Single pass submerged arc welding method for high penetration fillet weld

Abstract

This invention discloses a single-pass submerged arc welding method for high-penetration fillet welds, comprising: cleaning the area to be welded before welding without beveling; rotating the submerged arc welding jig to a first predetermined angle with the horizontal plane, and placing the workpiece panel on the jig to achieve a near-ship-shaped welding position; adjusting the submerged arc welding torch vertically downwards, first aligning the submerged arc welding wire with the right-angle vertex of the T-shaped fillet weld, and then setting the wire offset to a second predetermined range; setting the submerged arc welding process parameters, and using single-pass submerged arc welding to weld the T-shaped fillet weld. This invention solves the welding problems of insufficient and unstable penetration depth in T-shaped fillet submerged arc welds without beveling, and can obtain reliable high-penetration welds; the submerged arc weld has a uniform and aesthetically pleasing appearance, eliminates the beveling process and associated costs, and significantly improves welding efficiency. This invention can be widely applied to the welding and fabrication of steel bridge components such as steel plate beam I-beams and steel tower medium-thick plate rib units.

Description

Technical Field

[0001] This invention relates to welding methods, specifically to a single-pass submerged arc welding method for high penetration fillet welds. Background Technology

[0002] As the main load-bearing component of steel plate girder bridges, the welding quality of longitudinal beams is particularly critical. When the longitudinal beam span is long or the stress is complex, it is often necessary to improve the welding requirements of the main welds (welds between the web and the top and bottom plates of the longitudinal beam), upgrading from ordinary non-grooved fillet welds to deep penetration groove welds with grooves, or even full penetration fillet welds. However, considering the increased cost of the groove opening process and the low welding efficiency and difficulty in ensuring the post-weld appearance of gas-shielded welding grooves, single-pass submerged arc welding without grooves is generally used instead during steel beam fabrication. This effectively utilizes the large heat input characteristic of submerged arc welding to achieve an equivalent larger penetration depth. At the same time, UT ultrasonic testing is used during the fabrication process to ensure the penetration depth requirements or effective weld thickness requirements of the original design groove.

[0003] When welding the main welds of longitudinal beams of steel plate girders using single-pass submerged arc welding, the components are generally placed on a ship-shaped jig. The conventional process involves setting the jig angle to 45°, centering the submerged arc welding torch at the right-angle vertex of the weld joint, using increased welding current and voltage, and reducing welding speed to achieve the designed penetration depth. However, this often results in an excessively large weld bead size after welding, while the internal penetration depth fails to meet the requirements. Further increasing the welding parameters exacerbates joint deformation, causing the penetration depth to fluctuate unstablely, failing to meet the designed high penetration depth requirements (generally, a single-sided requirement of ≥6mm, but considering allowance and first-pass inspection pass rate, ≥7mm is required in actual fabrication).

[0004] Therefore, how to perform single-pass submerged arc welding to meet the high penetration requirements of fillet welds and maintain the stability of penetration depth is an urgent problem to be solved. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a single-pass submerged arc welding method for high penetration fillet welds.

[0006] Technical solution: The present invention provides a single-pass submerged arc welding method for high penetration fillet welds, comprising the following steps:

[0007] (1) Do not beveling; clean the area to be welded before welding.

[0008] (2) Rotate the submerged arc welding jig until the angle α with the horizontal plane is within the first set range, and place the workpiece panel on the jig so that the welding position is close to the ship shape.

[0009] (3) Adjust the submerged arc welding torch so that the torch is vertically downward. First, align the submerged arc welding wire with the right-angle vertex of the T-shaped fillet weld, and then set the offset amount b of the welding wire to be within the second set range.

[0010] (4) Set the submerged arc welding process parameters and use single-pass submerged arc welding to weld T-shaped fillet welds to obtain high penetration fillet welds.

[0011] Furthermore, in step (1), if the joint plate thickness exceeds a certain value, preheating treatment is required before welding. For steel plates on both sides of the welded joint with a material not exceeding Q370 grade, the preheating temperature should be ≥50℃ when the plate thickness is ≥50mm. For steel plates on both sides of the welded joint with a material not lower than Q420 grade, the preheating temperature should be ≥50℃ when the plate thickness is >28mm.

[0012] Furthermore, in steps (2) and (3), when the rotation angle of the submerged arc welding jig is limited (e.g., the rotation angle of the hydraulic rotating jig for plate rib unit does not exceed 45°), the angle compensation is performed by tilting the welding gun.

[0013] Further, first rotate the submerged arc welding jig to an angle α1 with the horizontal plane. After the workpiece panel is placed on the jig, adjust and rotate the submerged arc welding torch clockwise so that it intersects the vertical line at an angle α2, and the center of the welding wire cross section is aligned with the right-angle vertex of the T-shaped fillet weld. The jig tilt angle α1 + welding torch tilt angle α2 = normal jig tilt angle α. Then set the off-center amount b of the welding wire.

