Method for evaluating hydrogen resistance of welded joint of high-strength steel closed part

Abstract

The invention discloses a method for evaluating the hydrogen resistance of a welded joint of a high-strength steel closed part, which comprises the following steps of: S1, preparing a slow tensile sample and a welding seam sample, and cleaning the surfaces of the slow tensile sample and the welding seam sample; s2, carrying out diffusible hydrogen analysis on the weld joint sample by utilizing a thermal desorption method to obtain the diffusible hydrogen content of the sample; s3, carrying out polarization treatment on the surface of the slow tensile sample; s4, setting a hydrogen charging current, and carrying out a dynamic hydrogen charging slow tensile test to obtain the fracture stress of the sample; and S5, obtaining the ratio TSW / TS of the fracture stress to the tensile strength of the sample, and judging the hydrogen resistance of the welded joint of the high-strength steel closed part according to the ratio TSW / TS. According to the method, the hydrogen concentration and the fracture stress are combined, the relation between the delayed cracking fracture stress and the hydrogen concentration under different welding process conditions is obtained, the hydrogen resistance of the high-strength steel closed part welding joint is judged by combining the tensile strength of the material, and a reference is provided for the delayed cracking risk of the high-strength steel welding head.

Description

Technical Field

[0001] This invention relates to the field of welding failure evaluation, and more specifically, to a method for evaluating the hydrogen resistance of welded joints of high-strength steel closed-end components. Background Technology

[0002] High-strength steel is increasingly used in the automotive industry due to its higher strength and excellent overall performance. In the forming process of high-strength steel parts, especially closed-end parts, welding is often used for connection, in addition to the forming process itself. However, the main problem encountered in the application of high-strength steel welding is weld joint cracking.

[0003] Currently, welding cracks take many forms. From an essential perspective, cracks can be classified into cold cracks, hot cracks, reheat cracks, lamellar tears, and stress corrosion cracks. Cold cracks are a relatively common type of crack defect in welding production, generally forming after welding and cooling to lower temperatures. Cold cracks typically form below the martensitic transformation temperature under the combined effects of restraint stress, hardened structures, and hydrogen. Cracks can propagate along grain boundaries or through transgranular cleavage. In some cases, cold crack formation has a certain delay, meaning it doesn't form immediately after welding but has a certain incubation period, which can last for several months. The formation of cold cracks is related to hydrogen diffusion; hydrogen in the weld joint diffuses and accumulates under stress, leading to crack initiation. Therefore, this type of cold crack is also called hydrogen-induced delayed cracking. There are two main sources of diffusible hydrogen that form cold cracks. One source is the material itself, which retains a certain concentration of diffusible hydrogen during the production and processing process. Studies have shown that the content of diffusible hydrogen in the material is closely related to the density of point defects and line defects in the material's microstructure. After the material is cold-stamped, the number of defects inside it will change accordingly, such as a significant increase in dislocation density. This means that the number of hydrogen trap sites in the material's microstructure increases, providing a basis for hydrogen enrichment in the heat-affected zone during subsequent welding. The other source is introduced during the welding process, such as the decomposition of hydrogen and moisture in the protective gas, and the decomposition of moisture and oil adsorbed on the material surface.

[0004] Therefore, in order to avoid failure of high-strength steel welded joints during application, it is necessary to study a method that can evaluate the hydrogen embrittlement performance of high-strength steel welded joints. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints. This method combines hydrogen concentration with fracture stress to obtain the relationship between delayed cracking fracture stress and hydrogen concentration under different welding process conditions. Furthermore, it combines the tensile strength of the material to determine the hydrogen resistance of high-strength steel closed-end welded joints, providing a reference for assessing the risk of delayed cracking in high-strength steel welded joints.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints includes the following steps:

[0008] S1, prepare slow tensile test specimens and weld specimens, and perform surface cleaning;

[0009] S2, The diffusible hydrogen content of the weld sample was obtained by using the thermal desorption method.

[0010] S3, polarize the surface of the slow-stretched sample;

[0011] S4, set the hydrogen charging current and conduct a dynamic hydrogen charging slow tensile test to obtain the fracture stress of the sample;

[0012] S5, obtain the ratio TS of the fracture stress to the tensile strength of the specimen. W / TS, and based on this, determine the hydrogen resistance of the welded joint of the high-strength steel closed component.

[0013] Preferably, the process of step S1 is as follows:

[0014] The welded joint was cut off using wire cutting and then degreased with alcohol.

[0015] The cut-off welded joints are processed into rectangular slow-tension specimens with weld seams.

