A method for evaluating atmospheric corrosion resistance of steel welded joints

Abstract

The present invention relates to a method for evaluating the atmospheric corrosion resistance of steel welded joints. The present invention utilizes a scanning electrochemical workstation to perform potential scanning on the surface of a welded joint sample, thereby characterizing the corrosion potential of various parts of the welded joint sample for studying the corrosion resistance of the welded joint sample. The welded joint sample is pretreated with solutions of different simulated atmospheric environments to simulate a thin liquid film formed on the surface of the sample under the corrosive environment, thereby studying the corrosion resistance of the welded joint under different atmospheric environments and providing a corrosion resistance basis for the selection of welding materials and the formulation of welding process parameters. The welded joint is studied to quickly and accurately evaluate the corrosion resistance of various areas of the welded joint. The corrosion mechanisms of the welded joint in different atmospheric environments are different. Different thresholds are set according to the severity of the corrosive environment and while fully considering the weld heat affected zone as a weak position of the welded joint, so that the evaluation results are more accurate and reasonable.

Description

Technical Field

[0001] The present invention relates to the technical field of metal materials, in particular to a method for evaluating the atmospheric corrosion resistance of steel welded joints. Background Art

[0002] In recent years, corrosion failure caused by welded joints in engineering structures has become increasingly prominent. Steel structures need to be manufactured through welding processes during use. When considering the corrosion resistance of the overall structural parts, it is necessary not only to study the corrosion resistance of the parent material, but also to pay attention to the corrosion resistance of each area of ​​the welded joint. Due to the unevenness of the organization and composition of the joint, the corrosion resistance of the joint is different from that of the parent material, which can easily become a weak link and reduce the service life of the steel structure.

[0003] The risk of corrosion damage to welded joints can be reduced to a certain extent by rationally selecting welding materials and formulating optimal welding process parameters. However, there is currently a lack of methods to quickly and effectively evaluate the corrosion resistance of welded joints.

[0004] The potential difference between different areas of the weld joint is different, so the corrosion resistance is different. Since the area of ​​each area is small, the sample area tested by the macro electrochemical method is large, and it is difficult to accurately perform electrochemical testing on each area of ​​the weld joint. In order to solve the difficulties of the existing technology, the present invention proposes a method for evaluating the atmospheric corrosion resistance of steel weld joints using micro-area electrochemistry.

[0005] Chinese patent publication number CN114252391A discloses a method for evaluating the industrial atmospheric corrosion resistance of steel welded joints. The welded joint is placed in an electrolytic cell for electrolysis testing. The electrolyte contains 0.1-1% Na2SO4, 0.1-0.4% NaHSO3, and a pH value of 2-4. After the electrolysis test, the height difference ratio between the base material, the heat-affected zone, and the weld is used for judgment. This method requires height measurement using a metallographic microscope, which is subjective. In addition, this method is only applicable to industrial atmospheric environments and has limitations, making it impossible to objectively evaluate the atmospheric corrosion resistance of the welded joint.

[0006] Chinese patent publication number CN 102788745B discloses a method for testing and evaluating the corrosion resistance of welds. The method uses a 0.5% to 6% NaCl solution and a 0.1% to 2% CH3COOH solution for electrolysis. The surface morphology of the sample is then scanned using a surface profilometer. The ratio of the heat-affected zone and the weld to the base material height are calculated and compared. The closer the two are to 1, the better the corrosion resistance of the weld. This method requires the use of a profilometer for height measurement. If uneven corrosion occurs in a certain area of ​​the weld, it is easy to cause inaccurate height measurement, thereby introducing errors. The electrolyte accelerates corrosion and cannot simulate the atmospheric environment.

