A CMT welding repair method suitable for ZG35Cr1Mo casting defects

Abstract

The present application belongs to the field of welding, and particularly relates to a CMT welding repair method suitable for ZG35Cr1Mo casting defects, comprising the following steps: step one, polishing and cleaning the defect part of the casting, and constructing a welding groove; step two, before welding repair, using oxyacetylene to locally heat the welding area, so that the surface temperature is located at 280 DEG C; using a CMT welding device and configuring pure nickel welding wire ERNi-1 to perform backing welding on the casting, after the backing welding is completed, using a SMAW device and configuring a nickel-based electrode ENi6182 to perform filling welding on the casting, after the filling welding is completed, using the oxyacetylene heating method to locally heat the surface of the welding bead, and the surface temperature is located at 400 DEG C; step three, detecting the casting after welding to determine the repair state of the casting. The present application provides a CMT welding repair method suitable for ZG35Cr1Mo casting defects, and the purpose is to solve the deficiency of the prior art in repairing ZG35Cr1Mo castings.

Description

Technical Field

[0001] This invention belongs to the field of welding repair, specifically relating to a CMT welding repair method suitable for defects in ZG35Cr1Mo castings. Background Technology

[0002] Medium carbon steel is a class of metallic materials with excellent properties. Its carbon content typically ranges from 0.3% to 0.6%. Due to its high strength, good hardness, and reliable machinability, it is widely used in machinery manufacturing, engineering construction, and the automotive industry. Especially in applications requiring heavy loads and high strength, medium carbon steel is often the preferred material. ZG35Cr1Mo is a medium carbon low-alloy quenched and tempered steel, belonging to the category of medium carbon steel. Due to its high manganese (Mn) and chromium (Cr) content, ZG35Cr1Mo exhibits excellent corrosion resistance and wear resistance; this characteristic makes it a suitable material for manufacturing many large castings, such as the hinges of arch gates in hydroelectric power stations.

[0003] Because ZG35Cr1Mo castings are typically heavy, large, and complex in shape, they are prone to defects such as porosity, looseness, and inclusions during the casting process. These problems seriously affect the quality and performance of the castings and may become crack initiation points, threatening their safe use. In addition, improper handling during installation and the combined effects of corrosion fatigue, hydrogen embrittlement, and internal stress release during service can easily lead to cracking.

[0004] In order to repair ZG35Cr1Mo castings, the applicant previously applied for a technical solution (Method for Repairing Carbon Quenched and Tempered Steel Structures Without Preheating or Post-Welding Heat Treatment, CN121223225A) to repair ZG35Cr1Mo castings using CMT welding equipment. However, in practice, it was found that this technical solution still has shortcomings, which makes the repaired ZG35Cr1Mo castings prone to cracking. Summary of the Invention

[0005] This invention provides a CMT welding repair method for defects in ZG35Cr1Mo castings, aiming to overcome the shortcomings of existing technologies for repairing ZG35Cr1Mo castings.

[0006] To achieve the above objectives, this invention provides a CMT welding repair method for defects in ZG35Cr1Mo castings, comprising the following steps: Step 1: Grind and clean the defective parts of the casting and construct the welding bevel; Step 2: Before welding repair, use oxyacetylene to locally heat the welding area so that the surface temperature is 280℃. The casting was subjected to root pass welding using CMT welding equipment and pure nickel welding wire ERNi-1. During the root pass welding process, after the first root pass welding, the weld bead was locally heated with oxyacetylene to bring the surface temperature to 400°C. After the root pass welding was completed, the casting was subjected to fill pass welding using SMAW equipment and nickel-based welding rod ENi6182. After the fill pass welding was completed, the weld bead was locally heated with oxyacetylene to bring the surface temperature to 400°C. Step 3: Perform post-weld inspection on the casting to determine its repair status.

