A method for determining welding parameters of high-strength steel

Abstract

The application provides a high-strength steel welding parameter determination method, which comprises the following steps: performing chemical composition detection on a base material, calculating a carbon equivalent and a cold crack sensitivity index, selecting a welding material and determining a heat input window; setting initial welding parameters, determining heat input matching degree; welding under the initial welding parameters to obtain a first welding test piece, measuring the highest hardness of a heat affected zone and characterizing a microstructure embrittlement feature; welding under different preheating temperatures to obtain a second welding test piece, measuring a target section crack rate, and determining a critical crack-free preheating temperature; calculating a cold crack comprehensive index based on the carbon equivalent, the cold crack sensitivity index, the heat input matching degree, the highest hardness of the heat affected zone, the microstructure embrittlement feature and the target section crack rate, and evaluating the risk level of the initial welding parameters. Through the application, the cold crack risk of high-strength steel welding parameters can be accurately predicted, and the welding parameters can be corrected.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a method for determining welding parameters for high-strength steel. Background Technology

[0002] High-strength steel, due to its high alloy content and strong hardenability, is highly sensitive to diffusible hydrogen and restraint stress during welding, making it extremely prone to cold cracking during post-weld cooling or delayed stages. For thick plate components, gusset plates, and high-restraint welds in steel towers, the occurrence of cold cracks directly endangers structural safety; therefore, effective control of cold cracks is a crucial aspect of engineering implementation.

[0003] Currently, the commonly used methods for assessing cold crack sensitivity in engineering mainly include the index method, hardness method, and oblique Y-groove test method, but all of them have obvious limitations.

[0004] The index method relies on single empirical criteria such as carbon equivalent (CE) (IIW) or cold crack sensitivity index (Pcm), and estimates are based solely on the chemical composition of the base material. It cannot reflect key factors such as actual thermal cycling, joint restraint, and diffusible hydrogen content. As a result, cracks often occur after welding even when the criteria are met, leading to insufficient accuracy in the evaluation results.

[0005] While the hardness method can reflect the degree of hardening in the heat-affected zone of welding, the hardness value cannot be used as a sufficient criterion for whether cracks have formed. Furthermore, the test results are greatly affected by the location of the test point and the loading conditions, making it difficult to independently guide process decisions. It also suffers from insufficient evaluation accuracy.

[0006] The oblique Y-groove test is a direct means of evaluating cold crack sensitivity and can obtain quantitative results such as crack rate. However, existing test methods generally lack a systematic correlation with composition criteria and microstructure, making it difficult to quantitatively transform key data such as critical preheating temperature into an engineering-executable preheating regime and heat input window.

[0007] In existing technologies, there are methods that use hot crack sensitivity coefficients and combine them with finite element simulation to optimize welding parameters for high-strength steel. However, these methods mainly target hot cracking problems and do not address the formation mechanism and prediction of cold cracks. Furthermore, their evaluation system does not take into account the embrittlement characteristics of the MA component and coarse martensite in the coarse-grained heat-affected zone, which are precisely the core reasons for delayed cold cracking.

[0008] In summary, existing technologies have not yet formed a multi-dimensional evaluation method that can quantitatively couple composition criteria, mechanical properties, crack measurement and microstructure characteristics, nor can they directly output process modification schemes with clear physical basis based on the evaluation results, resulting in a long-term disconnect between laboratory evaluation and engineering application.

[0009] In view of this, it is necessary to improve the existing methods for assessing cold crack sensitivity in order to solve the above problems.

[0010] It should be noted that the above description of the background technology is only for the purpose of providing a clear and complete explanation of the technical solutions of the present invention and facilitating understanding by those skilled in the art. It should not be assumed that the above technical solutions are known to those skilled in the art simply because they have been described in the background section of the present invention. Summary of the Invention

[0011] The purpose of this invention is to solve the problems of insufficient accuracy of existing cold crack sensitivity assessment methods, lack of systematic correlation with composition criteria and microstructure, and inability to correct process parameters based on assessment results.

[0012] To achieve the above objectives, the present invention provides a method for determining welding parameters of high-strength steel, comprising: Chemical composition testing is performed on the base material, and carbon equivalent and cold crack sensitivity index are calculated based on the test results. Welding materials that match the set strength of the base material are selected, and the corresponding heat input window is determined based on the characteristics of the base material and the preset process conditions. Set initial welding parameters, including initial heat input, initial preheating temperature, and initial interpass temperature. Determine the heat input matching degree based on the relationship between the initial heat input and the interval of the heat input window. Welding was performed under initial welding parameters to obtain a first welded specimen. The highest hardness of the heat-affected zone of the first welded specimen was measured, and the microstructure of the coarse-grained heat-affected zone of the first welded specimen was characterized to obtain the microstructure embrittlement characteristics of the coarse-grained heat-affected zone. Only the initial preheating temperature in the initial welding parameters is adjusted, and welding is performed at different preheating temperatures, including the initial preheating temperature, to obtain a second welded specimen. The target cross-sectional crack rate of the second welded specimen at each preheating temperature is measured, and the lowest value of the preheating temperature corresponding to the target cross-sectional crack rate of zero is determined as the critical crack-free preheating temperature. The cold cracking comprehensive index is calculated based on carbon equivalent, cold cracking sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate. The risk level of the initial welding parameters is then assessed based on the cold cracking comprehensive index. If the risk level is medium or high, the initial welding parameters are corrected according to the preheating strategy based on the critical crack-free preheating temperature, and the risk level is reassessed after correction until the risk level is low.

[0013] As a further improvement of the present invention, the calculation of the comprehensive cold cracking index based on carbon equivalent, cold cracking sensitivity index, heat input matching degree, maximum hardness of the heat-affected zone, microstructure embrittlement characteristics, and target section crack rate includes: Risk assessments were conducted on carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section, respectively. Based on the risk assessment results, scores were assigned to carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate. The comprehensive cold crack index is calculated based on the scoring results of carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section.

[0014] As a further improvement of the present invention, the risk assessment of carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate includes: If the carbon equivalent is ≤0.35, the risk assessment result of the carbon equivalent is low risk; if the carbon equivalent is >0.35 and ≤0.40, the risk assessment result of the carbon equivalent is medium risk; if the carbon equivalent is >0.40, the risk assessment result of the carbon equivalent is high risk. If the cold crack sensitivity index is ≤0.17, the risk assessment result of the cold crack sensitivity index is low risk; if the cold crack sensitivity index is >0.17 and ≤0.20, the risk assessment result of the cold crack sensitivity index is medium risk; if the cold crack sensitivity index is >0.20, the risk assessment result of the cold crack sensitivity index is high risk. If the initial heat input is within the heat input window, the risk assessment result of the heat input matching degree is low risk; if the initial heat input exceeds the heat input window and the excess amount is ≤ a set threshold, the risk assessment result of the heat input matching degree is medium risk; if the initial heat input exceeds the heat input window and the excess amount is > a set threshold, the risk assessment result of the heat input matching degree is high risk. If the highest hardness of the heat-affected zone is ≤300, the risk assessment result for the highest hardness of the heat-affected zone is low risk; if the highest hardness of the heat-affected zone is >300 and ≤350, the risk assessment result for the highest hardness of the heat-affected zone is medium risk; if the highest hardness of the heat-affected zone is >350, the risk assessment result for the highest hardness of the heat-affected zone is high risk. If the embrittlement characteristic is the absence of MA components and coarse martensite, the risk assessment result of the embrittlement characteristic is low risk; if the embrittlement characteristic is that the area ratio of MA components is <5% and coarse martensite is absent, the risk assessment result of the embrittlement characteristic is medium risk; if the embrittlement characteristic is that the area ratio of MA components is ≥5% and / or coarse martensite is present, the risk assessment result of the embrittlement characteristic is high risk. If the target cross-section crack rate is 0, the risk assessment result of the target cross-section crack rate is low risk; if the target cross-section crack rate is >0 and ≤20%, the risk assessment result of the target cross-section crack rate is medium risk; if the target cross-section crack rate is >20%, the risk assessment result of the target cross-section crack rate is high risk.

[0015] As a further improvement of the present invention, the step of assigning scores to carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate based on risk assessment results includes: If the risk assessment result is low risk, then 1 point will be awarded; If the risk assessment result is medium risk, then 2 points will be awarded; If the risk assessment result is high risk, then 3 points will be awarded.