[0007] Chinese patent publication number 201510752079.8 discloses a method for evaluating the corrosion performance of welded joints based on potential testing technology. A suitable corrosive solution is prepared according to the service environment, a drop of corrosive solution is dripped, and the potential of the weld, base material and heat-affected zone is measured using an electrochemical test device. The degree of corrosion of the welded joint is evaluated by calculating the potential difference between the three areas, thereby determining whether the selected welding material and welding process parameters meet the corrosion resistance requirements. The disadvantage of this method is that it is difficult to ensure the uniformity of the area of ​​the dripping droplet, which causes errors. Moreover, if the area of ​​the heat-affected zone is very small, it is difficult to control the droplet to be completely located within the heat-affected zone, which easily leads to errors. Summary of the Invention

[0008] The present invention provides a method for evaluating the atmospheric corrosion resistance of steel welded joints. The method conducts in-situ research on the welded joints without destroying the surface of the sample, and can quickly and accurately evaluate the corrosion resistance of various areas of the welded joints, providing a corrosion resistance basis for the selection of welding materials and the formulation of welding process parameters. Since the corrosion mechanisms of welded joints in different atmospheric environments are different, different thresholds are set according to the severity of the corrosion environment and full consideration is given to the weld heat affected zone as a weak position of the welded joint, so that the evaluation results are more accurate and reasonable.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A method for evaluating the atmospheric corrosion resistance of steel welded joints comprises the following steps:

[0011] Step 1: Cut a weld joint specimen with a length of 20 to 50 mm and a width of 10 to 30 mm, determine the position of the weld, heat-affected zone and parent material, and mark them;

[0012] Step 2: Prepare solutions simulating different atmospheric environments: deionized water is used for the pastoral atmospheric environment; (0.01-0.02) mol / L NaHSO3 + (0.01-0.02) mol / L NaHCO3 + (0.001-0.005) mol / L (NH4)2SO4 + (0.001-0.003) mol / L NaNO3 + (0.001-0.003) NaF is used for the industrial atmospheric environment; and 0.1-3.5% NaCl solution is used for the marine atmospheric environment.

[0013] Step 3: Saturate the filter paper with the corresponding solution, spread it on the surface of the weld joint sample, and spray the test paper intermittently until it is saturated;

[0014] Step 4: Place the processed sample horizontally on the SKP system test platform, connect the lower surface of the sample to the micro-area electrochemical workstation, control the distance between the probe and the sample surface to be 80-110 μm, the amplitude to be 25-55 μm, and the probe frequency to be 50-80 μm;

[0015] Step 5: Scan and test the weld, heat-affected zone, and base material in the order of the weld;

[0016] Step 6: After the test, obtain the potential distribution diagram and obtain the average point values ​​of the weld area, heat-affected zone, and base material area;

[0017] Step 7: Set different thresholds to evaluate the atmospheric corrosion resistance of steel welded joints under different atmospheric environments, including the following:

[0018] (1) Pastoral atmosphere:

[0019] if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0020] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, that is, the welding process is not selected rationally, among which U 焊缝 、U 母材 、U 热影响区 Respectively represent the average point values ​​of the weld area, heat-affected zone, and base material area;

[0021] (2) Industrial atmosphere

[0022] if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0023] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, which means that the welding process is not selected rationally;

[0024] (3) Marine atmosphere:

[0025] If if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0026] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. The corrosion resistance of the welded joint is poor, which means that the welding process is not selected properly.

[0027] Furthermore, the sample in step 1 is ground and polished so that the roughness of the surface to be corroded of the sample is less than or equal to 0.6 μm. When determining the positions of the weld, the heat-affected zone, and the base material, ferric chloride FeCl3, dihydrate oxalic acid C2H2O4·2H2O, hydrogen peroxide H2O2, and water H2O are used in a mass ratio of 30-50:20-40:60-120:340-400 to corrode the weld joint sample. The sample is then polished again, cleaned, dried, and placed in a dryer for later use.

[0028] Furthermore, in step 4, the probe diameter is selected to be 150 or 500 μm.