[0007] Preferably, in step two, when using CMT welding equipment for root pass welding, the welding current is 210A-240A, and the welding current of the first weld pass is greater than that of the second and third weld passes, and the welding current of the fourth and fifth weld passes is greater than that of the second and third weld passes. In step two, when using CMT welding equipment for root pass welding, the arc voltage is 12-14V, and the arc voltage of the first to third weld passes is less than that of the fourth and fifth weld passes. In step two, when using CMT welding equipment for root pass welding, the wire feed speed is 7-8 m / min; In step two, when using CMT welding equipment for root pass welding, the shielding gas is 100% Ar with a flow rate of 15-20 L / min.

[0008] Preferably, in step two, when performing the root pass welding with the CMT welding equipment, the welding should be performed by oscillation, with an oscillation amplitude ≤20mm. During the welding process, the welding line energy should be controlled to be ≤30kJ / cm and the welding speed ≥50mm / min. After each weld, the arc starting point, arc ending point, and both sides of the weld bead are ground. The ground surface is smooth and without sharp edges. Along the weld direction, the overall surface is free of burrs, pits, and poor welding areas after grinding. The weld bead is also cleaned.

[0009] Preferably, in step one, the angle between the two side walls of the welding bevel is 90 degrees; In step two, when using CMT welding equipment to perform the root pass welding, the distance between the second and third weld passes and the first weld pass is reduced, thereby increasing the welding overlap rate.

[0010] Preferably, in step two, when using SMAW welding equipment for filler welding, the welding current is 100-110A.

[0011] Preferably, in step three, the casting is subjected to post-weld quality inspection, post-weld metallographic inspection, and mechanical property inspection to determine the repair status of the casting.

[0012] Preferably, the process also includes a fourth step: ultrasonic stress relief of the casting.

[0013] Preferably, the process also includes step five, which involves monitoring the use of the casting.

[0014] The beneficial effects of this invention are as follows: In this solution, the welding area is preheated to 280 degrees before welding, which can further remove surface impurities in the welding area, reduce the temperature difference between the welding area and the substrate, reduce the hardened structure generated during the welding process, and reduce the probability of cold cracking from the source.

[0015] Secondly, during hinge repair, the temperature of the weld area drops rapidly to 60℃ after the first root pass weld. This rapid cooling after welding leads to high residual stress in the weld joint. Therefore, this solution employs oxyacetylene heating after the first root pass to locally heat the weld surface, controlling the surface temperature at 400℃, thereby resolving the issue of high residual stress.

[0016] Third, after welding is completed, reheating the welded area to 400℃ can reduce the microhardness of the heat-affected zone, with the highest microhardness being less than 300HV. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a CMT welding repair method applicable to defects in ZG35Cr1Mo castings.

[0018] Figure 2 This is a schematic diagram of the crack depth detection using the potential difference method in step one.

[0019] Figure 3 This is a schematic diagram of the welding groove constructed in step one.

[0020] Figure 4 This is a schematic diagram of the root pass and fill pass welding performed in step two.

[0021] Figure 5 This is a cross-sectional view of the ZG35Cr1Mo casting after repair (defects still exist at this time).

[0022] Figure 6 This is a schematic diagram of the welding bevel in Example 2.

[0023] Figure 7 This is a cross-sectional view of the ZG35Cr1Mo casting after repair (the defect has now been repaired). Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0025] Example 1 The basics are as follows: Figure 1 As shown, a CMT welding repair method for defects in ZG35Cr1Mo castings includes the following steps: Step 1: Before proceeding with the repair, first determine the condition of the casting (including the material composition, metallographic structure, and mechanical properties of the casting). If the casting has any defects, it indicates that the casting has manufacturing defects and the repair of the casting should be abandoned.