[0016] As a further improvement of the present invention, the formula for calculating the cold crack comprehensive index is: CCI=w1X1+w2X2+w3X3+w4X4+w5X5+w6X6; Wherein, CCI refers to the cold cracking comprehensive index, X1 refers to the carbon equivalent score, X2 refers to the cold cracking sensitivity index score, X3 refers to the maximum hardness of the heat-affected zone score, X4 refers to the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature score, X5 refers to the microstructure embrittlement characteristics score, X6 refers to the heat input matching score, and w1, w2, w3, w4, w5, and w6 refer to the set weight coefficients corresponding to carbon equivalent, cold cracking sensitivity index, maximum hardness of the heat-affected zone, target cross-sectional crack rate of the second welded specimen at the initial preheating temperature, microstructure embrittlement characteristics, and heat input matching degree, respectively.

[0017] As a further improvement of the present invention, w1 is 0.10, w2 is 0.15, w3 is 0.25, w4 is 0.30, w5 is 0.10, and w6 is 0.10.

[0018] As a further improvement of the present invention, the step of assessing the risk level of the initial welding parameters based on the cold cracking comprehensive index includes: If the comprehensive index of cold cracking is ≤1.5, the risk level of the initial welding parameters is assessed as low risk; If the comprehensive cold cracking index is greater than 1.5 and less than or equal to 2.2, the risk level of the initial welding parameters is assessed as medium risk. If the comprehensive cold cracking index is greater than 2.2, the risk level of the initial welding parameters is assessed as high risk.

[0019] As a further improvement of the present invention, the step of correcting the initial welding parameters according to the preheating strategy based on the critical crack-free preheating temperature includes: If the cold crack comprehensive index is greater than 1.5 and less than or equal to 1.8, the initial preheating temperature is corrected to T0+20℃, the initial interlayer temperature is corrected to less than or equal to 180℃, and the initial heat input is reduced by no more than 2kJ / cm. If the cold crack comprehensive index is greater than 1.8 and less than or equal to 2.2, the initial preheating temperature is corrected to T0+40℃, the initial interlayer temperature is corrected to ≤200℃, and the initial heat input is reduced by no more than 3kJ / cm. If the cold crack comprehensive index is greater than 2.2, the initial preheating temperature is corrected to T0+60℃, the initial interlayer temperature is corrected to ≤220℃, and the initial heat input is reset. T0 refers to the critical crack-free preheating temperature.

[0020] As a further improvement of the present invention, the determining method further includes: If the highest hardness of the heat-affected zone is >350HV, the initial preheating temperature is corrected to T0+30℃, the initial interlayer temperature is kept unchanged, and the initial heat input is reduced by no more than 2kJ / cm. If the target cross-sectional crack rate of the second welded specimen is >20% at the initial preheating temperature, the initial preheating temperature is corrected to T0+50℃, the initial interpass temperature is corrected to ≤200℃, and the initial heat input is reduced by no more than 5kJ / cm.

[0021] As a further improvement of the present invention The determination of the maximum hardness of the heat-affected zone of the first welded specimen includes: setting multiple hardness measuring points sequentially from the weld center to the base material of the first welded specimen, measuring the hardness corresponding to each hardness measuring point, and obtaining the maximum hardness of the heat-affected zone. And / or, The method involves adjusting only the initial preheating temperature in the initial welding parameters, performing welding at different preheating temperatures including the initial preheating temperature using a bevel Y-groove test method, and measuring the crack rate of multiple sections of the second welded specimen after a set time following welding. The highest cross-sectional crack rate is taken as the target crack rate. The formula for calculating the cross-sectional crack rate R is: Where l refers to the total length of the cross-section crack, and L refers to the total length of the cross-section weld.

[0022] Compared with the prior art, the beneficial effects of the present invention are: In this invention, the chemical composition of the base material is tested, and the carbon equivalent and cold crack sensitivity index are calculated based on the test results. Welding materials that match the set strength of the base material are selected, and the corresponding heat input window is determined based on the characteristics of the base material and preset process conditions. Initial welding parameters are set, and the heat input matching degree is determined based on the interval relationship between the initial heat input and the heat input window. Welding is performed under the initial welding parameters to obtain a first welded specimen. The highest hardness of the heat-affected zone of the first welded specimen is measured, and the microstructure of the coarse-grained heat-affected zone of the first welded specimen is characterized to obtain the embrittlement characteristics of the coarse-grained heat-affected zone. Only the initial preheating temperature in the initial welding parameters is adjusted, including the initial preheating temperature... Welding was carried out at different preheating temperatures to obtain a second welded specimen. The target cross-sectional crack rate of the second welded specimen was measured at each preheating temperature. The lowest preheating temperature corresponding to a target cross-sectional crack rate of zero was determined as the critical crack-free preheating temperature. The cold cracking comprehensive index was calculated based on carbon equivalent, cold cracking sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target cross-sectional crack rate. The risk level of the initial welding parameters was assessed based on the cold cracking comprehensive index. If the risk level was medium or high, the initial welding parameters were corrected according to the preheating strategy based on the critical crack-free preheating temperature, and the risk level was reassessed after correction until the risk level was low. Therefore, by quantitatively coupling six dimensions—composition criteria (i.e., carbon equivalent, cold cracking sensitivity index, and heat input matching degree), mechanical testing (i.e., maximum hardness of the heat-affected zone), crack testing (i.e., crack rate of the target section), and microstructure characterization (i.e., microstructure embrittlement characteristics)—into a single comparable evaluation index (i.e., comprehensive cold cracking index), and based on this, the initial welding parameters are modified. After modification, the comprehensive cold cracking index must be re-evaluated until the risk level is low before the process can be confirmed as feasible, thus ensuring the engineering reliability of the welding parameters. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the steps of the method for determining welding parameters of high-strength steel as shown in this invention. Figure 2 This is a schematic diagram illustrating the steps for calculating the comprehensive index of cold cracking as shown in this invention; Figure 3 This is a schematic diagram of a Y-shaped bevel. Figure 4 This is a schematic diagram of the microstructure of the weld zone of the welded joint prepared in Example 1; Figure 5 This is a schematic diagram of the microstructure of the coarse-grained heat-affected zone of the welded joint prepared in Example 1; Figure 6 This is a schematic diagram of the cracks in the welding cold crack sensitivity test conducted using the oblique Y groove test method before the welding parameters were corrected in Example 2. Figure 7 This is a schematic diagram of the cracks in Example 2, where the welding parameters were modified using the oblique Y-groove test method for welding cold crack sensitivity testing. Figure 8 This is a schematic diagram of the embrittlement microstructure of the coarse-grained heat-affected zone of the welded joint prepared in Comparative Example 1. Figure 9 This is a schematic diagram of the crack sensitivity characteristics of the welded joint prepared in Comparative Example 1. Figure 10 Comparative diagrams show the distribution of microhardness HV0.2 in various characteristic regions (including weld zone, fusion line, coarse grain heat-affected zone, fine grain heat-affected zone, and base material zone) of the welded joints of Example 1, Comparative Example 1, and Comparative Example 2 under a test force of 0.2 kgf. Figure 11 Radar charts showing the performance scores of the welded joints in Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0025] Please refer to Figures 1 to 11 As shown, this invention illustrates several specific embodiments of a method for determining welding parameters of high-strength steel (hereinafter referred to as the "determination method"). This determination method is used to modify the welding parameters relied upon during the welding of high-strength steel (e.g., Q690 grade low-alloy high-strength steel) to obtain low-risk welding parameters. It can be specifically applied to the manufacture of iron tower components to reduce or avoid cold cracks formed in the post-weld cold cracking or delayed stage of high-strength steel, thus ensuring the reliability of the welding project.

[0026] It should be noted that, firstly, six dimensions—composition criteria (i.e., carbon equivalent, cold crack sensitivity index, and heat input matching degree), mechanical testing (i.e., maximum hardness of the heat-affected zone), crack testing (i.e., crack rate of the target section), and microstructure characterization (i.e., microstructure embrittlement characteristics)—are quantitatively coupled into a single comparable evaluation index (i.e., the comprehensive cold crack index). Secondly, a complete definition of the comprehensive cold crack index is given, including the threshold values ​​for the six input dimensions, scoring rules, weighting coefficients, and criteria for risk level. Thirdly, a correction rule for the risk level derived from the comprehensive cold crack index is established, providing correction methods (correction amounts and their physical / metallurgical basis) for preheating temperature, interpass temperature, and heat input, rather than empirical qualitative adjustments. Fourthly, the correction rule simultaneously considers the contradictory relationship between "increasing the preheating temperature to reduce hardening" and "controlling the upper limit of the interpass temperature to prevent toughness deterioration," achieving synergistic optimization of safety and toughness. Fifth, a complete closed loop of assessment, grading, correction, and verification has been formed. After correction, the comprehensive cold cracking index must be reassessed until the risk level is low before the process can be confirmed as feasible, thus ensuring the engineering reliability of welding parameters.

