Evaluation method for repair welding reheating crack tendency of 12Cr1MoVG thick-wall heat-resistant steel
By conducting thermal simulation test and tensile test on 12Cr1MoVG steel during the welding process, the cross-section shrinkage rate is measured, and the problems of complex and inaccurate rethermal crack sensitivity evaluation methods in the prior art are solved, and the accurate evaluation of the tendency of rethermal cracks of the material is achieved.
Patent Information
- Application Number
- CN202411790532.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-06
- Publication Date
- 2025-03-11
AI Technical Summary
There are insufficient methods for evaluating the sensitivity of rethermal cracks in the repair welding process of 12Cr1MoVG steel. The existing methods are complex, the results are not accurate enough, and their applicability to non-ferromagnetic materials and alloy steels is limited.
By performing thermal simulation tests on the welding thermal cycle process of the coarse crystal zone welding of the heat-affected area to be tested, the coarse crystal zone sample in the heat-affected area is obtained, and the sample is stretched at a set strain rate under preset temperature conditions until the sample is broken, and the cross-section shrinkage rate is measured to evaluate the sensitivity of reheat cracks.
This method can accurately simulate the thermal influence of the coarse crystal zone during actual welding, reflect the tendency of reheating cracks of the material during repair welding, and the evaluation results are more objective and reliable, avoiding the complexity and inaccuracy of the existing methods.
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Abstract
Description
Technical Field
[0001] The invention belongs to the field of materials, and in particular relates to a method for evaluating the tendency of reheat cracks in 12Cr1MoVG thick-wall heat-resistant steel repair welding. Background Art
[0002] The heat-resistant steel commonly used in the main steam-water pipelines of thermal power plants is 12Cr1MoVG steel, which is a low-alloy pearlite heat-resistant steel and belongs to ferritic steel. This steel replaces part of the chromium and molybdenum elements with a small amount of vanadium, and its high-temperature performance is improved. It still has good high-temperature oxidation resistance and corrosion resistance at 580°C. Its thermal strength and long-lasting plasticity are also better than most Cr-Mo steels. Because the manufacturing cost of this steel is low, it is widely used in the manufacture of power station boiler superheaters, reheaters and steam pipelines. 12Cr1MoV steel contains carbide-forming elements such as Cr, Mo, and V. Although it enhances the corrosion resistance and high-temperature strength of the steel, it will also cause reheat cracks. 12Cr1MoVG steel is a common steel grade for the main steam pipeline. Repair welding process is often used during operation and maintenance. The influence trend of the repair welding process on its reheat crack sensitivity is not clear. The probability of reheat cracks in the welding repair process of 12Cr1MoVG steel is greatly increased, resulting in an increase in welding repair costs, affecting production efficiency and welding joint safety.
[0003] The existing methods for evaluating the sensitivity of repair welding reheat cracks include: magnetic susceptibility measurement method, C-type notch ring test, inclined Y groove butt crack test, etc., among which: Magnetic susceptibility measurement method: This method is mainly applicable to ferromagnetic materials, and determines whether the material has cracks by measuring the change in the material's magnetic susceptibility. Its disadvantage is that it cannot be applied to non-ferromagnetic materials, and for some alloy steels, the correlation between the change in magnetic susceptibility and cracks may not be obvious enough, affecting the accuracy of the judgment.
[0004] C-notch ring test: This method applies tensile stress to a ring specimen with a C-notch and observes the cracks in the specimen under the action of stress and temperature. Its main disadvantage is that the operation is relatively complicated and requires high equipment and operation technology. In addition, due to the fixed geometry and size of the specimen, it may not fully represent the stress distribution of the actual component.