[0026] When determining the material composition, metallographic structure, and mechanical properties of a casting, first identify the corresponding testing area. Then, remove surface paint, oil, and impurities from the testing area. Next, use a sanding wheel or flap wheel to polish the surface of the testing area until it is smooth and reveals a metallic luster. The area of ​​the testing area should not be less than 50 cm². 2 Finally, clean and smooth the test area with alcohol or acetone to ensure no impurities are present. After determining the test area, use a mobile full-spectrum direct-reading spectrometer or other in-situ testing instruments to select at least 6 test points within the test area, with each point at least 5 mm apart, to test the material composition of the casting. After testing the material composition, sequentially polish the test area with 120#, 500#, 800#, and 2000# sandpaper, and after each polishing step, mechanically polish the polished area to 1.5 μm or less using diamond polishing paste; then etch the surface with 4% nitric acid alcohol etching solution; finally, observe the metallographic structure of the area using a metallographic microscope. After testing the metallographic structure, conduct in-situ mechanical property testing on the test area using in-situ mechanical property testing equipment. The main principle of in-situ mechanical property testing is as follows: Under the action of an electromechanical load application mechanism, a spherical indenter is vertically pressed into the surface of the casting. Continuous loading and unloading are performed at the same measuring point. The load and displacement of the indentation are measured in real time using displacement and load sensors to obtain the load-displacement test curve of the indentation. Then, the indentation load-displacement test curve is converted into a series of stress and strain data points. The least squares method is then used to fit the constitutive equation of the metallic material to ultimately determine the constitutive relationship and strength properties of the tested material. Simultaneously, at least three points are randomly selected in each testing area for testing to obtain more accurate material hardness, tensile strength, yield strength, and other performance parameters. In this embodiment, there is no restriction on the order of testing material composition, metallographic structure, and mechanical properties; even testing only one or two of these properties is acceptable. The test results should meet the following standards.

[0027] element C Si Mn P S Cr Mo Standard requirements 0.30-0.37 0.30-0.60 0.50-0.80 ≤0.030 ≤0.030 0.80-1.20 0.20-0.30 Table 1 shows the material composition of the hinge. After completing the above tests and confirming that the casting is in a qualified state, defect inspection can proceed. Defect inspection mainly utilizes magnetic particle (MT), penetrant (PT), and ultrasonic (UT) testing methods to comprehensively examine the casting for defects. Special attention should be paid to irregularly shaped areas such as radius corners, shaft hole bosses, and stiffeners, as well as locations of improper welding during installation. When cracks are detected, the potential difference method should be used to determine the crack depth. Figure 2 As shown, the basic principle of the potential difference method is to apply a constant current to both ends of the cracked specimen, so as to generate a constant electric field in the thickness direction of the test piece. By measuring this electric field, real-time data of the crack depth can be obtained.

[0028] After identifying the defects in the casting, the defective areas are ground and cleaned, and a welding bevel is constructed. Specifically, a handheld angle grinder or rotary file is used to grind the defective area layer by layer, avoiding excessive grinding in one go that could affect the workpiece's structure or performance. Simultaneously, the depth of each grinding layer should be strictly controlled, not exceeding 2mm per layer, to ensure material stability and uniformity. After each grinding cycle, non-destructive testing techniques (such as ultrasonic testing, magnetic particle testing, or penetrant testing) should be used to simultaneously check the defect treatment to ensure that the defects have been effectively removed and to prevent residual defects from affecting the casting quality. If the test results show that defects still exist, the same grinding and testing steps must be repeated until the defects are completely eliminated. After defect cleaning is completed, a handheld angle grinder or rotary file is used to prepare the welding bevel in the ground area. The welding bevel is elongated and open-ended, such as... Figure 3 As shown. During the preparation of the weld bevel, the tool should be kept stable, and the grinding force should be controlled to ensure that the bevel shape is uniform, the surface is smooth, and there are no sharp corners. After the weld bevel is prepared, the surface of the bevel should be ground with a sanding wheel or a blade to remove the surface hardening layer generated during the bevel preparation process.

