinding the weld, a thin grinding wheel is used to grind layer by layer until the defect is reached.

[0020] As a further solution of the present invention: for the position where the welding thickness exceeds 30 mm, forward and reverse symmetrical uniform welding is adopted to prevent welding thermal cracks caused by excessive stress on one side.

[0021] As a further solution of the present invention: the vibration exciter is rigidly mounted on the wave crest of the welded component, and the sensor is adsorbed at a distance of about 3m from one side of the vibration exciter.

[0022] As a further solution of the present invention: multiple equally divided areas are vibrated one by one in a counterclockwise or clockwise manner, with a cumulative vibration time of 240 minutes.

[0023] As a further solution of the present invention: after the weld thickness reaches 5 mm, the back shielding gas is stopped.

[0024] As a further solution of the present invention: during double-sided welding, the back side is ground with a grinder, and the roughness after grinding is no greater than Ra3.2 and there are no defects visible to the naked eye.

[0025] Compared with the prior art, the invention has the following beneficial effects: it can effectively prevent thermal cracks, reduce stress and avoid cracking; it adopts three welding methods, namely, metal arc welding, tungsten inert gas welding and arc welding, and metal arc welding and tungsten inert gas welding use special shielding gas and conventional welding materials to achieve the control of the relative magnetic permeability of the weld, which has high economic benefits. The relative magnetic permeability of the weld can be controlled without post-weld heat treatment, which solves the problem that large components or on-site components cannot be heat treated.

[0026] Other features and advantages of the present invention will be disclosed in detail in the following specific embodiments and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of a welding method for a low magnetic stainless steel structure of a Tokamak device according to an embodiment of the present application;

[0028] Figure 2 It is an application Figure 1 Schematic diagram of the key components of the tokamak device of the method.

[0029] List of reference numerals: base lower platform 1, upper platform inner ring 2, upper platform outer ring 3, load-bearing interlayer inner ring 4, load-bearing interlayer outer ring 5, outer ring I-beam - cylindrical vertical plate 6, outer ring I-beam - lower side circular ring 7, outer ring I-beam - outer side vertical plate 8, outer ring I-beam - inner side vertical plate 9. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] like Figure 1 and Figure 2 As shown, a welding method for a low magnetic stainless steel structure of a Tokamak device comprises the following steps:

[0032] Step 1: Grind and clean the groove surface to be welded and the parent material within 20mm of the groove surface to be welded before welding. Check the roughness of the surface to be welded before welding, and the roughness is required to be no greater than Ra3.2;

[0033] Step 2, when welding, multi-layer and multi-pass welding technology is used for welding. During the welding process, a symmetrical and uniform segmented back-welding method is used to control welding stress and welding deformation; wherein, when welding with electrode arc welding, the thickness of a single weld bead shall not be greater than 2 mm of the electrode diameter, and the width of a single weld bead shall not be greater than 3 times of the electrode diameter; when welding with tungsten inert gas arc welding and metal arc gas shielded welding, the thickness of a single weld bead shall not be greater than 2 mm of the welding wire diameter, and the width of a single weld bead shall not be greater than 4 times of the welding wire diameter. For positions where the welding thickness exceeds 30 mm, positive and negative symmetrical uniform welding is used to prevent excessive stress on one side from causing welding thermal cracks;

[0034] Step 3: After welding is completed, internal stress is released by aging treatment, wherein multiple sleepers are used to support the welded components, and multiple sleepers are evenly arranged in the circumferential direction to divide the welded components into multiple equal areas; an exciter is used to perform multi-order vibration aging treatment on multiple equal areas in turn to eliminate internal stress. The exciter is rigidly clamped at the wave crest of the welded component, and the sensor is adsorbed approximately 3m away from one side of the exciter. Multiple sections are vibrated one by one in a counterclockwise or clockwise manner, and the cumulative vibration time is 240 minutes.

[0035] Specifically, the size of the Tokamak device component to be aged is φ17600×865mm, φ represents the diameter, and weighs about 188.8 tons. It is large in size and heavy in weight. According to the vibration aging process rules, it is supported by sleepers at 6 points. The 6 sleepers are about 800×300×200mm in size and placed on the ground. The placement principle is to divide the component into 6 equal areas along the perimeter.