[0005] Inclined Y-groove butt crack test: This method is to process the specimen into a form with an inclined Y-groove, and then conduct a welding test to evaluate the reheat crack sensitivity of the material based on the crack generation. The disadvantage is that the size and shape of the specimen may affect the generation and expansion of cracks, resulting in differences between the test results and actual engineering applications. At the same time, this method usually requires a larger specimen size, which may cause material waste for some precious or difficult-to-prepare materials. Summary of the invention
[0006] The purpose of the present invention is to provide a method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding. In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides a method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding, comprising the following steps: Step 1, performing a thermal simulation test of a welding thermal cycle process of a coarse grain zone of a repair welding on a test sample to obtain a coarse grain zone sample of a heat affected zone; Step 2, under a preset temperature condition, stretching the obtained coarse grain region sample at a set strain rate until the coarse grain region sample is broken at the test temperature, thereby obtaining a cross section of the coarse grain region sample; Step 3, obtaining the shrinkage rate of the cross section of the coarse grain area sample, and using the shrinkage rate to evaluate the reheat crack sensitivity of the test sample.
[0007] Preferably, the sample to be tested comprises two clamping sections and a testing section, wherein the testing section is arranged between the two clamping sections.
[0008] Preferably, one end of the two clamping sections connected to the testing section is a truncated cone structure.
[0009] Preferably, a thermal simulator of model Gleeble540 is used to conduct a thermal simulation test of the welding thermal cycle process of the coarse grain zone of the repair welding on the test section to obtain a coarse grain zone sample of the heat affected zone of the 12Cr1MoVG repair welding.
[0010] Preferably, the obtained coarse grain region sample is stretched at a set strain rate under the condition of 500° C. to 750° C. until the coarse grain region sample is broken at the test temperature.
[0011] Preferably, the set strain rate is 0.001 mm / s.
[0012] Preferably, the reduction in area is calculated by the following formula:
[0013] Where Z is the cross-sectional shrinkage rate; D 0 D is the diameter of the sample before stretching; 1 is the diameter of the sample after fracture.
[0014] Preferably, in step 3, the reheat crack sensitivity of the test sample is evaluated with the shrinkage rate, and the specific method is: When the cross-sectional shrinkage is less than 5%, the reheat crack sensitivity of the tested sample is judged to be extremely sensitive; When the cross-sectional shrinkage is greater than or equal to 5% and less than 10%, the reheat crack sensitivity of the test sample is judged to be relatively sensitive; When the cross-sectional shrinkage is greater than or equal to 10% and less than 20%, the reheat crack sensitivity of the test sample is judged to be slightly sensitive; When the cross-sectional shrinkage is greater than or equal to 20%, the reheat crack sensitivity of the test sample is determined to be insensitive.
[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for evaluating the tendency of reheat cracking in repair welding of 12Cr1MoVG thick-walled heat-resistant steel. By conducting a thermal simulation test of the welding thermal cycle process of the coarse-grained zone of the test sample, the thermal influence of the coarse-grained zone in the actual welding process can be accurately simulated, thereby obtaining a coarse-grained zone sample that is closer to the actual situation. This helps to more accurately reflect the tendency of the material to reheat crack during the repair welding process; at the same time, by conducting a tensile test on the coarse-grained zone sample at a set strain rate under preset temperature conditions until the sample breaks, this step can scientifically and systematically examine the mechanical properties and deformation behavior of the material at different temperatures. By measuring the shrinkage rate of the cross-section of the coarse-grained zone sample, the reheat crack sensitivity of the material can be quantified, making the evaluation result more objective and reliable. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 This is a schematic diagram of the structure of the sample to be tested described in the embodiment of the present application; Figure 2 This is a schematic diagram of the diameter measurement of the sample to be tested in the embodiment of the present application; Figure 3 This is the sensitive trend of reheat cracking with temperature changes in the embodiments of the present application. DETAILED DESCRIPTION
[0017] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.
[0018] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, wholes, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or combinations thereof.
[0019] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.
[0020] As used in the specification and appended claims of this application, the term "if" can be interpreted as "when" or "uponce" or "in response to determining" or "in response to detecting", depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" can be interpreted as meaning "uponce it is determined" or "in response to determining" or "uponce [described condition or event] is detected" or "in response to detecting [described condition or event]", depending on the context.
