Method for eliminating residual stress of dissimilar metal welding joint for nuclear power and product

Abstract

The present application relates to a kind of methods and products for eliminating residual stress of dissimilar metal welding joint for nuclear power, comprising: preparing dissimilar metal welding joint sample for nuclear power, and determining pulse current parameters according to the size of sample;Dissimilar metal welding joint sample for nuclear power is symmetrically clamped on the positive and negative electrode of pulse power supply, residual stress treatment is carried out according to the set parameter and time, and the treated dissimilar metal welding joint sample for nuclear power is obtained;Residual stress detection is carried out to the treated dissimilar metal welding joint sample for nuclear power.The present application directly acts pulse current on dissimilar metal welding joint, promotes dislocation movement by the interaction of electron and dislocation, thereby plastic deformation is generated, and residual stress of dissimilar metal welding joint is eliminated.The method has the characteristics of green energy saving, simple operation, easy control, regionalization directional efficient processing, can effectively remove residual stress of dissimilar metal welding joint, and improve the stress corrosion resistance of material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of residual stress elimination, and particularly relates to a method for eliminating residual stress of a dissimilar metal welding joint for nuclear power and a product. BACKGROUND

[0002] The dissimilar metal welding joint is an important transition part for connecting a low alloy steel pressure vessel and a stainless steel pipeline, which is formed by welding a low alloy steel nozzle and a stainless steel safety end with stainless steel or nickel-based alloy solder. Related nuclear power operation accidents and researches show that the dissimilar metal welding joint often fails prematurely, which endangers the normal operation of the nuclear power station. The main reason for the failure of the dissimilar metal welding joint is the corrosion cracking caused by the existence of residual stress under the service environment.

[0003] In the manufacturing process, the dissimilar metal welding joint is easily affected by processes such as welding, cutting and assembly, and residual stress is generated, which becomes a hidden danger of stress corrosion cracking of the welding joint and seriously endangers the safe operation of the nuclear power station. Among them, the thermal stress generated by the melting and solidification, cooling and shrinkage of the weld metal is the main reason for the generation of residual stress. Generally, the temperature for eliminating residual stress by heat treatment is 600-700 DEG C. However, the dissimilar metal weld and the similar metal weld on site are not subjected to post-weld heat treatment in order to avoid possible sensitization effect, that is, to prevent the carbide formed by the combination of carbon and chromium in the steel from precipitating in the grain boundary, so that the grain boundary appears chromium-poor and local grain boundary corrosion occurs, reducing the stress corrosion resistance of the material. Therefore, it is difficult to eliminate the residual stress of the dissimilar metal welding joint by conventional heat treatment. Therefore, it is necessary to seek a new method to effectively reduce or eliminate the residual stress in the welding joint to solve this problem.

[0004] The existing technology one utilizes the impact of heated gas and high-speed particle flow on the weld zone and its vicinity at the same time to improve the stress distribution by generating compressive stress on the joint surface; however, the process is complex, the energy consumption and processing cost are high, and it does not meet the requirements of the current industrial green development plan. The existing technology two utilizes ultrasonic impact technology to eliminate the residual stress of the welding joint; however, the energy output of the ultrasonic treatment is unstable, and the treatment effect is uncertain. The existing technology three utilizes laser heat treatment effect to eliminate the residual stress of the X80 pipeline steel welding joint; however, the heat treatment speed is slow, and the processing time is too long for large workpieces, which is low in efficiency.

[0005] Since the dissimilar metal welding joint of the key component may have a large residual stress, which is easy to induce crack initiation and propagation, and the welding joint is difficult to eliminate the residual stress by conventional heat treatment. Therefore, it is necessary to study a method for eliminating the residual stress of the dissimilar metal welding joint for nuclear power. SUMMARY

[0006] In order to overcome the above problems existing in the prior art, the application provides a method for eliminating residual stress of a dissimilar metal welded joint for nuclear power and a product, which are used to solve the above problems existing in the prior art.

[0007] A method for eliminating residual stress of a dissimilar metal welded joint for nuclear power, the method comprising:

[0008] S1. Preparing a dissimilar metal welded joint sample for nuclear power, and determining pulse current parameters according to the size of the sample;

[0009] S2. Symmetrically clamping the dissimilar metal welded joint sample for nuclear power on the positive and negative electrodes of a pulse power supply, and performing residual stress elimination treatment according to the set parameters and time to obtain a treated dissimilar metal welded joint sample for nuclear power;

[0010] S3. Detecting residual stress of the treated dissimilar metal welded joint sample for nuclear power.