[0016] Weld specimens are obtained by shearing the slow-tension specimen.

[0017] Degrease the slow tensile test specimens and weld specimens in alcohol to ensure that the specimen surfaces are clean and free of oil.

[0018] Preferably, in step S3, the surface of the slow-stretched sample is polarized using an electrochemical sample method, and the polarization current is the anodic current.

[0019] Preferably, in step S4, the hydrogen charging current is the cathode current, and the hydrogen charging current I = 200 / TS + C H / 3, TS is the tensile strength of the specimen, C H The diffusible hydrogen content of the sample.

[0020] Preferably, in step S4, during the dynamic hydrogen-charging slow stretching test, the hydrogen charging solution is NaOH solution, and the slow stretching rate is 4*10. -4 mm / s~1*10 -5 mm / s.

[0021] Preferably, in step S5, the method for determining the hydrogen resistance of the high-strength steel closed-end welded joint is as follows:

[0022] When TS W When / TS≥0.85, there is no risk of hydrogen embrittlement in the welded joint of high-strength steel closed-end components;

[0023] When 0.75≤TS W When / TS < 0.85, the welded joint of high-strength steel closed-end components is at slight risk of hydrogen embrittlement.

[0024] When 0.5≤TS W When / TS<0.75, the welded joint of high-strength steel closed-end component has a moderate risk of hydrogen embrittlement.

[0025] When TS W When / TS < 0.5, the welded joint of a high-strength steel closed component is at serious risk of hydrogen embrittlement.

[0026] The hydrogen resistance evaluation method for high-strength steel closed-end welded joints provided by this invention has the following advantages:

[0027] 1. This invention can obtain the delayed cracking resistance of welded joints for high-strength automotive steel parts, and can be combined with welding processes to improve the hydrogen embrittlement resistance of high-strength steel welded joints and reduce the risk of cracking.

[0028] 2. This invention, starting from the characteristics of welded joints, provides a method for evaluating the hydrogen resistance of high-strength steel closed-joint welded joints from the perspective of fracture stress. Using this method, not only can the hydrogen concentration of the welded joint of high-strength steel parts be obtained, but the hydrogen concentration can also be combined with fracture stress to obtain the relationship between delayed cracking fracture stress and hydrogen concentration under different welding process conditions. The fracture stress values ​​and hydrogen concentrations obtained using this invention can provide a reference for the delayed cracking risk of high-strength steel welded joints and provide guidance for improving the hydrogen resistance and safe use of high-strength steel parts through welding process improvements.

[0029] 3. This invention is applicable to the evaluation of hydrogen resistance of welded joints of high-strength automotive steel closed components, and can also be applied to other high-strength metal materials. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to the present invention.

[0031] Figure 2 This is a schematic diagram of a typical high-strength steel closed component of the present invention;

[0032] Figure 3 This is a schematic diagram of the slow-tension specimen of the present invention. (a) is a structural diagram of the slow-tension specimen, and (b) is a side view of (a).

[0033] Figure 4 This is a sampling diagram of hydrogen diffusion analysis of the weld seam according to the present invention. Detailed Implementation

[0034] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] The principle of this invention is that the weld seam of the welded joint is the weakest point after welding because the hydrogen concentration at this location is higher than that at other locations after welding, and the microstructure undergoes certain changes. The welded joint has the most defects, and it is the location that most easily adsorbs and absorbs hydrogen atoms using the electrochemical hydrogen charging method. Under tensile stress, it is most prone to cracking. Therefore, the fracture stress of the welded joint can be obtained through a dynamic hydrogen charging slow tensile test.

[0036] Combination Figure 1 As shown, the present invention provides a method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints, comprising the following steps:

[0037] S1, prepare slow tensile test specimens and weld specimens, and perform surface cleaning;

[0038] The specific process is as follows:

[0039] (1) Cut the welded joint using wire cutting and remove the oil with alcohol;

[0040] Welding template preparation: The sample with the weld joint is cut from the part using wire cutting method. Figure 2 (At point A in the middle), then degrease with alcohol to remove surface grease. Typical parts and cutting diagrams are shown below. Figure 2 As shown;

[0041] (2) The cut-off welded joint is processed into a rectangular slow tensile specimen with weld seam;

[0042] Slow-tension specimen preparation: The cut welded joint sample is processed into a rectangular slow-tension specimen with the weld seam, ensuring the weld seam is in the center. The edges are milled, and a hole is drilled in the center of the top. (Specific details are as follows...) Figure 3 As shown in (a) and (b), 10 slow tensile specimens were processed for each material;

[0043] (3) Shear the slow tensile specimen to obtain the weld specimen.