[0029] Step two involves using CMT welding equipment with pure nickel welding wire ERNi-1 to perform the root pass welding on the casting, and then using SMAW equipment with nickel-based welding rod ENi6182 to perform the fill pass welding. Using CMT welding equipment and pure nickel welding wire ERNi-1 for the root pass welding reduces the base metal dilution rate and inhibits the hardening of the fusion zone caused by carbon diffusion in the base metal. Further fill pass welding using SMAW equipment and nickel-based welding rod ENi6182 enhances the joint strength.

[0030] It should be noted that CMT welding equipment can transfer most of the arc heat to the welding wire to form molten droplets. Upon contact with the base metal, the arc is stopped and the welding wire is retracted, allowing the molten droplets to fall onto the base metal. The heat of the droplets melts the base metal, achieving an alternating "cold-hot" process during welding. This method results in an extremely low base metal dilution rate (i.e., the proportion of molten base metal to the total weld metal), with a low content of hardened martensite, leading to high welding efficiency. Furthermore, pure nickel welding wire ERNi-1 and nickel-based welding electrode ENi6182 are the optimal choices after multiple trials. Pure nickel welding wire ERNi-1 and nickel-based welding electrode ENi6182 do not form carbides with carbon, and carbon has very low solubility, preventing the formation of hard and brittle martensite in the weld metal. Pure nickel welding wire ERNi-1 can isolate carbon in the base metal and has good plasticity, greatly reducing the tendency to crack. Subsequently, nickel-based welding electrode ENi6182 was used as a filler layer on top of the pure nickel welding wire ERNi-1. The advantage of this combination method is that, firstly, using pure nickel welding wire ERNi-1 as the underlayer eliminates the influence of the ZG35Cr1Mo base material, resulting in excellent resistance to cold and hot cracking. Secondly, due to the superior mechanical properties of nickel-based welding electrode ENi6182, using it as a filler layer ensures adequate welding quality and the mechanical properties of the repaired area.

[0031] The specific welding repair steps are as follows: S1: Clean the surface of the area to be welded, removing oil and impurities, with acetone or alcohol. S2: Localize the welding area using oxyacetylene heating to maintain a surface temperature of 280℃. S3: Once the temperature reaches the standard, perform the first root pass welding using CMT welding equipment. After slag removal, use oxyacetylene heating to locally heat the weld bead, maintaining a surface temperature of 400℃. Then, perform the second, third, and subsequent root passes sequentially until the root pass is complete. After each pass, slag removal and grinding are performed. S4: Perform the filler pass welding using SMAW welding equipment. After each pass, perform slag removal and grinding. After the filler pass is completed, use oxyacetylene heating to locally heat the weld bead, maintaining a surface temperature of 400℃. Heating the welding area to 400℃ reduces the microhardness, with a maximum microhardness less than 300 HV. When the maximum microhardness of the heat-affected zone exceeds 300 HV, the hardening tendency will increase significantly, and the risk of cracking of the weld joint will increase significantly.

[0032] The specific operation for the root pass welding is as follows: First, at the start of the root pass welding, control the welding torch to initiate an arc at the bottom of the bevel for 3-4 seconds. After initiating the arc, begin the first pass welding. After completing the single pass welding, grind the weld seam at the start and end of the arc, as well as both sides of the weld, to make the surface smooth and free of sharp edges. Use a stainless steel wire brush to clean the weld seam. After cleaning, use oxyacetylene to heat the local welding area until the surface temperature reaches 400℃, and then proceed with the subsequent root pass welding. After the root pass welding is completed, use oxyacetylene heating to locally heat the surface of the weld seam, controlling the surface temperature at 400℃. After heating, remove slag from the weld seam and grind it.