[0021] In addition, in the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.
[0022] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.
[0023] Example 1 The present embodiment provides a method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding, comprising the following steps: Step 1: Prepare the test sample Sampling was conducted along the axial direction of the 12Cr1MoVG main heat steam pipe which was in high temperature state and had been in service for a set period of time (the service temperature of the 12Cr1MoVG main heat steam pipe was 520℃~580℃. Long-term operation would cause the microstructure of 12Cr1MoVG to change, and the grain boundary precipitates would increase the reheat crack sensitivity. The sample was prepared by using the test material with long service period to more accurately reflect the working conditions of production practice). After machining, the following Figure 1 The test sample shown includes two clamping sections and a test section, wherein the test section is arranged between the two clamping sections.
[0024] One end where the two clamping sections are connected to the testing section is a truncated cone structure.
[0025] Step 2, performing a thermal simulation test of the welding thermal cycle process of the coarse grain zone of the test section of the test sample to be tested, and obtaining a coarse grain zone sample of the heat affected zone; Step 3, under the temperature condition of 500° C. to 750° C., the obtained coarse grain area sample is stretched at a set strain rate until the coarse grain area sample is broken at the test temperature, thereby obtaining a cross section of the coarse grain area sample; Step 4, obtaining the shrinkage rate of the cross section of the coarse grain area sample, and using the shrinkage rate to evaluate the reheat crack sensitivity of the test sample.
[0026] Example 2 On the basis of Example 1, this example provides a method for evaluating the reheating crack tendency of 12Cr1MoVG thick-walled heat-resistant steel repair welding. In step 2, a thermal simulation test of the welding thermal cycle process of the coarse-grained zone of the repair welding is performed on the test section using a thermal simulator of model Gleeble540 to obtain a coarse-grained zone sample of the heat-affected zone of the 12Cr1MoVG repair welding.
[0027] Example 3 On the basis of Example 1, this example provides a method for evaluating the tendency of reheating cracks in repair welding of 12Cr1MoVG thick-walled heat-resistant steel. In step 3, the obtained coarse-grained zone sample is heated to 500°C~750°C, and strain is applied at a tensile rate of 0.001mm / s at the test temperature until the sample is broken, and the broken sample is air-cooled to room temperature; the coarse-grained zone sample is slowly stretched at a strain rate until it is broken at the test temperature (the purpose of stretching at a set strain rate is to prevent the material from cracking due to intergranular reheating cracks as much as possible).
[0028] Example 4 On the basis of Example 1, this example provides a method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-walled heat-resistant steel repair welding. In step 4, an electronic vernier caliper is used to measure the diameter of the test section before and after the fracture. The measurement method is as follows: Figure 2 As shown, the cross-sectional reduction rate (ROA) is calculated using formula (1-1): (1-1) Where Z is the cross-sectional shrinkage rate; D 0 D is the diameter of the sample before stretching; 1 is the diameter of the sample after fracture.
[0029] Example 5 On the basis of Example 1, this example provides a method for evaluating the tendency of reheat cracking in repair welding of 12Cr1MoVG thick-walled heat-resistant steel. In step 4, the reheat crack sensitivity of the test sample is evaluated with the shrinkage rate, as shown in Table 1: Table 1 Reheat crack sensitivity evaluation criteria based on ROA
[0030] Example 6 This embodiment provides a method for evaluating the reheat crack tendency of 12Cr1MoVG thick-walled heat-resistant steel repair welding. Example: The reheat crack sensitivity of the coarse-grained zone of the long-term 12Cr1MoVG steel repair welding is operated as follows.
