A laser-arc hybrid welding method for T-joint of high-strength steel for ship structure

Abstract

The present application relates to the field of ship structure protection, and particularly relates to a laser-arc hybrid welding method for high-strength steel T-joint of ship structure. The method comprises the following steps: S1, establishing arc welding parameters, and preliminarily testing to determine the range of welding parameters; S2, developing a finite element calculation simulation model based on SYSWELD software, and estimating the influence of the moving heat source on the connecting components; S3, detecting the samples welded with different parameters; and S4, deeply detecting the samples welded with different parameters. The present application improves the design level of ship structure materials, significantly shortens the preparation cycle of ship structure materials, simplifies the preparation process, reduces the production cost, and promotes the transformation and application of high-strength and high-toughness steel materials in the design of next-generation ship structure and transportation scale.

Description

Technical Field

[0001] This invention relates to the field of ship hull structure protection, and in particular to a laser-arc composite welding method for high-strength steel T-joints used in ship hull structures. Background Technology

[0002] The structural safety of a ship is crucial for maritime transportation, and welding quality directly affects the structural integrity and stability of the hull. Good welding techniques ensure the secure connection of all hull components, reducing structural damage and leaks caused by weld defects, thus improving hull safety. As a vital component of civilian assets, the hull requires a long service life and good durability. Excellent welding techniques reduce the risk of corrosion at welds, extend the hull's service life, lower maintenance costs, and ensure long-term effective operation. Furthermore, welding quality directly impacts a ship's performance. Through appropriate welding processes and material selection, the hull's weight can be reduced, increasing the ship's carrying capacity and navigation efficiency, thereby enhancing a nation's maritime transportation and fleet combat capabilities. Excellent hull structural steel welding technology is one of the foundations of national defense. Modern naval equipment requires high-strength, corrosion-resistant hull structures, all of which rely on advanced welding technology. Therefore, the importance of hull structural steel welding technology is directly related to the improvement of national defense capabilities and the development of modernization. In addition, good welding techniques can improve the hull's service life and performance, reduce maintenance costs and energy consumption, and provide a guarantee for national resource conservation and improved economic efficiency.

[0003] With the rapid development of high-energy lasers, a key technical challenge is how to leverage their advantages to overcome the shortcomings of traditional arc welding methods. The emerging hybrid laser arc welding (HLAW) technology urgently needs to combine the advantages of both laser and arc welding processes to reduce complex weld preparation and solve the problem of joining complex materials that are difficult to weld. For ship hull structures using high-strength steel as medium-thickness plates, which are difficult to weld, HLAW technology, through its high-energy process, can achieve high penetration and high welding speed, making it an effective joining method.

[0004] Addressing the limitations of existing arc welding techniques, such as the difficulty in welding irregular shapes and the limited depth of penetration, and leveraging the advantages of high-energy lasers to overcome the shortcomings of traditional arc welding methods is a key technical challenge. The development of Hybrid Laser Arc Welding (HLAW) technology urgently needs to combine the advantages of both laser and arc welding processes, reducing complex weld preparation work and solving the problem of composite joining between difficult-to-weld materials. For ship hull structures using high-strength steel as medium-thickness plates, which are difficult to weld, HLAW technology, through its high-energy process, can achieve high penetration depth and high welding speed, making it an effective joining method. Summary of the Invention

[0005] This invention is based on the shipbuilding assembly stage where stiffeners are connected to horizontal plates (the working area of ​​this stage is long and narrow), and aims to enhance the welding quality during the manufacturing process of the plates. This invention discloses a method for obtaining full penetration T-joints using HLAW in a shipyard environment.

[0006] The technical problem to be solved by this invention is to address the shortcomings of existing arc welding technology, such as irregular welding and limited depth of action. By introducing high-energy laser, the welding quality of ship hull steel structures can be improved. The laser source and arc source are configured and installed on the equipment. The welding position and angle are controlled by considering laser beam parameters, laser power, welding speed, arc source power, welding torch angle, incident angle (β) between the welding torch and the web plate, and laser beam incident angle, thereby improving the welding quality.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] A laser-arc hybrid welding method for high-strength steel T-joints used in ship hull structures includes the following steps:

[0009] S1. Connect the WeldAnalyst HKS-P1000 measuring device, used for analyzing the welding process, to the arc power source to record signals. Establish the following arc welding parameters: pulse frequency, peak arc current, arc current, and voltage command value. Conduct preliminary tests to determine the range of welding parameters. These parameters provide a stable guarantee for producing a series of welds with repeatable quality, ignoring defects formed at the joint ends.