[0033] When using CMT welding equipment for root pass welding, the welding current is 210A-240A. Specifically, the welding current for the first pass is greater than that for the second and third passes, while the welding current for the fourth and fifth passes is less than that for the second and third passes. Specifically, the welding current for the first pass is 240-230A, for the second and third passes it is 230-220A, and for the fourth and fifth passes it is 220-210A. The first pass directly affects the root of the bevel and the blunt edge, requiring a higher heat input (240-230A) to ensure sufficient melting of the base material. As the number of weld layers increases, the overall heat accumulation on the workpiece gradually increases; maintaining a high current can easily lead to overheating of the molten pool. For the second and third weld passes, which serve as transition layers, the current is appropriately reduced to 230-220A to ensure the quality of interlayer fusion and effectively buffer the peak heat input. For the fourth and fifth weld passes, the current is further reduced to 220-210A, taking advantage of the low heat input characteristics of the CMT process to precisely control the volume of the molten pool.

[0034] When using CMT welding equipment for root pass welding, the arc voltage of the CMT welding equipment is 12-14V, and the arc voltage of the first to third weld passes is greater than that of the fourth and fifth weld passes. Specifically, the arc voltage of the first to third weld passes is 14-13V, and the arc voltage of the fourth and fifth weld passes is 12-13V. The higher arc voltage (14-13V) used in the first to third weld passes allows the arc cone angle to be appropriately widened, expanding the heat source's coverage of the bevel sidewalls and root, ensuring full fusion of the sidewalls and uniform penetration of the root, avoiding incomplete penetration or groove defects. The voltage is reduced to 12-13V for the fourth and fifth weld passes, making the arc more concentrated and the heat-affected zone narrower. This effectively prevents an excessively wide molten pool due to early heat accumulation, significantly improving the surface smoothness of the root pass before the cap weld.

[0035] When using CMT welding equipment for root pass welding, the shielding gas is 100% Ar (99.9% purity; Ar has low reactivity and does not react with other gases in the air), with a flow rate of 15 L / min and a wire feed speed of 7-8 m / min. The wire extension should be controlled to 15 mm. A longer extension can lead to insufficient gas shielding; a shorter extension makes it difficult to observe the weld pool.

[0036] When using CMT welding equipment for root pass welding, oscillation welding is required, with an oscillation amplitude of ≤20mm. During the welding process, the welding heat input should be controlled to ≤30kJ / cm, and the welding speed should be ≥50mm / min. After each pass, the arc initiation, arc termination, and both sides of the weld should be ground. The ground surface should be smooth, without sharp edges. Along the weld direction, the overall surface should be free of burrs, pits, and welding defects after grinding. The weld should also be cleaned.

[0037] The specific operation for filler welding is as follows: First, control the arc ignition of the welding torch between layers at the beginning, with an arc ignition time of 3-4 seconds. After arc ignition, begin the first welding pass. After completing the single-pass welding, grind the weld seam during arc ignition and termination, as well as both sides of the weld bead, to make the surface smooth and free of sharp edges. Clean the weld bead using a stainless steel wire brush. After cleaning, use oxyacetylene to heat the local welding area until the surface temperature reaches 150-300℃, then proceed with the second welding pass. After completing the interlayer welding, use oxyacetylene heating to locally heat the surface of the weld bead, controlling the surface temperature at 400℃. After heating, remove slag from the weld bead and grind it. After the filler welding is completed, the repaired area should be 2-3mm higher than the surface of the ZG35Cr1Mo casting. Finally, use machining equipment to grind and correct the surface of the repaired area of ​​the casting, completing the defect repair of the casting.

[0038] It should be noted that after the first root pass welding, the temperature will drop to 60°C very quickly. The rapid cooling rate after welding will result in large residual stress. Therefore, in this embodiment, after the first root pass welding is completed, slag removal and grinding are performed. Oxyacetylene heating is used to locally heat the surface of the weld, and the surface temperature is controlled at 400°C to avoid the problem of large residual stress caused by the temperature drop after welding.

[0039] Step 3: Perform post-weld inspection on the casting to determine its repair status.

