A method for optimizing heat treatment based on residual stress threshold value against corrosion cracking
By determining the residual stress threshold value of welded components through thermo-mechanical coupled finite element modeling and electrochemical testing, and optimizing the heating band width and insulation temperature, the stress corrosion cracking problem of cylindrical welded components was solved, achieving efficient stress corrosion cracking prevention and control.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA UNIV OF PETROLEUM (EAST CHINA)
- Filing Date
- 2026-03-09
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing technology, the residual tensile stress after welding of cylindrical welded components is not properly controlled, resulting in a high risk of stress corrosion cracking in the heat-affected zone of the weld, and the parameters of local heat treatment after welding need to be readjusted.
By establishing a thermo-mechanical coupled finite element welding model, the residual tensile stress in the heat-affected zone of the weld was determined. Four-point bending specimens were prepared for electrochemical testing to determine the residual stress threshold value. Local heat treatment optimization was carried out in combination with the heating band width coefficient, and suitable heating band width and heat preservation temperature parameters for corrosion cracking resistance were selected.
Precise control of residual tensile stress on the inner wall of welded components keeps it below the cracking threshold, significantly improving the prevention and control of stress corrosion cracking. In-depth analysis of the stress corrosion cracking mechanism of materials provides optimization solutions for heat treatment processes.
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Figure CN121805037B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of numerical simulation research technology for heat treatment, specifically to a heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value. Background Technology
[0002] In the fields of oil extraction, long-distance oil and gas transportation, and oil refining, thick-walled cylindrical welded components (butt welds of pipelines transporting oil and gas and closure welds of hydrogenation reactors in refining processes) are key core components that ensure the safe and stable operation of the industry. Their service environment is characterized by strong corrosion, and they are subjected to the combined effects of media erosion, alternating loads, and residual welding tensile stress for a long time. Corrosion cracking (SCC) has become one of the most common failure modes of such components, seriously threatening the safety and continuity of oil production, and even causing safety accidents such as oil and gas leaks and equipment explosions, resulting in serious economic losses.
[0003] In the petroleum industry, thick-walled cylindrical welded components (especially heavy-duty components with a wall thickness > 50 mm) are mostly formed using welding processes. During welding, the uneven distribution of the temperature field inevitably generates high residual tensile stress in the weld zone and heat-affected zone. In the heat-affected zone of cylindrical welded joints, due to the inhomogeneity of the microstructure and the presence of significant residual tensile stress, it becomes a high-frequency area for stress corrosion cracking (SCC), the consequences of which are often very severe. Traditional methods for preventing SCC include isolating the corrosive medium and reducing residual stress, such as applying weld overlays or coatings to isolate the corrosive medium; and reducing residual stress through heat treatment, aging vibration, and shot peening. Currently, post-weld local heat treatment to reduce residual stress is a highly efficient and economical means of preventing SCC, but it still has the following limitations: different welded joints require different locations for SCC, and the post-weld local heat treatment parameters need to be readjusted. Summary of the Invention
[0004] This invention proposes an optimized heat treatment method for corrosion cracking prevention based on residual stress threshold value, in order to solve the problem of improper control of residual tensile stress after welding in existing cylindrical welded components, resulting in a high risk of stress corrosion cracking in the weld heat-affected zone.
[0005] This invention adopts the following technical solution: an optimized heat treatment method for corrosion cracking resistance based on residual stress threshold value, comprising the following steps:
[0006] S1. Based on the cylindrical structure and physical properties of different materials, a thermo-mechanical coupled finite element welding model is established to determine the residual tensile stress in the heat-affected zone of the inner wall after welding.
[0007] S2. Prepare a four-point bending specimen with a weld heat-affected zone, prepare the target specimen by stress-relief annealing and four-point bending moment loading, load the residual tensile stress corresponding to the yield stress, and calculate the loading displacement under different stresses through a finite element model.
[0008] S3. The residual stress threshold value that induces corrosion cracking is determined by electrochemical testing of the target sample obtained in S2.
