Welding method for reducing welding residual stress and improving surface morphology of thick steel plate

Abstract

A welding method for reducing residual stress and improving surface morphology in thick steel plates is disclosed, relating to the field of welding. The method includes the following steps: applying a large-diameter impact head to the target area of ​​the weld joint on the thick high-strength steel plate using full-coverage ultrasonic impact treatment; and applying a small-diameter impact head to the target area of ​​the weld joint on the thick high-strength steel plate using full-coverage ultrasonic impact treatment. This method utilizes the deep strengthening function of the large-diameter impact head and the surface finishing function of the small-diameter impact head to achieve a synergistic effect, reducing residual stress in the thick high-strength steel plate while simultaneously lowering surface roughness.

Description

Technical Field

[0001] This application relates to the field of welding, and more specifically, to a welding method for reducing residual stress and improving surface morphology in thick steel plates. Background Technology

[0002] With the rapid development of major national projects towards high parameters and lightweight construction, 800 / 1000MPa high-strength steel has been widely used in key structures such as hydraulic and electrical pressure steel pipes and long-span bridges due to its excellent mechanical properties and significant weight reduction advantages. However, during the welding process of thick plate high-strength steel, high-amplitude residual tensile stress is easily generated due to concentrated heat input and high restraint, which significantly reduces fatigue life, easily induces microcracks, and weakens resistance to stress corrosion, seriously threatening structural safety.

[0003] Traditional residual stress control methods, such as multi-layer multi-pass welding and post-weld heat treatment, can only achieve 20%-35% stress reduction and have limitations such as high energy consumption, long cycle time, and difficulty in on-site implementation. Research on precise control of residual stress in thick high-strength steel plates is still insufficient. Impact strengthening technology induces dynamic plastic deformation on the surface of the welded joint through controllable shock waves, which can form a high-amplitude, uniformly distributed residual compressive stress layer. This provides a feasible technical path to overcome the bottleneck of residual stress control in the welding of thick high-strength steel plates. However, existing ultrasonic impact technology faces a core adaptation problem in the control of residual stress in the welding of 800 / 1000MPa grade thick high-strength steel plates: the high strength characteristics of high-strength steel require the residual compressive stress layer to have sufficient depth to completely cover the heat-affected zone of thick plate welding; however, a single-size impact head cannot simultaneously achieve both strengthening depth and surface integrity. The strengthening layer formed by a small-diameter impact head is not deep enough, and the stress relief effect is limited; although a large-diameter impact head can increase the depth of the compressive stress layer, it is prone to causing a sharp increase in surface roughness and surface microcrack initiation, resulting in damage to surface integrity. Summary of the Invention

[0004] The purpose of this application is to provide a welding method for reducing residual stress and improving surface morphology in thick steel plates. This method achieves synergistic effect by utilizing the deep strengthening function of a large-diameter impact head and the surface finishing function of a small-diameter impact head, thereby reducing residual stress in thick high-strength steel plates while lowering surface roughness.

[0005] This application is implemented as follows: This application provides a welding method for reducing residual stress and improving surface morphology in thick steel plates, comprising the following steps: A large-diameter impact head was used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick plate high-strength steel. A small-diameter impact head was used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates.

[0006] In some alternative implementations, the welded joint is formed using standard welding processes.

[0007] In some alternative implementations, the welded joint includes a weld area, a heat-affected zone, and a weld toe transition area.

[0008] In some alternative implementations, the diameter of the large-diameter impact head is 3-5 mm.

[0009] In some alternative implementations, the diameter of the small-diameter impact head is 1.5-2.5 mm.

[0010] In some alternative implementations, the ultrasonic shock treatment has an impact frequency of 20-40 kHz.

[0011] In some alternative implementations, the impact amplitude of the ultrasonic shock treatment is 30-50 μm.

[0012] In some alternative implementations, full-coverage ultrasonic impact treatment is defined as the ratio of the area of ​​the plastic deformation region to the total area of ​​the region to be treated after ultrasonic impact treatment reaching 100% or more.