[0010] S2. A finite element method (FEM) simulation model was developed using SYSWELD software to estimate the impact of a moving heat source on the connected components. The model follows the thermo-elastic-plastic phase of the welding process, providing thermal simulation results and mechanical effects on the structure. The heat output is the highest temperature reached at each node (representing nodes belonging to the fusion zone FZ, heat-affected zone HAZ, or base material BM), and the mechanical response, particularly deformation (displacement of mesh nodes) and residual stress (Von Mises), is obtained to guide experiments.

[0011] Specifically, the meshing of the FE nodes in the 2D and 3D sections is defined with reference to the geometry of the weld fusion zone FZ. The mesh consists of multiple 3D finite elements, refined at the joint, with node spacing ranging from the fusion zone FZ to the base material away from the joint. The global heat source is a combination of Gaussian mathematical models to simulate the laser source, and the Goldak double ellipsoidal mathematical model represents the GMA source, with the dimensions of the combined heat source adjusted. The two heat sources are combined to simulate the volumetric heat flux distribution of the HLAW process, using the same spacing between the two heat sources as in experimental welding tests to obtain accurate results.

[0012] S3. Inspect samples welded with different parameters. To meet the standard quality control requirements for T-type samples, a series of tests are selected for characterization and evaluation. Tests include visual inspection, radiographic testing (RT), and defect detection.

[0013] S4. Conduct in-depth testing on samples welded with different parameters. This includes cross-sectional metallographic evaluation and microhardness mapping using the ultrasonic contact impedance (UCI) method (microhardness testing at different locations on the weld). Based on the test results, further testing items are added to each weld. Only welds that meet the requirements for visual inspection and non-destructive testing are then subjected to metallographic analysis, analyzing the dendrite size and shape under different laser effects and in the fusion zone.

[0014] The beneficial effects of this invention are as follows:

[0015] A fully penetrated 8 mm T-joint can be obtained in a single step using a reasonable HLAW welding head angle on a horizontal T-joint suitable for industrial applications. No root sealing is required, and the weld is prepared using a zero-gap square bevel edge. The welding speed for horizontal T-joints with 8 mm high-strength steel thickness can reach up to 2.2 m / min, significantly improving processing efficiency compared to traditional methods such as conventional arc welding, and possessing great potential for enhancing industrial production.

[0016] The experimental steel was melted in a 150 kg vacuum induction furnace and cast into ingots. The measured chemical composition was Fe-0.055C-0.2Si-1.0Mn-0.6Mo-0.6Cr-2.0Cu-4.0Ni-0.07Nb-0.02Ti-0.8Al (wt.%). The ingots were reheated to 1150℃ and held for 2 hours. They were then hot-rolled to a thickness of 13 mm on a φ450 mm two-roll mill at a final rolling temperature of 850℃. After hot rolling, the steel samples were cooled to room temperature in air at a measured cooling rate of 1–6℃ / s. They were then aged at 550℃ for 2 hours and finally cooled in air.

[0017] The yield strength of Cr-Mo bainitic steel is 1155 MPa. Figure 4 At a low temperature of -40℃, the impact energy absorbed by this steel is approximately 55.3 J. Figure 5 The finer grain size and moderate dislocation density enable Cr-Mo bainitic steel to maintain high impact toughness. This invention offers advantages over existing technologies.

[0018] This invention provides a design method for strengthening and toughening steel materials for ship hull structures at a low cost, thereby improving the design level of ship hull structure materials, significantly shortening the preparation cycle of ship hull materials, simplifying the preparation process, reducing production costs, and promoting the transformation and application of high-strength and tough steel materials in next-generation ship structure design and transportation scale design.

[0019] This invention employs large-scale database simulation calculations, combined with casting, rolling, and aging methods, to design a Cr-Mo bainitic steel for ship hull structures. By optimizing the alloy composition, the manufacturing process of bainitic steel is simplified, eliminating controlled cooling and offline quenching processes, improving the mechanical properties of low-carbon ultra-high-strength steel, and achieving on-demand customization of new ship hull structure materials to meet ship design and performance requirements. Attached Figure Description

[0020] Figure 1 Here is a diagram of the laser welding experimental setup for an embodiment:

[0021] Figure 2 This is the laser geometry configuration of the embodiment;

[0022] Figure 3 This is the geometric configuration of the GMA source in the embodiment;