[0009] S4. Based on the residual stress threshold value obtained in S3, and combined with the basic formula for heating band width, different heating band width coefficients are selected to perform thermo-mechanical coupled finite element simulations of the local heat treatment process of the cylindrical welded component. The residual tensile stress in the weld zone and heat-affected zone is obtained, and the heating band width coefficient with a stable residual tensile stress below the threshold value is selected as the optimized width correction coefficient. The design formula for the width of the heating band that meets the requirements for corrosion and crack resistance was obtained, and the optimization of the heating band width and the determination of the local heat treatment insulation temperature parameters were completed.
[0010] Furthermore, S1 specifically includes establishing a thermo-mechanical coupled finite element welding model based on the cylindrical structure and physical properties of the target material, determining the welding heat flux parameters, obtaining the temperature field of the welding process, using the temperature field as a known condition to carry out stress field analysis in finite element software, and determining the residual tensile stress in the heat-affected zone of the inner wall welding.
[0011] Further, S2 includes S2.1, which involves preparing a four-point bending standard specimen with a weld heat-affected zone based on the cylindrical structure and physical properties of the target material. The four-point bending standard specimen is then subjected to stress-relief annealing, and the four-point bending moment loading method is used to re-stress the specimen to obtain the four-point bending target specimen. The stress loading formula is:
[0012] ;
[0013] In the formula, The maximum tensile stress in the heat-affected zone of the target specimen after welding during four-point bending is given. The elastic modulus of the target material. The thickness of the standard specimen for four-point bending. The maximum deflection between the two external support points. The distance between the two external support points. This is the distance between the inner and outer support points.
[0014] Furthermore, S2 includes S2.2, which loads the residual tensile stress by performing a tensile test on a standard specimen of the target material to obtain the yield stress, and loads residual tensile stresses corresponding to 0%, 30%, and 50% of the yield stress onto the four-point bending target specimen, respectively.
[0015] Furthermore, S2 includes S2.3, the displacement of the loading residual tensile stress. The residual tensile stress obtained in S2.2 is used to obtain the loading displacement of the four-point bending target specimen under different residual tensile stresses through a four-point moment-stress-displacement coupled finite element model on a two-dimensional plane.
[0016] Further, S3 includes S3.1, which involves encapsulating the four-point bending target sample obtained in S2, exposing only the heat-affected zone of the four-point bending target sample, and immersing the encapsulated four-point bending target sample in the target corrosion solution for different immersion times. The charge transfer resistance of the four-point bending target sample that meets the immersion time requirement is obtained through electrochemical impedance spectroscopy. and double-layer capacitors The corrosion current density was obtained by electrochemical polarization curve testing of the four-point bending target sample that met the immersion time requirement. and self-corrosion potential ;
[0017] according to and The value of the passivation film stability factor is established. formula:
[0018] ;
[0019] In the formula, As a passivation film stability factor, This is residual tensile stress. As the reference stress, Residual tensile stress The charge transfer resistance below, Reference stress The charge transfer resistance below, These are the weighting coefficients. The value ranges from 0.2 to 0.3. Residual tensile stress The double-layer capacitance value below, Reference stress Underlying double-layer constant-phase element;
[0020] Setting the passivation film stability threshold and passivation film imbalance threshold , Less than At that time, the passivation film exhibits stability. Between and When the passivation film deteriorates, it tends to deteriorate. Greater than At that time, the passivation film becomes unbalanced and ruptures.
[0021] Furthermore, S3 includes S3.2, and then combined with... and The value determines the stability of the passivation film;
[0022] Under the same corrosion conditions, The value increases and value corresponding Decrease or The value continuously decreases with prolonged immersion time, indicating that the passivation film is stable; The value decreases and value corresponding Significantly increased or As the immersion time continued to increase, the passivation film was determined to be unstable.
[0023] For the first time Exceed At the same time The value decreases and value corresponding Significantly increased or As the immersion time continues to increase, the corresponding residual tensile stress is determined as the residual stress threshold value that will trigger corrosion cracking.
[0024] Furthermore, S4 includes S4.1, which uses the residual tensile stress in the cylindrical weld zone and heat-affected zone after local heat treatment being lower than the residual stress threshold value for initiating corrosion cracking obtained in S3 as a safety criterion.
[0025] Calculate the width of the heating band in localized heat treatment:
[0026] ;
[0027] In the formula, The width of the heating zone for localized heat treatment. The value is the heating zone width coefficient, and it is in the range of 1 to 3. The actual wall thickness of the cylindrical welded component and .