[0029] Furthermore, in the test in step five, the lateral step is 25-50 μm / point and the longitudinal step is 10-25 μm / point.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) In-situ research on welded joints can be conducted without damaging the sample surface, thereby quickly and accurately evaluating the corrosion resistance of each area of ​​the welded joint, providing a corrosion resistance basis for the selection of welding materials and the formulation of welding process parameters;

[0032] 2) Since the corrosion mechanism of welded joints in different atmospheric environments is different, different thresholds are set according to the severity of the corrosion environment and full consideration of the weld heat affected zone as the weak position of the welded joint to make the evaluation results more accurate and reasonable. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention are further described below:

[0034] A method for evaluating the atmospheric corrosion resistance of steel welded joints. A scanning electrochemical workstation is used to study the surface corrosion potential of a very small micro-area. The present invention uses a scanning electrochemical workstation to perform potential scanning on the surface of a welded joint sample, thereby characterizing the corrosion potential of various parts of the welded joint sample for studying the corrosion resistance of the welded joint sample. The welded joint sample is pretreated with solutions of different simulated atmospheric environments to simulate the thin liquid film formed on the surface of the sample in the corrosive environment, thereby studying the corrosion resistance of the welded joint in different atmospheric environments, providing a corrosion resistance basis for the selection of welding materials and the formulation of welding process parameters. The method specifically includes the following steps:

[0035] Step 1: Use wire cutting to cut a welding joint sample with a length of 20 to 50 mm and a width of 10 to 30 mm. The surface of the sample is polished with 240#, 400#, 600#, and 1000# sandpaper in sequence to make the roughness of the corrosion surface of the sample less than or equal to 0.6μm. Use metallographic etching agent to erode the welding joint sample, preliminarily determine the position of the weld, heat-affected zone and parent material and mark them; polish the sample again, clean it, dry it, and put it in a dryer for later use.

[0036] Step 2. Prepare solutions simulating different atmospheric environments: deionized water is used for rural atmospheric environment, (0.01-0.02) mol / L NaHSO3+(0.01-0.02) mol / L NaHCO3+(0.001-0.005) mol / L(NH4)2SO4+(0.001-0.003) mol / L NaNO3+(0.001-0.003) NaF is used for industrial atmospheric environment, and 0.1-3.5% NaCl solution is used for marine atmospheric environment.

[0037] Step 3: Saturate the filter paper with the corresponding solution and spread it flat on the surface of the weld joint sample. However, due to the volatilization of the solution in the air and the participation of part of the solution in the chemical reaction, the test paper will become dry and the amount of solution will decrease. Therefore, spray the corresponding solution every 1 to 3 minutes until the filter paper is saturated. Spray 4 to 8 times in total. Let it stand for 3 to 10 minutes before testing.

[0038] Step 4: Place the processed sample on the SKP system test platform. Connect the lower surface of the sample to the micro-area electrochemical workstation through conductive glue. Adjust the sample level. The probe diameter is 150 or 500 μm. The distance between the probe and the sample surface is controlled at 80-110 μm. A probe distance that is too high will result in a signal feedback value that is too low, and a probe distance that is too low will easily cause the probe to touch the sample. The amplitude is 25-55 μm, and the probe frequency is 50-80 μm.

[0039] Step 5. Select the surface scanning mode. Determine the scanning area based on the weld, heat-affected zone, and base material areas marked in step 1. Starting from the weld area, scan in the order of weld, heat-affected zone, and base material. Select a test area with a length of 20 to 60 mm and a width of 10 to 50 mm. The horizontal step is 25 to 50 μm / point and the vertical step is 10 to 25 μm / point.

[0040] Step 6. After the test, obtain the potential distribution diagram and use the drawing software to make a three-dimensional matrix diagram. Select five points in the weld area, heat-affected zone, and base material area respectively, record the potential of the point, and obtain the average potential value of the area.

[0041] Step 7. Set different thresholds to evaluate the atmospheric corrosion resistance of steel welded joints under different atmospheric environments. The severity of the environment is from weak to strong, namely, rural atmosphere, industrial atmosphere, and marine atmosphere. Therefore, the selected thresholds are different. When the potential of the weld is fixed, the potential of the heat-affected zone under different atmospheric environments after the welding process is the highest. The high potential improves the corrosion resistance and avoids severe corrosion of the heat-affected zone in harsh environments. Therefore, three different thresholds are selected according to the three environments: rural atmosphere 1.15, industrial atmosphere 1.25, and marine atmosphere 1.35. The specific contents include the following:

[0042] (1) Pastoral atmosphere:

[0043] if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0044] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, that is, the welding process is not selected rationally, among which U 焊缝 、U 母材 、U 热影响区 Represent the average potential values ​​of the weld zone, heat-affected zone, and base material zone respectively;

[0045] (2) Industrial atmosphere

[0046] if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0047] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, which means that the welding process is not selected rationally;

[0048] (3) Marine atmosphere:

[0049] If if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable;

[0050] if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. The corrosion resistance of the welded joint is poor, which means that the welding process is not selected properly.