[0011] According to the above-mentioned aspects and any possible implementation manners, further provided is an implementation manner, and the S1 specifically comprises:

[0012] S11. Cutting and processing a welding bevel by wire cutting on 316L and 508 steel raw materials, double V-shaped, a bevel angle of 60°, polishing, polishing and washing the surface to be welded, and finally drying for standby;

[0013] S12. Using argon as a protective gas for a welding process, first welding an isolation layer on the bevel surface of the 508 steel, and finally welding the isolation layer and the 316L to obtain a welded sample;

[0014] S13. Cutting the welded sample into a certain size, detecting residual stress in the size sample, and recording data for standby.

[0015] According to the above-mentioned aspects and any possible implementation manners, further provided is an implementation manner, and the certain size is 100 mm x 15 mm x 2 mm.

[0016] According to the above-mentioned aspects and any possible implementation manners, further provided is an implementation manner, and the set parameters and time are specifically: a pulse frequency of 200 Hz-20000 Hz, a pulse width of 10 μs-600 μs, a current density of 1 A / mm 2 -1000 A / mm 2 , and a pulse time of 10 min-120 min.

[0017] According to the above-mentioned aspects and any possible implementation manners, further provided is an implementation manner, and the pulse frequency is 1000 Hz, and the average current is 3.15 A / mm 2, the pulse width is 200us, and the pulse time is 60min.

[0018] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the pulse frequency is 2000Hz, the average current is 1.83A / mm 2 , the pulse width is 100us, and the pulse time is 30min.

[0019] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the pulse frequency is 500Hz, the average current is 1.66A / mm 2 , the pulse width is 400us, and the pulse time is 60min.

[0020] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the pulse waveform adopted by the pulse current treatment is a sharp wave, a square wave or a sine wave.

[0021] According to the aspect and any possible implementation manner described above, further provided is an implementation manner, wherein the residual stress data detected by S3 is compared with the residual stress data recorded in S13 to verify the elimination.

[0022] The application further provides a dissimilar metal welded joint sample for nuclear power, which is obtained by the method.

[0023] Advantages of the application

[0024] Compared with the prior art, the application has the following advantages:

[0025] The method for eliminating residual stress of a nuclear power heterogeneous metal welding joint according to the present application comprises: preparing a nuclear power heterogeneous metal welding joint sample, and determining pulse current parameters according to the size of the sample; symmetrically clamping the nuclear power heterogeneous metal welding joint sample on the positive and negative poles of a pulse power source, and performing residual stress elimination treatment according to the set parameters and time to obtain a treated nuclear power heterogeneous metal welding joint sample; and detecting the residual stress of the treated nuclear power heterogeneous metal welding joint sample. The present application directly applies pulse current to the heterogeneous metal welding joint, promotes dislocation movement through the interaction between electrons and dislocations, and thus produces plastic deformation to eliminate the residual stress of the heterogeneous metal welding joint. The method has the characteristics of green energy saving, simple and easy-to-control operation, and regionalized directional efficient treatment, can effectively remove the residual stress of the heterogeneous metal welding joint, and improve the stress corrosion resistance of the material. By using the method, the sensitization effect caused by high temperature can be avoided, the residual stress of the welding joint can be effectively eliminated in whole or in part, the stress corrosion resistance of the welding joint can be improved, the treatment time is relatively short, the treatment operation is simple and easy to control, and the treatment effect is stable. The effectiveness of the method is not limited to the nuclear power heterogeneous metal welding joint, but is also applicable to other metal welding materials. Compared with other existing methods for removing welding residual stress, the present application can effectively eliminate the residual stress of the material, has stable effect, and has the advantages of green energy saving, simple and easy-to-control operation, and efficient treatment in a specified area, and the technology has important application potential. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 A comparison chart of residual stress values before and after pulse current treatment for Example 1;

[0027] Figure 2 A comparison chart of residual stress values before and after pulse current treatment for Example 2;

[0028] Figure 3 A comparison chart of residual stress values before and after pulse current treatment for Example 3;

[0029] Figure 4 A flowchart of the method according to the present application. DETAILED DESCRIPTION

[0030] In order to better understand the technical solutions of the present application, the present application includes but is not limited to the specific embodiments described below, and similar technologies and methods should be considered as falling within the scope of protection of the present application. In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail with reference to the drawings and specific embodiments.