[0028] Furthermore, S4 includes S4.2, selecting different heating zone width coefficients. =1~3, perform thermo-mechanical coupled finite element simulation on the local heat treatment process of the cylindrical welded component, obtain the residual tensile stress in the cylindrical weld zone and heat-affected zone, and screen out the residual stress threshold values that can keep the actual residual tensile stress stably below the residual stress threshold value that induces corrosion cracking. Value, when When the value is less than 2, the residual tensile stress is higher than the residual stress threshold, posing a risk of stress corrosion cracking; when When the value is greater than 2.5, the heating range and energy consumption increase, thus determining the optimal value range to be 2–2.5. The optimized width correction factor This leads to the design formula for the width of the heating band that is adapted to resist corrosion and cracking, thus optimizing the width of the heating band.
[0029] The design formula for the width of the heating band is:
[0030] ;
[0031] In the formula, The width of the local heat treatment heating band has been optimized to meet the requirements of corrosion and crack resistance. The optimized width correction factor and Within the range of 2 to 2.5, The actual wall thickness of the cylindrical welded component and .
[0032] Furthermore, S4 includes S4.3, where the local heat treatment holding temperature is selected based on the treatment standard of the target sample in S2, and the selected local heat treatment holding temperature is set as the control temperature of the heating belt, thus completing the determination of the local heat treatment holding temperature parameters.
[0033] Compared with the prior art, the present invention has the following beneficial effects:
[0034] This invention accurately reproduces the residual tensile stress within the 0%~50% yield strength range of the weld heat-affected zone through a four-point bending test. Combined with an electrochemical threshold identification method, it determines the residual stress threshold value for corrosion cracking prevention and constructs a thermo-mechanical coupled finite element simulation. This invention overcomes the limitation of low accuracy in controlling residual stress of traditional heat treatment parameters, and stably regulates the residual tensile stress on the inner wall of the component to below the cracking threshold value, thus significantly improving the effect of stress corrosion cracking prevention and control.
[0035] This invention also provides an in-depth analysis of the core mechanism of stress corrosion cracking in materials, establishes a quantitative threshold mechanism for the evolution of residual stress and passivation film in the weld heat-affected zone, correlates residual stress with electrochemical parameters, and reveals the correlation mechanism between residual stress and the dynamic evolution of passivation film, providing a technical solution for optimizing the heat treatment process of similar welded components under corrosive environments. Attached Figure Description
[0036] Figure 1 The diagram shows the residual tensile stress of the welded components of the DH36 cylindrical shell after local heat treatment.
[0037] Figure 2 The stress-strain curve of the DH36 cylinder is shown.
[0038] Figure 3 This is a graph showing the relationship between the downward displacement and the tensile stress on the lower surface of a DH36 cylindrical tube.
[0039] Figure 4Electrochemical impedance spectroscopy of DH36 four-point bending target samples under different residual tensile stresses after immersion for 5 days;
[0040] Figure 5 Electrochemical impedance spectroscopy of DH36 four-point bending target samples under different residual tensile stresses after 10 days of immersion.
[0041] Figure 6 Electrochemical impedance spectroscopy of DH36 four-point bending target samples under different residual tensile stresses after 15 days of immersion.
[0042] Figure 7 Electrochemical impedance spectroscopy of DH36 four-point bending target samples under different residual tensile stresses after 20 days of immersion;
[0043] Figure 8 The finite element analysis model of the DH36 cylinder four-point bending specimen is shown in the figure.
[0044] Figure 9 The graph shows the evolution of axial stress over time at a typical monitoring point A on the inner wall of the heat-affected zone of the DH36 cylinder welded under different heating band widths and temperatures.
[0045] Figure 10 Curves showing the evolution of axial stress over time at point B on the inner wall of the welded heat-affected zone of DH36 cylinder under different heating band widths and temperatures.
[0046] Figure 11 Axial stress distribution curves of the weld-heat affected zone path on the inner wall of DH36 cylindrical components at different heating band widths and temperatures;
[0047] Figure 12 Flowchart of the present invention. Detailed Implementation
[0048] The present invention will be further illustrated below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the invention in any way. It should be understood that the described embodiments are merely some, not all, of the embodiments described in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.
