A SMAW welding repair method suitable for ZG35Cr1Mo casting defects

Abstract

The present application belongs to the field of welding, and particularly relates to a SMAW 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 SMAW welding equipment and configuring nickel-based electrode ENi6182 to weld and repair the defect part of the casting, after each welding, using flame to heat the welding area to 450 DEG C, and keeping the heating state to hammer, hammering on both sides of the welding bead once; step three, detecting the casting after welding to determine the repair state of the casting. The present application provides a SMAW welding repair method suitable for ZG35Cr1Mo casting defects, and the purpose is to solve the defects of ZG35Cr1Mo casting repair in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of welding repair, specifically relating to a SMAW welding repair method 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 method for repairing carbon quenched and tempered steel structures without preheating or post-weld heat treatment (CN121223225A), which uses SMAW welding combined with hammering to repair ZG35Cr1Mo castings. 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 SMAW 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 SMAW welding repair method suitable 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 defective parts of the casting were repaired by welding using SMAW welding equipment and nickel-based welding rod ENi6182. After each weld and cleaning of the slag, before grinding the weld, the weld was heated to 450°C with a flame and hammered while keeping the flame heated. The weld was hammered once on each side. After the filler weld is completed, the surface of the weld bead is locally heated by oxyacetylene heating, and the surface temperature is 400℃. Step 3: Perform post-weld inspection on the casting to determine its repair status.

[0007] Preferably, in step two, the root pass and fill pass are performed using SMAW welding equipment, and the hammering force during the root pass is less than that during the fill pass.

[0008] Preferably, in step two, when using SMAW welding equipment for welding repair, the welding current is 100-120A, and the welding current of the first weld pass is greater than the welding current of subsequent weld passes.

[0009] Preferably, the welding process involves oscillating the welding rod, with the oscillation amplitude not exceeding 5 times the diameter of the welding rod. When welding multiple layers and multiple passes, the arc initiation and arc termination of the weld should be staggered, and the arc termination should fill the crater. During the welding process, the welding heat input should be controlled to ≤30kJ / cm, and the welding speed should be ≥50mm / min.

[0010] Preferably, after the weld bead is ground, the weld area is baked with oxyacetylene between passes at a temperature of 150~300℃. For welding passes that come into contact with the base material, the temperature at the arc initiation position before welding should not be less than 150℃, and for other passes, the interpass temperature should be controlled to be ≤150℃.

[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 step five, which involves ultrasonic stress relief of the casting.

[0013] Preferably, the process also includes a sixth step: monitoring the use of the casting.

[0014] The beneficial effects of the present invention are as follows: The present invention completes the welding repair by using a process of local preheating combined with heating and hammering of each weld pass, in conjunction with ENi6182 nickel-based welding rods; at the same time, by controlling the temperature during welding and the timing of hammering, the mechanical properties and structural stability of the repaired area can be improved, thereby solving the shortcomings of the prior art. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a SMAW welding repair method applicable to defects in ZG35Cr1Mo castings.

[0016] Figure 2 This is a schematic diagram of the crack depth detection using the potential difference method in step one.

[0017] Figure 3 This is a schematic diagram of the welding bevel constructed in step two.

[0018] Figure 4 This is a schematic diagram of the root pass and fill pass welding performed in step three.

[0019] Figure 5 The metallographic structure and microhardness diagrams of the welded areas in Comparative Example 1 and Comparative Example 2 are shown.

[0020] Figure 6 The image shows the metallographic structure and microhardness of the welded area in Example 1. Detailed Implementation

[0021] 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.

[0022] Example 1 The basics are as follows: Figure 1 As shown, a SMAW 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.

[0023] 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. 2Finally, 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.

[0024] 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.

[0025] 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.

[0026] Step 2: Before welding repair, the local welding area at the welding position is heated with oxyacetylene to control the surface temperature at 280℃ before welding repair operation.

[0027] During welding repair, SMAW welding equipment and nickel-based welding rod ENi6182 are used to weld and repair the defective parts of the casting. After each weld and cleaning of the slag, before grinding the weld, the weld is heated to 450°C with a flame and then hammered. During hammering, the weld is hammered once on each side.