[0023] Figure 4 These are voltage signals recorded during the test analysis of the embodiment;

[0024] Figure 5 These are current signals recorded during the test analysis of the embodiment;

[0025] Figure 6 This is the 2D mesh model information established in the embodiment;

[0026] Figure 7 This is the 3D mesh model information established in the example;

[0027] Figure 8 This refers to the two-dimensional cross-sectional model information of the laser heat source established in the embodiment;

[0028] Figure 9 This is the two-dimensional cross-sectional model information of the welding torch heat source established in the embodiment;

[0029] Figure 10 This refers to the welding clamp model information established in the embodiment;

[0030] Figure 11 This refers to the post-weld support model information established in the embodiment;

[0031] Figure 12 This is a hybrid laser T-connector sample from an embodiment;

[0032] Figure 13 This is a front view of the weld seam of the sample obtained in the example;

[0033] Figure 14 The image shows the root side of the weld of the sample obtained using the technique described in this embodiment.

[0034] Figure 15The embodiment uses finite element simulation to calculate the residual stress and Von Misses in the side view of the joint;

[0035] Figure 16 The embodiment calculates the residual stress and Von Misses of the root side view using finite element simulation.

[0036] Figure 17 The embodiment calculates the residual stress and Von Misses of the flange view using finite element simulation;

[0037] Figure 18 This is an X-ray test of the front and root of a welded T-joint sample from an embodiment;

[0038] Figure 19 This is the microstructure of the laser-melted weld seam obtained by welding a T-joint in the embodiment;

[0039] Figure 20 This is one of the magnified microscopic images of the laser melting zone obtained from welding the T-joint in the embodiment;

[0040] Figure 21 This is the second magnified microscopic image of the laser melting zone obtained from welding the T-joint in the embodiment;

[0041] Figure 22 This is the third magnified microscopic image of the laser melting zone obtained from welding the T-joint in the embodiment;

[0042] Figure 23 This is the fourth magnified microscopic image of the laser melting zone obtained from welding the T-joint in the embodiment;

[0043] Figure 24 This is the average width value of the weld dendrite structure obtained from welding the T-joint in the embodiment;

[0044] Figure 25 This is a Vickers microhardness diagram of the weld seam in Example T;

[0045] Figure 26 This is a Vickers microhardness diagram of the weld seam in Example T. Detailed Implementation

[0046] The specific technical solutions of the present invention will be described with reference to the embodiments.

[0047] Step 1: Equipment Configuration

[0048] The laser used for welding tests was a 16 kW TruDisk 16002 disk laser with a wavelength of 1030 nm and a beam area of ​​9 mm × mrad. The laser beam was transmitted through an optical fiber with a core diameter of 200 µm. The beam diameter at the focal point was 420 µm. A Qineo Pulse 600 microprocessor-controlled welding machine with a maximum current of 600 A was used as the arc power source. The experimental configuration developed at the BAM facility (Berlin, Germany) is as follows: Figure 1 As shown. Welding was performed using a flexible laboratory mixing apparatus that employed a GMA welding torch ( Figure 1 a) and laser beam source ( Figure 1 The decoupled configuration in section b) measures 73cm (length) × 12cm × 12cm and includes a collimating lens and a focusing lens. The mixing head remains fixed. Figure 1 c) In the movable workbench ( Figure 1 (d) During this process, the position of the welding optics remains unchanged. A mixture of 82% argon and 18% CO2 (trade name Corgon18) is used as the shielding gas, driven by a GMA at a flow rate of 18 liters / minute.

[0049] Step 2: Parameter Settings

[0050] Before conducting the hybrid welding test, vertical plates were fixed at both ends and the middle of the welding path using tack welding. Spot welding was performed using SMAW (Small Sandwich Arc Welding) with coated electrodes, followed by HLAW T-shaped welding at the 2F (horizontal) welding position. The laser beam was positioned by adjusting the incident angle and focal point. Next, the working angle of the GMA welding torch and the corresponding parameters for the arc process were configured. The heat input of the laser beam and the GMA process was adjusted by controlling the laser power, welding speed, and arc source power (by adjusting the arc current and voltage).