[0049] like Figure 12As shown, in this embodiment, a thermo-mechanically coupled finite element welding model was constructed using an 80mm thick DH36 cylindrical structure. Submerged arc welding was performed on the 80mm thick DH36 cylindrical structure at a welding voltage of 22V, a current of 160V, and a welding speed of 20cm / min. The tensile stress in the heat-affected zone of the inner wall at the weld joint was approximately 200MPa, and the tensile stress in the heat-affected zone of the outer wall was 300MPa. The residual tensile stresses on the inner and outer walls at the weld joint after welding were also determined. Figure 1 As shown.
[0050] Based on the structural and physical properties of an 80mm thick DH36 cylinder, a four-point bending standard specimen with a weld heat-affected zone was prepared. The four-point bending standard specimen was then subjected to stress-relief annealing, and the four-point bending moment loading method was used to re-stress the specimen, thus preparing the DH36 four-point bending target specimen. The stress loading formula is:
[0051] ;
[0052] In the formula, The maximum tensile stress in the heat-affected zone of the target specimen after welding during four-point bending is given. The elastic modulus of the target material. The thickness of the standard specimen for four-point bending. The maximum deflection between the two external support points. The distance between the two external support points. The distance between the inner and outer support points;
[0053] The standard specimen for the four-point bending test is made of Hastelloy C276 alloy material;
[0054] Tensile tests were performed on standard specimens of DH36 material using a universal testing machine. The stress-strain curves of DH36 were then analyzed. Figure 2 As shown, the yield stress of DH36 was determined to be 360 MPa. Then, the corresponding yield stress was applied to the four-point bending target specimen of DH36. )for , , The residual tensile stresses are 180 MPa, 108 MPa and 0 MPa, respectively.
[0055] The loading displacement was obtained through a four-point moment-stress-displacement finite element simulation, and the result was obtained from the curves of the downward displacement versus the tensile stress on the lower surface. Figure 3 , and thus , , The displacements under residual tensile stress were 0.316 mm, 0.191 mm, and 0 mm.
[0056] For annealed load stress of , , The DH36 four-point bending target sample was encapsulated with epoxy latex, exposing only the heat-affected zone of the target sample with an area of 1 mm². The encapsulated target sample was then immersed in the target corrosion solution, and the electrochemical impedance characteristics of the target sample under different immersion times were detected. Electrochemical impedance tests were performed on target samples immersed for 5 days, 10 days, 15 days, and 20 days, respectively. Figure 4 , Figure 5 , Figure 6 , Figure 7 Electrochemical impedance spectroscopy (EIS) spectra of target samples with different immersion times were obtained, and calculations were performed using the EIS spectra. , , Charge transfer resistance of the target sample and double-layer capacitors ;
[0057] Setting the passivation film stability threshold and passivation film imbalance threshold passivation film stability threshold and passivation film imbalance threshold Criterion values obtained by joint calibration of electrochemical parameters and morphological results were used to evaluate different loading stresses under the same corrosion solution, the same packaged exposed area of 1 mm², the same immersion time of 5 days, 10 days, 15 days, and 20 days, and the same test procedure. The target samples were subjected to batch electrochemical tests. After the open-circuit potential stabilized, electrochemical impedance spectroscopy was performed, and the charge transfer resistance was obtained by fitting the same equivalent circuit. With double-layer constant phase element Simultaneously, the self-corrosion potential was obtained by fitting the polarization curve. With self-corrosion current density ; through various loading stresses and Calculate the corresponding And for The response to changes in applied stress was tested multiple times. As stress increases, a stable and reproducible inflection point first appears, and the impedance characteristic corresponding to this inflection point is as follows: From slow change to continuous decline The change shifts from slow to continuous increase, and SEM observation of the heat-affected zone surface shows that the corrosion product film changes from a continuous and dense state to exhibiting dispersed fine cracks, micro-defects, and localized peeling without large-area flaking or defect penetration. This inflection point corresponds to... Defined as the passivation film stability threshold ,Sure The value is 2, and the loading stress is further increased when... As stress increases, a second stage of stable and reproducible abrupt inflection point occurs, and the impedance characteristics corresponding to this inflection point are as follows: A step-like or order-of-magnitude