A method of welding repair of a component of a material susceptible to reheat cracking

Abstract

The present application relates to a kind of welding repair methods of reheat crack sensitive material parts, including the preheating of the component to be repaired at 250~300 ℃, using the electrode with diameter of 2.5~3.2mm, the welding groove surface of component is cladded with 90~130A current and forms cladding layer and is polished flat, using the electrode with diameter of 4.0~5.0mm, the welding groove surface of component is filled with 140~180A current and is covered, while welding filling process is carried out to the weld with ultrasonic impact, after covering, the weld toe part of component is carried out with ultrasonic impact, in turn, 500~600 ℃, 700~750 ℃ tempering is carried out.The present application improves the structure of welding heat affected zone, reduces the level of welding residual stress, reduces stress concentration, can effectively avoid the reheat crack of large thick wall reheat crack sensitive material valve during the heat treatment stress relief process after welding repair.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a welding repair method for components made of materials sensitive to reheat cracking. Background Technology

[0002] In subcritical and supercritical thermal power generating units, the valve bodies of high-pressure main steam valves are generally made of alloy cast steel (such as ZG15Cr1Mo1V). However, the valve bodies obtained by casting usually have casting defects such as sand holes, shrinkage cavities, and slag inclusions. After long-term service in high temperature and high pressure environments, they are prone to cracks. Once cracks are found in the valve body, it needs to be welded and repaired before it can continue to be used.

[0003] Alloy cast steel (such as ZG15Cr1Mo1V) has a high tendency for reheat cracking, and reheat cracking may occur during post-weld heat treatment. Therefore, the welding repair of thick-walled (50-300mm) alloy cast steel (such as ZG15Cr1Mo1V) valve bodies presents a high level of technical difficulty.

[0004] Currently, the "heterogeneous cold welding method" can be used to repair valve bodies. This involves removing the defects and then filling the gaps with nickel-based welding materials. After welding, no post-weld heat treatment is required; the material is directly cooled to room temperature. This method is simple, requires no post-weld heat treatment, and does not cause reheat cracking, making it widely used. However, this repair method also has drawbacks: due to the different coefficients of linear expansion between the base material and the welding material, thermal stress exists. Without post-weld heat treatment, the residual stress level is high, resulting in a high overall stress level at the joint. Furthermore, without post-weld heat treatment, a hardened structure exists in the heat-affected zone. Additionally, due to the different carbon content, carbon migration occurs at the interface. Therefore, valve bodies repaired using this method often experience significant cracking in the welded area after a period of use.

[0005] In addition, the conventional "homogeneous hot welding method" can be used, which involves using welding materials of the same material for filling and performing post-weld heat treatment immediately after welding to relieve stress. The weld joint obtained by this method has no hardened structure, the overall stress level of the joint is relatively low, and the safety and reliability are relatively high. However, no targeted technical measures are taken based on the conditions for the occurrence of reheat cracks. During the welding repair process, reheat cracks are easily generated in the coarse-grained zone of the weld heat-affected zone. Once reheat cracks occur, welding repair needs to be carried out again, and repeated welding and heat treatment will seriously damage the performance of the valve body. Summary of the Invention

[0006] The purpose of this invention is to provide a welding repair method for components made of materials susceptible to reheat cracking.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A welding repair method for components made of materials susceptible to reheat cracking includes the following steps:

[0009] (1) Preheat the parts to be repaired at a temperature of 250-300℃ for 2-4 hours. After reaching the preheating temperature, maintain the temperature within the preheating range for 2-4 hours before welding.

[0010] (2) Using welding rods with a diameter of 2.5-3.2mm, apply a current of 90-130A to the welding bevel surface of the component to form a cladding layer. After the cladding is completed, grind the cladding layer smooth.

[0011] (3) Using welding rods with a diameter of 4.0-5.0 mm, fill and cover the weld bevel surface of the component with a current of 140-180 A, and simultaneously subject the weld to ultrasonic impact during the welding filling process.

[0012] (4) After the cover is completed, ultrasonic impact is performed on the weld toe area of ​​the component.

[0013] (5) Tempering treatment: First, perform medium-temperature tempering at 500-600℃, and then perform high-temperature tempering at 700-750℃.

[0014] Preferably, the above technical solution further includes removing the cracks in the component to be repaired before step (1), and drilling a hole at the tip of the crack. The drilling depth is the crack detection depth + (3-5) mm, the drilling diameter is 5-10 mm, and the hole is a stop hole. The number of holes is two.

[0015] Preferably, in the above technical solution, the material of the welding rod in steps (2) and (3) is the same as the material of the part to be repaired, such as welding rod with grade R317L.