[0027] Specifically, refer to Figure 1 As shown, the determination method includes the following steps S1 to S5.

[0028] Step S1: Perform chemical composition testing on the base material, calculate the carbon equivalent and cold cracking sensitivity index based on the test results, select welding materials that match the set strength of the base material, and determine the corresponding heat input window based on the characteristics of the base material and the preset process conditions.

[0029] The base material is subjected to chemical composition analysis to obtain the mass percentages of chemical elements such as C, Si, Mn, Cr, Mo, Ni, V, Ti, Nb, P, and S in the base material, and based on this, the carbon equivalent CE(IIW) and the cold crack sensitivity index Pcm are calculated. Chemical composition analysis can be performed using conventional methods such as direct-reading spectroscopy combined with carbon and sulfur analysis. Since this chemical composition analysis is not the inventive point of this invention, it is not described in detail in the embodiments of this invention.

[0030] The formula for calculating carbon equivalent CE(IIW) is: CE(IIW)=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15.

[0031] The formula for calculating the cold crack sensitivity index Pcm is: Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0032] The symbols for each chemical element represent the mass percentage of that element in the parent material.

[0033] Chemical composition analysis is performed on the proposed welding materials to obtain the mass percentage of their main alloying elements, thereby determining the welding material and strength matching relationship. Welding materials that meet the set strength matching relationship with the base material are selected. Strength matching relationships include: equal strength matching, high strength matching, and low strength matching. For example, taking Q690D grade low-alloy high-strength steel as the base material: If the set strength matching relationship is equal strength matching, Mn-Mo-Ti welding wire with equal strength matching to Q690D grade low-alloy high-strength steel can be selected as the welding material. If the set strength matching relationship is high strength matching, Ni-Cr-Mo welding wire with high strength matching to Q690D grade low-alloy high-strength steel can be selected as the welding material. If the set strength matching relationship is low strength matching, C-Mn-Si welding wire with low strength matching to Q690D grade low-alloy high-strength steel can be selected as the welding material.

[0034] The corresponding heat input window is determined based on the characteristics of the base material and the preset process conditions. The characteristics of the base material include: the strength grade and thickness of the base material. The preset process conditions include: joint type, welding method, welding material specifications, and pre-welding procedure qualification results.

[0035] Specifically, the strength grade of the base material directly determines its sensitivity to hardening tendency. For Q690 grade low-alloy high-strength steel, its carbon equivalent CE(IIW) is usually in the range of 0.30~0.40, and its cold cracking sensitivity index Pcm is usually in the range of 0.14~0.18. It belongs to a steel with a medium to high hardening tendency. The heat input window should not be too wide to avoid excessive hardening due to too low heat input or severe grain coarsening due to too high heat input.

[0036] The thickness of the base material affects heat dissipation and constraint during welding. For medium-thick plates with a thickness of 16-25mm, the heat dissipation rate is relatively fast, with a cooling time from 800℃ to 500℃. For shorter temperatures, the lower limit of heat input should be appropriately increased to suppress excessive martensite formation; at the same time, due to the increased confinement caused by the increase in plate thickness, the upper limit of heat input also needs to be appropriately controlled to avoid excessively high peak temperature dwell time exacerbating grain coarsening.

[0037] The joint type determines the welding restraint and stress concentration. Commonly used joint types in tower components, such as butt joints, T-joints, and gusset plate joints, exhibit increasing restraint in that order. For high-restraint joints, the heat input window should be adjusted towards the upper-middle direction to reduce the cooling rate and decrease the tendency for cold cracking.

[0038] The welding method affects thermal efficiency and deposition efficiency. For gas metal arc welding, the commonly used heat input range is about 10~25kJ / cm; if flux-cored wire arc welding or submerged arc welding is used, the upper and lower limits of the window need to be adjusted accordingly due to the different thermal efficiencies.

[0039] The strength matching relationship between the welding material and the base metal has a significant impact on the heat input window. Under equal strength matching, a heat input window of approximately 14~20 kJ / cm is recommended; under low strength matching, the heat input window can be moderately shifted upward to reduce the hardness of the heat-affected zone; under high strength matching, the heat input window should be moderately shifted downward to fully utilize the strength advantage of the welding material, but excessive hardness must be prevented.

[0040] Pre-welding procedure qualification results provide a basis for verifying the heat input window. Before assessing the risk level of the initial welding parameters, the heat input window, determined by comprehensively considering the base metal strength grade, base metal thickness, joint type, and welding method, can be verified and fine-tuned based on historical welding procedure qualification data of similar base metals and joint types, or by referring to the recommended values ​​of relevant welding standards (such as EN1011-2, AWSD1.1). The pre-qualification results can also provide the actual heat input boundary values ​​for cold cracking of this steel grade under specific working conditions, which can be used to correct the upper and lower limits of the heat input window.

[0041] It should be noted that this heat input window is not fixed. Its rationality will be cross-validated by the detection results of subsequent step S3 (i.e., maximum hardness and microstructure embrittlement characteristics) and step S4 (i.e., target cross-sectional crack rate). If the verification results indicate that one boundary of the heat input window is too loose (for example, the hardness exceeds the limit or the target cross-sectional crack rate exceeds the standard under this boundary condition), the heat input window will be contracted and adjusted during the correction process to optimize the heat input window and thus ensure the accuracy of the subsequent risk level assessment.

[0042] Step S2: Set the initial welding parameters and determine the heat input matching degree based on the relationship between the initial heat input and the heat input window interval.

[0043] The initial welding parameters are those that require risk level assessment. The initial welding parameters include: initial heat input, initial preheating temperature, and initial interpass temperature.

[0044] The heat input window is the recommended welding heat input range determined in step S1 based on the characteristics of the base material and the preset process conditions. If the initial heat input is within the heat input window, the heat input matching degree is matched; if the initial heat input exceeds the heat input window and the excess amount is ≤ the set threshold, the heat input matching degree is deviated; if the initial heat input exceeds the heat input window and the excess amount is > the set threshold, the heat input matching degree is severely deviated.

[0045] It should be noted that the threshold is a process boundary value used to measure whether the initial heat input exceeds the heat input window acceptable. For example, in a specific implementation scenario involving Q690D grade low-alloy high-strength steel, 20mm thick plate, equal strength matching, and gas metal arc welding, the heat input window is 14~20kJ / cm, and the threshold can be set to 2kJ / cm. If the initial heat input is within the range of 14~20kJ / cm, the heat input matching degree is matched; if the initial heat input is within the range of 12~14kJ / cm or 20~22kJ / cm, the heat input matching degree is deviated; if the initial heat input is less than 12kJ / cm or greater than 22kJ / cm, the heat input matching degree is severely deviated.

[0046] Step S3: Welding is performed under the initial welding parameters to obtain the first welded specimen. The highest hardness of the heat-affected zone of the first welded specimen is measured, and the microstructure of the coarse-grained heat-affected zone of the first welded specimen is characterized to obtain the microstructure embrittlement characteristics of the coarse-grained heat-affected zone.

[0047] Welding is performed using the initial welding parameters (including initial heat input, initial preheating temperature, and initial interpass temperature) set in step S2 to prepare the first welded specimen. Any applicable welding method can be used, such as gas metal arc welding (GMAW), flux-cored wire arc welding (FCAW), or submerged arc welding (SAW), etc., and this embodiment does not impose specific limitations on this method.

[0048] In one embodiment, determining the highest hardness of the heat-affected zone of the first welded specimen includes: sequentially setting multiple hardness measuring points from the weld center to the base material of the first welded specimen, measuring the hardness corresponding to each hardness measuring point, and finally obtaining the highest hardness of the heat-affected zone.

[0049] Specifically, hardness samples were taken from the cross-section of the welded joint of the first welded specimen, and multiple microhardness test points were sequentially established along the weld center, fusion line, coarse-grained heat-affected zone, fine-grained heat-affected zone, and base metal direction. The spacing between two adjacent microhardness test points in the same area was 0.5 mm, and the load was HV0.5 (4.9 N). At least five microhardness test points were arranged in each area. The microhardness value corresponding to each microhardness test point was measured, and the maximum value among all microhardness test points was taken as the highest hardness of the heat-affected zone under the initial welding parameters.

[0050] The first welded specimen was characterized by metallographic microscopy using an optical microscope (OM) and / or a scanning electron microscope (SEM). The proportions and distributions of acicular ferrite (AF), granular bainite (GB), and lath bainite (LB) in the weld zone were identified. The presence, size, and density of coarse lath martensite and MA components (i.e., martensite-austenite islands) in the coarse-grained heat-affected zone were also determined. For the first welded specimen with cracks, the crack initiation location, propagation path, and fracture morphology (dimples / cleavage / quasi-cleavage) were observed using a scanning electron microscope. Based on this, the embrittlement characteristics of the coarse-grained heat-affected zone were obtained.