[0013] In some alternative implementations, the ratio C of the area of ​​the plastic deformation region after ultrasonic impact treatment to the total area of ​​the region to be treated is calculated using the following formula: ; In the formula, r It is the radius of the deformed area after impact; S This represents the total area of ​​the region to be processed. N The effective number of impacts.

[0014] In some alternative implementations, the thickness of the high-strength steel plate is 40-60 mm, and the tensile strength is above 780 MPa.

[0015] The beneficial effects of this application are as follows: The welding method for reducing residual stress and improving surface morphology in thick steel plates provided by this application includes the following steps: using a large-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates; and using a small-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates. The welding method for reducing residual stress and improving surface morphology in thick steel plates provided by this application first uses a large-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates to achieve deep plastic deformation and the introduction of residual compressive stress. Subsequently, a small-diameter impact head is used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates to complete surface microstructure refinement and surface morphology finishing. Thus, the deep strengthening function of the large-diameter impact head and the surface finishing function of the small-diameter impact head are synergistically combined to reduce residual stress in the welding of thick high-strength steel plates while simultaneously reducing surface roughness. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic flowchart illustrating the welding method for reducing residual stress and improving surface morphology in thick steel plates, as provided in the embodiments of this application. Figure 2 A schematic diagram of the ultrasonic impact region in the welding method for reducing residual stress and improving surface morphology of thick steel plates provided in the embodiments of this application; Figure 3 A three-dimensional ultrasonic impact simulation model for the welding method of reducing residual stress and improving surface morphology in thick steel plates provided in the embodiments of this application; Figure 4 A calculation diagram of the impact coverage of ultrasonic multi-head impact in the welding method for reducing residual stress and improving surface morphology of thick steel plates provided in the embodiments of this application; Figure 5 A calculation diagram of the impact coverage of ultrasonic multi-head impact in the welding method for reducing residual stress and improving surface morphology of thick steel plates provided in the embodiments of this application; Figure 6 This is a schematic diagram showing the residual stress distribution under different working conditions in the welding method for reducing residual stress and improving surface morphology of thick steel plates provided in the embodiments of this application.

[0018] Markings in the diagram: 100, impact target platform; 110, impact head; Detailed Implementation To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0023] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0025] The following describes in further detail the features and performance of the welding method for reducing residual stress and improving surface morphology in thick steel plates according to the present application, with reference to embodiments.

[0026] like Figure 1 As shown in the figure, this application provides a welding method for reducing residual stress and improving surface morphology in thick steel plates, including the following steps: Step 1: Prepare a welded joint of thick plate high-strength steel formed by standard welding process; the welded joint includes the weld area, heat-affected zone and weld toe transition area; Step 2: Use a large-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick plate high-strength steel to achieve deep plastic deformation and the introduction of residual compressive stress; optionally, the diameter of the large-diameter impact head is 3-5mm. Optionally, the impact frequency of the ultrasonic impact treatment is 20-40kHz, and the impact amplitude is 30-50μm.

[0027] Step 3: Use a small-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick plate high-strength steel to refine the surface microstructure and improve the surface morphology. Optionally, the diameter of the small-diameter impact head is 1.5-2.5mm.

[0028] Among them, full-coverage ultrasonic impact treatment means that the ratio of the area of ​​the plastic deformation region to the total area of ​​the region to be treated after ultrasonic impact treatment reaches more than 100%.

[0029] The ratio C of the area of ​​the plastic deformation region to the total area of ​​the region to be treated after ultrasonic impact treatment is calculated using the following formula: ; In the formula, r is the radius of the deformed region after impact; S is the total area of ​​the region to be treated; and N is the effective number of impacts.

[0030] Among them, the nominal size of the large-diameter impact head is larger than that of the small-diameter impact head. Through two-stage impact, a synergistic mechanism of deep strengthening and surface finishing is formed. The synergistic improvement effect of this combination on the mechanical response of the welded joint is verified by simulation using ABAQUS finite element software combined with the Johnson-Cook material constitutive model.