[0028] When performing welding repairs using SMAW welding equipment, the welding current is 100-120A, with the welding current for the first weld pass being greater than that for subsequent weld passes. Specifically, the welding current for the first weld pass is set to 110-120A, and the welding current for subsequent weld passes is set to 100-110A. By setting the welding current for the first weld pass to 110-120A, a critical heat input sufficient to overcome the oxide film and thermal conductivity resistance of the base material is provided for the ENi6182 nickel-based molten pool; subsequent weld passes are then welded at a welding current of 100-110A, which matches the hammering temperature of 450°C.

[0029] The following describes the specific repair procedures during welding: S1: Clean the surface of the area to be welded, removing oil, impurities, etc., with acetone or alcohol. S2: Heat the localized welding area to 280 degrees Celsius using oxyacetylene. S3: Once the required temperature is reached, turn on the SMAW welding equipment to perform the welding repair. During the welding repair, first perform the root pass, then the fill pass (e.g., ...). Figure 4(As shown). After each weld and slag removal, before grinding the weld bead, heat the weld area to 450°C with a flame and then hammer it, hammering once on each side of the weld bead. After the filler weld is completed, use oxyacetylene heating to locally heat the surface of the weld bead, controlling the surface temperature at 400°C. This localized heating method reduces the hardness of the hardened structure in the heat-affected zone, thereby reducing the tendency for cold cracking.

[0030] In this embodiment, during welding, the welding process requires oscillation, and the oscillation amplitude should not exceed 5 times the diameter of the welding rod; when welding multiple layers and multiple passes, the arc start and arc end of the weld should be staggered, and the arc end should fill the arc crater; during the welding process, the welding line energy should be controlled to ≤30kJ / cm, and the welding speed should be ≥50mm / min.

[0031] In this embodiment, after each weld pass, the weld slag is cleaned, and the weld is heated to 450°C with a flame. After heating, both sides of the weld bead are hammered once with a welding hammer at a frequency of 2 times / second, and the hammer marks need to be continuous and uniform. After hammering, the arc start and end points of the previous weld are ground to ensure that the surface is free of sharp edges, and the interlayer cleaning is carefully performed. The root pass and fill pass are performed using SMAW welding equipment. The hammering force during the root pass should be less than that during the fill pass. The core purpose of using a smaller hammering force during the root pass is to protect the fusion zone and avoid excessive impact that could induce microcracks or interface delamination. During the fill pass, the weld bead is far from the base metal interface, and the accumulation of multiple layers increases the overall plasticity reserve. At this time, increasing the hammering force can further enhance the stress reduction effect.

[0032] It should be noted that the weld temperature drops rapidly after each weld and oxy-acetylene heating, making it impossible to achieve the desired 450℃ hammering effect. Therefore, the flame temperature must be maintained at 450℃ throughout the hammering process to ensure better repair results. 450℃ is the optimal solution after testing, as this temperature is located at the bainitic phase transformation temperature. Performing continuous, uniform hammering at this temperature (2 blows per second) allows the weld metal to undergo sufficient mechanical deformation in its optimal plastic state, effectively releasing welding tensile stress. Furthermore, it avoids the risks of excessively high temperatures leading to coarsening of nickel-based alloy grains or excessively low temperatures causing work hardening cracking.

[0033] After grinding the weld bead, to further eliminate moisture on the weld surface, oxyacetylene is used to bake the welding area between passes. The baking temperature is controlled between 150 and 300°C. The pre-weld temperature at the arc-starting position of the weld pass in contact with the base metal should not be less than 150°C, and the inter-pass temperature is controlled to be ≤150°C for the remaining passes. The pre-weld temperature at the arc-starting position of the weld pass in contact with the base metal should not be less than 150°C. This setting slows down the cooling rate of the arc-starting molten pool, inhibiting martensitic transformation; it also reduces the temperature gradient between the base metal and the weld, weakening the peak thermal stress. Controlling the inter-pass temperature to ≤150°C ensures that the weld melt has fully solidified and completed phase transformation before the next weld pass, preventing the liquid film from cracking under thermal cycling; it also limits the heat accumulation effect, preventing excessive precipitation of brittle phases such as δ-phase or Laves phase at grain boundaries.

[0034] Step 4: Perform post-weld inspection on the casting to determine its repair status.

[0035] 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.

[0036] After quality inspection, post-weld metallographic examination is performed. Metallographic examination requires a suitable area after welding. First, the area to be inspected is progressively polished using 120#, 500#, 800#, and 2000# sandpaper. After each polishing stage, diamond polishing compound is used to mechanically polish the area to 1.5μm or less. Then, the surface is etched with a 4% nitric acid alcohol etching solution. Finally, the metallographic structure of the welded area is observed using a metallographic microscope. Under the action of welding thermal cycling, the microstructure of the base material near the fusion line undergoes significant changes. At high magnification, acicular ferrite structures can be observed in localized areas. The microstructure morphology of the fusion zone of the welded casting is shown below. Figure 6 As shown.