[0036] The vibrator is rigidly mounted on the bottom plate at the lower end. The vibrator mounting principle is: it is mounted in an easy-to-mount position and rigidly mounted at the wave crest of the component. The sensor is adsorbed about 3m away from one side of the vibrator. Due to the large size and heavy weight of the component, the welding volume is large and complex. During the vibration aging treatment, a multi-order vibration aging treatment process is used to meet the requirements of the vibration stress relief process. A total of 6 vibrations are performed. After one vibration is completed, the position of the vibrator is moved counterclockwise in sequence. Each vibration time is 40 minutes, and the cumulative vibration time is 240 minutes.

[0037] When the welds between layers are poorly formed during welding, the welds are ground or additional tungsten inert gas arc welding passes are added to avoid interlayer unfusion. Ultrasonic testing is used to determine whether there are welding defects during welding. For welds with a thickness of more than 40 mm, ultrasonic testing is performed once when the cladding metal reaches 10 mm, when the cladding metal reaches 50% of the total thickness, and when all welding is completed. When welding defects are found during ultrasonic testing, they are repaired. After the defects are repaired, the original non-destructive process is used for secondary testing. When grinding the welds, a thin grinding wheel is used to grind layer by layer until the defect is reached.

[0038] During multi-layer welding, the arc is not started and extinguished at the same point, and the distance between the arc extinguishing point and the arc starting point is more than 200mm; when closing the arc, the circle arc closing method is adopted until the arc pit is filled and then the arc is cut off to ensure that no arc pit cracks are generated.

[0039] During welding, a humidifying towel is used on the back to ensure that the weld can be cooled quickly, and the interlayer temperature is controlled to be ≤150℃, so as to avoid the occurrence of welding thermal cracks and prevent the appearance of coarse single-phase grain structure, thus improving the comprehensive mechanical properties of the weld. Water is strictly prohibited from entering the weld during welding.

[0040] As a preferred embodiment, for all vacuum welds and non-vacuum welds in the Tokamak device that bear the load of the main structure, tungsten inert gas arc welding is used for welds with a thickness of no more than 20 mm, and tungsten inert gas arc welding is used for base welding and arc welding is used for filling and covering of welds with a thickness of more than 20 mm; non-vacuum welds that do not bear the load of the main structure are welded by metal arc welding.

[0041] Different welding materials are used for different welding methods. To prevent welding thermal cracks, the impurity element content of the welding materials is strictly controlled, with S element ≤ 0.020% and P element ≤ 0.030%.

[0042] As a specific implementation method, for tungsten inert gas welding, ER308L welding material is used for welding, and the shielding gas is 96% Ar + 4% N2, and the deviation of the proportion of N2 does not exceed ± 0.25%. As a strong austenitizing element, N can effectively inhibit the formation of delta ferrite phase and play an effect of controlling the relative magnetic permeability of the weld. Too small a proportion of N2 will lead to incomplete austenitization of the weld structure, and the relative magnetic permeability of the weld will not meet the technical requirements. However, N is also prone to form nitride structures with poor plasticity and toughness, which is not conducive to the mechanical properties of the weld. On the other hand, the supersaturated N in the molten pool is difficult to completely dissolve, and nitrogen pores may be formed, resulting in a decrease in weld performance.

[0043] For arc welding, E310Mo welding material is used. The Ni content of this welding material is 20%~22%, the Mn content is 1.0%~2.5%, and the Mo content is 2.0%~3.0%. Both Mn and Ni are austenitizing elements, which can effectively inhibit the formation of delta ferrite phase. At the same time, the Mo element is introduced into the weld, which can prevent the occurrence of thermal cracks in the weld.

[0044] For gas metal arc welding, ER308L welding material is used for welding, and the shielding gas is 91%Ar+2%C02+7%N2, and the proportion deviation of N2 does not exceed ±0.25%. As a strong austenitizing element, N can effectively inhibit the formation of delta ferrite phase and control the relative magnetic permeability of the weld. Too small a proportion of N2 will lead to incomplete austenitization of the weld structure, and the relative magnetic permeability of the weld will not meet the technical requirements. However, N is also prone to form nitride structures with poor plasticity and toughness, which is not conducive to the mechanical properties of the weld. On the other hand, the supersaturated N in the molten pool is difficult to completely dissolve, and nitrogen pores may be formed, resulting in a decrease in weld performance. At the same time, when stainless steel is welded with gas metal arc welding, the arc stability is relatively poor, so it is necessary to introduce oxidizing gas to stabilize the arc and improve the quality of the weld. The common oxidizing gas is O2, but because N2 is introduced into the shielding gas, N2 and O2 are prone to produce NO toxic gas under the action of the arc, which has an adverse effect on safety and environmental protection. Therefore, C02 is selected instead of O2 as the oxidizing gas.

