A method for evaluating thin sheet austenitic alloy laser welding solidification cracking susceptibility test

Abstract

The application discloses a method for evaluating the solidification cracking sensitivity of a thin-plate austenitic alloy laser welding test, which mainly comprises a welding test sample, a clamping device and an evaluation method. The welding test sample is composed of a rectangular shape and a funnel shape. During welding, welding is started from one end of the rectangular shape along the center line direction, passes through the long neck of the funnel, and finally terminates at the bottom edge of the funnel, thereby forming a full penetration weld with solidification cracks. The surface of the clamping device is designed in a zigzag shape and is clamped on one side of the welding test sample, thereby playing the roles of fixing the welding test sample and reducing the heat conduction of the clamping device to the welding test sample. After welding, the vertical distance between the crack end and the bottom edge of the funnel of the welding test sample is measured. The method can realize quantitative evaluation of the solidification cracking sensitivity of the austenitic alloy laser welding and can compare the solidification cracking sensitivities of welding test samples with different sizes.

Description

Technical Field

[0001] This invention belongs to the field of welding technology and relates to a method for testing the solidification crack sensitivity of austenitic alloys in laser welding. Specifically, it is a test method for evaluating the solidification crack sensitivity of austenitic alloys such as stainless steel and nickel-based alloys, which have high hot crack sensitivity, in laser welding. Background Technology

[0002] Austenitic stainless steel and nickel-based alloys possess excellent corrosion resistance and high-temperature performance, making them widely used in chemical, energy, and nuclear power industries. However, austenitic alloys have poor thermal conductivity and a high coefficient of linear expansion, resulting in a significant tendency for solidification cracking during welding. Solidification cracks affect weld quality, reduce various properties of the welded joint, lead to weld fracture, and cause safety issues. Therefore, a quantitative assessment of the solidification crack susceptibility of austenitic alloys during welding is crucial for evaluating joint performance, controlling weld composition, and optimizing welding processes.

[0003] Traditional arc welding relies primarily on an electric arc as the heat source, resulting in a slow cooling rate, a large heat-affected zone, and often significant deformation of the workpiece after welding. Laser welding, on the other hand, offers highly concentrated energy and rapid welding speed, allowing for joint performance with minimal deformation. However, the high cooling rate during laser welding can affect weld solidification behavior, potentially inducing solidification cracks. Therefore, assessing the susceptibility to solidification cracking in laser welding of austenitic alloys such as stainless steel and nickel-based alloys is of great significance.

[0004] In the prior art, patent document CN104400244A discloses a method for evaluating the hot crack sensitivity of titanium alloy welding. This method uses a symmetrical trapezoidal specimen with an arc-shaped cross-section to evaluate the hot crack sensitivity of thin-walled titanium alloy spun parts obtained under different chemical compositions or preparation conditions. However, the shortcomings of this prior art are: 1) The welding specimen is a cylindrical specimen, and a rectangular notch must be made before welding, resulting in no stable transition stage at the beginning of welding; 2) The surface of the holding device is flat, and the heat conduction effect is significantly affected when the welding specimen is fixed and held; 3) The index for evaluating crack sensitivity is the crack rate, which is calculated by dividing the crack length by the weld length. This index is affected by the weld length and specimen size, and different weld lengths and specimen sizes result in different crack rates. In reality, the welding solidification crack sensitivity is not significantly related to the weld length and specimen size. Summary of the Invention

[0005] To address the limitations of existing technologies, this invention presents a test method for evaluating the susceptibility of laser welding to solidification cracking in thin-walled austenitic alloys. It proposes a specially designed welding specimen, clamping device, and evaluation method to achieve the evaluation of the susceptibility of laser welding to solidification cracking in austenitic stainless steel and nickel-based alloys, which are highly susceptible to hot cracking.