[0051] Step S4: Adjust only the initial preheating temperature in the initial welding parameters, and perform welding at different preheating temperatures including the initial preheating temperature to obtain a second welded specimen. Measure the target cross-sectional crack rate of the second welded specimen at each preheating temperature, and determine the lowest value of the preheating temperature corresponding to the target cross-sectional crack rate being zero as the critical crack-free preheating temperature.

[0052] Keeping the initial heat input and initial interpass temperature constant, and adjusting only the initial preheating temperature, welding cold cracking sensitivity tests were conducted at different preheating temperatures, including the initial preheating temperature, to prepare the second welded specimen.

[0053] In some implementations, the reference Figure 3 As shown, the welding cold crack sensitivity test adopts the oblique Y groove test method. Figure 3 A schematic diagram of the inclined Y-bevel is shown. Since the inclined Y-bevel test method is a standard test method in the field (e.g., it can be performed according to GB / T4675.1 or ISO17642-2), and is not the core inventive point of this invention, its specific operation process will not be described in detail in each embodiment; only the key parameters and steps directly related to this determination method will be briefly described.

[0054] In this embodiment, the dimensions of the base material test plate for the oblique Y-groove test method are: length 200mm, width 75mm, thickness consistent with the actual thickness of the base material (16~25mm), groove angle 60°, root gap 2mm, and constraint weld length 80mm. Second welding specimens are welded at different preheating temperatures, including the initial preheating temperature. The preheating temperature can be, for example, room temperature, 80℃, 120℃, 150℃, 200℃, etc., and the specific value is set according to the initial preheating temperature and the expected correction range.

[0055] After welding, following a set time (e.g., 48 hours), crack detection was performed on the second welded specimens at different preheating temperatures. Crack detection included surface crack detection and root crack detection. Surface crack detection was performed using a combination of visual inspection and magnetic particle testing, while root crack detection was performed visually after the second welded specimen fractured by bending. The cross-sectional crack rate was determined by taking multiple cross-sections (e.g., 5 cross-sections) at equal intervals along the weld length and observing the crack length of each cross-section using an optical microscope. The formula for calculating the cross-sectional crack rate R is: Where l refers to the total length of the cross-section crack, and L refers to the total length of the cross-section weld.

[0056] The highest cross-sectional crack rate among multiple cross-sectional crack rates at the same preheating temperature is taken as the target cross-sectional crack rate corresponding to that preheating temperature. By comparing the target cross-sectional crack rates at different preheating temperatures, the lowest preheating temperature corresponding to a target cross-sectional crack rate of zero is determined as the critical crack-free preheating temperature.

[0057] It should be noted that the physical significance of the critical crack-free preheating temperature lies in the fact that above this preheating temperature, the welding cooling rate has been reduced to a level sufficient to significantly reduce the amount of martensite transformation while allowing sufficient time for diffuse hydrogen to escape, thereby completely eliminating the conditions for cold cracking under the current welding conditions. The critical crack-free preheating temperature serves as the quantitative benchmark for process reverse correction in the subsequent step S5.

[0058] Furthermore, the oblique Y-groove test method simulates the most severe cracking conditions in actual engineering by concentrating stress with high restraint. The causal chain of increased preheating temperature, decreased cooling rate, reduced martensite transformation, increased hydrogen diffusion escape time, and decreased risk of cold cracking is the basic thermodynamic and kinetic basis for the control of cold cracking by preheating temperature.

[0059] Step S5: Calculate the comprehensive cold cracking index based on carbon equivalent, cold cracking sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate. Assess the risk level of the initial welding parameters based on the comprehensive cold cracking index.

[0060] The initial welding parameters are classified into three risk levels: low, medium, and high. If the risk level is medium or high, the initial welding parameters are modified according to the preheating strategy, based on the critical crack-free preheating temperature. The risk level is then reassessed until it reaches the low risk level.

[0061] In one implementation, the reference Figure 2 As shown, the comprehensive cold crack index is calculated based on carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics and target section crack rate, including the following steps S51 to S53.

[0062] Step S51: Conduct risk assessments on carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section, respectively.

[0063] In one implementation, if the carbon equivalent is ≤0.35, the risk assessment result is low risk; if the carbon equivalent is >0.35 and ≤0.40, the risk assessment result is medium risk; and if the carbon equivalent is >0.40, the risk assessment result is high risk. Carbon equivalent CE(IIW) comprehensively reflects the contribution of alloying elements to the hardening tendency of steel. The higher the carbon equivalent, the greater the tendency to form martensite during welding cooling, and the higher the risk of cold cracking. Based on recommended IIW values ​​and extensive engineering practice statistics, when the carbon equivalent CE(IIW) >0.40, the risk of cold cracking increases significantly under conventional preheating conditions; therefore, its risk assessment result is determined to be high risk.

[0064] In one implementation, if the cold crack sensitivity index is ≤0.17, the risk assessment result is low risk; if the cold crack sensitivity index is >0.17 and ≤0.20, the risk assessment result is medium risk; and if the cold crack sensitivity index is >0.20, the risk assessment result is high risk. The cold crack sensitivity index Pcm is more sensitive to low-carbon high-strength steel because it increases the weight of carbon (i.e., C) (the mass percentage of C is directly taken in the calculation formula of the cold crack sensitivity index Pcm), making it more suitable for predicting cold cracks in Q690 grade low-carbon microalloyed steel. Based on the IIW recommended values ​​and a large number of engineering practice statistics, when the cold crack sensitivity index Pcm >0.20, the risk of cold cracking increases significantly under conventional preheating conditions, therefore its risk assessment result is determined to be high risk.

[0065] In one implementation, if the initial heat input is within the heat input window, the heat input matching degree is considered a match, and the risk assessment result of the heat input matching degree is low risk; if the initial heat input exceeds the heat input window and the excess amount is ≤ a set threshold, the heat input matching degree is considered a deviation, and the risk assessment result of the heat input matching degree is medium risk; if the initial heat input exceeds the heat input window and the excess amount is > a set threshold, the heat input matching degree is considered a severe deviation, and the risk assessment result of the heat input matching degree is high risk.

[0066] In one implementation, if the maximum hardness of the heat-affected zone (HAZ) is ≤300, the risk assessment result for the maximum hardness of the HAZ is low risk; if the maximum hardness of the HAZ is >300 and ≤350, the risk assessment result for the maximum hardness of the HAZ is medium risk; and if the maximum hardness of the HAZ is >350, the risk assessment result for the maximum hardness of the HAZ is high risk. The maximum hardness of the HAZ directly reflects the degree of hardening during the welding cooling process. When the maximum hardness of the HAZ exceeds 350 HV, it indicates that a large amount of high-carbon martensite has formed in this region, which is highly susceptible to cold cracking under the combined action of diffusing hydrogen and restraint stress. The 350 HV threshold is derived from the hardness control requirements for high-strength steel welding in AWSD1.1 and EN1011-2. Based on engineering statistical experience, it is known that for every 50 HV increase in the maximum hardness of the HAZ (from 300 to 350), the probability of cold cracking jumps from approximately 5% to over 30%.

[0067] In one embodiment, if the embrittlement characteristic is the absence of MA components and coarse martensite, the risk assessment result for the embrittlement characteristic is low risk; if the embrittlement characteristic is that the area fraction of MA components is <5% and coarse martensite is absent, the risk assessment result for the embrittlement characteristic is medium risk; if the embrittlement characteristic is that the area fraction of MA components is ≥5% and / or coarse martensite is present, the risk assessment result for the embrittlement characteristic is high risk. MA components are hard and brittle phases, and the hardness difference between them and the surrounding bainitic matrix creates localized stress concentrations, which are preferential sites for cold crack initiation. Published literature indicates that when the area fraction of MA in CGHAZ exceeds 5%, the impact energy at -40℃ decreases significantly (from >60J to <30J), and the crack risk increases substantially.

[0068] It should be noted that coarse martensite, or coarse acicular martensite, refers to the lanceolate martensite that appears as coarse needles under an optical microscope on the metallographic surface after etching treatment. This is a specialized term in the field of heat treatment within the discipline of metallic materials science. The formation of coarse martensite primarily stems from uncontrolled heat treatment processes, particularly excessively high quenching temperatures. When austenite grains grow abnormally, carbides dissolve excessively, leading to the formation of coarse acicular martensite after quenching. For example, literature indicates that CrWMn steel molds quenched at 870℃ (excessively high) or heated to 1100℃ for 30 minutes followed by oil quenching will form this type of microstructure. This microstructure significantly increases the internal heat treatment stress of the material, leading to a substantial increase in brittleness and making it highly susceptible to failure modes such as cracking, chipping, or breakage during service. Furthermore, the resulting retained austenite further exacerbates the risk of crack propagation during subsequent machining processes (especially grinding).