[0040] After welding repair, the welded area is first inspected using methods such as visual inspection, magnetic particle (MT), penetrant (PT), and ultrasonic testing (UT) to ensure that the weld surface is free of defects such as undercut, weld beads, weld discontinuities, porosity, and cracks. If any quality defects are found, secondary repair or abandonment of the repair process will be considered.

[0041] After quality inspection, metallographic examination was performed on the welded area. Metallographic examination required a suitable area after welding. First, the area to be inspected was progressively polished using 120#, 500#, 800#, and 2000# sandpaper. After each polishing stage, diamond polishing compound was used to mechanically polish the area to 1.5μm or less. Then, the surface was etched with a 4% nitric acid alcohol etching solution. Finally, the metallographic structure of the welded area was observed using a metallographic microscope. Under the thermal cycling of welding, the microstructure of the base material near the fusion line underwent significant changes. At high magnification, acicular ferrite structures could be observed in localized areas. The test results showed that the width of the heat-affected zone in the CMT weld repair area was approximately 1mm.

[0042] After metallographic testing, mechanical property testing is performed. This requires obtaining the mechanical properties of the repaired welded area using an indentation method at a suitable location after welding. Under the action of welding thermal cycling, the hardness and strength of the heat-affected zone of the weld should both be slightly increased compared to the pre-weld test, achieving the purpose of weld repair.

[0043] Step 4: Perform ultrasonic stress relief on the repaired casting.

[0044] After completing the repair and inspection, the fusion line position was clearly identified in the repaired area where the weld had been ground smooth. Using an ultrasonic stress relief device, the impact head was aimed at the cladding metal 2-3 mm from the fusion line and repeatedly impacted back and forth. The impact head remained perpendicular to the weld surface throughout the impact process, and the indentation coverage after impact was ≥100%, with an indentation depth of 0.3-0.5 mm. Finally, the blind hole method was used to detect residual stress in the weld area, comparing the changes in residual stress before and after ultrasonic stress relief.

[0045] Step 5: Monitoring the use of the repaired casting.

[0046] To determine whether the casting is usable, post-weld monitoring should be conducted at least once within one month after welding. The monitoring should include magnetic particle (MT), penetrant (PT), and ultrasonic (UT) non-destructive testing of each welded area. If available, acoustic equipment can be used to monitor the welded area in real time.

[0047] Example 2 The difference between this embodiment and Embodiment 1 is that, in Embodiment 1, during the second and third root pass welding, the molten pool is prone to flowing downwards, leading to localized incomplete fusion defects, as shown in the following description. Figure 5 As shown.

[0048] Therefore, to solve the above problems, in this embodiment, during the second and third root pass welding operations, the distance between the second and third root pass welding and the first root pass welding is reduced, thereby increasing the welding lap ratio; simultaneously, the angle between the two side walls of the welding groove is set to 90°, such as... Figure 6 As shown, the grinding thickness was increased to address the issue of excessive pure nickel underlayer thickness at the weld joint. Through these measures, it was found in practice that the problem of localized incomplete fusion defects was resolved. The cross-sectional view of the ZG35Cr1Mo casting after the solution is shown below. Figure 7 As shown.

[0049] Comparative Example 1 The difference between this comparative example and Example 1 is that, in this example, the shielding gas for the CMT welding equipment during welding repair is 100% Ar, and the gas flow rate is 21 L / min. Other repair steps remain unchanged to complete the welding repair. Afterwards... Comparative Example 2 The difference between this comparative example and Example 1 is that, in this example, the shielding gas of the CMT welding equipment is 100% Ar and the gas flow rate is 14 L / min, while the other repair steps remain unchanged to complete the welding repair.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that, in this example, the shielding gas of the CMT welding equipment is 100% Ar and the gas flow rate is 20 L / min, while the other repair steps remain unchanged to complete the welding repair.