[0051] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0052] [Example 1]

[0053] The corrosion performance study steps of carbon steel Q345B welded joints in a simulated rural atmosphere are as follows:

[0054] Step 1: Use wire cutting to cut a 20mm long and 15mm wide weld joint sample, grind and polish the sample surface step by step, and use 4% nitric alcohol to etch the weld joint sample to preliminarily determine the position of the weld, heat-affected zone and parent material and mark them; polish the sample again, clean it, dry it, and place it in a desiccator for later use.

[0055] Step 2: Deionized water is used as the pretreatment solution for the rural atmospheric environment.

[0056] Step 3: Saturate filter paper with deionized water and spread it on the surface of the Q345B weld joint sample. Spray the corresponding solution every 1 minute until the filter paper is saturated. Spray 5 times in total. Let it sit for 3 minutes before testing.

[0057] Step 4: Place the processed sample on the SKP system test platform. Connect the lower surface of the sample to the micro-area electrochemical workstation through conductive glue. Adjust the sample level. The probe diameter is 150μm and the distance between the probe and the sample surface is controlled at 90μm. A probe distance that is too high will result in a signal feedback value that is too low, and a probe distance that is too low will easily cause the probe to touch the sample. The amplitude is 25μm and the probe frequency is 50μm.

[0058] Step 5. Select the surface scanning mode. Determine the scanning area based on the weld, heat-affected zone, and base material areas marked in step 1. Starting from the weld area, scan in the order of weld, heat-affected zone, and base material. Select a test area of ​​20 mm long and 40 mm wide, with a horizontal step of 25 μm / point and a vertical step of 10 μm / point.

[0059] Step 6. After the test, obtain the potential distribution diagram and use the drawing software to make a three-dimensional matrix diagram. Select five points in the weld area, heat-affected zone, and base material area respectively, record the potential of the point, and obtain the average potential value of the area.

[0060] Step 7: Pastoral atmosphere: This shows that the welding material selection is reasonable. It is judged that the corrosion resistance of the welded joint of Q345B steel is good, that is, the welding process is reasonably selected.

[0061] [Example 2]

[0062] The corrosion performance study steps of Q500qE bridge steel welded joints in a simulated industrial atmosphere are as follows:

[0063] Step 1: Use wire cutting to cut a 50mm long and 30mm wide weld joint sample, grind and polish the sample surface step by step, and use 4% nitric acid to etch the weld joint sample to preliminarily determine the position of the weld, heat-affected zone and parent material and mark them; polish the sample again, clean it, dry it, and place it in a desiccator for later use.

[0064] Step 2: Prepare a solution simulating an industrial atmospheric environment, using 0.02mol / L NaHSO3+0.01mol / LNaHCO3+0.003mol / L(NH4)2SO4+0.001mol / L NaNO3+0.001NaF.

[0065] Step 3: Saturate the filter paper with the corresponding solution and spread it flat on the surface of the weld joint sample. Spray the corresponding solution every 1 minute until the filter paper is saturated. Spray 5 times in total. Let it sit for 3 minutes before testing.

[0066] Step 4: Place the processed sample on the SKP system test platform. Connect the lower surface of the sample to the micro-area electrochemical workstation through conductive glue. Adjust the sample level. The probe diameter is 500μm and the distance between the probe and the sample surface is controlled at 110μm. A probe distance that is too high will result in a signal feedback value that is too low, and a probe distance that is too low will easily cause the probe to touch the sample. The amplitude is 50μm and the probe frequency is 80μm.

[0067] Step 5. Select the surface scanning mode. Determine the scanning area based on the weld, heat-affected zone, and base material areas marked in step 1. Starting from the weld area, scan in the order of weld, heat-affected zone, and base material. Select a test area of ​​30 mm long and 30 mm wide, with a horizontal step of 50 μm / point and a vertical step of 25 μm / point.