[0031] Step 1, firstly, a thermal simulation test of a welding thermal cycle process of a coarse grain area of a repair welding is performed on the sample to obtain a coarse grain area sample; Step 2, based on the coarse grain area sample, a stainless steel fixture is used for heating and stretching, the heating rate is 10°C / s, and the heating peak temperatures are 500°C, 550°C, 600°C, 630°C, 690°C, 720°C, and 750°C respectively; Step 3, applying strain at a tensile rate of 0.001 mm / s at the test temperature until the sample is broken, and air-cooling the broken sample to room temperature; Step 4: Use an electronic digital display vernier caliper to measure the reduction of area (ROA) of the sample, and evaluate the reheat crack sensitivity of the coarse-grained zone of the 12Cr1MoVG steel repair weld according to the criteria shown in Table 1.
[0032] According to the method of testing the cross-sectional shrinkage rate in step 4, the cross-sectional shrinkage rate at different test temperatures was measured. The measurement results are shown in Table 2.
[0033] According to the evaluation results, the reheating crack sensitivity trend of 12Cr1MoVG steel with temperature changes is as follows Figure 3 As shown, the results show that in the temperature range of 630℃~690℃, the reheat crack sensitivity of the coarse-grained area of the repair weld is the highest.
[0034] Table 2 Sectional shrinkage and reheat crack sensitivity assessment
[0035] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.
Claims
1. A method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-walled heat-resistant steel repair welding, characterized in that: The following steps are involved: Step 1, performing a thermal simulation test of a welding thermal cycle process of a coarse grain zone of a repair welding on a test sample to obtain a coarse grain zone sample of a heat affected zone; Step 2, under a preset temperature condition, stretching the obtained coarse grain region sample at a set strain rate until the coarse grain region sample is broken at the test temperature, thereby obtaining a cross section of the coarse grain region sample; Step 3, obtaining the shrinkage rate of the cross section of the coarse grain area sample, and using the shrinkage rate to evaluate the reheat crack sensitivity of the test sample.
2. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-walled heat-resistant steel repair welding according to claim 1, characterized in that: The sample to be tested includes two clamping sections and a testing section, wherein the testing section is arranged between the two clamping sections.
3. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-walled heat-resistant steel repair welding according to claim 2, characterized in that: One end where the two clamping sections are connected to the testing section is a truncated cone structure.
4. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding according to claim 1, characterized in that: The thermal simulation test of the thermal cycle process of the coarse grain zone of the repair welding was carried out on the test section using a thermal simulator of model Gleeble540, and the coarse grain zone specimen of the heat affected zone of the repair welding of 12Cr1MoVG was obtained.
5. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding according to claim 1, characterized in that: Under the condition of 500℃~750℃, the obtained coarse grain area sample is stretched at a set strain rate until the coarse grain area sample is broken at the test temperature.
6. A method for evaluating the tendency of reheat cracking of 12Cr1MoVG thick-walled heat-resistant steel repair welding according to claim 1 or 5, characterized in that: The set strain rate is 0.001 mm / s.
7. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding according to claim 1, characterized in that: The area reduction ratio is calculated by the following formula: Where Z is the cross-sectional shrinkage rate; D0 is the diameter of the sample before stretching; D1 is the diameter of the sample after breaking.
8. The method for evaluating the tendency of reheat cracking in 12Cr1MoVG thick-wall heat-resistant steel repair welding according to claim 1, characterized in that: In step 3, the reheat crack sensitivity of the test sample is evaluated with the shrinkage rate, and the specific method is: When the cross-sectional shrinkage is less than 5%, the reheat crack sensitivity of the tested sample is judged to be extremely sensitive; When the cross-sectional shrinkage is greater than or equal to 5% and less than 10%, the reheat crack sensitivity of the test sample is judged to be relatively sensitive; When the cross-sectional shrinkage is greater than or equal to 10% and less than 20%, the reheat crack sensitivity of the test sample is judged to be slightly sensitive; When the cross-sectional shrinkage is greater than or equal to 20%, the reheat crack sensitivity of the test sample is determined to be insensitive.