decrease trend appears. A multiple-order surge occurs, and it is related to the polarization parameter. Decrease and Increase or Consistent with the increasing immersion time, and with SEM observation showing that the corrosion product film undergoes flaking, forming a network of interconnected cracks and exhibiting obvious defect penetration, and when evidence of crack morphology consistent with stress corrosion cracking can be obtained on the surface or cross-section / section surface, the abrupt change inflection point is considered... Defined as the passivation film imbalance threshold ,Sure The value is 15, hence the determination. Less than At that time, the passivation film exhibits stability. Between and When the passivation film deteriorates, it tends to deteriorate. Greater than At that time, the passivation film becomes unbalanced and ruptures;
[0058] According to different stresses and The value of the passivation film stability factor is established. The formula is as follows:
[0059] ;
[0060] In the formula, As a passivation film stability factor, This is residual tensile stress. As the reference stress, Residual tensile stress The charge transfer resistance below, Reference stress The charge transfer resistance below, These are the weighting coefficients. The value ranges from 0.2 to 0.3. Residual tensile stress The double-layer capacitance value below, Reference stress Underlying double-layer constant-phase element;
[0061] The data obtained from the electrochemical impedance spectroscopy are shown in Table 1.
[0062] Table 1 shows the impedance test data.
[0063] .
[0064] As can be seen from Table 1, based on the passivation film resistance of the target samples under different immersion times and different yield stresses... Capacitance of passivation film Charge transfer resistance Double-layer constant phase element and passivation film stability factor It can be seen that, After soaking for 20 days, The value is greater than for the first time The value is 15. Soaking for 20 days The residual tensile stress corresponding to the value is determined as the residual stress threshold value that will trigger corrosion cracking, which is 180 MPa.
[0065] The safety criterion is that the residual tensile stress in the weld zone and heat-affected zone of the component after local heat treatment is lower than the residual stress threshold value of 180 MPa that will induce corrosion cracking.
[0066] Existing post-weld heat treatment methods for carbon steel and low-alloy steel welded components (JB / T 6046-1992), post-weld heat treatment specifications for pressure equipment (GB / T 30583-2014), cylindrical specimens, and corresponding local heat treatment heating zone parameters, i.e., heating zone width. ,
[0067] Calculate the width of the heating band in localized heat treatment:
[0068] ;
[0069] In the formula, The width of the heating band for localized heat treatment. It is a width correction factor and Within the range of 1 to 3, The actual wall thickness of the cylindrical welded component and ;
[0070] This invention introduces stress corrosion cracking (SCC) failure mechanism as a criterion for optimizing heating band parameters, using whether the post-weld residual tensile stress is lower than the material's SCC residual stress threshold as the evaluation basis. Different heating band width coefficients ( =1~3), a thermo-mechanical coupling analysis was performed on the local heat treatment process of the cylindrical welded component to obtain the residual stress distribution characteristics of the weld zone and heat-affected zone after cooling to room temperature. The actual residual tensile stress in the weld zone and heat-affected zone of the component was obtained. The results show that when When the value is less than 2, insufficient heating band width leads to excessive temperature gradient, and the residual tensile stress in the weld toe and inner surface area remains higher than the SCC threshold value, posing a risk of stress corrosion cracking; when When the value exceeds 2.5, the reduction in residual stress tends to saturate, while the heating range and energy consumption increase significantly, leading to a decrease in engineering economy and operability. Considering the safety, distribution stability, and engineering adaptability of residual stress, we selected the residual stress threshold value that ensures the actual residual tensile stress is below the threshold value that triggers corrosion cracking. The optimal value range was determined to be 2 to 2.5, and the value range was determined to be 2 to 2.5. The optimized width correction factor This leads to the design formula for the width of the heating band that meets the requirements for corrosion and crack resistance, thus optimizing the width of the heating band.
[0071] Heating strip width design formula:
[0072] ;
[0073] In the formula, The width of the local heat treatment heating band has been optimized to meet the requirements of corrosion and crack resistance. The optimized width correction factor and Within the range of 2 to 2.5, The actual wall thickness of the cylindrical welded component and .