[0031] The specific steps for constructing the simulation model are as follows: Step 1: Based on the material mechanical properties, geometric configuration and welding process data of the welded joint of thick plate high-strength steel, construct a high-fidelity simulation model; Step 2: Import the initial residual stress field obtained from the welding thermo-mechanical coupling analysis as a predefined field into the ultrasonic impact simulation model to restore the true initial stress state of the welded joint. Step 3, as follows Figure 2 and Figure 3As shown, the target analysis area is defined in the welded joint area and defined as the impact target 100. CIN3D8 infinite element boundary conditions are applied to the outer boundary of the impact target 100 to simulate the stress environment of a semi-infinite workpiece, while eliminating the interference of boundary effects on stress wave propagation and reflection. Step 4: The Johnson-Cook constitutive model is used to characterize the dynamic plastic behavior of thick plate high-strength steel under high-frequency impact load, and to simulate the stress field evolution, plastic strain distribution and surface morphology change law in the impact target 100 region during the phased impact process using the impact head 110.

[0032] The first stage of impact treatment, applied by the large-diameter impact head, and the second stage of impact treatment, applied by the small-diameter impact head, both adopt a full-coverage process mode, so that the ultrasonic impact treatment coverage reaches 100%, and the treatment area forms continuous, uniform and complete impact marks.

[0033] like Figure 4 and Figure 5 As shown, the coverage rate of ultrasonic impact treatment is defined as the ratio of the area of ​​the plastic deformation region after ultrasonic impact treatment to the total area of ​​the region to be treated. A coverage rate exceeding 100% refers to the ratio of the actual impact treatment time to the baseline time required to achieve 100% coverage. The region with an equivalent plastic strain (PEEQ) greater than 0 after impact treatment is the plastic deformation region, and the coverage rate is calculated using the following formula: ; Where r is the radius of the deformed region after impact; S is the area of ​​the region to be treated; N is the effective number of impacts; and C is the coverage rate.

[0034] When the coverage rate is less than 100%, the coverage rate is changed by altering the impact layout of the impact zone. A 200% coverage rate is achieved by conducting two 100% full-coverage impacts on the same area.

[0035] Process effect verification steps: The process effect verification steps include residual stress extraction and calculation, specifically: A Python script was written to extract residual stress data of each node from the ABAQUS finite element simulation database. The script can adjust the circular area of ​​the extraction region. The residual stress averaging method was used to calculate the average residual stress of all nodes in a circular region with a diameter of 0.7 mm at different layer depths. The diameter of the circular region is consistent with the diameter of the X-ray spot.

[0036] The process effect verification step also includes the extraction and calculation of surface roughness, specifically: The coordinate data of the target surface nodes are extracted in batches using a Python script and exported. The coordinate data is then imported into an external data analysis tool to calculate the core parameter of surface roughness Ra, which is calculated using the following formula.

[0037] ; in, y(x) is the sampling length of the profile curve, and y(x) is the ordinate distance from a point on the surface profile curve to the centerline.

[0038] The welding method for reducing residual stress and improving surface morphology in thick steel plates provided in this application firstly uses a large-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick high-strength steel plate to achieve deep plastic deformation and introduce residual compressive stress. Then, a small-diameter impact head is used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick high-strength steel plate to complete the surface microstructure refinement and surface morphology finishing. Thus, the deep strengthening function of the large-diameter impact head and the surface finishing function of the small-diameter impact head are synergistically combined to significantly reduce the residual stress in the welded thick high-strength steel plate while reducing the surface roughness.