[0044] Weld sample taking: using a shearing method to... Figure 4 The middle section of the slow tensile specimen is sheared. To ensure the accuracy of the hydrogen diffusion test, the shearing should be performed as close to the weld area as possible, with the sampling position no more than 2 mm away from the weld. The weld should be completely cut off. (Specific details are as follows...) Figure 4 As shown at point B, three weld samples were processed for each material.

[0045] (4) Place the slow tensile test specimen and weld test specimen in alcohol to degrease them and ensure that the surface of the test specimen is clean and free of oil.

[0046] Surface cleaning: Before the test, immerse the test sample in alcohol for 20 minutes to degrease it and ensure that the surface is clean and free of oil;

[0047] S2, The diffusible hydrogen content of the weld sample was obtained by using the thermal desorption method.

[0048] Diffusion hydrogen analysis: Using a hydrogen analyzer, the sample was heated at 400±50℃ for 30±10 min using the thermal desorption method to obtain the diffusion hydrogen content C. H Three samples were taken for analysis, and the average value was taken.

[0049] S3, polarize the surface of the slow-stretched sample;

[0050] Surface polarization: To eliminate surface residues and improve the accuracy of slow tensile tests, the surface of the slow tensile specimen is polarized using an electrochemical method before the test. The polarization current is the anodic current (e.g., 0.5–2 mA / cm). 2 (anode current), polarization time 10±5 min;

[0051] S4, set the hydrogen charging current and conduct a dynamic hydrogen charging slow tensile test to obtain the fracture stress of the sample;

[0052] Hydrogen charging current setting: The hydrogen charging current is the cathode current, which can be calculated using the formula I = 200 / TS + C. H / 3, TS is the tensile strength of the specimen, C H The diffusible hydrogen content of the sample.

[0053] Slow tensile test: Tension is performed using the dynamic hydrogen-charging slow tensile test method. The hydrogen charging solution is a NaOH solution (the concentration of NaOH can be 0.5-1.0 mol / L), and the hydrogen charging current is the current set above (i.e., I = 200 / TS + C). H / 3), slow stretching rate is 4*10 -4 mm / s~1*10 -5 mm / s, and the fracture stress TS was obtained after the test. W ;

[0054] S5, obtain the ratio TS of the fracture stress to the tensile strength of the specimen. W / TS, and based on this, determine the hydrogen resistance of the welded joint of the high-strength steel closed component.

[0055] Hydrogen resistance evaluation: After the experiment, the fracture stress was compared with the tensile strength of the test material, i.e., TS. W The / TS ratio is used to determine the hydrogen resistance of welded joints of high-strength steel closed components.

[0056] When TS W When / TS≥0.85, there is no risk of hydrogen embrittlement in the welded joint of high-strength steel closed-end components;

[0057] When 0.75≤TS W When / TS < 0.85, the welded joint of high-strength steel closed-end components is at slight risk of hydrogen embrittlement.

[0058] When 0.5≤TS W When / TS<0.75, the welded joint of high-strength steel closed-end component has a moderate risk of hydrogen embrittlement.

[0059] When TS W When / TS < 0.5, the welded joint of the high-strength steel closed component is at risk of severe hydrogen embrittlement.

[0060] Example 1

[0061] This embodiment uses a DP1180 lap welded sample as the test object, and the specific operation is as follows:

[0062] 1. Preparation of welding template: The sample with the welding joint is cut from the part using wire cutting method. Figure 2 (At point A), then use alcohol to remove the surface grease;

[0063] 2. Slow-tension specimen processing: The cut sample is processed into a rectangular slow-tension specimen with a weld, with a size of 85mm*15mm. The weld is ensured to be centered. The edges are milled, and an 8mm diameter hole is drilled at the top center. (Specific details are as follows...) Figure 3 As shown, 10 slow tensile specimens were processed for each material;

[0064] 3. Weld seam sample taking: using a shearing method to sample the weld seam. Figure 3 The middle section of the slow-stretched sample was sheared. To ensure the accuracy of the hydrogen diffusion test, the shearing was performed as close to the weld area as possible, with the sampling position no more than 2mm away from the weld. The weld was then completely cut off. (Specific details are as follows...) Figure 4 As shown at point B, three weld samples were processed for each material.