[0051] The laser source and arc source are geometrically configured and mounted onto the workpiece, with different parameters considered to control the position and angle, such as... Figure 2 and Figure 3 The angles considered were: the downward angle between the laser beam and the GMA torch (α), the incident angle between the GMA torch and the web (β), and the incident angle of the laser beam from the flange (γ). Further geometric positioning parameters were: the working distance between the laser beam and the GMA (a), the vertical laser offset distance from the flange (b), and the horizontal GMA offset distance from the web (c). In all welding experiments, the tip of the GMA filler wire was precisely placed on the joint with a protrusion of 16 mm and a focal position of -3 mm.

[0052] The joints were welded using a T-joint configuration with a technical gap of 0 mm. Laser power varied from 7 kW to 10 kW, and welding speeds ranged from 1.8 m / min to 2.2 m / min. Filler wire feed rates were tested at 12 m / min and 15 m / min.

[0053] Step 3: Parameter Range

[0054] The WeldAnalyst HKS-P1000 measuring device, used for analyzing the welding process, was connected to the arc power source to record signals generated by the GMA process. The arc welding parameters were established as follows: pulse frequency 286 Hz, peak arc current 563 A, base arc current 68 A, voltage command value 32 V. The arc voltage and arc current curves were measured using GMA analysis and corrected after welding testing. Figure 4 and Figure 5 As shown, the results were recorded between 2.60 ms and 2.61 ms.

[0055] Step 4: Finite element modeling

[0056] A simulation model was built using SYSWELD to estimate the impact of a moving heat source on the connected components. The meshing of the FE nodes in the 2D and 3D sections is as follows: Figure 6 and Figure 7 As shown, the geometry of the weld fusion zone (FZ) is used as a reference for definition. The final mesh consists of 127,575 3D finite elements, refined at the joint, with node distances ranging from 0.13 mm (fusion zone) to 4.38 mm (base material away from the joint). The global heat source is a combination of Gaussian mathematical models, such as... Figure 8 As shown, this is used to simulate a laser source, while the Goldak double ellipsoidal mathematical model represents a GMA source, as... Figure 9 As shown. Considering the actual measurements of the molten pool during welding, the dimensions of the combined heat source were carefully adjusted. The two heat sources were combined to simulate the volumetric heat flux distribution of the HLAW process, using the same spacing (3.5 mm) between the two heat sources as in the experimental welding test to obtain accurate results. The finite element model created the actual dimensions of the weldment (300 mm × 100 mm × 8 mm), with the joint located at position 2F below the butt-joint T-joint, and natural air cooling conditions selected. Nodes located at the two left corners of the flange mesh ( Figure 10 The red dots (indicated by the symbol) are clamped on all axes (X, Y, and Z) during welding. The movement of the four nodes located at the corners of the lower flange surface is restricted to the -Y axis after welding, as shown below. Figure 12 As shown. S355J2G3 is a material selected from the SYWELD software database for model execution, considering that this material can be used for both base metal and filler wire because it has similar thermal and mechanical properties.

[0057] Step 5: Weld Inspection

[0058] Sample of hybrid laser T-joint made of 8 mm thick EH36 structural steel, as shown in the image. Figure 12 As shown. This invention analyzes the effects of several experimental variables, such as hybrid welding head configuration, the relative positions of the arc and laser sources (laser-guided or arc-guided process), filler wire composition, laser power (and energy density), and welding rate. The subsequent experimental methods allow us to adapt to these variables to obtain a stable welding process and acceptable shipbuilding quality joints. The welded samples underwent in-depth testing, including visual inspection, RT, cross-sectional metallography, and microhardness mapping via UCI, such as... Figure 13 and Figure 14 As shown, each point represents a microhardness measurement. Only welds that meet the requirements for visual inspection and non-destructive testing are then subjected to metallographic analysis.

[0059] Step 6: Finite Element Results

[0060] The simulation of hybrid welding performed with the highest heat input (maximum global energy 584 J / mm) resulted in the highest deformation. Figures 15 to 17 The distortion values ​​obtained through simulation and experimental measurements show that the displacement in the model is asymmetrical due to the constraint position on one side of the flange. To obtain better deformation prediction accuracy, the external fixture was adjusted in the finite element model based on actual experiments. Finally, the maximum residual stress value appears in the center region of the weld, exceeding the elastic limit of the base material (375 MPa). These residual stress results are related to the deformation generated in the free edges of the flange and web.

[0061] Step 7: X-ray inspection

[0062] Figure 8 The results of X-ray radiographic testing of the weld seam of the welded sample are presented. The X-rays represent a symmetrical image of the actual sample. Visible welding defects such as cracks or porosity are not visible in the radiographs. Due to the spot welding performed by fixing the web to the flange, the melt receives additional material flow, which does not affect the root of the joint in that area, nor does it create irregularities at that point in the joint.