[0051] Welding repairs of hinges were performed using the repair methods of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively, and the following comparative results were obtained: Shielding gas flow rate of CMT welding equipment Welding status Example 1 15L / min No abnormalities were found. Comparative Example 1 21L / min Localized pores appear Comparative Example 2 14L / min Localized pores appear Comparative Example 3 20L / min No abnormalities were found. By comparing the repair results of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that when the shielding gas flow rate of the CMT welding equipment is between 15 and 20 L / min, welding can proceed normally without causing adverse effects. When the shielding gas flow rate of the CMT welding equipment is greater than 20 L / min, the gas flow rate is too fast, causing heat loss due to the gas, which in turn causes the temperature of the weld pool to drop, affecting the welding state. When the shielding gas flow rate of the CMT welding equipment is less than 15 L / min, the gas flow rate is too slow, and the shielding gas cannot effectively form a gas protective layer, allowing external air to easily enter the welding area, thus affecting the welding effect.

[0052] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A CMT welding repair method for defects in ZG35Cr1Mo castings, characterized in that: Includes the following steps: Step 1: Grind and clean the defective parts of the casting and construct the welding bevel; Step 2: Before welding repair, use oxyacetylene to locally heat the welding area so that the surface temperature is 280℃. The casting was subjected to root pass welding using CMT welding equipment and pure nickel welding wire ERNi-1. During the root pass welding process, after the first root pass welding, the weld bead was locally heated with oxyacetylene to bring the surface temperature to 400°C. After the root pass welding was completed, the casting was subjected to fill pass welding using SMAW equipment and nickel-based welding rod ENi6182. After the fill pass welding was completed, the weld bead was locally heated with oxyacetylene to bring the surface temperature to 400°C. Step 3: Perform post-weld inspection on the casting to determine its repair status.

2. The CMT welding repair method according to claim 1, characterized in that: In step two, when using CMT welding equipment for root pass welding, the welding current is 210A-240A, and the welding current of the first weld pass is greater than that of the second and third weld passes, while the welding current of the fourth and fifth weld passes is less than that of the second and third weld passes. In step two, when using CMT welding equipment for root pass welding, the arc voltage is 12-14V, and the arc voltage of the first to third weld passes is greater than that of the fourth and fifth weld passes. In step two, when using CMT welding equipment for root pass welding, the wire feed speed is 7-8 m / min; In step two, when using CMT welding equipment for root pass welding, the shielding gas is 100% Ar with a flow rate of 15-20 L / min.

3. The CMT welding repair method according to claim 1, characterized in that: In step two, when performing the root pass welding with the CMT welding equipment, it is necessary to oscillate during welding with an oscillation amplitude of ≤20mm. During the welding process, the welding heat input should be controlled to be ≤30kJ / cm and the welding speed should be ≥50mm / min. After each weld, the arc starting point, arc ending point, and both sides of the weld bead are ground. The ground surface is smooth and without sharp edges. Along the weld direction, the overall surface is free of burrs, pits, and poor welding areas after grinding. The weld bead is also cleaned.

4. The CMT welding repair method according to claim 1, characterized in that: In step one, the angle between the two side walls of the welding bevel is 90 degrees; In step two, when using CMT welding equipment to perform the root pass welding, the distance between the second and third weld passes and the first weld pass is reduced, thereby increasing the welding overlap rate.

5. The CMT welding repair method according to claim 1, characterized in that: In step two, when using SMAW welding equipment for filler welding, the welding current is 100-110A.

6. The CMT welding repair method according to claim 1, characterized in that: In step three, the casting is subjected to post-weld quality inspection, post-weld metallographic inspection, and mechanical property inspection to determine the repair status of the casting.

7. The CMT welding repair method according to any one of claims 1 to 6, characterized in that: It also includes step four, which involves ultrasonic stress relief of the casting.

8. The CMT welding repair method according to claim 7, characterized in that: It also includes step five, which involves monitoring the use of the castings.

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