[0065] 4. Surface cleaning: Before the test, immerse the test sample in alcohol for 20 minutes to degrease it and ensure that the surface is clean and free of oil;

[0066] 5. Diffusion hydrogen analysis: Using a hydrogen analyzer, the sample was heated to 400℃ for 30 min using the thermal desorption method to obtain the diffusion hydrogen content C. H Three samples were taken for analysis, and the average value was taken.

[0067] 6. Surface Polarization: To eliminate surface residue and improve the accuracy of the slow tensile test, the sample surface is polarized using an electrochemical method before the test. The polarization current is 0.5 mA / cm², which is the anodic current. 2 Polarization time 10 min;

[0068] 7. Hydrogen charging current setting: The hydrogen charging current is the cathode current, which can be calculated using the formula: I = 200 / TS + C H / 3, TS test material tensile strength;

[0069] 8. Slow Tensile Test: Tensile testing was conducted using a dynamic hydrogen-charging slow tensile test method. The hydrogen charging solution was a 0.5 mol / L NaOH solution, the hydrogen charging current was the same as the current I in step 7, and the slow tensile rate was 2*10. -4 mm / s, and the fracture stress TS was obtained after the test. W The experiment was repeated 5 times and the average value was taken.

[0070] 9. Evaluation of hydrogen resistance: After the experiment, the fracture stress is compared with the tensile strength of the test material, i.e., TS. W The / TS ratio, calculated from Table 1, is 0.874, which is above 0.85, indicating that the welded joint has excellent hydrogen resistance.

[0071] Table 1

[0072]

[0073] Example 2

[0074] The test subject in this embodiment is a DP1470 lap weld sample, and the specific operation is as follows:

[0075] 1. Preparation of welding template: The sample with the welding joint is cut from the part using wire cutting method. Figure 2 (As shown at point A in the middle), then use alcohol to remove the surface grease;

[0076] 2. Slow-tension specimen processing: The cut sample is processed into a rectangular slow-tension specimen with a weld, with a size of 85mm*15mm. The weld is ensured to be centered. The edges are milled, and an 8mm diameter hole is drilled at the top center. (Specific details are as follows...) Figure 3 As shown, 10 slow tensile specimens were processed for each material;

[0077] 3. Weld seam sample taking: using a shearing method to sample the weld seam. Figure 2 Partially, samples were sheared. To ensure the accuracy of the hydrogen diffusion test, the shearing was performed as close to the weld area as possible, with the sampling location no more than 2 mm away from the weld. The weld was then completely cut off, as detailed below. Figure 4 As shown at point B, three weld samples were processed for each material.

[0078] 4. Surface cleaning: Before the test, immerse the test sample in alcohol for 20 minutes to degrease it and ensure that the surface is clean and free of oil;

[0079] 5. Diffusion hydrogen analysis: Using a hydrogen analyzer, the sample was heated to 400℃ for 30 min using the thermal desorption method to obtain the diffusion hydrogen content C. H Three samples were taken for analysis, and the average value was taken.

[0080] 6. Surface Polarization: To eliminate surface residue and improve the accuracy of the slow tensile test, the sample surface is polarized using an electrochemical method before the test. The polarization current is 0.5 mA / cm², which is the anodic current. 2 Polarization time 10 min;

[0081] 7. Hydrogen charging current setting: The hydrogen charging current is the cathode current, which can be calculated using the formula: I = 200 / TS + C H / 3, TS test material tensile strength;

[0082] 8. Slow Tensile Test: Tensile testing was conducted using a dynamic hydrogen-charging slow tensile test method. The hydrogen charging solution was a 0.5 mol / L NaOH solution, the hydrogen charging current was the same as the current I in step 7, and the slow tensile rate was 4*10. -4 mm / s, and the fracture stress TS was obtained after the test. W The experiment was repeated 5 times and the average value was taken.

[0083] 9. Evaluation of hydrogen resistance: After the experiment, the fracture stress is compared with the tensile strength of the test material, i.e., TS. W The / TS ratio, calculated from Table 2, is 0.617, which falls within the range of 0.5 to 0.75, indicating that the welded joint has a moderate risk of hydrogen embrittlement.

[0084] Table 2

[0085]

[0086] Example 3

[0087] The test object in this embodiment is an MS1500 L-type welded sample, and the specific operation is as follows:

[0088] 1. Preparation of welding template: The sample with the welding joint is cut from the part using wire cutting method. Figure 2 (As shown at point A in the middle), then use alcohol to remove the surface grease;

[0089] 2. Slow-tension specimen processing: The cut sample is processed into a rectangular slow-tension specimen with a weld, with a size of 85mm*15mm. The weld is ensured to be centered. The edges are milled, and an 8mm diameter hole is drilled at the top center. (Specific details are as follows...) Figure 3 As shown, 10 slow tensile specimens were processed for each material;

[0090] 3. Weld seam sample taking: using a shearing method to sample the weld seam. Figure 2 Partially, samples were sheared. To ensure the accuracy of the hydrogen diffusion test, the shearing was performed as close to the weld area as possible, with the sampling location no more than 2 mm away from the weld. The weld was then completely cut off, as detailed below. Figure 4 As shown at point B, three weld samples were processed for each material.