[0016] Preferably, in step (2), the thickness of the weld layer is controlled within 3.0 mm; the grinding amount of the cladding layer is 1.3 to 1.7 mm.

[0017] Preferably, in step (3), multi-layer, multi-pass welding is used for filling, the thickness of the weld layer is controlled within 4.0 mm, and the interpass temperature is controlled between 250 and 350°C.

[0018] Preferably, in step (3), an ultrasonic impact is performed every 8-10 cm of welding, and during the ultrasonic impact process: the middle of the weld bead is impacted first, and then the two sides are impacted, with the impact needle perpendicular to the surface of the weld bead.

[0019] Preferably, in steps (3) and (4), the ultrasonic impact amplitude is 25-35 μm, the ultrasonic impact current is 2-3 A, the ultrasonic impact frequency is 18-20 kHz, and the ultrasonic impact speed is 80-120 mm / min.

[0020] Preferably, in step (4), a groove with a diameter of 1.5 to 2.5 mm is formed at the weld toe by ultrasonic impact.

[0021] Preferably, in step (5), the temperature is increased to 500-600℃ at a heating rate of 6000-6500℃ / hour and held for 2-4 hours. Then, the temperature is increased to 700-750℃ at a heating rate of 9000-9750℃ / hour and held for δ×(2-3) minutes. After tempering, the temperature is cooled to room temperature, where δ is the thickness of the repaired area of ​​the component in mm.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] This invention avoids the problems of high stress levels in welded joints, hardened structures in the weld heat-affected zone, and carbon migration at the interface that exist in the "heterogeneous cold welding method" for valve shell repair, effectively improving the safety and reliability of the welded joint. At the same time, it avoids the disadvantages of the conventional "homogeneous hot welding method," which is prone to reheat cracking during implementation, leading to repeated repairs that severely damage the valve shell. It improves the microstructure of the weld heat-affected zone, reduces the level of residual stress in the weld, and reduces stress concentration. It can effectively prevent reheat cracking from occurring in valves made of thick-walled reheat crack-sensitive materials during the stress relief process of heat treatment after weld repair. Attached Figure Description

[0024] Appendix Figure 1 This is a photograph of the valve shell to be repaired in this invention;

[0025] Appendix Figure 2 This is a schematic diagram of the cladding layer welding in this invention;

[0026] Appendix Figure 3 This is a schematic diagram of the cladding layer polishing process in this invention;

[0027] Appendix Figure 4 This is a schematic diagram of ultrasonic impact on the weld toe in this invention;

[0028] Appendix Figure 5 This is a graph showing the temperature-time relationship for tempering treatment. Detailed Implementation

[0029] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] A welding repair method for components made of materials susceptible to reheat cracking includes:

[0031] Defect removal and preheating treatment:

[0032] The cracks in the component to be repaired are removed, and a hole is drilled at the tip of the crack. The drilling depth is the crack detection depth + (3~5) mm, and the drilling diameter is 5~10 mm. The hole is a stop hole to prevent the crack from spreading during the removal process.

[0033] The parts to be repaired are preheated at a temperature of 250–300°C. After reaching the preheating temperature, they are kept at a constant temperature for 2–4 hours. The preheating temperature of 250–300°C can reduce the temperature gradient, which is beneficial to reduce the level of residual welding stress and can also optimize the microstructure of the weld heat-affected zone before heat treatment.

[0034] welding:

[0035] Use welding electrodes with a diameter of 2.5-3.2mm. The material of the welding electrode should be the same as that of the part to be repaired, such as welding electrode with the grade R317L. Apply a current of 90-130A to the welding groove surface of the part to form a cladding layer. When welding with a current of 90-130A, the heat input is low and the heat-affected zone is narrow, which can improve the microstructure of the coarse grain area to a certain extent. After the cladding is completed, grind the cladding layer flat. When welding subsequent welds, it can play a tempering role in the heat-affected zone, further improving the microstructure of the heat-affected zone.

[0036] Use welding rods with a diameter of 4.0 to 5.0 mm. The material of the welding rods should be the same as that of the parts to be repaired, such as R317L welding rods. Use a current of 140 to 180 A to fill and cover the weld bevel surface of the parts. During the filling process, stop welding every 8 to 10 cm and then perform ultrasonic impact on the weld. During the ultrasonic impact, first impact the middle of the weld bead, and then impact both sides to make the weld bead produce dense and uniform "pockmarks". The impact needle is perpendicular to the surface of the weld bead.

[0037] The ultrasonic impact amplitude is 25-35μm, the ultrasonic impact current is 2-3A, the ultrasonic impact frequency is 18-20kHz, and the ultrasonic impact speed is 80-120mm / min. The ultrasonic impact frequency is thousands of times higher than that of conventional pneumatic hammer impact, and the impact head is easier to control than the hammer head. The impact uniformity is high. Ultrasonic impact can effectively reduce welding residual stress before welding.