[0014] Furthermore, in step (2), the first setting range is 48° to 58°.

[0015] Furthermore, in step (3), the second setting range is 3.5 to 5 mm.

[0016] Furthermore, in step (3), the offset of the welding wire is set by adjusting the horizontal scale of the welding torch to offset the welding wire away from the panel side, so as to ensure that the axis of the welding torch is parallel to the initial centering line after offset.

[0017] Further, in step (4), the submerged arc welding process parameters are: welding current of 740-800A, welding voltage of 28-32V, welding speed of 260-300mm / min, power supply polarity of DC reverse connection, dry extension of 28-35mm, and heat input of 41.4-59.1KJ / cm.

[0018] This invention ensures that the actual usage parameters fall within the above-mentioned specified range. The greater the jig inclination angle, the greater the off-center amount, the greater the welding current, and the smaller the welding speed, the greater the penetration depth of the fillet weld obtained after welding.

[0019] Invention Principle: Compared with existing technologies, the main innovation of this invention lies in the setting of the submerged arc welding fixture inclination angle and the wire offset, which solves the welding problem of insufficient and unstable penetration depth in T-shaped corner submerged arc welds without beveling. Through experimental welding, it was found that under conventional process parameters, T-shaped corner submerged arc welds exhibit large weld leg size, small and unstable internal penetration depth. After experimentation and research on the macroscopic cross-sectional characteristics of welds with greater penetration depth, targeted optimization was performed on the fixture inclination angle and offset factors. Post-weld formation was observed and compared to determine the required key process parameter configuration. Under these process parameters and appropriate welding parameters, the obtained submerged arc welds exhibit uniform and aesthetically pleasing appearance, high internal penetration depth, and good stability.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0021] (1) The present invention uses submerged arc welding to weld T-shaped fillet welds. No beveling is required before welding, saving the beveling process and cost; the weld has a uniform and beautiful appearance after welding.

[0022] (2) This invention solves the welding problem of insufficient and unstable penetration depth of T-shaped submerged arc welds without beveling. While obtaining high penetration depth submerged arc welds, it can effectively ensure the first-time flaw detection pass rate of the corresponding weld penetration depth.

[0023] (3) The welding method of the present invention can meet the design requirements of high penetration depth with only single-pass submerged arc welding, which can greatly improve the welding efficiency of similar joint types such as the main weld of steel plate beam and the rib unit of steel tower. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing the key process parameters for submerged arc welding under a conventional jig.

[0025] Figure 2 This is a schematic diagram showing the key process parameters for submerged arc welding under a restricted jig;

[0026] Figure 3 These are schematic diagrams of the macroscopic cross-sectional penetration depth of the weld in Examples 1 and 2;

[0027] Figure 4 This is a schematic diagram of the weld penetration depth in the macroscopic cross-section of Example 3;

[0028] Figure 5 This is a schematic diagram of the macroscopic cross-sectional penetration depth of the weld in Comparative Examples 1 and 2. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Example 1: The chemical composition of the Q420qD bridge structural steel used in this example is shown in Table 1, and the mechanical properties are shown in Table 2.

[0031] Table 1 Chemical composition of Q420qD bridge structural steel (t32) base material

[0032]

[0033] Table 2 Mechanical properties of Q420qD bridge structural steel (t32) base material

[0034]

[0035] In this embodiment, the test steel plate to be welded is 32mm thick and has dimensions of 32×200×800mm. The joint type is a T-shaped fillet weld. The welding material used is SUG35, the diameter of the submerged arc welding wire is Φ5.0mm, and the submerged arc welding flux is SAFB1 (SJ101q).

[0036] The chemical composition of the SUG35 (Φ5.0) submerged arc welding wire core is shown in Table 3, and the mechanical properties of the cladding metal are shown in Table 4. The chemical composition of the SAFB1 (SJ101q) submerged arc welding flux is shown in Table 5, and the mechanical properties of the cladding metal are shown in Table 6.

[0037] Table 3 Chemical composition of SUG35 (Φ5.0) submerged arc welding wire core

[0038]

[0039] Table 4 Mechanical properties of cladding metal from SUG35 (Φ5.0) submerged arc welding wire

[0040]

[0041] Table 5 Chemical composition of SAFB1 (SJ101q) submerged arc welding flux

[0042]

[0043] Table 6 Mechanical properties of cladding metal in combination with SAFB1(SJ101q) submerged arc welding flux and submerged arc welding wire

[0044]

[0045] A single-pass submerged arc welding method for high penetration fillet welds, comprising the following steps:

[0046] (1) Do not beveling. Clean the area to be welded before welding and preheat the welding joint area (more than 100mm away from each side of the joint) to not less than 50℃.