[0069] In one implementation, if the target cross-section crack rate is 0, the risk assessment result of the target cross-section crack rate is low risk; if the target cross-section crack rate is >0 and ≤20%, the risk assessment result of the target cross-section crack rate is medium risk; if the target cross-section crack rate is >20%, the risk assessment result of the target cross-section crack rate is high risk.

[0070] Step S52: Based on the risk assessment results, assign scores to carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section.

[0071] In one implementation, if the risk assessment result is low risk, 1 point is awarded; if the risk assessment result is medium risk, 2 points are awarded; and if the risk assessment result is high risk, 3 points are awarded.

[0072] Step S53: Calculate the comprehensive cold crack index based on the scoring results of carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section.

[0073] In one implementation, the formula for calculating the cold cracking composite index is: CCI=w1X1+w2X2+w3X3+w4X4+w5X5+w6X6.

[0074] Wherein, CCI refers to the cold cracking comprehensive index, X1 refers to the carbon equivalent score, X2 refers to the cold cracking sensitivity index score, X3 refers to the maximum hardness of the heat-affected zone score, X4 refers to the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature score, X5 refers to the microstructure embrittlement characteristics score, X6 refers to the heat input matching score, and w1, w2, w3, w4, w5, and w6 refer to the set weight coefficients corresponding to carbon equivalent, cold cracking sensitivity index, maximum hardness of the heat-affected zone, target cross-sectional crack rate of the second welded specimen at the initial preheating temperature, microstructure embrittlement characteristics, and heat input matching degree, respectively.

[0075] Furthermore, w1 is set to 0.10, w2 to 0.15, w3 to 0.25, w4 to 0.30, w5 to 0.10, and w6 to 0.10. The aforementioned w1, w2, w3, w4, w5, and w6 correspond one-to-one with X1, X2, X3, X4, X5, and X6, respectively, all having positive weights and constituting a normalized weighted reorganization, satisfying w4 > w3 > w2 > w1 = w5 = w6, and w1 + w2 + w3 + w4 + w5 + w6 = 1.00. Among these, w4, w3, and w2 are used to characterize the main contributions of measured crack results, heat-affected zone hardness, and cold crack sensitivity index to cold crack risk, while w1, w5, and w6 are used to characterize the auxiliary constraint contributions of compositional priors, microstructural embrittlement characteristics, and thermal input matching degree to cold crack risk. This allows the comprehensive cold crack index to reflect the primary and secondary relationships among the various evaluation indicators. Specifically, the weighting coefficient w1 for carbon equivalent is set to 0.10, based on the prior composition criterion and moderate sensitivity. The weighting coefficient w2 for cold crack sensitivity index is set to 0.15, based on its superior predictive ability for cold cracking in low-carbon high-strength steel compared to carbon equivalent. The weighting coefficient w3 for the highest hardness in the heat-affected zone is set to 0.25, based on its direct reflection of hardening degree and strong correlation with crack risk. The weighting coefficient w4 for the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature is set to 0.30, based on its most direct crack verification result and highest weight. The weighting coefficient w5 for microstructural embrittlement characteristics is set to 0.10, based on its microstructural auxiliary criterion. The weighting coefficient w6 for thermal input matching degree is set to 0.10, based on process boundary conditions.

[0076] It should be noted that the set weighting coefficient w4 corresponding to the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature is the largest, as it is the most direct crack verification result, reflecting the combined effects of composition, thermal cycling, restraint, and hydrogen content. The set weighting coefficient w3 corresponding to the highest hardness in the heat-affected zone is the second largest, since hardness is a direct measure of hardening degree and is strongly correlated with crack risk. The set weighting coefficient w2 corresponding to the cold crack sensitivity index is higher than the set weighting coefficient w1 corresponding to the carbon equivalent, because the cold crack sensitivity index has a better predictive ability for cold cracks in low-carbon high-strength steel. The sum of the aforementioned w1, w2, w3, w4, w5, and w6 is 1.00.

[0077] More specifically, the weighted coefficients w1 (corresponding to carbon equivalent), w2 (corresponding to cold crack sensitivity index), w3 (corresponding to the highest hardness of the heat-affected zone), w4 (corresponding to the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature), w5 (corresponding to the microstructure embrittlement characteristics), and w6 (corresponding to the heat input matching degree) have the following relationships: First, w1, w2, w3, w4, w5, and w6 are normalized. The sum of w1, w2, w3, w4, w5, and w6 is 1.00. Therefore, the comprehensive cold crack index is numerically represented as the weighted average of the six assigned scores. Since the scores for carbon equivalent, cold crack sensitivity index, maximum hardness of the heat-affected zone, crack rate of the target section, embrittlement characteristics of the microstructure, and heat input matching degree are assigned as 1, 2, or 3, the comprehensive cold crack index ranges from 1.00 to 3.00. This ensures that the criterion thresholds of 1.5 and 2.2 in the risk level assessment both fall within this range, guaranteeing the comparability and consistency between the comprehensive cold crack index and the risk level. Secondly, w1, w2, w3, w4, w5, and w6 have a numerical ranking relationship. w1, w2, w3, w4, w5, and w6 satisfy w4 > w3 > w2 > w1 = w5 = w6. The principle followed by the numerical ranking is: the closer the detection result of the index is to the direct verification result of cold cracking, the larger the set weight coefficient corresponding to that index. The target cross-section crack rate is the terminal result directly measured using the oblique Y-groove test method. It comprehensively reflects the coupling effect of the base metal chemical composition, welding thermal cycle, joint restraint, and diffusible hydrogen content. Therefore, the set weight coefficient w4 corresponding to the target cross-section crack rate is the largest. The maximum hardness of the heat-affected zone is a direct mechanical measure of the degree of hardening and is strongly correlated with crack risk. However, the maximum hardness of the heat-affected zone is a cause of crack formation, not a direct result of crack formation. Therefore, the set weight coefficient w3 corresponding to the maximum hardness of the heat-affected zone is the second largest. The cold crack sensitivity index and carbon equivalent are both a priori criteria based on the base metal chemical composition. However, the cold crack sensitivity index increases the weight of carbon in the calculation, and its ability to predict cold cracks in Q690 grade low-carbon microalloyed high-strength steel is better than that of carbon equivalent. Therefore, w2 is greater than w1. The microstructure embrittlement characteristics and the heat input matching degree are used as microstructure auxiliary criteria and process boundary criteria, respectively. The set weight coefficients corresponding to the microstructure embrittlement characteristics and the heat input matching degree are taken as smaller values. Finally, w1, w2, w3, w4, w5, and w6 are grouped according to their evidentiary nature. The first group consists of a priori criteria that can be determined before trial welding without requiring welding tests, including carbon equivalent, cold cracking sensitivity index, and heat input matching degree, with a sum of corresponding set weight coefficients of w1+w2+w6=0.35. The second group consists of measured criteria that require testing on actual welded specimens, including the highest hardness of the heat-affected zone, embrittlement characteristics of the microstructure, and crack rate of the target section, with a sum of corresponding set weight coefficients of w3+w4+w5=0.65.Therefore, the weight of the measured criteria in the comprehensive cold crack index is about twice that of the a priori criteria, which reflects the evaluation principle of this determination method, which takes measured evidence as the main basis and a priori estimation of composition and process as a supplement, and avoids the problem of insufficient prediction accuracy caused by relying solely on composition criteria.

[0078] In one implementation, the risk level of the initial welding parameters is assessed based on the cold cracking composite index, including: if the cold cracking composite index is ≤1.5, the risk level of the initial welding parameters is assessed as low risk; if the cold cracking composite index is >1.5 and ≤2.2, the risk level of the initial welding parameters is assessed as medium risk; if the cold cracking composite index is >2.2, the risk level of the initial welding parameters is assessed as high risk. When the risk level of the initial welding parameters is low risk, welding can be performed using the current initial welding parameters; when the risk level of the initial welding parameters is medium risk, subsequent correction steps can be performed to correct the initial welding parameters; when the risk level of the initial welding parameters is high risk, subsequent correction steps can be performed to correct the initial welding parameters, or the welding material can be replaced and the initial welding parameters reset.