[0006] The technical solution of this invention is achieved through the following steps:

[0007] Step (1), welding specimen design. Cut a composite shape welding specimen with a combination of rectangle and funnel shape. The rectangular design of the welding specimen can avoid the interference of unstable factors during the welding process on the sensitivity to cracks, allowing the welding process to enter a stable state; the long neck design of the funnel of the welding specimen can promote the formation of solidification cracks; the bottom edge design of the funnel of the welding specimen plays the role of terminating solidification cracks.

[0008] Step (2), clamping device design. The upper surface of the clamp has a groove with a width of 5 mm and a depth of 15 mm at its center, and there are right-angled triangular serrations arranged side by side on both sides of the groove; the lower surface of the pressure plate has right-angled triangular serrations arranged side by side, and the edge of the pressure plate is 10-20 mm away from the center of the weld. This can not only fix the welding sample in step (1), but also reduce the heat conduction effect of the clamping device on the welding sample in step (1) and improve the accuracy of crack assessment.

[0009] Step (3), welding process. Wipe the area to be welded of the welding sample in step (1) with acetone, place the welding sample on the clamp of the clamping device in step (2), and fix it on one side of the welding sample in step (1) with a pressure plate. The laser tilt angle is between 5-30°, and argon is used as the shielding gas to protect the weld from both sides. Welding starts from one end of the rectangle along the center line of the welding sample in step (1), passes through the long neck of the funnel, and finally terminates at the bottom edge of the funnel to form a full penetration weld with solidification cracks.

[0010] Step (4), Evaluation Method: After welding, measure the vertical distance between the crack tip and the bottom edge of the welded specimen funnel. Based on the principle of similar triangles, calculate the distance between the solidification crack tip and the waistline on one side of the welded specimen funnel shape along the direction perpendicular to the welding direction. Define this distance as the quantitative index for assessing solidification crack sensitivity—the critical restraint index. Compare the critical restraint index to complete the laser welding solidification crack sensitivity assessment.

[0011] Furthermore, the thickness of the thin plate austenitic alloy is 0.5-5.0 mm.

[0012] Furthermore, in step (1), the length of the rectangular welding specimen is 30-50 mm and the width is 20-30 mm.

[0013] Furthermore, in step (3), the welding start end is the middle position of the rectangular length end of the welding sample in step (1).

[0014] Furthermore, the method for determining the width of the long neck of the welding sample funnel in step (1) is as follows: cut a square with a side length of 100 mm from the thin sheet metal material used, and weld it from one end of the edge to the other end at an appropriate distance d from one side of the square, parallel to the edge, to ensure that the weld is continuous and fully penetrated. By adjusting the above distance d, a suitable distance for generating welding solidification cracks is obtained, ensuring that solidification cracks can be caused when welding to the long neck of the funnel as mentioned in step (3), that is, the width of the long neck of the welding sample funnel in step (1) is 2d.

[0015] Furthermore, the distance d is between 3 and 8 mm.

[0016] Furthermore, in step (1), the width of the long neck of the welding sample funnel is 6-16 mm, and the length is 5-20 mm.

[0017] Furthermore, in step (1), the bottom edge dimension of the welding sample funnel is 30-50 mm, and the length of the funnel excluding the long neck is 100-150 mm.

[0018] Furthermore, in step (3), the laser power is 1.0-3.0 kW, the defocusing amount is -10 to +10 mm, and the welding speed is 0.2 mm-2.0 mm.

[0019] Furthermore, in step (3), the flow rate of argon gas for protection on the front side of the weld is 15-20 L / min, and the flow rate of argon gas for protection on the back side is 15-20 L / min.

[0020] Furthermore, the distance between the end of the solidification crack and the waistline on one side of the funnel shape of the welded specimen mentioned in the evaluation method of step (4) needs to be calculated using the principle of similar triangles, and the size of the funnel shape of the welded specimen used for calculation comes from the result of the vernier caliper measurement of the shape of the funnel of the welded specimen in step (1) before welding.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) The weld specimen described in this invention for evaluating solidification crack susceptibility testing has a rectangular design that avoids the phenomenon that the weld at the initiation end is not fully penetrated due to laser emission delay, thus affecting the initiation of welding cracks and realizing the transition from unsteady welding to steady welding stage; the funnel-shaped design can realize the transition from steady welding to the crack initiation, propagation and termination stages. This design can improve the stability of solidification crack susceptibility testing.