[0063] Step 8: Metallographic Structure

[0064] The cross-section of the welded sample was subjected to in-depth metallographic analysis using an optical microscope to study the microstructure of different regions (laser and GMA regions), such as... Figure 19 As shown. Figures 20 to 23Magnified microscopic images of the laser- and GMA fusion zones are depicted. Dendrites growing from the base metal toward the weld center are observed in both the laser and GMA regions. The size and shape of the dendrites depend on the solidification conditions of each region. Due to the faster solidification rate, the laser region is dominated by smaller and narrower dendrites. In contrast, the GMA region exhibits larger and wider dendrites due to the slower cooling of the weld pool. The average width of these dendrites is shown in... Figure 24 The average width measured in the laser fusion region was significantly lower than that measured in the GMA region. This fact is related to the lower heat input, which promotes a faster cooling rate in the fusion region, resulting in smaller dendrites.

[0065] Step 9: Vickers Hardness

[0066] Figure 25 and Figure 26 The microhardness map obtained from the HV 0.5 Vickers hardness test of the weld sample is shown. The upper fusion zone is mainly affected by the electric arc process, while the lower zone is mainly affected by the laser source. The hardness value of the arc zone is below 300 HV. The microhardness value of the connecting flange and web area is below 380 HV, which meets the requirements of ISO 15614-14, Bureau Veritas NR 216 DT R10 E, and Lloyd's Register material manufacturing, testing, and certification. Due to the high cooling rate, the laser-treated area at the weld root exhibits a hardness value above 380 HV.

[0067] This invention enables the production of fully penetrated 8mm T-shaped welds in horizontal positions on industrially applicable T-shaped samples using a suitable HLAW welding head angle. This process requires only one step, eliminates the need for root sealing, and utilizes a zero-gap square bevel edge. The welding speed for horizontal T-joints with 8mm high-strength steel thickness can reach up to 2.2 m / min, significantly improving processing efficiency compared to traditional methods such as arc welding, and demonstrating immense potential for industrial-scale production.

Claims

1. A laser-arc hybrid welding method for high-strength steel T-joints used in ship hull structures, characterized in that, Includes the following steps: S1. Connect the WeldAnalyst HKS-P1000 measuring device for analyzing the welding process to the arc power source to record signals; establish arc welding parameters and conduct preliminary tests to determine the range of welding parameters; S2. Use SYSWELD software to develop a finite element simulation model to estimate the impact of a moving heat source on the connecting components. The model follows the thermo-elastic-plastic stage of the welding process and provides thermal simulation results and mechanical effects on the structure. Heat output is the highest temperature reached at each node: indicating the node belonging to the fusion zone (FZ), heat-affected zone (HAZ), or base material (BM); Obtain the mechanical response, including deformation and residual stress, to guide the experiment; S3. Test samples welded with different parameters; S4. Conduct in-depth testing on samples welded with different parameters; perform cross-sectional metallographic evaluation and microhardness mapping using the ultrasonic contact impedance (UCI) method; based on the test results, add test items for each weld, i.e., perform metallographic analysis on welds that meet the requirements for visual inspection and non-destructive testing, and analyze the dendrite size and shape of different laser effects and fusion zones.

2. The laser-arc hybrid welding method for high-strength steel T-joints in ship hull structures according to claim 1, characterized in that, The arc welding parameters set in S1 are as follows: pulse frequency, peak arc current, arc current, and voltage command value.

3. The laser-arc hybrid welding method for high-strength steel T-joints in ship hull structures according to claim 1, characterized in that, The S2 method is as follows: Finite element (FE) nodes in the 2D and 3D sections are meshed, defined with the geometry of the weld fusion zone FZ as a reference; the mesh consists of multiple 3D finite elements, refined at the joint, with node distances ranging from the fusion zone FZ to the base material far from the joint; the global heat source is a combination of Gaussian mathematical models used to simulate the laser source, and the Goldak double ellipsoidal mathematical model represents the GMA source, adjusting the size of the combined heat source; the two heat sources are combined to simulate the volumetric heat flux distribution of the HLAW process, using the same spacing between the two heat sources as in the experimental welding test to obtain accurate results.

4. The laser-arc hybrid welding method for high-strength steel T-joints in ship hull structures according to claim 1, characterized in that... The S3 test includes visual inspection, radiographic testing, and defect detection.

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