[0079] It should be noted that the three risk levels are determined as follows: a cold cracking composite index of 1.5 corresponds to all indicators being at the boundary between low and medium risk (e.g., a cold cracking composite index of 1.5), at which point the crack test has not yet shown any cracks, but some indicators are close to their upper limits. A cold cracking composite index of 2.2 corresponds to most indicators entering the medium- and high-risk range, indicating that the crack test has already shown any cracks or that the hardness has exceeded the limit. This threshold can be optimized and calibrated according to specific working conditions in actual use.

[0080] The initial welding parameters are corrected based on the critical crack-free preheating temperature obtained in step S4. The critical crack-free preheating temperature is the lowest preheating temperature corresponding to the complete disappearance of cracks (i.e., zero crack rate in the target section) in the oblique Y-groove test method under the current welding material and initial heat input. Therefore, the preheating temperature correction is incrementally adjusted from this starting point. The basis for the correction is as follows: First, by increasing the preheating temperature, the welding cooling rate is reduced, the martensite transformation amount is decreased, the hardness of the heat-affected zone is reduced, and the escape time of diffusing hydrogen is extended, ultimately achieving the goal of reducing the risk of cold cracking. Second, by controlling the upper limit of the interpass temperature, it is prevented from causing coarsening of CGHAZ grains and MA components due to excessively high interpass temperature. While excessively high interpass temperature reduces hardness, it also deteriorates toughness; therefore, an upper limit is set. Third, by reducing the heat input, the weld pool size and heat-affected zone width are reduced, the residence time of the peak temperature in the coarse-grained heat-affected zone is reduced, and the degree of grain coarsening is decreased. However, excessively low heat input will increase the hardening tendency; therefore, it needs to be adjusted in conjunction with the preheating temperature.

[0081] In one embodiment, the initial welding parameters are modified according to a preheating strategy based on the critical crack-free preheating temperature. This includes: if the cold cracking index is >1.5 and ≤1.8, the initial preheating temperature is modified to T0+20℃, the initial interpass temperature is modified to ≤180℃, and the initial heat input is reduced by no more than 2kJ / cm for a slight modification to compensate for hardening tendency. If the cold cracking index is >1.8 and ≤2.2, the initial preheating temperature is modified to T0+40℃, the initial interpass temperature is modified to ≤200℃, and the initial heat input is reduced by no more than 3kJ / cm for a moderate modification to suppress martensite formation. If the cold cracking index is >2.2, the initial preheating temperature is modified to T0+60℃, the initial interpass temperature is modified to ≤220℃, and the initial heat input is reset. This state is high-risk and requires replacement of welding materials. Here, T0 refers to the critical crack-free preheating temperature.

[0082] In one embodiment, the determination method further includes: if the highest hardness of the heat-affected zone is >350HV, then the initial preheating temperature is corrected to T0+30℃, the initial interpass temperature is kept unchanged, and the initial heat input is reduced by no more than 2kJ / cm, thereby performing a single-item correction for hardness exceeding the limit. If the target cross-sectional crack rate of the second welded specimen is >20% at the initial preheating temperature, then the initial preheating temperature is corrected to T0+50℃, the initial interpass temperature is corrected to ≤200℃, and the initial heat input is reduced by no more than 5kJ / cm, thereby performing a correction for crack rate exceeding the limit.

[0083] It should be noted that the logic for determining the preheating temperature increment is explained as follows: An increase of 20℃ is a slight correction. Based on the preheating temperature calculation method in Annex C of EN1011-2, when the cold crack sensitivity index Pcm increases by 0.01, a preheating temperature increase of approximately 15-25℃ is recommended. When the cold crack composite index CCI > 1.5 and ≤ 1.8, the risk increment is equivalent to a shift of approximately 0.01 in the cold crack sensitivity index Pcm; therefore, +20℃ is used. An increase of 40℃ is a moderate correction. When the cold crack composite index CCI > 1.8 and ≤ 2.2, multiple indicators enter the medium-risk range, and cross-sectional cracks may have already appeared in the crack test. In this case, the cooling time needs to be adjusted. Extending the cooling time by approximately 50% to suppress martensite formation corresponds to an increase of approximately 40°C in the preheating temperature (based on the Rosenthal heat conduction model). (Preheating temperature relationship calculation). Increasing by 60℃ is a significant correction. When the Cold Crack Composite Index (CCI) > 2.2, it indicates that cracks have occurred or multiple indicators have seriously exceeded limits. Conventional preheating correction is insufficient to eliminate the risk, and it is necessary to consider changing the welding material matching scheme while significantly increasing the preheating temperature.

[0084] The determination logic for the upper limit of interlayer temperature is described as follows. The basis for gradually relaxing the upper limit of interlayer temperature from 180°C to 220°C but not exceeding 220°C is: published literature shows that when the interlayer temperature of Q690 low-alloy high-strength steel exceeds 220°C, grains are significantly coarsened in the coarse-grained heat-affected zone after multiple thermal cycles, the area fraction of M-A constituents exceeds 7%, the impact energy at -40°C drops to less than 30J, and the toughness is seriously deteriorated. Therefore, 220°C is the absolute upper limit of interlayer temperature.

[0085] After correction, the following verifications are performed: (1) Under the corrected preheating temperature and heat input conditions, the inclined Y-groove test is re-performed to ensure that the target crack rate is zero; (2) The maximum hardness of the heat-affected zone is re-measured to ensure that the maximum hardness of the heat-affected zone is ≤ 350HV (preferably ≤ 300HV); (3) Microstructure characterization is re-performed to ensure that there are no a large amount of M-A constituents and no coarse martensite; (4) The comprehensive cold cracking index is recalculated to ensure that the risk grade of the corrected welding parameters evaluated according to the comprehensive cold cracking index is low risk. If the correction fails, the next round of correction is continued until the risk grade is low risk.

[0086] Two examples (i.e., Example 1 and Example 2) and two comparative examples (i.e., Comparative Example 1 and Comparative Example 2) are shown below for comparative description.

[0087] Example 1: Q690D low-alloy high-strength steel is selected as the base metal, and Mn-Mo-Ti series welding wire with strength matching the base metal is selected, and the metal grade of the Mn-Mo-Ti series welding wire is ER55-D2-Ti. The thickness of the base metal is 20mm, the carbon equivalent is 0.34, and the cold cracking sensitivity index is 0.16. The initial heat input is 17kJ / cm, the initial preheating temperature is 120°C, and the initial interlayer temperature is 150°C.

[0088] Refer Figure 4 and Figure 5 , Figure 4 shows the microstructure schematic diagram of the weld zone of the welded joint prepared in Example 1, Figure 5 shows the microstructure schematic diagram of the coarse-grained heat-affected zone of the welded joint prepared in Example 1. From Figure 4 and Figure 5 , it can be seen that the weld zone of the welded joint is dominated by acicular ferrite and granular bainite, and the coarse-grained heat-affected zone is dominated by refined bainite structure. No continuous coarse martensite or a large amount of M-A constituents are observed, indicating that the degree of microstructure embrittlement of the welded joint under the initial welding parameters is low, and the lower maximum hardness of the heat-affected zone is consistent with the detection result that the crack rate of the target section is zero.

[0089] Assessment Results: The highest hardness of the heat-affected zone is 285 HV (1 point), and the crack rate of the target section is 0 (1 point). The microstructure embrittlement characteristics are refined bainite, with no coarse martensite or MA components (1 point). Carbon equivalent is scored 1 point, cold crack sensitivity index is scored 1 point, and heat input matching degree is scored 1 point. The calculated cold crack comprehensive index CCI = 0.10×1 + 0.15×1 + 0.25×1 + 0.30×1 + 0.10×1 + 0.10×1 = 1.00. Based on the cold crack comprehensive index, the risk level of the initial welding parameters is assessed as low risk, and the current initial welding parameters can be maintained.

[0090] Example 2: In a supplementary operating condition used to verify the risk of cold cracking when the preheating temperature is insufficient, the base material and welding materials were the same as in Example 1, with a carbon equivalent of 0.34 and a cold cracking sensitivity index of 0.16. The initial heat input was 17 kJ / cm, the initial preheating temperature was 80°C, and the initial interpass temperature was 150°C. This operating condition was used to establish a preheating temperature variable control with Example 1.

[0091] Assessment Results: The highest hardness of the heat-affected zone is 320 HV (2 points), the crack rate of the target section is 12% (2 points), the microstructure embrittlement characteristics are that the area ratio of MA components is <5% and there is no coarse martensite (2 points), carbon equivalent is 1 point, cold crack sensitivity index is 1 point, and heat input matching degree is 1 point. The cold crack comprehensive index CCI is calculated as 0.10×1+0.15×1+0.25×2+0.30×2+0.10×2+0.10×1=1.65. Based on the cold crack comprehensive index, the risk level of the initial welding parameters is assessed as medium risk, and the initial welding parameters are corrected.