[0091] 4. Surface cleaning: Before the test, immerse the test sample in alcohol for 20 minutes to degrease it and ensure that the surface is clean and free of oil;

[0092] 5. Diffusion hydrogen analysis: Using a hydrogen analyzer, the sample was heated to 400℃ for 30 min using the thermal desorption method to obtain the diffusion hydrogen content C. H Three samples were taken for analysis, and the average value was taken.

[0093] 6. Surface Polarization: To eliminate surface residue and improve the accuracy of the slow tensile test, the sample surface is polarized using an electrochemical method before the test. The polarization current is 0.5 mA / cm², which is the anodic current. 2 Polarization time 10 min;

[0094] 7. Hydrogen charging current setting: The hydrogen charging current is the cathode current, which can be calculated using the formula: I = 200 / TS + C H / 3, TS test material tensile strength;

[0095] 8. Slow Tensile Test: Tensile testing was conducted using a dynamic hydrogen-charging slow tensile test method. The hydrogen charging solution was a 0.5 mol / L NaOH solution, the hydrogen charging current was the same as the current I in step 7, and the slow tensile rate was 1*10. -4 mm / s, and the fracture stress TS was obtained after the test. W The experiment was repeated 5 times and the average value was taken.

[0096] 9. Evaluation of hydrogen resistance: After the experiment, the fracture stress is compared with the tensile strength of the test material, i.e., TS. W The / TS ratio, calculated from Table 3, is 0.791, which falls within the range of 0.75 to 0.85. This indicates that the welded joint has a slight risk of hydrogen embrittlement.

[0097] Table 3

[0098]

[0099]

[0100] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for evaluating the hydrogen resistance of welded joints of high-strength steel closed-end components, characterized in that, Includes the following steps: S1, prepare slow tensile test specimens and weld specimens, and perform surface cleaning; S2, The diffusible hydrogen content of the weld sample was obtained by using the thermal desorption method. S3, polarize the surface of the slow-stretched sample; S4, set the hydrogen charging current and conduct a dynamic hydrogen charging slow tensile test to obtain the fracture stress of the sample; S5, obtain the ratio TS of the fracture stress to the tensile strength of the specimen. W / TS, and based on this, determine the hydrogen resistance of the welded joint of the high-strength steel closed component.

2. The method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to claim 1, characterized in that: The process of step S1 is as follows: The welded joint was cut off using wire cutting and then degreased with alcohol. The cut-off welded joints are processed into rectangular slow-tension specimens with weld seams. Weld specimens are obtained by shearing the slow-tension specimen. Degrease the slow tensile test specimens and weld specimens in alcohol to ensure that the specimen surfaces are clean and free of oil.

3. The method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to claim 1, characterized in that: In step S3, the surface of the slow-stretched sample is polarized using an electrochemical sample method, with the polarization current being the anodic current.

4. The method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to claim 1, characterized in that: In step S4, the hydrogen charging current is the cathode current, and the hydrogen charging current I = 200 / TS + C H / 3, TS is the tensile strength of the specimen, C H The diffusible hydrogen content of the sample.

5. The method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to claim 1, characterized in that: In step S4, during the dynamic hydrogen-charging slow stretching test, the hydrogen charging solution used is NaOH solution, and the slow stretching rate is 4*10. -4 mm / s~1*10 -5 mm / s.

6. The method for evaluating the hydrogen resistance of high-strength steel closed-end welded joints according to claim 1, characterized in that, In step S5, the method for determining the hydrogen resistance of the high-strength steel closed-end welded joint is as follows: When TS W When / TS≥0.85, there is no risk of hydrogen embrittlement in the welded joint of high-strength steel closed-end components; When 0.75≤TS W When / TS < 0.85, the welded joint of high-strength steel closed-end components is at slight risk of hydrogen embrittlement. When 0.5≤TS W When / TS<0.75, the welded joint of high-strength steel closed-end component has a moderate risk of hydrogen embrittlement. When TS W When / TS < 0.5, the welded joint of the high-strength steel closed component is at risk of severe hydrogen embrittlement.

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