[0039] Example: This application provides a welding method for reducing residual stress and improving surface morphology in thick steel plates, comprising the following steps: Step 1: Prepare the welded joint of thick plate high-strength steel formed by standard welding process. The steel plate selected is XG800CF steel plate as shown in Table 1 and Table 2. Table 1 Mechanical and technological properties of XG800CF steel plates

[0040] Table 2 Chemical composition of XG800CF steel plate

[0041] Step 2: Use a large-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick plate high-strength steel. The diameter of the large-diameter impact head is 4mm, the impact frequency of the ultrasonic impact treatment is 27kHz, and the impact amplitude of the ultrasonic impact treatment is 40μm.

[0042] Step 3: Use a small-diameter impact head to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on the thick plate high-strength steel. The diameter of the small-diameter impact head is 2mm, the impact frequency of the ultrasonic impact treatment is 27kHz, and the impact amplitude of the ultrasonic impact treatment is 40μm.

[0043] Simulation of a welded joint of 800MPa thick high-strength steel plate was conducted. The properties of the XG800CF steel plate welded joint were used as the properties of the ultrasonic impact target. The actual set frequency of the ultrasonic impact equipment was 27kHz, the amplitude was 40μm, the diameter of the large-diameter impact head was 4mm, and the diameter of the small-diameter impact head was 2mm. An infinite element boundary of CIN3D8 elements was set around the target. Three impact conditions were established for comparison. Condition 1: Use only a 4mm large-diameter impact head to perform 100% coverage impact on the target platform; Condition 2: Two impacts with 4mm large-diameter impact heads have achieved 100% coverage of the target platform, reaching 200% coverage. In the third working condition, the target platform was impacted with a 4mm large-diameter impact head for 100% coverage in the first operation, and then with a 2mm small-diameter impact head for 100% coverage in the second operation, achieving 200% coverage.

[0044] Based on the comparative analysis of working conditions one and two, and Figure 6 The results show that, under different coverage rates, the residual compressive stress exhibits an evolutionary characteristic of first increasing and then decreasing until it decays to zero and transforms into residual tensile stress. Furthermore, the residual stress values ​​and roughness corresponding to 100% and 200% coverage rates do not change significantly with further increases in coverage rate, with overall changes less than 10%. This indicates that when the coverage rate reaches 100%, the residual compressive stress and roughness introduced by the process have reached a saturation state, thus eliminating the interference of increasing coverage rate on the experimental data.

[0045] Table 3 shows the surface roughness of the welded joints on the thick plate high-strength steel under working conditions 1, 2 and 3. It can be seen that the surface roughness can be effectively reduced by sequentially using a large-diameter impact head to perform 100% coverage impact on the target table and a small-diameter impact head to perform 100% coverage impact on the target table.

[0046] Table 3 Surface roughness under different working conditions

[0047] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A welding method for reducing residual stress and improving surface morphology in thick steel plates, characterized in that, Includes the following steps: A large-diameter impact head was used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick plate high-strength steel. A small-diameter impact head was used to perform full-coverage ultrasonic impact treatment on the target area of ​​the welded joint on thick high-strength steel plates.

2. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The welded joint is formed using standard welding procedures.

3. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The welded joint includes a weld area, a heat-affected zone, and a weld toe transition area.

4. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The diameter of the large-diameter impact head is 3-5mm.

5. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The diameter of the small-diameter impact head is 1.5-2.5mm.

6. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The impact frequency of the ultrasonic shock treatment is 20-40 kHz.

7. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The impact amplitude of the ultrasonic shock treatment is 30-50 μm.

8. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The full-coverage ultrasonic impact treatment is defined as the ratio of the area of ​​the plastic deformation region to the total area of ​​the region to be treated after ultrasonic impact treatment reaching more than 100%.

9. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 8, characterized in that, The ratio C of the area of ​​the plastic deformation region to the total area of ​​the region to be treated after ultrasonic impact treatment is calculated using the following formula: ； In the formula, r It is the radius of the deformed area after impact; S This represents the total area of ​​the region to be processed. N The effective number of impacts.

10. The welding method for reducing residual stress and improving surface morphology in thick steel plates according to claim 1, characterized in that, The thickness of the high-strength steel plate is 40-60mm, and the tensile strength is above 780MPa.

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