[0037] 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.

[0038] Step 5: Perform ultrasonic stress relief on the repaired casting.

[0039] 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.

[0040] Step Six: Monitoring the Use of Repaired Castings.

[0041] 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.

[0042] Comparative Example 1 The difference between this comparative example and Example 1 is that, in this comparative example, after the filler weld is completed, an oxyacetylene heating method is used to locally heat the surface of the weld, and the surface temperature is controlled at 300°C.

[0043] The metallographic structure was then observed using an optical microscope, and the microhardness of the heat-affected zone was tested using a microhardness tester.

[0044] Comparative Example 2 The difference between this comparative example and Example 1 is that, in this comparative example, after the filler weld is completed, an oxyacetylene heating method is used to locally heat the surface of the weld, and the surface temperature is controlled at 500°C.

[0045] The metallographic structure was then observed using an optical microscope, and the microhardness of the heat-affected zone was tested using a microhardness tester.

[0046] By comparing Example 1 (e.g.) Figure 6 Comparative Example 1 and Comparative Example 2 (e.g.) Figure 5 The microhardness test results clearly show that heating the welded area to 400℃ can reduce the microhardness, with the highest microhardness being less than 300HV. When the highest microhardness of the heat-affected zone exceeds 300HV, the hardening tendency increases significantly, and the risk of cracking in the weld joint increases significantly.

[0047] Comparative Example 3 The difference between this comparative example and Example 1 is that in this example, the sample is heated to 400°C and hammered, while other steps remain unchanged. The repair effect at the welded area is then inspected.

[0048] Comparative Example 4 The difference between this comparative example and Example 1 is that in this example, the sample is heated to 500°C and hammered, while other steps remain unchanged. The repair effect at the welded area is then inspected.

[0049] Welding repairs of hinges were performed using the repair methods of Example 1, Comparative Example 3, and Comparative Example 4, respectively, and the following comparative results were obtained: Temperature during hammering Load status Comparative Example 3 400℃ Fine cracks appeared under a 70-ton load. Comparative Example 4 500℃ Fine cracks appeared under a 70-ton load. Example 1 450℃ No abnormalities were observed under a 70-ton load. By comparing the repair methods of Example 1, Comparative Example 3, and Comparative Example 4, and performing hammering at 450°C, the repaired casting joints showed better mechanical properties and stronger load-bearing capacity, enabling them to be used stably for a long time under rated working load, further verifying the rationality of the 450°C hammering parameter in this repair method.

[0050] 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 SMAW 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 defective parts of the casting were repaired by welding using SMAW welding equipment and nickel-based welding rod ENi6182. After each weld and cleaning of the slag, before grinding the weld, the weld was heated to 450°C with a flame and hammered while keeping the flame heated. The weld was hammered once on each side. After the filler weld is completed, the surface of the weld bead is locally heated by oxyacetylene heating, and the surface temperature is 400℃. Step 3: Perform post-weld inspection on the casting to determine its repair status.

2. The SMAW welding repair method according to claim 1, characterized in that: In step two, the root pass and fill pass are performed using SMAW welding equipment. The hammering force during the root pass is less than that during the fill pass.

3. The SMAW welding repair method according to claim 1, characterized in that: In step two, when using SMAW welding equipment for welding repair, the welding current is 100-120A, and the welding current of the first weld pass is greater than the welding current of subsequent weld passes.

4. The SMAW welding repair method according to claim 1, characterized in that: During welding, the welding should be performed by oscillation, with the oscillation amplitude not exceeding 5 times the diameter of the welding rod. When welding multiple layers and multiple passes, the arc start and arc end of the weld should be staggered, and the arc crater should be filled when the arc ends. During the welding process, the welding heat input should be controlled to ≤30kJ / cm, and the welding speed should be ≥50mm / min.

5. The SMAW welding repair method according to claim 4, characterized in that: After the weld beads are ground, the welding area is baked with oxyacetylene between passes at a temperature of 150~300℃. For welding passes that come into contact with the base material, the temperature at the arc initiation position before welding should not be less than 150℃, and for other passes, the interpass temperature should be controlled to be ≤150℃.

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

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

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