[0031] It should be apparent that the embodiments described herein are merely a few of the many embodiments of the present application, and not all of the embodiments. Based on the embodiments described herein, all other embodiments obtained by those of ordinary skill in the art without creative efforts are within the scope of the present application.

[0032] The terms used in the embodiments of the present application are merely for the purpose of describing the specific embodiments, and are not intended to limit the present application. The singular forms "a," "an," and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0033] As shown in Figure 4 The present application provides a method for eliminating residual stress of a dissimilar metal welding joint for nuclear power, the method comprising:

[0034] S1. Preparing a dissimilar metal welding joint sample for nuclear power, and determining the pulse current parameters according to the size of the sample;

[0035] S2. Symmetrically clamping the dissimilar metal welding joint sample for nuclear power on the positive and negative electrodes of a pulse power source, and performing residual stress elimination treatment according to the set parameters and time, to obtain a treated dissimilar metal welding joint sample for nuclear power;

[0036] S3. Detecting the residual stress of the treated dissimilar metal welding joint sample for nuclear power.

[0037] The present application performs pulse current treatment on the dissimilar metal welding joint for nuclear power, wherein the set parameters and time are specifically: the parameter range of the pulse current treatment is frequency 200Hz-20000Hz, pulse width 10us-600us, current density 1A / mm 2 -1000A / mm 2 , and pulse time 10min-120min. The pulse current treatment adopts pulse waveforms which can be sharp wave, square wave, sine wave, etc.

[0038] In step S2, the dissimilar metal welded joint sample for nuclear power is symmetrically clamped on the positive and negative electrodes of the pulse power source by the clamp, and pulse current treatment is carried out according to the set parameters and time. The pulse current generator is used as the power source, and the two ends of the sample are connected with the positive and negative electrodes of the pulse power device through metal sheets (copper sheets, etc.). The pulse power is turned on, the pulse current is applied to the welded joint, and the pulse temperature is raised to a fixed temperature. After keeping warm for a period of time, it is air-cooled. The pulse current directly acts on the dissimilar metal welded joint. The electrons generated by the current interact with the dislocations of the dissimilar metal welded joint, promote the movement of the dislocations, reduce the dislocation density, and thus make the welded joint deform plastically and release the residual stress of the dissimilar metal welded joint. At the same time, the pulse current generates Joule heat in the dissimilar metal welded joint, which is beneficial to the reduction of residual stress. In addition, the pulse current promotes the dissolution of carbides at the grain boundaries of 316L, avoiding the sensitization effect caused by high temperature.

[0039] Preferably, the dissimilar metal welded joint for nuclear power is welded by argon arc welding of conventional 316L stainless steel and SA-508 low alloy steel on the market, and the welding material is 52 nickel-based alloy.

[0040] Preferably, the pulse current treatment device used is a pulse power source.

[0041] Preferably, the pulse current treatment of the dissimilar metal welded joint for nuclear power is carried out at room temperature.

[0042] Preferably, the S1 specifically comprises:

[0043] S11. The 316L and 508 steel raw materials are cut and the welding groove is processed by wire cutting, the double V-shaped groove angle is 60°, the welding surface is polished, polished, washed, and finally dried for standby;

[0044] S12. Use argon as the protective gas for the welding process, first weld the isolation layer on the groove surface of the 508 steel, and finally weld the isolation layer and the 316L to obtain the welded sample;

[0045] S13. Cut the welded sample into a certain size, detect the residual stress in the size sample, and record the data for standby.

[0046] Preferably, it further comprises a verification step S4, comparing the residual stress data obtained by the residual stress detection of S3 with the residual stress data recorded in S13 to verify the elimination condition.

[0047] As the embodiment of the present application, the present application also provides a nuclear power heterogeneous metal welding joint sample, which is obtained by the method of the present application. The test shows that the residual tensile stress in the nuclear power heterogeneous metal welding joint sample is completely eliminated, and residual compressive stress is generated, and the generated residual compressive stress can improve the hardness and strength of the sample material, thereby preventing the expansion of cracks, and further improving the fatigue life of the nuclear power heterogeneous metal welding joint. The residual tensile stress in the sample before welding is positive, and the greater the value, the more harmful to the sample, which can reduce the stress corrosion resistance of the material; the residual compressive stress generated after welding is negative, and the smaller the negative value, the more beneficial to the sample, which can improve the stress corrosion resistance of the material.