[0047] (2) Rotate the submerged arc welding jig to an angle α of 58° with the horizontal plane, and place the test piece panel on the jig so that the welding position is close to the ship shape;

[0048] (3) Adjust the submerged arc welding torch so that it is vertically downward. First, align the submerged arc welding wire with the right-angle vertex of the T-shaped fillet weld. Then, adjust the horizontal scale of the welding torch to move the welding wire away from the panel. Set the offset of the welding wire, b, to 5mm (e.g., Figure 1 (as shown)

[0049] (4) Set the submerged arc welding process parameters as shown in Table 7, and use single-pass submerged arc welding to weld T-shaped fillet welds.

[0050] The mechanical properties of the welded joints are shown in Table 9. The macroscopic cross-sectional acid etching photographs of the weld after welding (see...) Figure 3 (Right side weld), the penetration depth of the T-shaped fillet weld can be measured to be 8.6 mm, and the effective weld thickness is 14.7 mm.

[0051] Table 7 Welding process parameters for Example 1

[0052]

[0053] Example 2: Example 2 and Example 1 were fabricated by welding on the same test piece. The main difference is that in Example 1, the weld was a fillet weld on the right side of the joint of the test piece (see Example 1). Figure 3 (Right side), the jig used is in a conventional state; the fillet weld on the left side of the joint of the test piece in Example 2 (see Figure 3 (Left side), the jig used is in a restricted small tilt angle state, and the amount of welding wire off-center varies. Welding is performed according to the following steps:

[0054] (1) Do not beveling. Clean the area to be welded before welding and preheat the welding joint area (more than 100mm away from each side of the joint) to not less than 50℃.

[0055] (2) Rotate the submerged arc welding jig until the angle α1 with the horizontal plane is 45° (e.g., Figure 2 (As shown), and place the test piece panel on the jig so that the welding position is close to the ship's shape;

[0056] (3) Adjust and rotate the submerged arc welding torch clockwise so that the angle α2 between it and the vertical line is 7° (e.g., Figure 2 As shown), the center of the welding wire cross section is aligned with the right angle vertex of the T-shaped fillet weld. Then, adjust the horizontal scale of the welding gun to offset the welding wire away from the panel (ensuring that the welding gun axis is parallel to the initial centering line after offset). Set the offset amount b of the welding wire to 4mm.

[0057] (4) Set the submerged arc welding process parameters as shown in Table 8, and use single-pass submerged arc welding to weld T-shaped fillet welds.

[0058] The mechanical properties of the welded joints are shown in Table 9. The macroscopic cross-sectional acid etching photographs of the weld after welding (see...) Figure 3(Left weld bead) The penetration depth of the T-shaped fillet weld can be measured to be 7.7 mm, and the effective weld thickness is 14.4 mm.

[0059] Table 8 Welding process parameters for Example 2

[0060]

[0061] Table 9 Mechanical properties of welded joints in Examples 1 and 2

[0062]

[0063] Example 3: Based on Example 1, the difference is that the test steel plate material is Q500qD, the welding material is SUG, the diameter of the submerged arc welding wire is 5.0mm, the submerged arc welding flux is SAFB1 (SJ105q); the jig tilt angle is 48°, the welding torch offset b is 3.5mm, and the welding process parameters used are shown in Table 10.

[0064] Table 10 Welding process parameters for Example 3

[0065]

[0066] The mechanical properties of the welded joints are shown in Table 11. The macroscopic cross-sectional acid-etched photographs of the weld after welding (see...) Figure 4 (Left weld bead) The penetration depth of the T-shaped fillet weld can be measured to be 7.4 mm, and the effective weld thickness is 14.2 mm.

[0067] Table 11 Mechanical properties of welded joints in Example 3

[0068]

[0069] Comparative Example 1: Based on Example 1, the difference is that the jig tilt angle is 45°, the welding torch offset b is 0.5mm, and the welding process parameters are shown in Table 12.

[0070] Because the optimal jig angle and offset were not considered, the acid etching photographs of the macroscopic cross-section of the weld after welding (see...) Figure 5 (Right side weld) The weld leg size of the T-shaped fillet weld is relatively large, reaching 15mm; while the penetration depth is relatively small, only 5.4mm was measured.

[0071] Table 12 Welding process parameters for Comparative Example 1

[0072]

[0073] Comparative Example 2: The test specimen used in Comparative Example 2 is the same as that in Comparative Example 1, the difference being that the right side of the joint of the test specimen in Comparative Example 1 is fitted with a fillet weld (see Comparative Example 1). Figure 5 (Right side), the fillet weld on the left side of the joint of the test piece in Comparative Example 2 (see right side). Figure 5 (Left side). Welding process parameters are shown in Table 13.