[0023] (2) The clamping device for evaluating solidification crack susceptibility testing described in this invention has a serrated shape design that reduces the large-area contact between the clamps and pressure plates and the welded specimen, thereby reducing the heat conduction effect on the welded specimen. This design can improve the accuracy of solidification crack susceptibility testing.

[0024] (3) The evaluation method for assessing solidification crack susceptibility testing described in this invention can compare the solidification crack susceptibility of laser-welded metallic materials with different compositions, different sample sizes, and different weld lengths, and reduce the workload of testing. This method can improve the adaptability and convenience of solidification crack susceptibility testing. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the welding specimen used in this invention;

[0026] Figure 2 This is a schematic diagram of the structure of the pressure plate used in this invention;

[0027] Figure 3 This is a schematic diagram of the laser welding solidification crack sensitivity test of the present invention;

[0028] Figure 4 This is a schematic diagram of the cross-section for the laser welding solidification crack sensitivity test of the present invention;

[0029] Explanation of symbols in the attached drawings:

[0030] 1. Welding sample; 2. Fixture; 3. Pressure plate; 4. Laser; 5. Front protective gas tube; 6. Back protective gas tube; 7. Weld. Detailed Implementation

[0031] This invention proposes a test method for evaluating the susceptibility of laser welding of austenitic alloys in thin plates to solidification cracking. The specific implementation steps are as follows:

[0032] (1) Welding Specimen Design: A composite shape of rectangular and funnel-shaped welding specimens is cut. The thickness of the welding specimen is 0.5-5.0 mm. The rectangular length of the welding specimen is 30-50 mm, and the width is 20-30 mm. This design avoids interference with crack sensitivity caused by unstable factors during the initial welding process, allowing the welding process to enter a stable state. The width of the long neck of the welding specimen funnel is 6-16 mm, and the length is 5-20 mm; the bottom edge of the funnel is 30-50 mm, and the length of the funnel excluding the long neck is 100-150 mm. This design promotes the formation of solidification cracks; the bottom edge design of the welding specimen funnel serves to terminate solidification cracks.

[0033] (2) Clamping device design: The upper surface of the clamp has a groove with a width of 5 mm and a depth of 15 mm at its center, and there are right-angled triangular serrations arranged side by side on both sides of the groove; the lower surface of the pressure plate has right-angled triangular serrations arranged side by side, and the edge of the pressure plate is 10-20 mm away from the center of the weld. This can fix the welding sample in step (1) and reduce the heat conduction effect of the clamping device on the welding sample in step (1), thereby improving the accuracy of crack assessment. The clamp has a groove with a width of 5 mm and a depth of 15 mm at its center, which is used to pass shielding gas through the back of the weld for protection.

[0034] (3) Welding process: Wipe the area to be welded of the welding sample in step (1) with acetone, place the welding sample on the clamp of the clamping device in step (2), and fix it on one side of the welding sample in step (1) with a pressure plate. The laser power is 1.0-3.0kW, the defocusing amount is -10-+10 mm, the laser tilt angle is between 5-30°, the welding speed is 0.2 mm-2.0 mm, the shielding gas is argon, the flow rate is 15-20 L / min, and the weld is protected on both sides. Welding starts from one end of the rectangle along the center line of the welding sample in step (1), passes through the long neck of the funnel, and finally terminates at the bottom edge of the funnel to form a full penetration weld with solidification cracks.

[0035] (4) Evaluation method: After welding, the vertical distance between the crack tip and the bottom edge of the welded specimen funnel is measured. Based on the principle of similar triangles, the distance between the solidification crack tip and the waistline on one side of the welded specimen funnel shape is calculated along the direction perpendicular to the welding direction. This distance is defined as the quantitative index for evaluating the susceptibility to solidification cracks - the critical restraint index. The susceptibility to solidification cracks in laser welding is evaluated by comparing the critical restraint index.