[0038] Ultrasonic impact and tempering treatment:

[0039] After the cover is completed, the weld toe area of ​​the component is subjected to ultrasonic impact. The ultrasonic impact amplitude is 25–35 μm, the ultrasonic impact current is 2–3 A, the ultrasonic impact frequency is 18–20 kHz, and the ultrasonic impact speed is 80–120 mm / min. A groove with a diameter of 1.5–2.5 mm is formed at the weld toe to improve stress concentration. This step optimizes its geometry, reduces stress concentration, and generates beneficial compressive stress.

[0040] Tempering treatment: Heat to 500-600℃ at a heating rate of 6000-6500℃ / hour and hold for 2-4 hours. This step can partially eliminate residual welding stress and reduce the temperature difference between the inner and outer walls of the valve body, preparing for subsequent rapid heating. Then heat to 700-750℃ at a heating rate of 9000-9750℃ / hour and hold for δ×(2-3) minutes to reduce the dwell time in the reheat crack sensitive temperature range. After tempering, cool to room temperature. Where: δ is the thickness of the repaired area of ​​the component in mm.

[0041] Example 1:

[0042] right Figure 1 The valve body (wall thickness 200mm) made of ZG15Cr1Mo1V material shown is repaired by welding, including the following steps:

[0043] S1: Clean the crack by mechanical grinding or machining. Use a Φ5mm drill bit to drill two crack stop holes at the crack tip. The depth of the crack stop holes is the crack detection depth + 3mm.

[0044] S2: After the weld bevel size inspection and non-destructive testing are qualified, clean the bevel and surrounding area, and then use the flexible ceramic resistance heating method to preheat before welding. The preheating temperature is 275℃ and the preheating time is 3 hours.

[0045] S3: Using Φ3.2mm R317L welding rods, the entire weld bevel is clad using arc welding at a current of 110A. The weld layer thickness is controlled within 3.0mm. After the cladding layer is welded, it is smoothed by mechanical grinding, with the grinding amount controlled to approximately 1.5mm. Figure 2 , 3 As shown;

[0046] S4: Use Φ4.0mm R317L welding rods for multi-layer, multi-pass welding filler. The welding current is 160A, the weld thickness is controlled within 4.0mm, and the interpass temperature is controlled at 300℃. During filler welding, stop welding every 8-10cm and immediately use an ultrasonic impactor to treat the weld. First impact the center of the weld, then impact both sides, so that the impact needle is perpendicular to the weld surface. The impact amplitude is 30μm, the impact current is 2.5A, the impact frequency is 20kHz, and the impact speed is 100mm / min.

[0047] S5: After the cover is completed, immediately use an ultrasonic impactor to impact the weld toe area. The impact amplitude is 30μm, the impact current is 2.5A, the impact frequency is 20kHz, and the impact speed is 100mm / min; and a groove with a diameter of about 2mm is formed at the weld toe. Figure 4 As shown;

[0048] S6: Tempering treatment: Heat to 550℃ at a rate of 33℃ / hour and hold for 3 hours; then increase the heating rate by 50% to 47℃ / hour, raise to 740℃, and hold for approximately 7 hours; after holding at this temperature, slowly cool down; (The text abruptly ends here, so the translation stops as well.) Figure 5 As shown;

[0049] S7: After the post-weld heat treatment is completed and cooled to room temperature for 24 hours, the repaired valve body is subjected to magnetic particle testing and ultrasonic testing.

[0050] Comparative Example 1:

[0051] right Figure 1 The valve body made of ZG15Cr1Mo1V material shown was repaired by welding using the "dissimilar cold welding method", which includes the following steps:

[0052] S1: Clean the crack by mechanical grinding or machining, and drill two crack stop holes with a depth of 3mm and a crack detection depth at the crack tip using a Φ5mm drill bit.

[0053] S2: After the weld bevel size inspection and non-destructive testing are qualified, clean the bevel and surrounding area, and then use an oxyacetylene flame for preheating before welding at a temperature of 100℃.

[0054] S3: Use Φ3.2mm ENiCrFe~3 welding rods and perform multi-layer, multi-pass welding to fill the entire welding groove through arc welding, with the interpass temperature not exceeding 100℃;

[0055] S4: After covering, let it cool slowly to room temperature;

[0056] S5: After cooling to room temperature for 24 hours, perform a permeation test on the repaired valve shell.