[0074] Comparative Example 2 also did not consider setting the optimal jig tilt angle and offset. Unlike Comparative Example 1, the welding current and voltage for submerged arc welding were increased. This is evident from the macroscopic cross-sectional acid etching photographs of the weld after welding (see...). Figure 5 (Left side weld) The weld leg size of the T-shaped fillet weld is still too large, with a height of 16mm and a width of 14mm; although the penetration depth has increased slightly, it still does not meet the requirement of 7mm, and is only measured at 6.2mm.

[0075] Table 13 Welding process parameters for Comparative Example 2

[0076]

[0077] Comparative Examples 1 and 2 show that, without changing the inclination angle and offset of the T-shaped fillet weld jig, simply changing the welding process parameters has little effect on the weld penetration depth, and fails to meet the high design requirements. By changing the inclination angle and offset of the T-shaped fillet weld jig, the original symmetry was broken, resulting in an asymmetrical distribution of the submerged arc weld body at both ends of the centerline, and an offset towards the vertical plate side as much as possible. The lateral projection length of the near-conical weld section (longer than the height of the cone) provides additional penetration margin. Therefore, Examples 1, 2, and 3 achieved a stable penetration depth greater than 7mm after welding. Furthermore, the weld appearance was excellent, and after UT ultrasonic testing, the internal quality of the welds met the Class II requirements of the "Railway Steel Bridge Manufacturing Specification" (Q / CR 9211-2015). The weld yield strength, tensile strength, and elongation after fracture were all greater than the standard values ​​of the base material (cited from GB / T 714-2015 standard). The highest hardness HV10 of the three zones of the welded joint was ≤380 (cited from Q / CR 9211-2015 standard).

[0078] In summary, this invention employs a single-pass submerged arc welding method for high-penetration fillet welds. By designing appropriate T-shaped fillet weld jig inclination angles and offsets, and adapting suitable welding process parameters, the resulting welded joint exhibits excellent appearance and internal quality. All mechanical properties of the welded joint meet the requirements of relevant standards (Q / CR 9211-2015 and GB / T 714-2015), and the single-sided penetration depth of the weld consistently reaches over 7mm. This verifies the operability and applicability of the proposed high-penetration single-pass submerged arc fillet weld welding method.

[0079] This invention has been applied to the welding fabrication of steel plate beams for the Nanjing-Chuzhou Expressway and steel towers (medium-thick plate rib units) for the Guangzhou Wanlong Bridge, with significant results. It has important demonstrative and reference value for solving the welding problems of insufficient penetration and instability of T-shaped submerged arc welds without beveling.

Claims

1. A single-pass submerged arc welding method for high penetration fillet welds, applicable to non-full penetration T-joints, characterized in that, Includes the following steps: (1) Do not beveling; clean the area to be welded before welding. (2) Rotate the submerged arc welding jig until the angle α with the horizontal plane is within the first set range, and place the workpiece panel on the jig so that the welding position is close to the ship shape; the first set range is 48°~58°; (3) Adjust the submerged arc welding torch so that the torch is vertically downward. First, align the submerged arc welding wire with the right-angle vertex of the T-shaped fillet weld. Then, set the offset amount b of the welding wire to the second set range. The second set range is 3.5 to 5 mm. (4) Set the submerged arc welding process parameters and use single-pass submerged arc welding to weld T-shaped fillet welds to obtain stable high penetration fillet welds with a depth of ≥7mm; the submerged arc welding process parameters are: welding current of 740~800A, welding voltage of 28~32V, welding speed of 260~300mm / min, power supply polarity of DC reverse polarity, dry extension of 28~35mm, and heat input of 41.4~59.1KJ / cm.

2. The single-pass submerged arc welding method for high penetration fillet welds according to claim 1, characterized in that, In step (1), if the thickness of the joint plate exceeds a certain value, preheating treatment is required before welding.

3. The single-pass submerged arc welding method for high penetration fillet welds according to claim 1, characterized in that, In steps (2) and (3), when the rotation angle of the submerged arc welding jig is limited, the angle is compensated by tilting the welding gun.

4. The single-pass submerged arc welding method for high penetration fillet welds according to claim 3, characterized in that, First, rotate the submerged arc welding jig to an angle α1 with the horizontal plane. After the workpiece panel is placed on the jig, adjust and rotate the submerged arc welding torch clockwise so that it intersects the vertical line at an angle α2, and the center of the welding wire cross section is aligned with the right-angle vertex of the T-shaped fillet weld. The jig tilt angle α1 + welding torch tilt angle α2 = normal jig tilt angle α. Then set the off-center amount b of the welding wire.

5. The single-pass submerged arc welding method for high penetration fillet welds according to any one of claims 1 to 4, characterized in that, In step (3), the offset of the welding wire is set by adjusting the horizontal scale of the welding gun to offset the welding wire away from the panel side, so as to ensure that the axis of the welding gun is parallel to the initial centering line after offset.

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