[0036] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Example 1:

[0037] First, a square with a side length of 100 mm is cut from a 2 mm thick 304 austenitic stainless steel plate. A suitable distance *d* is taken from one side of the square and welded parallel to that side from one end to the other, ensuring a continuous and fully penetrated weld. The appropriate distance *d* for generating weld solidification cracks is obtained by adjusting the distance, ultimately resulting in a funnel-shaped neck width of 2d = 10 mm for the welded specimen. Next, the required welded specimen is cut from the 2 mm thick 304 austenitic stainless steel plate, such as... Figure 1As shown. The rectangular shape of the welded specimen is 30 mm long and 20 mm wide. The long neck of the funnel of the welded specimen is 10 mm long and 10 mm wide. The length of the funnel without the long neck is 100 mm, and the width of the bottom edge of the funnel is 30 mm.

[0038] Wipe the area to be welded on the welding specimen with acetone. Place the welding specimen 1 on the clamp 2 of the clamping device and fix it to one side with a pressure plate 3, with the edge of the pressure plate 3 15 mm away from the center of the weld. The laser beam 4 starts welding from one end of the rectangle along the center line of the welding specimen, passes through the long neck of the funnel, and finally terminates welding at the bottom edge of the funnel, forming a full penetration weld with solidification cracks. The front shielding gas pipe 5 maintains the same movement trajectory as the laser beam 4 to provide frontal protection for the high-temperature area near the weld pool, while the back shielding gas pipe 6 can achieve back-side protection for the entire weld. The laser power during the welding process is 1.8 kW, the welding speed is 1 m / min, the defocusing amount is 0 mm, the laser tilt angle is 5°, and the shielding gas flow rate on both the front and back of the weld is 20 L / min.

[0039] Finally, the vertical distance between the crack tip and the bottom edge of the welded specimen funnel was measured. Based on the principle of similar triangles, the distance between the solidification crack tip and the waistline on one side of the welded specimen funnel shape, perpendicular to the welding direction, was calculated, which is the critical restraint index. In this example, the critical restraint index obtained experimentally was 17.7 mm. Example 2:

[0040] The specific operation of Example 2 is the same as that of Example 1, but the length of the rectangular welded specimen is 35 mm, and the width of the bottom edge of the funnel is 35 mm. The critical restraint index obtained by experiment in this example is 17.3 mm. Example 3:

[0041] The specific operation of Example 3 is the same as that of Example 1, but the experimental material used is 310S austenitic stainless steel. The critical restraint index obtained by experiment in this example is 23.7 mm. Example 4:

[0042] The specific operation of Example 4 is the same as that of Example 1, but the experimental material used is 310S austenitic stainless steel, the length of the rectangular welded specimen is 35 mm, and the width of the bottom edge of the funnel is 35 mm. The critical restraint index obtained by experiment in this example is 23.3 mm. Example 5:

[0043] The specific operation of Example 5 is the same as that of Example 1, but the length of the rectangular welded specimen is 40 mm, the width of the bottom edge of the funnel is 40 mm, the laser power is 1.6 kW, and the welding speed is 0.8 m / min. The critical restraint index obtained by experiment in this example is 19.6 mm. Example 6:

[0044] The specific operation of Example 6 is the same as that of Example 1, but the experimental material used is 310S austenitic stainless steel, the length of the rectangular welded specimen is 60 mm, the width of the bottom edge of the funnel is 60 mm, the laser power is 1.6 kW, and the welding speed is 0.8 m / min. The critical restraint index obtained by experiment in this example is 31.9 mm.