[0068] Step 6. After the test, obtain the potential distribution diagram and use the drawing software to make a three-dimensional matrix diagram. Select five points in the weld area, heat-affected zone, and base material area respectively, record the potential of the point, and obtain the average potential value of the area.

[0069] Step 7: Industrial atmosphere: This shows that the welding material selection is reasonable. It is judged that the corrosion resistance of Q500qE welded joint is poor, that is, the welding process selection is unreasonable.

Claims

1. A method for evaluating the atmospheric corrosion resistance of steel welded joints, characterized in that: The specific steps include: Step 1: Cut a weld joint specimen with a length of 20 to 50 mm and a width of 10 to 30 mm, determine the position of the weld, heat-affected zone and parent material, and mark them; Step 2: Prepare solutions simulating different atmospheric environments: deionized water is used for the pastoral atmospheric environment; (0.01-0.02) mol / L NaHSO3 + (0.01-0.02) mol / L NaHCO3 + (0.001-0.005) mol / L (NH4)2SO4 + (0.001-0.003) mol / L NaNO3 + (0.001-0.003) NaF is used for the industrial atmospheric environment; and 0.1-3.5% NaCl solution is used for the marine atmospheric environment. Step 3: Saturate the filter paper with the corresponding solution, spread it on the surface of the weld joint sample, and spray the test paper intermittently until it is saturated; Step 4: Place the processed sample horizontally on the SKP system test platform, connect the lower surface of the sample to the micro-area electrochemical workstation, control the distance between the probe and the sample surface to be 80-110 μm, the amplitude to be 25-55 μm, and the probe frequency to be 50-80 μm; Step 5: Scan and test the weld, heat-affected zone, and base material in the order of the weld; Step 6: After the test, obtain the potential distribution diagram and obtain the average point values ​​of the weld area, heat-affected zone, and base material area; Step 7: Set different thresholds to evaluate the atmospheric corrosion resistance of steel welded joints under different atmospheric environments, including the following: (1) Pastoral atmosphere: if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable; if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, that is, the welding process is not selected rationally, among which U 焊缝 、U 母材 、U 热影响区 Represent the average potential values ​​of the weld zone, heat-affected zone, and base material zone respectively; (2) Industrial atmosphere if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable; if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. Characterizes that the corrosion resistance of the welded joint is poor, which means that the welding process is not selected rationally; (3) Marine atmosphere: If if Characterizes that the corrosion resistance of the weld is poor and the welding material selection is unreasonable; if Characterize the reasonable selection of welding materials, regulations The corrosion resistance of the welded joint is good, that is, the welding process is selected reasonably. The corrosion resistance of the welded joint is poor, which means that the welding process is not selected properly.

2. A method for evaluating the atmospheric corrosion resistance of steel welded joints according to claim 1, characterized in that: The sample in step 1 is ground and polished so that the roughness of the surface to be corroded of the sample is less than or equal to 0.6 μm. When determining the positions of the weld, the heat-affected zone, and the base material, ferric chloride FeCl3, dihydrate oxalic acid C2H2O4·2H2O, hydrogen peroxide H2O2, and water H2O are used in a mass ratio of 30-50:20-40:60-120:340-400 to corrode the weld joint sample. The sample is then polished again, cleaned, dried, and placed in a desiccator for later use.

3. The method for evaluating the atmospheric corrosion resistance of steel welded joints according to claim 1, characterized in that: In the three steps, the test paper is sprayed with the corresponding solution at intervals of 1 to 3 minutes until the filter paper is saturated. The test paper is sprayed 4 to 8 times in total and the test is performed after standing for 3 to 10 minutes.

4. The method for evaluating the atmospheric corrosion resistance of steel welded joints according to claim 1, characterized in that: In step 4, the probe diameter is selected to be 150 or 500 μm.

5. The method for evaluating atmospheric corrosion resistance of steel welded joints according to claim 1, characterized in that: During the test in step 5, the lateral step is 25-50 μm / point and the longitudinal step is 10-25 μm / point.

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