[0045] The raw material of the Tokamak device is solid solution 06Cr19Ni10 or 022Cr19Ni10 stainless steel. The solid solution system is 1010~1150℃, and the cooling is fast. After the solid solution process, the raw material can meet the requirement of relative magnetic permeability <1.2. At the same time, in order to prevent welding hot cracks, the content of impurity elements is strictly controlled, among which S element ≤0.015% and P element ≤0.035%.

[0046] When the weld thickness reaches 5mm, stop the back shielding gas.

[0047] When double-sided welding, the back side is ground with a grinder. After grinding, the roughness is no greater than Ra3.2 and there are no defects visible to the naked eye.

[0048] The components of the Tokamak device are large vacuum container structures, among which the key components are ring frame structures. All vacuum welds are required to undergo 100% visual inspection, penetration testing, ultrasonic testing and leakage testing. Non-vacuum welds but welds that bear the load of the main structure are required to undergo 100% visual inspection, penetration testing, ultrasonic testing, and non-vacuum welds that do not bear the load of the main structure are required to undergo 100% visual inspection and penetration testing. This component is used as an example to illustrate the specific welding methods at different positions.

[0049] The component includes: a lower platform 1 of the base, an inner ring of the upper platform 2, an outer ring of the upper platform 3, an inner ring of the load-bearing interlayer 4, an outer ring of the load-bearing interlayer 5, an outer ring I-beam-cylindrical vertical plate 6, an outer ring I-beam-lower side ring 7, an outer ring I-beam-outer vertical plate 8, and an outer ring I-beam-inner vertical plate 9.

[0050] Because pure austenite is prone to thermal cracking, the groove processing should choose a larger weld width-to-depth ratio to reduce the melt dilution rate. At the same time, for thick plate materials, in order to avoid the influence of large welding stress, double-sided welding should be performed to prevent the accumulation of welding stress during welding and cause cracking during welding.

[0051] The welds between the parts of the lower platform 1 of the base, the welds between the parts of the inner ring 2 of the upper platform, the welds between the parts of the outer ring 3 of the upper platform, and the welds between the inner ring 2 of the upper platform and the outer ring 3 of the upper platform are all vacuum welds, which are welded by tungsten inert gas arc welding for base welding and arc welding for filling and covering. The welding groove adopts vertically symmetrical and left-right symmetrical grooves.

[0052] The welds between the various parts of the load-bearing interlayer outer ring 5 are vacuum welds, and the welds between the outer ring I-beam and the cylindrical vertical plate 6 and the welds between the outer ring I-beam and the lower circular ring 7 are non-vacuum welds but welds that bear the load of the main structure. They are welded by tungsten inert gas arc welding for base and arc welding for filling and covering. The welding groove adopts a single-sided left-right symmetrical groove.

[0053] The welds between the load-bearing interlayer outer ring 5 and the lower platform 1 of the base, and between the load-bearing interlayer outer ring 5 and the upper platform inner ring 2 are vacuum welds, which are welded by argon tungsten arc welding for base and arc welding for filling and covering. The welding groove is a single-sided groove that is symmetrical up and down.

[0054] The remaining welds are all fillet welds without grooves. Among them, the weld between the outer ring I-beam-cylinder vertical plate 6 and the outer ring I-beam-lower side ring 7, and the weld between the outer ring I-beam-cylinder vertical plate 6 and the upper platform outer ring 3 are non-vacuum welds but welds that bear the load of the main structure. They are welded by tungsten inert gas arc welding for base and arc welding for filling and covering. The weld between the load-bearing interlayer inner ring 4 and the lower platform 1 of the base, and the weld between the load-bearing interlayer inner ring 4 and the upper platform inner ring 2 are non-vacuum welds and welds that do not bear the load of the main structure. They are welded by metal arc welding.

[0055] For vacuum welds with a thickness of less than or equal to 20 mm, tungsten inert gas welding is used, and the welding groove is a symmetrical bevel groove.