[0092] By adjusting only the initial preheating temperature and performing welding at different preheating temperatures, including the initial preheating temperature, the lowest preheating temperature corresponding to a target crack rate of zero (i.e., the critical crack-free preheating temperature T0) was found to be 120℃. The theoretically corrected preheating temperature, calculated as T0 + 20℃, was then set at 140℃. Considering on-site temperature control fluctuations and safety margins for welding high-constraint thick plates, this embodiment sets the engineering preheating temperature to 160℃. The initial interpass temperature was corrected to ≤180℃. The initial heat input was corrected to be reduced by ≤2kJ / cm, for example, from 17kJ / cm to 15kJ / cm.

[0093] After correction, retest was carried out under the conditions of preheating temperature of 160°C and heat input of 15kJ / cm. The maximum hardness of the heat affected zone was reduced to 290HV (1 point assigned), the crack rate of the target section was reduced to 0 (1 point assigned), the structural embrittlement characteristic is no coarse martensite and M-A constituent (1 point assigned), 1 point is assigned for carbon equivalent, 1 point is assigned for cold crack sensitivity index, and 1 point is assigned for heat input matching degree. Calculate the comprehensive cold crack index CCI=0.10×1+0.15×1+0.25×1+0.30×1+0.10×1+0.10×1=1.00. According to the comprehensive cold crack index, the risk grade of this welding parameter is evaluated as low risk.

[0094] Refer to Figure 6 and Figure 7 , Figure 6 and Figure 7 shows the crack schematic diagrams of welding cold crack sensitivity test conducted by oblique Y-groove test method before and after the correction of welding parameters in Example 2. From Figure 6 and Figure 7 comparison, it can be seen that the welded joint before correction has cold cracks on the surface and in the section, and the crack rate of the target section is 12%; no cracks are observed in the welded joint after correction, and the crack rate of the target section is reduced to 0, which indicates that increasing preheating temperature and cooperatively adjusting heat input can effectively reduce cold crack sensitivity.

[0095] Comparative Example 1: As a control working condition for verifying the risk of the combination of high-strength matching welding wire and low heat input, the base metal is selected the same as that in Example 1. A Ni-Cr-Mo series welding wire with high-strength matching to the base metal is selected, and the metal grade of the Ni-Cr-Mo series welding wire is ER69-1. The carbon equivalent is 0.34, and the cold crack sensitivity index is 0.16. The initial heat input is 12kJ / cm, the initial preheating temperature is 80°C, and the initial interlayer temperature is 150°C.

[0096] Refer to Figure 8 and Figure 9 , Figure 8 shows a schematic diagram of the embrittled structure in the coarse-grained heat affected zone of the welded joint prepared in Comparative Example 1, Figure 9 shows a schematic diagram of the crack sensitivity characteristics of the welded joint prepared in Comparative Example 1. From Figure 8 and Figure 9 , it can be known that coarse martensite and M-A constituent enrichment appear in the coarse-grained heat affected zone of Comparative Example 1, and there are local stress concentration and crack initiation paths, which indicates that the combination of high-strength matching welding wire and low heat input will lead to too fast cooling rate, enhanced structural embrittlement and increased crack risk.

[0097] Evaluation results: the maximum hardness of the heat-affected zone is 365HV (score: 3 points), the crack rate of the target section is 28% (score: 3 points), the characteristic of structural embrittlement is the presence of a large amount of coarse martensite (score: 3 points), carbon equivalent is scored 1 point, cold crack sensitivity index is scored 1 point, and heat input matching degree is scored 2 points. Calculation of the comprehensive cold crack index CCI=0.10×1+0.15×1+0.25×3+0.30×3+0.10×3+0.10×2=2.40. According to the comprehensive cold crack index, the risk level of the initial welding parameters is assessed as high risk, and welding materials with different strength matching relationships can be replaced.

[0098] Comparative Example 2: As a control working condition for verifying the risk of the combination of low-strength matching welding wire and high heat input, the selection of base metal is the same as that in Example 1. A C-Mn-Si series welding wire with low-strength matching to the base metal is selected, and the metal grade of the C-Mn-Si series welding wire is ER50-6. The carbon equivalent is 0.34, and the cold crack sensitivity index is 0.16. The initial heat input is 21kJ / cm, the initial preheating temperature is 80°C, and the initial interpass temperature is 150°C.

[0099] Evaluation results: the maximum hardness of the heat-affected zone is 260HV (score: 1 point), the crack rate of the target section is 5% (score: 2 points), the characteristic of structural embrittlement is grain coarsening and M-A constituent <5% (score: 2 points), carbon equivalent is scored 1 point, cold crack sensitivity index is scored 1 point, and heat input matching degree is scored 2 points. Calculation of the comprehensive cold crack index CCI=0.10×1+0.15×1+0.25×1+0.30×2+0.10×2+0.10×2=1.50. According to the comprehensive cold crack index, the risk level of the initial welding parameters is assessed as the boundary between low risk and medium risk. Although both hardness and crack risk are low under this working condition, the strength reserve is insufficient (ER50-6 conforms to the low-strength matching relationship with the base metal), which cannot meet the load-bearing requirements of iron tower components.

[0100] The parameter values of Example 1, Example 2, modified Example 2, Comparative Example 1 and Comparative Example 2 are shown in the following table.

[0101]

[0102] Ref Figure 10 shown, Figure 10 shows a comparison diagram of the microhardness HV0.2 distribution of each characteristic region, namely the weld zone, fusion line, coarse-grained heat-affected zone, fine-grained heat-affected zone and base metal zone, of the welded joints prepared in Example 1, Comparative Example 1 and Comparative Example 2 under the test force of 0.2kgf. Wherein, line type 1 (i.e., the blue line) corresponds to Example 1, line type 2 (i.e., the orange line) corresponds to Comparative Example 1, and line type 3 (i.e., the green line) corresponds to Comparative Example 2. From Figure 10It can be seen that the coarse-grained heat-affected zone of Comparative Example 1 has the highest hardness exceeding 350HV, and has the highest cold cracking risk; the hardness distribution in each region of Example 1 is relatively gentle, and the maximum hardness of the heat-affected zone is lower than 300HV, indicating that its heat input and preheating procedures are relatively reasonable; the overall hardness of Comparative Example 2 is low but the weld strength reserve is insufficient, which needs to be comprehensively judged in combination with the strength matching result.

[0103] Refer to Figure 11 as shown, Figure 11 shows the radar charts of various performance scores of welded joints prepared in Example 1, Comparative Example 1 and Comparative Example 2. The various properties include low-temperature toughness, strength matching, structure uniformity, crack risk control and HAZ hardness control. From Figure 11 it can be seen that Example 1 has a high comprehensive score in strength matching, structure uniformity, crack risk control and HAZ hardness control; Comparative Example 1 has low scores in crack risk control and HAZ hardness control, and although Comparative Example 2 has low crack risk, its strength matching score is insufficient, indicating that the comprehensive evaluation method of the present invention can distinguish the main risk sources of different welding parameter combinations.

[0104] In conclusion, it can be seen that the determination method disclosed in the present invention has the following technical effects: (1) Compared with the single index method, the present invention integrates carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, structure embrittlement characteristics and target section crack rate to calculate the comprehensive cold crack index, which can more accurately predict the cold cracking risk of high-strength steel welding, avoid missed judgment and misjudgment of a single index, and solve the problem of insufficient prediction accuracy existing in the existing cold cracking sensitivity assessment methods that rely on single empirical criteria such as carbon equivalent CE (IIW) or cold crack sensitivity index Pcm.

[0105] (2) Evaluating the risk level of initial welding parameters according to the comprehensive cold crack index can directly drive the correction of welding parameters, and convert laboratory assessment results into executable preheating temperature, interpass temperature and heat input, which solves the problem that key data such as critical preheating temperature are difficult to be quantitatively converted into engineering-executable preheating procedures and heat input windows.

[0106] (3) The temperature increment in the correction rule for initial welding parameters is based on the basic principles of welding metallurgy ( relationship with preheating temperature, martensitic transformation kinetics, diffusion hydrogen escape kinetics), which has clear physical basis, and solves the problem of lack of quantitative setting basis for critical preheating temperature, interpass temperature and heat input in high-constraint welding of high-strength steel thick plates.

[0107] (4) Verification by Example 2 shows that the modified welding parameters (i.e., increasing the preheating temperature from 80°C to 160°C and decreasing the heat input from 17 to 15 kJ / cm) can reduce the cold cracking comprehensive index from 1.65 (medium risk) to 1.00 (low risk) and the target cross-section crack rate from 12% to 0, demonstrating a significant correction effect. This invention forms a multi-dimensional comprehensive evaluation model that integrates composition criteria, hardness testing, crack testing, and microstructure characterization, and can automatically generate process modification schemes based on the evaluation results.