[0048] The following is a specific embodiment

[0049] Embodiment 1

[0050] In this embodiment, the residual stress of the nuclear power heterogeneous metal welding joint is eliminated by pulse current. The specific steps are as follows:

[0051] First step: cut 316L and 508 steel into appropriate size by wire cutting, and process welding bevel, double V type, bevel angle is 60°. Use 180, 800, 2000 mesh sandpaper to polish the V type bevel in turn, and polish the welding bevel surface with 1 μm diamond polishing liquid, use distilled water and alcohol for washing, and finally dry for standby.

[0052] Second step: select appropriate welding parameters (welding current, welding speed, etc.) when welding, use argon as the protective gas in the welding process, first weld the isolation layer on the welding bevel surface of 508 steel, and finally weld the isolation layer with 316L welding bevel, to obtain the welded sample.

[0053] Third step: cut the welded joint into a sample of 100mm×15mm×2mm by wire cutting. Detect the residual stress of the original sample by X-ray diffraction method, and record the residual stress data at this time for standby.

[0054] Fourth step: fix the welded joint sample and copper sheet by clamp. Connect the pulse power supply with the two copper sheets, set the pulse current parameters as follows: frequency 1000Hz, average current 3.15A / mm 2 , pulse width 200μs, then turn on the pulse power supply to apply pulse current to the sample, and the duration is 60min. After the sample is naturally cooled, the sample treated by pulse current is taken out.

[0055] Fifth step: detect the residual stress of the pulse sample by X-ray diffraction method. The residual stress change graph before and after pulse current treatment is as follows: Figure 1The residual tensile stress of the original sample is 674.9 MPa, and the residual compressive stress generated after pulse current treatment is -82.3 MPa, so the residual stress elimination rate is 112.2%. This shows that after pulse current treatment, the residual tensile stress is completely eliminated, and residual compressive stress is generated. The generated residual compressive stress can improve the hardness and strength of the material, prevent crack propagation, and improve the fatigue life of the dissimilar metal welded joint for nuclear power.

[0056] Example 1 shows that pulse current can eliminate residual stress of the welded joint.

[0057] Example 2:

[0058] In this example, the residual stress of the dissimilar metal welded joint for nuclear power is eliminated by pulse current. The specific steps are as follows:

[0059] First step: cut 316L and 508 steel into appropriate size by wire cutting, and process the welding groove, double V type, groove angle is 60°. Use 180, 800, 2000 mesh sandpaper to polish the V type groove in turn, and polish the surface of the welding groove with 1 μm diamond polishing liquid, wash with distilled water and alcohol, and finally dry for standby.

[0060] Second step: choose appropriate welding parameters (welding current, welding speed, etc.) when welding, use argon as protective gas during welding process, first weld isolation layer on the surface of 508 steel welding groove, and finally weld isolation layer with 316L welding groove surface to obtain welded sample.

[0061] Third step: cut the welded joint into a sample of 100 mm x 15 mm x 2 mm by wire cutting. Detect the residual stress of the original sample by X-ray diffraction method, and record the data for standby.

[0062] Fourth step: fix the welded joint sample and copper sheet by clamp. Connect the pulse power supply with the two copper sheets, set the pulse current parameters as follows: frequency 2000 Hz, average current 1.83 A / mm 2 , pulse width 100 μs, then turn on the pulse power supply to pulse the sample for 30 min. After the sample is naturally cooled, take out the sample after pulse current treatment.

[0063] Fifth step: detect the residual stress of the pulse sample by X-ray diffraction method. The residual stress change graph before and after pulse current treatment is shown in Figure 2 . The measured residual stress of the original sample is 429.2 MPa, and the residual stress after pulse current treatment is 76.9 MPa, with an elimination of 352.2 MPa, and the residual stress elimination rate is 82.1%. This example further improves the pulse current density, which can completely eliminate the residual stress of the welded joint.

[0064] Example 2 shows that the pulse current can eliminate most of the residual stress of the welded joint.

[0065] Example 3:

[0066] This example eliminates the residual stress of the dissimilar metal welded joint for nuclear power by pulse current. The specific steps are as follows:

[0067] First step: cut 316L and 508 steel into appropriate size by wire cutting, and process the welding groove, double V type, groove angle is 60°. Use 180, 800, 2000 mesh sandpaper to polish the V type groove in turn, and polish the welding groove surface with 1 μm diamond polishing liquid, use distilled water and alcohol for washing, and finally dry for standby.

[0068] Second step: choose appropriate welding parameters (welding current, welding speed, etc.) when welding, use argon as the protective gas during the welding process, first weld the isolation layer on the welding groove surface of 508 steel, and finally weld the isolation layer with the welding groove surface of 316L, to obtain the welded sample.