[0056] The welding parameters of each weld are shown in Table 1.

[0057] Table 1 is the welding parameters of each weld:

[0058]

[0059] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0060] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A welding method for a low magnetic stainless steel structure of a Tokamak device, characterized in that: The following steps are involved: Step 1: Grind and clean the groove surface to be welded and the parent material within 20mm of the groove surface to be welded before welding. Check the roughness of the surface to be welded before welding, and the roughness is required to be no greater than Ra3.2; Step 2: Multi-layer and multi-pass welding technology is used for welding. During the welding process, a symmetrical and uniform segmented de-welding method is used to control welding stress and welding deformation; Step 3, after welding is completed, internal stress is released by aging treatment, wherein a plurality of sleepers are used to support the welded component, and the plurality of sleepers are evenly arranged in the circumferential direction to divide the welded component into a plurality of equal areas; an exciter is used to sequentially perform multi-order vibration aging treatment on the plurality of equal areas to eliminate internal stress; When the weld seam between layers is poorly formed during welding, the weld seam is ground or an additional tungsten inert gas arc welding pass is added to avoid interlayer unfusion. Ultrasonic testing is used to determine whether there are welding defects during welding. For welds with a thickness of more than 40 mm, ultrasonic testing is performed once when the cladding metal reaches 10 mm, when the cladding metal reaches 50% of the total thickness, and when welding is completed. If welding defects are found during ultrasonic testing, they are repaired. After the defects are repaired, the original non-destructive process is used for secondary testing. In the process of multi-layer welding, the arc is not started and extinguished at the same place, and the distance between the arc extinguishing point and the arc starting point is more than 200mm; the arc is closed by the circle arc closing method until the arc pit is filled and then the arc is cut off to ensure that no arc pit cracks are generated; During the welding process, a humidified towel is used on the back to ensure that the weld can be cooled quickly, and the interlayer temperature is controlled to be ≤150°C, so as to avoid the occurrence of welding thermal cracks and prevent the appearance of coarse single-phase grain structure, thereby improving the comprehensive mechanical properties of the weld. For all vacuum welds and non-vacuum welds in the Tokamak device that bear the load of the main structure, tungsten inert gas arc welding is used for welds with a thickness of no more than 20 mm, and tungsten inert gas arc welding is used for the base and arc welding is used for the filling and covering of welds with a thickness of more than 20 mm; for non-vacuum welds that do not bear the load of the main structure, gas metal arc welding is used for welding.

2. The welding method of a low magnetic stainless steel structure of a Tokamak device according to claim 1, characterized in that: For tungsten inert gas welding, ER308L welding material is used for welding, and the shielding gas is 96%Ar+4%N2, and the proportion deviation of N2 does not exceed ±0.25%; For stick arc welding, E310Mo welding consumables are used for welding; For metal-electrode gas shielded welding, ER308L welding material is used for welding, and the shielding gas is 91%Ar+2%C02+7%N2, and the deviation of the proportion of N2 does not exceed ±0.25%.

3. The welding method of a low magnetic stainless steel structure of a Tokamak device according to claim 1, characterized in that: The raw material of the Tokamak device is solid solution 06Cr19Ni10 or 022Cr19Ni10 stainless steel.

4. The welding method of a Tokamak device low magnetic stainless steel structure according to claim 1, characterized in that: When grinding the weld, use a thin grinding wheel to grind layer by layer until the defect is reached.

5. The welding method of a low magnetic stainless steel structure of a Tokamak device according to claim 1, characterized in that: For locations where the welding thickness exceeds 30mm, symmetrical and uniform welding is adopted to prevent welding thermal cracks caused by excessive stress on one side.

6. The welding method of a Tokamak device low magnetic stainless steel structure according to claim 1, characterized in that: The exciter is rigidly mounted on the wave crest of the welded component, and the sensor is adsorbed at a distance of 3 m from one side of the exciter.

7. The welding method of a Tokamak device low magnetic stainless steel structure according to claim 1, characterized in that: Multiple sections of vibration are performed one by one in a counterclockwise or clockwise manner on multiple equally divided areas, with a cumulative vibration time of 240 minutes.

8. The welding method of a Tokamak device low magnetic stainless steel structure according to claim 1, characterized in that: When the weld thickness reaches 5mm, stop the back shielding gas.

Images