[0057] Comparative Example 2:

[0058] right Figure 1 The valve body made of ZG15Cr1Mo1V material shown is repaired by welding using the "homogeneous thermal welding method", which includes the following steps:

[0059] S1: Clean the crack by mechanical grinding or machining, and drill two crack stop holes with a depth of 3mm and a crack detection depth at the crack tip using a Φ5mm drill bit.

[0060] S2: After the weld bevel size inspection and non-destructive testing are qualified, clean the bevel and surrounding area, and then use the flexible ceramic resistance heating method for preheating before welding at a preheating temperature of 275℃.

[0061] S3: Use Φ4.0mm R317L welding rods to perform multi-layer, multi-pass welding filling. The welding current is 160A, the weld layer thickness is controlled within 4.0mm, and the interpass temperature is controlled at 300℃.

[0062] S4: When filling the weld, stop welding every 8-10cm and immediately use a pneumatic hammer to hammer the weld. First hammer the middle of the weld, then hammer both sides to form dense "pockmarks" on the surface of the weld.

[0063] S5: After the topcoat is completed, immediately perform tempering treatment: the heating rate is 33℃ / hour, and the temperature is raised to 740℃ and kept constant; after the temperature is kept constant, slowly cool down.

[0064] S6: After the post-weld heat treatment is completed and cooled to room temperature for 24 hours, the repaired valve body is subjected to magnetic particle testing and ultrasonic testing.

[0065] The main factors influencing reheat cracking in ZG15Cr1Mo1V material include its chemical composition, wall thickness, microstructure of the coarse-grained region, welding residual stress level, and residence time in the reheat crack-sensitive temperature range (600–720℃). Given that the chemical composition and valve body wall thickness cannot be altered, based on the principles of improving the microstructure of the coarse-grained region, reducing welding residual stress level, and minimizing residence time in the reheat crack-sensitive temperature range, the valve body parameters repaired using the three methods described above are shown in the table below:

[0066]

[0067] This embodiment effectively eliminates the conditions for reheat cracking by improving the microstructure of the coarse-grained region, reducing the level of residual welding stress, and reducing the dwell time in the reheat crack sensitive temperature range. It effectively avoids the generation of reheat cracks in valves made of thick-walled reheat crack sensitive materials during the stress relief process of heat treatment after welding repair.

[0068] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A welding repair method for components made of materials susceptible to reheat cracking, characterized in that: Includes the following steps: (1) Preheat the parts to be repaired at a temperature of 250-300℃ for 2-4 hours. (2) Using welding rods with a diameter of 2.5 to 3.2 mm, apply a current of 90 to 130 A to the welding bevel surface of the component to form a cladding layer. After the cladding is completed, grind the cladding layer smooth. (3) Using welding rods with a diameter of 4.0 to 5.0 mm, fill and cover the weld bevel surface of the component with a current of 140 to 180 A, and simultaneously subject the weld to ultrasonic impact during the welding filling process. (4) After the cover is completed, ultrasonic impact is performed on the weld toe area of ​​the component to form a groove with a diameter of 1.5 to 2.5 mm at the weld toe through ultrasonic impact. (5) Tempering treatment: First, perform medium-temperature tempering at 500-600℃, then perform high-temperature tempering at 700-750℃. Increase the temperature to 500-600℃ at a heating rate of 6000-6500 / δ℃ / hour and hold for 2-4 hours. Then, increase the temperature to 700-750℃ at a heating rate of 9000-9750 / δ℃ / hour and hold for δ×(2-3) minutes. After tempering, cool to room temperature, where δ is the thickness of the repaired area of ​​the component in mm.

2. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: Before step (1), the cracks in the component to be repaired are removed and a hole is drilled at the tip of the crack. The drilling depth is the crack detection depth + (3~5) mm and the drilling diameter is 5~10 mm.

3. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: In steps (2) and (3), the material of the welding rod is the same as that of the part to be repaired.

4. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: In step (2), the thickness of the weld layer is controlled within 3.0 mm; the amount of grinding of the cladding layer is 1.3 to 1.7 mm.

5. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: In step (3), multi-layer, multi-pass welding is used for filling, the thickness of the weld layer is controlled within 4.0 mm, and the interpass temperature is controlled between 250 and 350°C.

6. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: In step (3), an ultrasonic impact is performed every 8-10 cm of welding.

7. The welding repair method for reheat-crack-sensitive material components according to claim 6, characterized in that: During ultrasonic impact: first impact the middle of the weld bead, then impact both sides, with the impact pin perpendicular to the weld bead surface.

8. The welding repair method for reheat-crack-sensitive material components according to claim 1, characterized in that: In steps (3) and (4), the ultrasonic shock amplitude is 25-35 μm, the ultrasonic shock current is 2-3 A, the ultrasonic shock frequency is 18-20 kHz, and the ultrasonic shock velocity is 80-120 mm / min.

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