[0069] Third step: cut the welded joint into 100 mm x 15 mm x 2 mm sample by wire cutting. Detect the residual stress of the original sample by X-ray diffraction method, and record the data for standby.

[0070] Fourth step: fix the welded joint sample with copper sheet by clamp. Connect the pulse power supply with two copper sheets, set the pulse current parameters as follows: frequency 500 Hz, average current 1.66 A / mm 2 , pulse width 400 μs, then open the pulse power supply to pulse the sample, the duration is 60 min. After the sample is naturally cooled, take out the sample after pulse current treatment.

[0071] Fifth step: detect the residual stress of the pulse sample by X-ray diffraction method. The residual stress change diagram before and after pulse current treatment is shown in Figure 3 . The measured residual stress of the original sample is 326.1 MPa, and that after pulse current treatment is 30.7 MPa. The residual stress elimination amount of pulse current is 295.4 MPa, and the residual stress elimination rate is 90.6%.

[0072] Example 3 shows that the pulse current can basically eliminate the residual stress of the welded joint.

[0073] Table 1 shows the residual stress change of the welded joint selected in example

[0074] Before pulse current treatment After pulse current treatment Stress relief amount Example 1 674.9 MPa -82.3 MPa 757.2 MPa Example 2 429.2 MPa 76.9 MPa 352.3 MPa Example 3 326.1 MPa 30.7 MPa 295.4 MPa

[0075] The foregoing description illustrates and describes several preferred embodiments of the present application, but it is to be understood that the application is not limited to the above-described forms, and that it should not be seen as excluding other embodiments, but rather as being applicable in a variety of other combinations, modifications and environments, and capable of being altered in various ways within the scope of the application as described in the claims, by the teaching or knowledge of the relevant art, or by the common general knowledge. Any alterations and further modifications in the application made by a person of ordinary skill in the art are to be construed as being within the scope of the application as defined in the appended claims.

Claims

1. A method for eliminating residual stress in dissimilar metal welded joints used in nuclear power plants, characterized in that, The method includes: S1. Prepare samples of dissimilar metal welded joints for nuclear power plants, and determine pulse current parameters based on the sample dimensions. The dissimilar metals are 316L stainless steel and SA-508 low-alloy steel. S1 specifically includes: S11. Cut 316L and 508 steel raw materials by wire cutting and process welding bevels, double-sided V-shape, bevel angle of 60°, grind, polish, wash, and finally dry for later use. S12. Using argon as the shielding gas for the welding process, first weld an isolation layer on the bevel surface of 508 steel, and finally weld the isolation layer to 316L to obtain a welded sample. S13. Cut the welded sample into a certain size, detect the residual stress in the sample of that size, and record the data for later use; S2. The sample of the dissimilar metal welded joint for nuclear power is symmetrically clamped on the positive and negative terminals of a pulse power supply, and residual stress is eliminated according to the set parameters and time to obtain the treated sample of the dissimilar metal welded joint for nuclear power. The set parameters and time are as follows: pulse frequency 200Hz~2000Hz, pulse width 10μs~600μs, current density 1A / mm 2 ~3.15A / mm 2 The pulse duration is 10min-120min. The pulsed current is applied directly to the dissimilar metal welded joint. The electrons generated by the current interact with the dislocations in the dissimilar metal welded joint, promoting dislocation movement and reducing dislocation density, thereby causing plastic deformation of the welded joint and releasing the residual stress in the dissimilar metal welded joint. S3. Perform residual stress testing on the processed samples of dissimilar metal welded joints for nuclear power plants.

2. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The specified dimensions are 100mm × 15mm × 2mm.

3. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The pulse frequency is 1000Hz, and the average current density is 3.15A / mm². 2 The pulse width is 200μs and the pulse duration is 60min.

4. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The pulse frequency is 2000Hz, and the average current density is 1.83A / mm². 2 The pulse width is 100μs and the pulse duration is 30min.

5. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The pulse frequency is 500Hz, and the average current density is 1.66A / mm². 2 The pulse width is 400μs and the pulse duration is 60min.

6. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The pulse waveform used in the pulse current processing is a spike, square wave, or sine wave.

7. The method for eliminating residual stress in dissimilar metal welded joints for nuclear power plants according to claim 1, characterized in that, The residual stress data obtained from S3 is compared with the residual stress data recorded in S13 to verify the elimination effect.

8. A sample of a dissimilar metal welded joint for nuclear power plants, characterized in that, Obtained by the method of any one of claims 1-7.

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