[0074] The local heat treatment holding temperature is selected based on the treatment standard of the target sample in S2. The selected local heat treatment holding temperature is set as the control temperature of the heating band, and the width of the heating band is selected. The diameter is 1120mm~1400mm, the heat preservation temperature is 680℃~760℃, and the heat treatment design parameters are set as shown in Table 2.
[0075] Table 2 shows the design parameters for heat treatment temperature.
[0076] .
[0077] The residual tensile stress after heat treatment was calculated according to the local heat treatment parameters in Table 2. The selection points and paths are as follows: Figure 8 .
[0078] The axial stresses at points A, B, and along the path are as follows: Figure 9 , Figure 10 and Figure 11 As shown, by Figure 9The typical monitoring point on the inner wall of the cylindrical component, point A, shows the dynamic response of axial stress during local heat treatment: During the heating stage, the axial tensile stress initially increases slightly due to thermal expansion constraints, then gradually decreases as the temperature homogenizes; during the heat preservation stage, the stress enters a stable relaxation state; during the cooling stage, the stress continues to decrease and eventually transforms into compressive stress, with all parameter curves ultimately falling within the compressive stress range below 0 MPa. Specifically, under the 1120 mm - 680 °C condition, the final compressive stress is approximately -200 MPa, achieving sufficient stress relaxation to eliminate the risk of corrosion cracking.
[0079] Depend on Figure 10 The evolution of axial stress at a typical monitoring point B on the outer wall of the cylindrical component can be observed: during the heating stage, the stress rapidly decreases and transforms into compressive stress, reaching its extreme value in about 2-3 hours; during the heat preservation stage, the stress stabilizes within the compressive stress range; during the cooling stage, the stress gradually rises and eventually transforms into tensile stress. Under the working conditions of 1120mm-680℃, the final tensile stress is approximately 300MPa, which is within the safe range of the material's yield strength and does not induce excessive plastic deformation.
[0080] Depend on Figure 11 The axial stress distribution characteristics along the weld-heat-affected zone path on the inner wall of the cylindrical component can be observed. The horizontal axis clearly marks the positions of the weld zone and the heat-affected zone. The vertical axis results show that the axial stress along the entire inner wall path is compressive stress, with stress values < 0 MPa. This meets the corrosion cracking resistance requirement that the stress on the inner wall surface in contact with the corrosive medium is below the corrosion cracking threshold of 180 MPa. Finally, the optimized local heat treatment parameters for corrosion cracking resistance of the 80 mm thick DH36 welded joint were determined as follows: heating band width... The diameter is 1120mm, and the heating band temperature is 680℃.
[0081] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.
Claims
1. A heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value, characterized in that, Includes the following steps: S1. Based on the cylindrical structure and physical properties of different materials, a thermo-mechanical coupled finite element welding model is established to determine the residual tensile stress in the heat-affected zone of the inner wall after welding. S2. Prepare a four-point bending specimen with a weld heat-affected zone, prepare the target specimen by stress-relief annealing and four-point bending moment loading, load the residual tensile stress corresponding to the yield stress, and calculate the loading displacement under different stresses through a finite element model. S3. The residual stress threshold value that induces corrosion cracking is determined by electrochemical testing of the target sample obtained in S2. S4. Based on the residual stress threshold value obtained in S3, the residual tensile stress in the cylindrical weld zone and heat-affected zone after local heat treatment is lower than the residual stress threshold value obtained in S3 that causes corrosion cracking, which is used as a safety criterion. Calculate the width of the heating band in localized heat treatment: ； In the formula, The width of the heating band for localized heat treatment. The value is the heating zone width coefficient, and it is in the range of 1 to 3. The actual wall thickness of the cylindrical welded component and ; Selecting different heating band width coefficients =1~3, perform thermo-mechanical coupled finite element simulation on the local heat treatment process of the cylindrical welded component, obtain the residual tensile stress in the cylindrical weld zone and heat-affected zone, and screen out the residual stress threshold value that can keep the actual residual tensile stress stably below the residual stress threshold value that induces corrosion cracking. Value, when When the value is less than 2, the residual tensile stress is higher than the residual stress threshold, posing a risk of stress corrosion cracking; when... When the value is greater than 2.5, the heating range and energy consumption increase, thus determining the optimal value range to be 2–2.