[0045] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A test method for evaluating the susceptibility of laser welding of austenitic alloys in thin plates to solidification cracking, characterized in that, Includes the following steps: (1) Welding specimen design: Cut a composite shape welding specimen with a combination of rectangle and funnel shape. The rectangular design of the welding specimen can avoid the interference of unstable factors during the welding process on the sensitivity to cracks, and allow the welding process to enter a stable state. The long neck design of the funnel of the welding specimen can promote the formation of solidification cracks. The bottom edge design of the funnel of the welding specimen plays the role of terminating solidification cracks. (2) Clamping device design: There is a groove with a width of 5 mm and a depth of 15 mm in the center of the upper surface of the clamp, and there are right-angled triangular serrations arranged side by side on both sides of the groove; the lower surface of the pressure plate has right-angled triangular serrations arranged side by side, and the edge of the pressure plate is 10-20 mm away from the center of the weld. This can fix the welding sample in step (1) and reduce the heat conduction effect of the clamping device on the welding sample in step (1), thereby improving the accuracy of crack assessment. (3) Welding process: Wipe the area to be welded of the welding sample in step (1) with acetone, place the welding sample on the clamp of the clamping device in step (2), and fix one side of the welding sample in step (1) with a pressure plate; the laser tilt angle is between 5-30°, and argon is used as the shielding gas to protect the weld from both sides; start welding from one end of the rectangle along the center line of the welding sample in step (1), pass through the long neck of the funnel, and finally terminate welding at the bottom edge of the funnel to form a full penetration weld with solidification cracks; (4) Evaluation method: After welding, the vertical distance between the crack end and the bottom edge of the welding specimen funnel is measured. According to the principle of similar triangles, the distance between the solidification crack end and the waistline on one side of the welding specimen funnel shape is calculated along the direction perpendicular to the welding direction. This distance is defined as the quantitative index for evaluating the solidification crack sensitivity - the critical restraint index. The laser welding solidification crack sensitivity evaluation is completed by comparing the critical restraint index.

2. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (1), the thickness of the welding sample is 0.5-5.0 mm.

3. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (1), the length of the rectangular welding specimen is 30-50 mm and the width is 20-30 mm.

4. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (3), the welding start end is the middle position of the rectangular length end of the welding sample in step (1).

5. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: The method for determining the width of the long neck of the welding sample funnel in step (1) is as follows: cut a square with a side length of 100 mm from the thin sheet metal material used, and weld it from one end of the edge to the other end at an appropriate distance d from one side of the square, parallel to the edge, to ensure that the weld is continuous and fully penetrated. By adjusting the above distance d, a suitable distance for generating welding solidification cracks is obtained, so as to ensure that solidification cracks can be caused when welding to the long neck of the funnel as mentioned in step (3), that is, the width of the long neck of the welding sample funnel in step (1) is 2d.

6. The test method for evaluating the susceptibility of laser welding solidification cracking in thin austenitic alloys according to claim 5, characterized in that: The distance d is 3-8 mm.

7. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (1), the width of the long neck of the welding sample funnel is 6-16 mm and the length is 5-20 mm.

8. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (1), the bottom edge dimension of the welding sample funnel is 30-50 mm, and the length of the funnel excluding the long neck is 100-150 mm.

9. The test method for evaluating the susceptibility to solidification cracking in laser welding of thin austenitic alloys according to claim 1, characterized in that: In step (3), the laser power is 1.0-3.0 kW, the defocusing amount is -10 to +10 mm, and the welding speed is 0.2 mm to 2.0 mm.

10. The test method for evaluating the susceptibility of laser welding solidification cracking in thin austenitic alloys according to claim 1, characterized in that: In step (3), the flow rate of argon gas for the front side of the weld is 15-20 L / min, and the flow rate of argon gas for the back side is 15-20 L / min.

11. The test method for evaluating the susceptibility of laser welding solidification cracking in thin austenitic alloys according to claim 1, characterized in that: The distance between the end of the solidification crack and the waistline on one side of the funnel shape of the welded specimen mentioned in the evaluation method in step (4) needs to be calculated using the principle of similar triangles, and the size of the funnel shape of the welded specimen used for calculation comes from the result of the vernier caliper measurement of the shape of the funnel of the welded specimen in step (1) before welding.

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