[0108] (5) It provides a complete data chain and decision-making basis for WPS compilation, welding process evaluation and on-site quality control in the production of iron tower components.

[0109] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0110] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for determining welding parameters of high-strength steel, characterized in that, include: Chemical composition testing is performed on the base material, and carbon equivalent and cold crack sensitivity index are calculated based on the test results. Welding materials that match the set strength of the base material are selected, and the corresponding heat input window is determined based on the characteristics of the base material and the preset process conditions. Set initial welding parameters, including initial heat input, initial preheating temperature, and initial interpass temperature. Determine the heat input matching degree based on the relationship between the initial heat input and the interval of the heat input window. Welding was performed under initial welding parameters to obtain a first welded specimen. The highest hardness of the heat-affected zone of the first welded specimen was measured, and the microstructure of the coarse-grained heat-affected zone of the first welded specimen was characterized to obtain the microstructure embrittlement characteristics of the coarse-grained heat-affected zone. Only the initial preheating temperature in the initial welding parameters is adjusted, and welding is performed at different preheating temperatures, including the initial preheating temperature, to obtain a second welded specimen. The target cross-sectional crack rate of the second welded specimen at each preheating temperature is measured, and the lowest value of the preheating temperature corresponding to the target cross-sectional crack rate of zero is determined as the critical crack-free preheating temperature. The cold cracking comprehensive index is calculated based on carbon equivalent, cold cracking sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate. The risk level of the initial welding parameters is then assessed based on the cold cracking comprehensive index. If the risk level is medium or high, the initial welding parameters are corrected according to the preheating strategy based on the critical crack-free preheating temperature, and the risk level is reassessed after correction until the risk level is low.

2. The determination method according to claim 1, characterized in that, The calculation of the comprehensive cold crack index based on carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of the heat-affected zone, microstructure embrittlement characteristics, and target section crack rate includes: Risk assessments were conducted on carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section, respectively. Based on the risk assessment results, scores were assigned to carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and target section crack rate. The comprehensive cold crack index is calculated based on the scoring results of carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of heat-affected zone, microstructure embrittlement characteristics, and crack rate of target section.

3. The determination method according to claim 2, characterized in that, The risk assessment includes carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of the heat-affected zone, microstructure embrittlement characteristics, and crack rate of the target section. If the carbon equivalent is ≤0.35, the risk assessment result of the carbon equivalent is low risk; if the carbon equivalent is >0.35 and ≤0.40, the risk assessment result of the carbon equivalent is medium risk; if the carbon equivalent is >0.40, the risk assessment result of the carbon equivalent is high risk. If the cold crack sensitivity index is ≤0.17, the risk assessment result of the cold crack sensitivity index is low risk; if the cold crack sensitivity index is >0.17 and ≤0.20, the risk assessment result of the cold crack sensitivity index is medium risk; if the cold crack sensitivity index is >0.20, the risk assessment result of the cold crack sensitivity index is high risk. If the initial heat input is within the heat input window, the risk assessment result of the heat input matching degree is low risk; if the initial heat input exceeds the heat input window and the excess amount is ≤ a set threshold, the risk assessment result of the heat input matching degree is medium risk; if the initial heat input exceeds the heat input window and the excess amount is > a set threshold, the risk assessment result of the heat input matching degree is high risk. If the highest hardness of the heat-affected zone is ≤300, the risk assessment result for the highest hardness of the heat-affected zone is low risk; if the highest hardness of the heat-affected zone is >300 and ≤350, the risk assessment result for the highest hardness of the heat-affected zone is medium risk; if the highest hardness of the heat-affected zone is >350, the risk assessment result for the highest hardness of the heat-affected zone is high risk. If the embrittlement characteristic is the absence of MA components and coarse martensite, the risk assessment result of the embrittlement characteristic is low risk; if the embrittlement characteristic is that the area ratio of MA components is <5% and coarse martensite is absent, the risk assessment result of the embrittlement characteristic is medium risk; if the embrittlement characteristic is that the area ratio of MA components is ≥5% and / or coarse martensite is present, the risk assessment result of the embrittlement characteristic is high risk. If the target cross-section crack rate is 0, the risk assessment result of the target cross-section crack rate is low risk; if the target cross-section crack rate is >0 and ≤20%, the risk assessment result of the target cross-section crack rate is medium risk; if the target cross-section crack rate is >20%, the risk assessment result of the target cross-section crack rate is high risk.

4. The determination method according to claim 3, characterized in that, The process involves assigning scores to carbon equivalent, cold crack sensitivity index, heat input matching degree, maximum hardness of the heat-affected zone, microstructure embrittlement characteristics, and target section crack rate based on the risk assessment results, including: If the risk assessment result is low risk, then 1 point will be awarded; If the risk assessment result is medium risk, then 2 points will be awarded; If the risk assessment result is high risk, then 3 points will be awarded.

5. The determination method according to claim 4, characterized in that, The formula for calculating the cold crack comprehensive index is: CCI=w1X1+w2X2+w3X3+w4X4+w5X5+w6X6; Wherein, CCI refers to the cold cracking comprehensive index, X1 refers to the carbon equivalent score, X2 refers to the cold cracking sensitivity index score, X3 refers to the maximum hardness of the heat-affected zone score, X4 refers to the target cross-sectional crack rate of the second welded specimen at the initial preheating temperature score, X5 refers to the microstructure embrittlement characteristics score, X6 refers to the heat input matching score, and w1, w2, w3, w4, w5, and w6 refer to the set weight coefficients corresponding to carbon equivalent, cold cracking sensitivity index, maximum hardness of the heat-affected zone, target cross-sectional crack rate of the second welded specimen at the initial preheating temperature, microstructure embrittlement characteristics, and heat input matching degree, respectively.

6. The determination method according to claim 5, characterized in that, The values ​​of w1, w2, w3, w4, w5, and w6 are all 0.

10.

7. The determination method according to claim 1, characterized in that, The assessment of the risk level of initial welding parameters based on the cold cracking comprehensive index includes: If the comprehensive index of cold cracking is ≤1.5, the risk level of the initial welding parameters is assessed as low risk; If the comprehensive cold cracking index is greater than 1.5 and less than or equal to 2.2, the risk level of the initial welding parameters is assessed as medium risk. If the comprehensive cold cracking index is greater than 2.2, the risk level of the initial welding parameters is assessed as high risk.

8. The determination method according to claim 1, characterized in that, The step of correcting the initial welding parameters based on the critical crack-free preheating temperature and according to the preheating strategy includes: If the cold crack comprehensive index is greater than 1.5 and less than or equal to 1.8, the initial preheating temperature is corrected to T0+20℃, the initial interlayer temperature is corrected to less than or equal to 180℃, and the initial heat input is reduced by no more than 2kJ / cm. If the cold crack comprehensive index is greater than 1.8 and less than or equal to 2.2, the initial preheating temperature is corrected to T0+40℃, the initial interlayer temperature is corrected to ≤200℃, and the initial heat input is reduced by no more than 3kJ / cm. If the cold crack comprehensive index is greater than 2.2, the initial preheating temperature is corrected to T0+60℃, the initial interlayer temperature is corrected to ≤220℃, and the initial heat input is reset. T0 refers to the critical crack-free preheating temperature.

9. The determining method according to claim 8, characterized in that, The determination method further includes: If the highest hardness of the heat-affected zone is >350HV, the initial preheating temperature is corrected to T0+30℃, the initial interlayer temperature is kept unchanged, and the initial heat input is reduced by no more than 2kJ / cm. If the target cross-sectional crack rate of the second welded specimen is >20% at the initial preheating temperature, the initial preheating temperature is corrected to T0+50℃, the initial interpass temperature is corrected to ≤200℃, and the initial heat input is reduced by no more than 5kJ / cm.

10. The determination method according to claim 1, characterized in that, The determination of the maximum hardness of the heat-affected zone of the first welded specimen includes: setting multiple hardness measuring points sequentially from the weld center to the base material of the first welded specimen, measuring the hardness corresponding to each hardness measuring point, and obtaining the maximum hardness of the heat-affected zone. And / or, The method involves adjusting only the initial preheating temperature in the initial welding parameters, performing welding at different preheating temperatures including the initial preheating temperature using a bevel Y-groove test method, and measuring the crack rate of multiple sections of the second welded specimen after a set time following welding. The highest cross-sectional crack rate is taken as the target cross-sectional crack rate. The formula for calculating the cross-sectional crack rate R is: Where l refers to the total length of the cross-section crack, and L refers to the total length of the cross-section weld.

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