5. The optimized width correction factor This leads to the design formula for the width of the heating band that is adapted to resist corrosion and cracking, thus completing the optimization of the heating band width and the determination of the local heat treatment insulation temperature parameters. The design formula for the width of the heating band is: ； In the formula, The width of the local heat treatment heating band has been optimized to meet the requirements of corrosion and crack resistance. The optimized width correction factor and Within the range of 2 to 2.5, The actual wall thickness of the cylindrical welded component and .
2. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S1 specifically includes establishing a thermo-mechanical coupled finite element welding model based on the cylindrical structure and physical properties of the target material, determining the welding heat flux parameters, obtaining the temperature field of the welding process, using the temperature field as a known condition to carry out stress field analysis in finite element software, and determining the residual tensile stress in the heat-affected zone of the inner wall welding.
3. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S2 includes S2.1, which involves preparing a four-point bending standard specimen with a weld heat-affected zone based on the cylindrical structure and physical properties of the target material. The four-point bending standard specimen is then subjected to stress-relief annealing, and the four-point bending moment loading method is used to re-stress the specimen to obtain the four-point bending target specimen. The stress loading formula is: ； In the formula, The maximum tensile stress in the heat-affected zone of the target specimen after welding during four-point bending is given. The elastic modulus of the target material. The thickness of the standard specimen for four-point bending. The maximum deflection between the two external support points. The distance between the two external support points. This is the distance between the inner and outer support points.
4. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S2 includes S2.2, which applies residual tensile stress. A tensile test is performed on a standard specimen of the target material to obtain the yield stress. Residual tensile stresses of 0%, 30%, and 50% of the corresponding yield stress are applied to the four-point bending target specimen, respectively.
5. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S2 includes S2.3, the displacement of the loading residual tensile stress. The residual tensile stress obtained from S2.2 is used to obtain the loading displacement of the four-point bending target specimen under different residual tensile stresses through a four-point moment-stress-displacement coupled finite element model on a two-dimensional plane.
6. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S3 includes S3.1, which involves encapsulating the four-point bending target sample obtained in S2, exposing only the heat-affected zone of the four-point bending target sample. The encapsulated four-point bending target sample is then immersed in the target corrosion solution for different immersion times. The charge transfer resistance of the four-point bending target sample that meets the immersion time requirement is obtained by electrochemical impedance spectroscopy. and double-layer capacitors The corrosion current density was obtained by electrochemical polarization curve testing of the four-point bending target sample that met the immersion time requirement. and self-corrosion potential ; according to and The value of the passivation film stability factor is established. formula: ； In the formula, As a passivation film stability factor, This is residual tensile stress. As the reference stress, Residual tensile stress The charge transfer resistance below, Reference stress The charge transfer resistance below, These are the weighting coefficients. The value ranges from 0.2 to 0.
3. Residual tensile stress The double-layer capacitance value below, Reference stress Underlying double-layer constant-phase element; Setting the passivation film stability threshold and passivation film imbalance threshold , Less than At that time, the passivation film exhibits stability. Between and When the passivation film deteriorates, it tends to deteriorate. Greater than At that time, the passivation film becomes unbalanced and ruptures.
7. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S3 includes S3.2, and then combined with and The value determines the stability of the passivation film; Under the same corrosion conditions, The value increases and value corresponding Decrease or The value continuously decreases with prolonged immersion time, indicating that the passivation film is stable; The value decreases and value corresponding Significantly increased or As the immersion time continued to increase, the passivation film was determined to be unstable. For the first time Exceed At the same time The value decreases and value corresponding Significantly increased or As the immersion time continues to increase, the corresponding residual tensile stress is determined as the residual stress threshold value that will trigger corrosion cracking.
8. The heat treatment optimization method for corrosion cracking resistance based on residual stress threshold value according to claim 1, characterized in that, S4 includes S4.3, where the local heat treatment holding temperature is selected based on the treatment standard of the target sample in S2. The selected local heat treatment holding temperature is set as the control temperature of the heating belt, thus completing the determination of the local heat treatment holding temperature parameters.